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Objective To evaluate tumor control, hearing, tinnitus, and balance outcomes of patients treated with CyberKnife (CK) radiosurgery for vestibular schwannoma (VS). Study design Retrospective series review. Setting Tertiary referral center. Patients All patients treated with CK radiosurgery for vestibular schwannoma by a multidisciplinary radiosurgical team from August 2005 to November 2011. The median age was 59 years, and mean follow-up was 40 months. Seventy-three patients were treated (63 primary radiosurgery and 10 postsurgical). Interventions CK radiosurgery, serial MRI imaging, comprehensive audiometry, Tinnitus Handicap Inventory (THI) scores, and Activities-Specific Balance Confidence Scale (ABC). Main outcome measures Tumor control defined as 2 mm linear growth or lower or less than 20% increase in tumor volume (TV), measured in cubic centimeter, after a minimum of 12 months of monitoring, audiogram profiles, THI, and ABC surveys. Results Of those treated with CK as primary modality, 83% had 0- to 2-mm growth (tumor control or stable) and 17% grew greater than 2 mm. Of the tumors that were stable, 29% shrank 2 mm or greater. Volumetric analysis found that 74% of tumors had less than 20% TV growth, whereas 26% exhibited 20% or greater increase in TV. Of those deemed stable, 65% shrank 20% or greater TV; 95% of patients did not need additional surgical intervention, 3 required salvage surgery and 1 underwent additional radiosurgery. The majority of patients started with Class D hearing, but of those with Class A or B hearing before treatment, 53.5% maintained serviceable hearing at 3 years of follow-up. The pretreatment and posttreatment median THI Grades were both 1. The pretreatment and posttreatment ABC scores were unchanged at 81%. Conclusion The LINAC-based CK (18 Gy over 3 fractions at 80% isodose line) provides tumor control rates comparable to other forms of radiosurgery. Analysis for tumor growth was positive for 17% using maximum linear diameters and 26% with a volumetric workstation. This discrepancy is consistent with previous reports where volumetric models were found to be more sensitive in establishing growth. Serviceable hearing was comparable to previous SRS and SRT reports with an overall hearing preservation of 53.5%. This number was 77% in those with pre-Class A hearing. SRS did not affect pretreatment tinnitus or vestibular function.

We performed an evaluation of the CyberKnife InCise MLC by comparing plan qualities for single and multiple brain lesions generated using the first version of InCise MLC, fixed cone, and Iris collimators. We also investigated differences in delivery efficiency among the three collimators. Twenty‐four patients with single or multiple brain mets treated previously in our clinic on a CyberKnife M6 using cone/Iris collimators were selected for this study. Treatment plans were generated for all lesions using the InCise MLC. Number of monitor units, delivery time, target coverage, conformity index, and dose falloff were compared between MLC‐ and clinical cone/Iris‐based plans. Statistical analysis was performed using the nonparametric Wilcoxon‐Mann‐Whitney signed‐rank test. The planning accuracy of the MLC‐based plans was validated using chamber and film measurements. The InCise MLC‐based plans achieved mean dose and target coverage comparable to the cone/Iris‐based plans. Although the conformity indices of the MLC‐based plans were slightly higher than those of the cone/Iris‐based plans, beam delivery time for the MLC‐based plans was shorter by 30%∼40%. For smaller targets or cases with OARs located close to or abutting target volumes, MLC‐based plans provided inferior dose conformity compared to cone/Iris‐based plans. The QA results of MLC‐based plans were within 5% absolute dose difference with over 90% gamma passing rate using 2%/2 mm gamma criteria. The first version of InCise MLC could be a useful delivery modality, especially for clinical situations for which delivery time is a limiting factor or for multitarget cases. PACS number(s): 87.53.Ly, 87.55.D‐

The use of small fields in radiation therapy techniques has increased substantially in particular in stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT). However, as field size reduces further still, the response of the detector changes more rapidly with field size, and the effects of measurement uncertainties become increasingly significant due to the lack of lateral charged particle equilibrium, spectral changes as a function of field size, detector choice, and subsequent perturbations of the charged particle fluence. This work presents a novel 3D dose volume-to-point correction method to predict the readings of a 0.015 cc PinPoint chamber (PTW 31014) for both small static-fields and composite-field dosimetry formed by fixed cones on the CyberKnife® M6™ machine. A 3D correction matrix is introduced to link the 3D dose distribution to the response of the PinPoint chamber in water. The parameters of the correction matrix are determined by modeling its 3D dose response in circular fields created using the 12 fixed cones (5 mm–60 mm) on a CyberKnife® M6™ machine. A penalized least-square optimization problem is defined by fitting the calculated detector reading to the experimental measurement data to generate the optimal correction matrix; the simulated annealing algorithm is used to solve the inverse optimization problem. All the experimental measurements are acquired for every 2 mm chamber shift in the horizontal planes for each field size. The 3D dose distributions for the measurements are calculated using the Monte Carlo calculation with the MultiPlan® treatment planning system (Accuray Inc., Sunnyvale, CA, USA). The performance evaluation of the 3D conversion matrix is carried out by comparing the predictions of the output factors (OFs), off-axis ratios (OARs) and percentage depth dose (PDD) data to the experimental measurement data. The discrepancy of the measurement and the prediction data for composite fields is also performed for clinical SRS plans. The optimization algorithm used for generating the optimal correction factors is stable, and the resulting correction factors were smooth in the spatial domain. The measurement and prediction of OFs agree closely with percentage differences of less than 1.9% for all the 12 cones. The discrepancies between the prediction and the measurement PDD readings at 50 mm and 80 mm depth are 1.7% and 1.9%, respectively. The percentage differences of OARs between measurement and prediction data are less than 2% in the low dose gradient region, and 2%/1 mm discrepancies are observed within the high dose gradient regions. The differences between the measurement and prediction data for all the CyberKnife based SRS plans are less than 1%. These results demonstrate the existence and efficiency of the novel 3D correction method for small field dosimetry. The 3D correction matrix links the 3D dose distribution and the reading of the PinPoint chamber. The comparison between the predicted reading and the measurement data for static small fields (OFs, OARs and PDDs) yield discrepancies within 2% for low dose gradient regions and 2%/1 mm for high dose gradient regions; the discrepancies between the predicted and the measurement data are less than 1% for all the SRS plans. The 3D correction method provides an access to evaluate the clinical measurement data and can be applied to non-standard composite fields intensity modulated radiation therapy point dose verification.

Purpose: The aim of this study was to assess the outcomes of patients treated with stereotactic body radiation therapy (SBRT) in patients with primary, recurrent, or metastatic lung lesions, with a focus on positron emission tomography (PET)/computed tomography (CT)–based management. Patients and Methods Fifty-one patients with primary stage I non–small-cell lung cancer (NSCLC; n = 26), recurrent lung cancer after definitive treatment (n = 12), or solitary lung metastases (n = 13) were treated with SBRT between 2005 and 2007. Patients were treated with the CyberKnife® Robotic Radiosurgery System with Synchrony™ respiratory tracking. A dose of 60 Gy was delivered in 3 fractions. All patients had CT or PET/CT performed at approximately 3-month intervals after treatment. Results: The median follow-up was 12 months. Local control at median follow-up was 85% in patients with stage I NSCLC, 92% in patients with recurrent lung cancer, and 62% in the patients with solitary lung metastasis. Analysis of the 28 patients with pre- and post-treatment PET/CT scans demonstrated that those with stable disease (n = 4) had a mean standardized uptake value (SUV) decrease of 28%, partial responders (n = 11) had a decrease of 48%, and patients with a complete response (n = 11) had a decrease of 94%. Patients with progressive disease (n = 2) had an SUV decrease of only 0.4%. Only 2 patients (7%) who had reduced fluorodeoxyglucose avidity later progressed locally. No correlations were found between pretreatment SUV and tumor response, disease progression, or survival. Overall 1-year survival rates were 81%, 67%, and 85% among the patients with primary NSCLC, recurrent lung cancer, and solitary lung metastases, respectively. Conclusion Stereotactic body radiation therapy with CyberKnife® is an effective treatment for patients with medically inoperable recurrent or metastatic lung cancer. Positron emission tomography/CT is valuable in staging, planning, and evaluating treatment response and might predict long-term outcome.

Studies of organs in the thorax and abdomen have shown that these organs can move as much as 40 mm due to respiratory motion. Without compensation for this motion during the course of external beam radiation therapy, the dose coverage to target may be compromised. On the other hand, if compensation of this motion is by expansion of the margin around the target, a significant volume of normal tissue may be unnecessarily irradiated. In hypofractionated regimens, the issue of respiratory compensation becomes an important factor and is critical in single-fraction extracranial radiosurgery applications. CyberKnife is an image-guided radiosurgery system that consists of a 6-MV LINAC mounted to a robotic arm coupled through a control loop to a digital diagnostic x-ray imaging system. The robotic arm can point the beam anywhere in space with 6 degrees of freedom, without being constrained to a conventional isocenter. The CyberKnife has been recently upgraded with a real-time respiratory tracking and compensation system called Synchrony. Using external markers in conjunction with diagnostic x-ray images, Synchrony helps guide the robotic arm to move the radiation beam in real time such that the beam always remains aligned with the target. With the aid of Synchrony, the tumor motion can be tracked in three-dimensional space, and the motion-induced dosimetric change to target can be minimized with a limited margin. The working principles, advantages, limitations, and our clinical experience with this new technology will be discussed.

Background Surgical resection is the standard of care for patients with resectable non-small cell lung carcinoma (NSCLC) or limited pulmonary metastases. Stereotactic radiosurgery (SRS) may offer an alternative option for high-risk patients who are not surgical candidates. We report our initial experience with SRS in the treatment of lung neoplasm. Methods Patients who were medically inoperable were offered SRS. Thoracic surgeons evaluated all patients, placed fiducials, and planned treatment in collaboration with radiation oncologists. A median dose of 20 Gy prescribed to the 80% isodose line was administered in a single fraction. The initial response rate, time to progression, and overall survival were evaluated. Results During a 2-year period, 32 patients, 27 with NSCLC and 5 with pulmonary metastases, underwent SRS. Fiducial placement resulted in a pneumothorax requiring a pigtail catheter in 9 patients (28%). An initial complete response was observed in 7 patients (22%) and partial response in 10 (31%). Disease was stable in 9 (28%) and progression occurred in 5 patients (16%), with a median time to local progression of 11 months. The median overall survival was 26 months. The probability of 1-year overall survival was 78% (95% confidence interval [CI], 65% to 94%) for the entire group and 91% (95% CI, 75% to 100%) for stage I patients. Conclusions Our preliminary experience indicates that SRS has reasonable results in this high-risk group of patients, with pneumothorax being a significant morbidity. Surgery continues to offer the best chance of cure for resectable patients; however, SRS offers an alternative to high-risk patients.

The sequence of incremental dose delivery during a radiotherapy fraction can potentially influence the radiobiological effect. This would be most noticeable during the long fractions characteristic of hypo-fractionated stereotactic radiotherapy and radiosurgery. We demonstrate here the spatio-temporal variation of dose delivery by the CyberKnife to a lung tumor and propose strategies to reduce and/or correct for any resultant dose-time cytotoxic effects.

The aim of this study was to assess the feasibility and toxicity of stereotactic radiosurgery (CK-SRS) using the CyberKnife® Frameless Radiosurgery System (Accuray Inc., Sunnyvale, CA) in the management of recurrent squamous cell carcinoma of the head and neck region (SCCHN). Between November 2001 and February 2004, 22 patients with recurrent, previously irradiated SCCHN were treated with CK-SRS. The following endpoints were assessed post-CK-SRS: local control (LC), cause-specific survival (CSS), overall survival (OS), symptom relief, and acute and late toxicity. Kaplan-Meier survival analyses were used to estimate the LC, CSS, and OS rates. Clinical symptoms were graded as “improved,” “stable,” or “progressed” after CK-SRS. Acute and late toxicity were graded according to the National Cancer Institute Common Toxicity Criteria (CTC) scale, version 2.0. Seventeen patients were followed until their death. The median follow-up in the remaining five patients was 19 months (range 11–40 months). The median survival time for the entire cohort was 12 months from the time of CK-SRS. The 2-year LC, CSS, and OS rates were 26%, 26%, and 22%, respectively. After CK-SRS, symptoms were improved or stable in all but one patient who reported increasing pain. The treatment was well tolerated, with one case each of Grade 2 and 3 mucositis. There were no acute Grade 4 or 5 CTC toxicities. There were no late toxicities in this cohort. Frameless stereotactic radiosurgery for recurrent SCCHN is feasible and safe in the setting of high doses of prior irradiation. The majority of patients experienced palliation of disease without excess toxicity.

BACKGROUND Postoperative stereotactic radiosurgery for brain metastases potentially offers similar local control rates and fewer long-term neurocognitive sequelae compared to whole brain radiation therapy, although patients remain at risk for distant brain failure (DBF). OBJECTIVE To describe clinical outcomes of adjuvant stereotactic radiosurgery for large brain metastases and identify predictors of intracranial failure and their implications on optimal patient selection criteria. METHODS We performed a retrospective review on 100 large (>3 cm) brain metastases in 99 patients managed by resection followed by postoperative stereotactic radiosurgery to a median dose of 22 Gy (range, 10-28) in 1 to 5 fractions (median, 3). Primary histology was nonsmall cell lung in 40%, breast cancer in 18%, and melanoma in 17%. Forty (40%) patients had uncontrolled systemic disease. RESULTS With a median follow-up of 12.2 months (range, 0.6-87.4), the 1-year Kaplan-Meier local control was 72%, DBF 64%, and overall survival 55%. Nine patients (9%) developed evidence of radiation injury, and 6 (6%) developed leptomeningeal disease. Uncontrolled systemic disease (P=.03), melanoma histology (P=.04), and increasing number of brain metastases (P

BACKGROUND The spine is the most common site of bony metastases in patients with osseous breast carcinoma metastases. Spine metastases are the source of significant pain and occasionally neurologic deficit in this patient population. Conventional external beam radiotherapy lacks the precision to allow delivery of large single-fraction doses of radiation and simultaneously limit the dose to radiosensitive structures such as the spinal cord. This study evaluated the clinical efficacy of the treatment of spinal breast carcinoma metastases with a single-fraction radiosurgical technique. METHODS In this prospective cohort evaluation, 68 breast carcinoma metastases to the spine in 50 patients were treated with a single-fraction radiosurgery technique with a follow-up period of 6–48 months, median 16 months. The most common indication for radiosurgery treatment was pain in 57 lesions, as a primary treatment modality in 8 patients, and for radiographic tumor progression, as a postsurgical boost, and for a progressive neurologic deficit in 1 patient each. RESULTS Tumor volume ranged from 0.8–197 cm3 (mean, 27.7 cm3). Maximum tumor dose was maintained at 15–22.5 Gy (mean, 19 Gy). No radiation-induced toxicity occurred during the follow-up period (6–48 mo). Long-term axial and radicular pain improvement occurred in 55 of 57 (96%) patients who were treated primarily for pain. Long-term radiographic tumor control was seen in all patients who underwent radiosurgery as their primary treatment modality, for radiographic tumor progression, or as a postsurgical treatment. CONCLUSIONS Spinal radiosurgery was found to be feasible, safe, and clinically effective for the treatment of spinal metastases from breast carcinoma. The results indicate the potential of radiosurgery in the treatment of patients with spinal breast metastases, especially those with solitary sites of spine involvement, to improve long-term palliation. Cancer 2005. © 2005 American Cancer Society.

Objective The role of stereotactic radiosurgery for the treatment of intracranial lesions is well established. Its use for the treatment of spinal lesions has been limited by the availability of effective target-immobilizing devices. Conventional external beam radiotherapy lacks the precision to allow delivery of large doses of radiation near radiosensitive structures such as the spinal cord. The CyberKnife (Accuray, Inc., Sunnyvale, CA) is an image-guided frameless stereotactic radiosurgery system that allows for the radiosurgical treatment of spinal lesions. This study evaluated the feasibility and effectiveness of the treatment of spinal lesions with a single-fraction radiosurgical technique using the CyberKnife. Methods The CyberKnife system uses the coupling of an orthogonal pair of x-ray cameras to a dynamically manipulated robot-mounted linear accelerator with six degrees of freedom that guides the therapy beam to the intended target without the use of frame-based fixation. Real-time imaging allows the tracking of patient movement. Cervical spine lesions were located and tracked relative to cranial bony landmarks; lower spinal lesions were tracked relative to fiducial bone markers. In this prospective cohort evaluation of a spine radiosurgery technique, 125 spinal lesions in 115 consecutive patients were treated with a single-fraction radiosurgery technique (45 cervical, 30 thoracic, 36 lumbar, and 14 sacral). There were 17 benign tumors and 108 metastatic lesions. All dose plans were calculated on the basis of computed tomographic images acquired from 1.25-mm slices with an inverse treatment planning technique. Radiosurgical circular cones ranging in diameter from 5 to 40 mm were used. Results Tumor volume ranged from 0.3 to 232 cm(3) (mean, 27.8 cm(3)). Seventy-eight lesions had received external beam irradiation previously. Tumor dose was maintained at 12 to 20 Gy to the 80% isodose line (mean, 14 Gy); canal volume receiving more than 8 Gy ranged from 0.0 to 1.7 cm(3) (mean, 0.2 cm(3)). No acute radiation toxicity or new neurological deficits occurred during the follow-up period (range, 9-30 mo; median, 18 mo). Axial and radicular pain improved in 74 of 79 patients who were symptomatic before treatment. Conclusion This is the first large prospective evaluation of this frameless image-guided spinal radiosurgery system. The CyberKnife system was found to be feasible, safe, and effective. The major potential benefits of radiosurgical ablation of spinal lesions are short treatment time in an outpatient setting with rapid recovery and symptomatic response. This technique offers a successful therapeutic modality for the treatment of a variety of spinal lesions as a primary treatment or for lesions not amenable to open surgical techniques, in medically inoperable patients, in lesions located in previously irradiated sites, or as an adjunct to surgery.

BACKGROUND: Historically, survival for even highly select cohorts of brain metastasis patients selected for SRS alone is

Background: This study evaluated the CyberKnife frameless image-guided radiosurgery system for the treatment of spinal lesions. Methods: This system utilizes the coupling of an orthogonal pair of X-ray cameras to a dynamically manipulated robot-mounted linear accelerator that guides the therapy beam to the intended target without the use of frame-based fixation. Cervical spine lesions are located and tracked relative to skull bony landmarks; lower spinal lesions are tracked relative to fiducial markers. 125 spinal lesions in 115 consecutive patients were treated with a single-fraction radiosurgery technique. Results: Tumor volume ranged from 0.3 to 232 ml (mean 27.8 ml). Tumor radiation dose was maintained at 12–20 Gy to the 80% isodose line (mean 14 Gy); the spinal cord or canal volume receiving greater than 8 Gy ranged from 0.0 to 1.7 ml (mean 0.2 ml). No acute radiation toxicity or new neurological deficits occurred during the follow-up period (3–24 months). Conclusions: The CyberKnife system was found to be feasible, safe and effective. The major potential benefits of radiosurgical ablation of spinal lesions are short treatment time in an outpatient setting with rapid recovery and good response.

Purpose: To investigate how respiration influences the motion of lung and pancreas tumors and to relate the observations to treatment procedures intended to improve dose alignment by predicting the moving tumor’s position from external breathing indicators. Methods and materials: Breathing characteristics for five healthy subjects were observed by optically tracking the displacement of the chest and abdomen, and by measuring tidal air volume with a spirometer. Fluoroscopic imaging of five radiotherapy patients detected the motion of lung and pancreas tumors synchronously with external breathing indicators. Results: The external and fluoroscopic data showed a wide range of behavior in the normal breathing pattern and its effects on the position of lung and pancreas tumors. This included transient phase shifts between two different external measures of breathing that diminished to zero over a period of minutes, modulated phase shifts between tumor and chest wall motion, and other complex phenomena. Conclusions: Respiratory compensation strategies that infer tumor position from external breathing signals, including methods of beam gating and dynamic beam tracking, require three-dimensional knowledge of the tumor’s motion trajectory as well as the ability to detect and adapt to transient and continuously changing characteristics of respiratory motion during treatment.

Background A significant number of patients have recurrent or persistent lung cancer despite complete resection or treatment with definitive chemoradiation. Stereotactic radiosurgery (SRS)/stereotactic body radiation therapy is emerging as an important modality for the treatment of early-stage lung neoplasm; SRS may also offer an alternative treatment option for patients with recurrent lung disease. We evaluated outcomes after treatment with SRS for recurrent lung neoplasm in a large series of patients. Methods Selected patients with limited recurrent, persistent, or progressive disease after one or more prior treatments for lung cancer were offered SRS. Thoracic surgeons evaluated all patients, placed fiducials when needed, and planned treatment in close collaboration with radiation oncologists and medical physicists. In our early experience, a single fraction of 20 Gy radiation was prescribed and was subsequently increased to 45 to 60 Gy in three to five fractions. The primary endpoint evaluated was overall survival. Results We treated 100 patients with recurrent lung cancer (median age 72 years) with SRS. The postprocedure 30-day mortality rate was 0%; median follow-up was 51 months (range, 5 to 123). The median overall survival for the entire group was 23 months (95% confidence interval: 19 to 41). The probability of 2-year and 5-year overall survival was 49% (95% confidence interval: 40% to 60%) and 31% (95% confidence interval: 23% to 43%), respectively. Conclusions Our experience indicates that SRS is safe, and offers an alternative modality for selected patients with recurrent oligometastatic or persistent lung cancer. Thoracic surgeons should actively participate in SRS and continue to evaluate the efficacy of this treatment strategy.

Background Few guidelines exist on stereotactic body radiation therapy (SBRT) treatment planning for recurrent head and neck cancer. We assessed the impact of retrospectively adding margins/automated PET volumes to the gross tumor volume (GTV) in patients with post-SBRT recurrences. Materials and methods We reviewed 89 patients with recurrent head and neck cancer treated with SBRT using no margin around the GTV. GTVs were recontoured with 1–5mm margins. PET-CT planned GTVs were also recontoured by adding PET-standardized uptake value (SUV) 3.5 , SUV 4.5 , SUV 40% max , and signal/background ratio (SBR) to the original GTV. We deformably registered recontoured GTVs to post-SBRT scans and assessed fraction of recurrence volume (RV) falling within the GTV, the "RV-GTV overlap." Results With non-PET-CT planning, median RV-GTV overlap increased from 11.7% to 48.2% using 5mm margins, and median GTV size increased by 41.8cc (156%). With PET-CT planning, RV-GTV overlap increased from 45% to 93.6% using 5mm margins, and GTV size increased by 34.8cc (140%). Adding SUV 3.5 and SBR increased RV-GTV overlap from 45% to 73.3% and 73.6%, with GTV size increases of 0.8 (3%) and 3.1cc (11%), respectively. Conclusions Recontouring increased recurrence coverage and also GTV size. Margins up to 5mm may reduce failures but could possibly increase toxicities. Automated PET contours may reduce near-miss failures with smaller increases in GTV size.

Background Stereotactic body radiation therapy (SBRT) has seen increasing use as a salvage strategy for selected patients with recurrent, previously-irradiated squamous cell carcinoma of the head and neck (rSCCHN). PET-CT may be advantageous for tumor delineation and evaluation of treatment failures in SBRT. We analyzed the patterns of failure following SBRT for rSCCHN and assessed the impact of PET-CT treatment planning on these patterns of failure. Methods We retrospectively reviewed 96 patients with rSCCHN treated with SBRT. Seven patients (7%) were treated after surgical resection of rSCCHN and 89 patients (93%) were treated definitively. PET-CT treatment planning was used for 45 patients whereas non-PET-CT planning was used for 51 patients. Categories of failure were assigned by comparing recurrences on post-treatment scans to the planning target volume (PTV) from planning scans using the deformable registration function of VelocityAI™. Failures were defined: In-field (>75% inside PTV), Overlap (20-75% inside PTV), Marginal ( Results Median follow-up was 7.4 months (range, 2.6–52 months). Of 96 patients, 47 (49%) developed post-SBRT failure. Failure distribution was: In-field–12.3%, Overlap–24.6%, Marginal–36.8%, Regional/Distant–26.3%. There was a significant improvement in overall failure-free survival (log rank p = 0.037) and combined Overlap/Marginal failure-free survival (log rank p = 0.037) for those receiving PET-CT planning vs. non-PET-CT planning in the overall cohort (n = 96). Analysis of the definitive SBRT subgroup (n = 89) increased the significance of these findings (overall failure: p = 0.008, Overlap/Marginal failure: p = 0.009). There were no significant differences in age, gender, time from prior radiation, dose, use of cetuximab with SBRT, tumor differentiation, and tumor volume between the PET-CT and non-PET-CT groups. Conclusions Most failures after SBRT treatment for rSCCHN were near misses, i.e. Overlap/Marginal failures (61.4%), suggesting an opportunity to improve outcomes with more sensitive imaging. PET-CT treatment planning showed the lowest rate of overall and near miss failures and is beneficial for SBRT treatment planning.

To assess the effect of stereotactic body radiotherapy (SBRT) dose and tumor volume on outcomes in patients with recurrent, previously irradiated squamous cell carcinoma of the head and neck.A total of 96 patients with recurrent, previously irradiated squamous cell carcinoma of the head and neck were treated with SBRT using Cyberknife and Trilogy-intensity-modulated radiosurgery. Kaplan-Meier survival analyses were used to estimate locoregional control (LRC) and overall survival rates. Response was evaluated using positron emission tomography/computed tomography or computed tomography and detailed physical examination.The median follow-up for all patients was 14 months (2-39 months). The median dose of prior radiation was 68.4 Gy (32-170 Gy). Patients were divided into 4 SBRT dose groups: I (15-28 Gy/n = 29), II (30-36 Gy/n = 22), III (40 Gy/n = 18), and IV (44-50 Gy/n = 27). The median gross tumor volume (GTV) was 24.3(3) cm (2.5-162 cm). For GTV ≤25 cm(3) (n = 50), complete response rates were 27.8%/30%/45.5%/45.5%, and for GTV25 cm(3) (n = 46), complete response rates were 20%/25%/42.8%/50% for SBRT groups I-IV, respectively. The 1-/2-/3-year LRC rates for doses 40 to 50 Gy were 69.4%/57.8%/41.1%, respectively, whereas for 15 to 36 Gy, they were 51.9%/31.7%/15.9%, respectively (P = 0.02). The overall 1- and 2-year overall survival rates were 58.9% and 28.4%, respectively. Treatment was well tolerated with no grade 4/5 toxicities.Dose escalation up to 50 Gy in 5 fractions is feasible with SBRT for recurrent head and neck squamous cell carcinoma. Higher SBRT doses were associated with significantly higher LRC rates. Large tumor volume required higher SBRT doses to achieve optimal response rates compared with smaller tumor volume.

Purpose: The aim of this study was to analyze results of stereotactic radiosurgery (SRS) as adjuvant therapy for resected brain metastases. Methods: Medical records of patients treated at a single institution with SRS to the postoperative cavity of brain metastases were retrospectively reviewed. Patients who completed the prescribed SRS regimen following gross-total resection and had no previous whole brain radiotherapy were included in the study. Kaplan-Meier analyses were used to estimate local (LC) and intracranial control (IC), and overall survival (OS) rates. Results: Between April 2005 and July 2010, 77 patients (median age 63 years) with 89 metastases met the inclusion criteria. The median prescription dose was 18 Gy (12–27 Gy) delivered in 1–3 fractions for a median target volume of 7.6 cm3 (0.5–59 cm3). The 6-month, 1-year, and 2-year LC rates were 76.1, 76.1, and 74.3%, respectively. The 6-month, 1-year, and 2-year IC rates were 75.2, 54, and 43.6%, respectively. With a median follow-up of 13.8 months, the median OS was 14.5 months (1.9–51.4 months) after SRS. The overall 6-month, 1-year, and 2-year OS rates were 91, 62.5, and 43.6%, respectively. Complications included 2 patients with radiation necrosis. Conclusion: Adjuvant radiosurgery to the tumor cavity of resected brain metastases is well-tolerated and achieves LC in the majority of patients.

Endoscopic endonasal surgery (EES) has been shown to be a feasible approach to cranial base tumors while reducing post-operative morbidity. Using the endoscopic endonasal approach alone or in combination with open approaches may provide advantages over conventional approaches. However, the balance between maximal resection and minimal injury to neurovascular structures frequently precludes gross total resection (GTR). Consequently, adjuvant radiation therapy may be an important option to improve local control (LC) of residual disease. In this retrospective series, we report clinical outcomes, morbidity, and LC of 40 patients with cranial base tumors treated with EES +/- combined open approach followed by fSRS (CyberKnife, Accuray Inc.). 26 patients had benign disease, 7 had newly diagnosed malignant disease, and 7 had previously resected malignant disease. Surgical outcomes were evaluable in all patients. LC after fSRS was evaluable in 39 patients and defined as no evidence of regrowth by MRI, CT, & physical examination. GTR was achieved in 12/40. Median post-operative length of stay (LOS) was 3 days. In multivariable analysis controlling for anatomic location and malignant histology, post-operative complications (n = 10) were significantly associated with patients having combined open and EES (p < 0.01, OR = 16.9). SRS was delivered in 1–5 sessions to a median marginal dose of 24.9 Gy. Median follow-up was 24.7 months (range, 1.5 to 61 months). LC was achieved in 89.7% (35/39) of evaluable patients. LC was achieved in 11/12 patients who had GTR. Median progression-free survival was 19.7 months (21.0 months for benign tumors (n = 26), 5.8 months for previously resected malignant disease (n = 7), and 21.2 months for newly diagnosed malignant disease (n = 7). Of the 31 patients who had symptomatic disease at presentation, 18 (58%) reported complete symptom resolution, 9 partial, and 4 no improvement. One patient who received two prior courses of radiation therapy developed osteosclerosis (grade III). Other adverse events were erythema (grade I, n = 5), nausea (grade II, n = 2), conjunctivitis (grade II, n = 1). EES followed by fSRS is a safe and effective management strategy for selected cranial base tumors. EES combined with an open surgical approach may result in increased complications. However, initial follow-up offers encouraging results indicating shorter time to recovery, acceptable LC rates compared to conventional approaches, and similar median time to progression for benign and newly diagnosed malignant disease.

Objectives: The aim of this study was to assess the safety and outcome of stereotactic body radiotherapy (SBRT) in patients with recurrent previously irradiated squamous cell carcinoma of the head and neck (rSCCHN). Methods: We reviewed our experience with 85 patients who received SBRT for rSCCHN between January 2003 and May 2008. The mean dose of SBRT was 35 Gy (range: 15-44 Gy). The following end points were evaluated: tumor response, time-to-progression, acute and late toxicities, local control (LC) rates and impact of tumor dose and tumor size on LC, and overall survival. Results: The median follow-up of all patients was 6 months (range: 1.3-39 months). For those patients who were alive at last follow-up (40%) the median follow-up was 17.6 months. The mean total dose of prior radiation to the primary site was 74 Gy (range: 32-170 Gy). Those patients who received SBRT

OBJECTIVE: The role of stereotactic radiosurgery for the treatment of intracranial benign tumors is well established. There is less experience and more controversy regarding its use for benign tumors of the spine. This study evaluated the clinical efficacy of radiosurgery as part of the treatment paradigm of selected benign tumors of the spine. METHODS: Seventy-three benign intradural extramedullary spinal tumors were treated with a radiosurgery technique and prospectively evaluated. Patient ages ranged from 18 to 85 years (mean age, 44 yr); the follow-up period was 8 to 71 months (median, 37 mo). Lesion location included 43 cervical, five thoracic, 19 lumbar, and six sacral. Tumor histology included neurofibroma (25 cases), schwannoma (35 cases), and meningioma (13 cases). Twenty-one cases were associated with neurofibromatosis Type 1, and nine patients had neurofibromatosis Type 2. Nineteen tumors (26%) had previously undergone open surgical resection, and six tumors (8%) had previously been treated with conventional external beam irradiation techniques. RESULTS: Similar radiation doses were prescribed for all three histopathologies. The maximum intratumoral dose was 1500 to 2500 cGy (mean, 2164 Gy). Tumor volume ranged from 0.3 to 93.4 cm 3 (mean, 10.5 cm 3 ; median, 4.11 cm 3 ). Radiosurgery was used for the treatment of postsurgical radiographic progression in 18 cases; it was used as the primary treatment modality in 14 cases; it was used for treatment of radiographic tumor progression in nine cases; and it was used for the treatment of postsurgical residual tumor in two cases. Long-term pain improvement occurred in 22 out of 30 cases (73%). Long-term radiographic tumor control was demonstrated in all cases. Three patients experienced new symptoms attributed to radiation-induced spinal cord toxicity 5 to 13 months after treatment. CONCLUSION: Single fraction radiosurgery was found to be clinically effective for the treatment of benign extramedullary spinal neoplasms. Although surgical extirpation remains the primary treatment option for most benign spinal tumors, radiosurgery was demonstrated to have short-term clinical benefits for the treatment of such lesions. The long-term efficacy of spinal radiosurgery for such tumors will be determined with longer follow-up periods. Its role in patients with neurofibromatosis will also be further defined with greater clinical experience.

Background Surgical resection is the standard of care for patients with resectable non-small cell lung cancer or selected patients with pulmonary metastases. Stereotactic radiosurgery may offer an alternative option for high-risk patients who are not surgical candidates. We report our initial experience with stereotactic radiosurgery in the treatment of lung neoplasm in 100 consecutive patients. Methods Patients who were medically inoperable were offered stereotactic radiosurgery. Thoracic surgeons evaluated all patients, placed fiducials, and performed treatment planning in collaboration with radiation oncologists. Initially, a median dose of 20 Gy prescribed to the 80% isodose line was administered in a single fraction, and this was subsequently increased to a total of 60 Gy in three fractions. The primary end point evaluated was overall survival. Results We treated 100 patients (median age, 70 years; 51 men, 49 women) with stereotactic radiosurgery: 46 (46%) with primary lung neoplasm, 35 (35%) with recurrent cancer, and 19 (19%) with pulmonary metastases. The median follow-up was 20 months. The median overall survival was 24 months. Local recurrence occurred in 25 patients. The probability of 2-year overall survival was 50% for the entire group, 44% for primary lung cancer, 41% for recurrent cancer, and 84% for metastatic cancer. Conclusions Our initial experience indicates that stereotactic radiosurgery has reasonable results in these high-risk patients. Resection continues to remain the standard treatment; however, stereotactic radiosurgery may offer an alternative in high-risk patients. Further prospective studies with different dose schema are needed to evaluate the efficacy of stereotactic radiosurgery.

Study design A prospective nonrandomized, longitudinal cohort study. Objective To evaluate the clinical outcomes of single-fraction radiosurgery as part of the management of metastatic spine tumors. Summary of background data The role of stereotactic radiosurgery for the treatment of spinal lesions has previously been limited by the availability of effective target immobilization and target tracking devices. Large clinical experience with spinal radiosurgery to properly assess clinical experience has previously been limited. Methods A cohort of 500 cases of spinal metastases underwent radiosurgery. Ages ranged from 18 to 85 years (mean 56). Lesion location included 73 cervical, 212 thoracic, 112 lumbar, and 103 sacral. Results The maximum intratumoral dose ranged from 12.5 to 25 Gy (mean 20). Tumor volume ranged from 0.20 to 264 mL (mean 46). Long-term pain improvement occurred in 290 of 336 cases (86%). Long-term tumor control was demonstrated in 90% of lesions treated with radiosurgery as a primary treatment modality and in 88% of lesions treated for radiographic tumor progression. Twenty-seven of 32 cases (84%) with a progressive neurologic deficit before treatment experienced at least some clinical improvement. Conclusions The results indicate the potential of radiosurgery in the treatment of patients with spinal metastases, especially those with solitary sites of spine involvement, to improve long-term palliation.

The role of stereotactic radiosurgery for the treatment of intracranial lesions is well established. Its use for the treatment of spinal lesions has been limited by the availability of effective tar

Purpose: Accuray has recently released a new collimator, the InCise™ Multileaf Collimator (MLC), for clinical use with the CyberKnife M6™ System. This work reports the results of measurements of output factors (OF) for fields shaped by the InCise™ Multileaf collimator, Iris collimator and fixed cones. Methods: The MLC consists of 41 pairs of 2.5 mm wide leaves projecting a minimum and maximum field size of 7.6 mm × 7.5 mm and 110 mm × 97.5 mm at 800 mm SAD. OF measurements were made using 6 different detectors: PTW stereotactic and electron diodes, PTW microDiamond detector, Sun Nuclear Edge diode, IBA SFD diode and PFD 3G photon diode. Measurements were made for 14 MLC field sizes and 12 cone/Iris field sizes (5mm to 60 mm diameter field sizes). All measurements were made in a Wellhofer water tank at the depth of maximum dose. Correction factors from Francescon et al (PMB 59, 2014, N11-N17; 17, 2012 3741–3748) were used to correct the diode responses for the fixed cone and Iris measurements. Results: For the MLC fields no correction factors are currently available. For the cones and Iris collimator, the average of corrected OF for all diodes ranged from 0.651 ± 0.014 (5mm cone) to 0.994 ± 0.001 (50 mm cone); for the Iris collimator the corresponding values are 0.510 ±0.004 and 0.997 ±0.000 respectively. The OF for the MLC field sizes ranged from 0.806 ±0.009 for the 7.6 mm × 7.5 mm field to 1.023± 0.003 for the 110 mm × 97.5 mm field size. Conclusion: The present results are the first set of output factor data reported for the InCise™ MLC, Iris collimator and the fixed cones for the CyberKnife M6™ system. Good agreement is obtained among all the corrected data for the cones and Iris data.

Purpose: Accuray recently released a new collimator, the InCise™ Multileaf Collimator (MLC), for clinical use with the CyberKnife M6™ System. This work reports the results of acceptance testing and commissioning measurements for this collimator. Methods: The MLC consists of 41 pairs of 2.5 mm wide leaves projecting a clinical maximum field size of 110 mm x 97.5 mm at 800 mm SAD. The leaves are made of tungsten, 90 mm in height and tilted by 0.5 degree. The manufacturer stated leaf positioning accuracy and reproducibility are 0.5 mm and 0.4 mm respectively at 800 mm SAD. The leaf over-travel is 100% with full interdigitation capability. Acceptance testing included, but are not limited to, the verification of the specifications of various parameters described above, leakage measurements and end-to-end tests. Dosimetric measurements included, but not limited to, measurements of output factors, open beam profiles, tissue-phantom ratios, beam flatness and symmetry, and patient specific QA. Results: All measurements were well within the manufacturer specifications. The values of output factors ranged from 0.804 (smallest field size of 7.6 mm x 7.5 mm) to 1.018 (largest field size of 110.0 mm x 97.5 mm). End-to-end test results for the various tracking modes are: Skull (0.27mm), fiducial (0.16mm), Xsight Spine (0.4mm), Xsight Lung (0.93 mm) and Synchrony (0.43mm). Measured maximum and average leakage was 0.37% and 0.3%, respectively. Patient-specific QA measurements with chamber were all within 5% absolute dose agreement, and film measurements all passed 2%/2mm gamma evaluation for more than 95% of measurement points. Conclusion: The presented results are the first set of data reported on the InCise™ MLC. The MLC proved to be very reliable and is currently in clinical use.

Background/Aims: Large clinical experience with spinal radiosurgery to properly assess clinical experience has previously been limited. This study evaluated the clinical outcomes of single fraction

Object. The role of stereotactic radiosurgery in treating renal cell carcinoma (RCC) metastases to the spine has previously been limited. In this study the authors evaluated the clinical outcome in patients with spinal RCC who underwent single-fraction radiosurgery. Methods. Forty-eight patients with 60 RCC metastases to the spine (six cervical, 26 thoracic, 18 lumbar, and 10 sacral) were treated with a single-fraction radiosurgery technique and were followed for a period of 14 to 48 months (median 37 months). All patients were successfully treated in an outpatient setting. The tumor volume ranged from 5.5 to 203 cm3 (mean 61.9 cm3). Forty-two of the total 60 lesions had been previously treated with external-beam radiation therapy (EBRT). The maximum tumor dose was maintained at 17.5 to 25 Gy (mean 20 Gy). The volume of the spinal cord exposed to greater than 8 Gy ranged from 0.01 to 3 cm3 (mean 0.64 cm3); the volume of the spinal canal at the cauda equina level exposed to greater than 8 Gy ranged from 0.01 to 2.2 cm3 (mean 0.65 cm3). No radiation-induced toxicity occurred during the follow-up period. Axial and radicular pain improved in 34 (89%) of 38 patients who were treated primarily for pain. Tumor control was demonstrated in seven of eight patients treated primarily for radiographically documented tumor progression. In time six patients required open surgical intervention for tumor progression that had caused neurological dysfunction after radiosurgery. Conclusions. Spinal radiosurgery can be a successful therapeutic modality for the delivery of large-dose single-fraction radiation to RCC spinal metastases that are often poorly controlled with conventional EBRT modalities.

Object Patients with symptomatic pathological compression fractures require a stabilization procedure for mechanical control of back pain as well as radiation therapy for the underlying malignant process. In this study the authors evaluated a treatment paradigm of closed fracture reduction and fixation in which kyphoplasty was used, followed by single-fraction spinal radiosurgery performed with the CyberKnife. Methods Twenty-six patients (six men and 20 women, mean age 72 years) with histologically confirmed pathological compression fractures (16 thoracic, 10 lumbar) were prospectively evaluated. For inclusion in the study, the patients' presenting symptoms were limited to pain without neurological deficits. Histological findings included 11 lung, nine breast, and four renal carcinomas, one cholangiocarcinoma, and one ocular melanoma. All patients underwent kyphoplasty of the affected vertebral body, for which a percutaneous transpedicular procedure was used. Fiducial markers that allow image guidance for CyberKnife radiosurgery were placed into the pedicles at the adjacent levels at the time of the kyphoplasty procedure. Patients then underwent single-fraction radiosurgery (at a mean of 12 days after kyphoplasty) in an outpatient setting. The tumor dose was maintained at 16 to 20 Gy to the 80% isodose line (mean 18 Gy). Treated tumor volume ranged from 12.7 to 37.1 cm3. Axial pain improved in 24 (92%) of 26 patients during the follow-up period of 7 to 20 months. Conclusions A combined kyphoplasty and spinal radiosurgery treatment paradigm was found to be safe and clinically effective for patients with pathological fractures without significant spinal canal compromise. This technique combines two minimally invasive surgical procedures, thereby avoiding the morbidity associated with open surgery while providing immediate fracture fixation as well as a single-fraction tumoricidal radiation dose.

Object The role of stereotactic radiosurgery for the treatment of intracranial lesions is well established. Its use for the treatment of spinal lesions has been limited by the availability of effective target-immobilizing devices. In this study the authors evaluated the CyberKnife Real-Time Image-Guided Radiosurgery System for spinal lesion treatment involving a single-fraction radiosurgical technique. Methods This frameless image-guided radiosurgery system uses the coupling of an orthogonal pair of x-ray cameras to a dynamically manipulated robot-mounted linear accelerator possessing six degrees of freedom, which guides the therapy beam to the target without the use of frame-based fixation. Cervical lesions were located and tracked relative to osseous skull landmarks; lower spinal lesions were tracked relative to percutaneously placed gold fiducial bone markers. Fifty-six spinal lesions in 46 consecutive patients were treated using single-fraction radiosurgery (26 cervical, 15 thoracic, and 11 lumbar, and four sacral). There were 11 benign and 45 metastatic lesions. Tumor volume ranged from 0.3 to 168 ml (mean 26.7 ml). Thirty-one lesions had previously received external-beam radiotherapy with maximum spinal cord doses. Dose plans were calculated based on computerized tomography scans acquired using 1.25-mm slices. Tumor dose was maintained at 12 to 18 Gy to the 80% isodose line; spinal cord lesions receiving greater than 8 Gy ranged from 0 to 1.3 ml (mean 0.3 ml). All patients tolerated the procedure in an outpatient setting. No acute radiation-induced toxicity or new neurological deficits occurred during the follow-up period. Axial and radicular pain improved in all patients who were symptomatic prior to treatment. Conclusions Spinal stereotactic radiosurgery involving a frameless image-guided system was found to be feasible and safe. The major potential benefits of radiosurgical ablation of spinal lesions are short treatment time in an outpatient setting with rapid recovery and symptomatic response. This procedure offers a successful alternative therapeutic modality for the treatment of a variety of spinal lesions not amenable to open surgical techniques; the intervention can be performed in medically untreatable patients, lesions located in previously irradiated sites, or as an adjunct to surgery.

Object The role of stereotactic radiosurgery for the treatment of intracranial lesions is well established. The experience with radiosurgery for the treatment of spinal and sacral lesions is more limited. Sacral lesions should be amenable to radiosurgical treatment similar to that used for their intracranial counterparts. The authors evaluated a single-fraction radiosurgical technique performed using the CyberKnife Real-Time Image-Guided Radiosurgery System for the treatment of the sacral lesion. Methods The CyberKnife is a frameless radiosurgery system based on the coupling of an orthogonal pair of x-ray cameras to a dynamically manipulated robot-mounted linear accelerator possessing six degrees of freedom, which guides the therapy beam to the intended target without the need for frame-based fixation. All sacral lesions were located and tracked for radiation delivery relative to fiducial bone markers placed percutaneously. Eighteen patients were treated with single-fraction radiosurgery. Tumor histology included one benign and 17 malignant tumors. Dose plans were calculated based on computerized tomography scans acquired using 1.25-mm slices. Planning treatment volume was defined as the radiographically documented tumor volume with no margin. Tumor dose was maintained at 12 to 20 Gy to the 80% isodose line (mean 15 Gy). Tumor volume ranged from 23.6 to 187.4 ml (mean 90 ml). The volume of the cauda equina receiving greater than 8 Gy ranged from 0 to 1 ml (mean 0.1 ml). All patients underwent the procedure in an outpatient setting. No acute radiation toxicity or new neurological deficits occurred during the mean follow-up period of 6 months. Pain improved in all 13 patients who were symptomatic prior to treatment. No tumor progression has been documented on follow-up imaging. Conclusions Stereotactic radiosurgery was found to be feasible, safe, and effective for the treatment of both benign and malignant sacral lesions. The major potential benefits of radiosurgical ablation of sacral lesions are relatively short treatment time in an outpatient setting and minimal or no side effects. This new technique offers a new and important therapeutic modality for the primary treatment of a variety of sacral tumors or for lesions not amenable to open surgical techniques.

Purpose: To evaluate the effect of breath-holding on the short-term reproducibility and long-term variability of tumor position during image-guided radiosurgery. Method: Thirteen patients have undergone single-fraction radiosurgery treatments during which the tumor was repeatedly imaged radiographically to observe its position. The imaging data were used to monitor the efficacy of breath-holding and to periodically readjust the alignment of the treatment beam with the tumor. These measurements have allowed the effects of breathing, heartbeat, patient movement, and instrumental uncertainties to be separately identified in the record of tumor position. Results: During inspiration breath-holding, the lung tumor position was reproducible to within 1 mm, on average, in the direction of maximum displacement during regular breathing, and to within 1.8 mm in three dimensions overall. The pancreas tumor position in three dimensions was reproducible to within 2.5 mm on average. Some patients showed a slow, steady drift of tumor position during the extended sequence of breath-holds, which was compensated by periodic retargeting of the treatment beam. Conclusion: Breath-holding can allow the reduction of tumor motion dosimetry margins to 2 mm or less for lung cancer treatments, provided that the treatment system can detect and adapt to long-term variations in the mean tumor position during a lengthy treatment fraction.

Purpose: With the sequential optimization algorithm in MultiPlan system, clinical objectives (homogeneity, PTV coverage, conformity, normal tissue protection) can be optimized in sequence. However, the prescription isodose line (RxIDL) varies widely among institutions, which can influence the optimized dose distribution. The aim of this study is to investigate the impact of different prescription isodose lines on plan quality for the treatment of brain metastases using CyberKnife Multiplan system. Methods: Ten patients with multiple metastases were selected for this study. Four plans were generated for each patient such that 100% of the target volume receives the prescribed dose of 18 Gy, which was 50%, 60%, 70%, and 80% prescription Isodose line, separately. The prescription isodose was calculated as the ratio of the prescription dose and the maximum dose in target volume. The dosimetric parameters, including PTV coverage, conformity index (CI), gradient index (GI) and the volume covered by 12 Gy (V12Gy) were analyzed. The plan Monitor Units (MU) and treatment time were also compared. Results: All plans can provide the same target coverage (100%) and similar conformity index (1.26, 1.30, 1.32, and 1.29 on average for 80%, 70%, 60%, and 50% RxIDL plans, separately); there was no difference in critical structure dose. The 50% RxIDL plans have much lower GI (4.21±1.79 for 50% and 5.56±2.92 for 80% RxIDL plans) and V12Gy (13.36±10.31cc for 50% and 15.87±11.85cc for 80% RxIDL plans). The variation in estimated treatment delivery time was insignificant. Conclusion: The dose falloff is much faster for the lower RxIDL plans in terms of GI and V12Gy. For 50% RxIDL plans, the average V12Gy decreases by 16% compared to 80% RxIDL plans, which indicates that the normal tissue can be better protected by decreasing the prescription Isodose line.

The Cyberknife™ is an image guided robot arm mounted linear accelerator capable of frameless stereotactic treatment of both intracranial as well as extracranial sites1–3. The Cyberknife utilizes a lightweight 6 MV X-band linear accelerator. The Cyberknife is used clinically for treatment of intracranial, head and neck, and spinal lesions. It is presently being proposed for use in treatment protocol to extracranial sites including the pancreas, lung, and prostate. The goal of this work is to characterize the Cyberknife linac for the development of a Monte Carlo treatment plan verification tool.

Fluoroscopic, ultrasonic and 4D CT studies of the organs in the thorax and abdomen have shown that some organs may move as much as 4 cm due to respiratory motion. If the motion is not compensated for during external beam radiation therapy, the dose coverage to target may be compromised. On the other hand, if the motion is compensated for with an increase of margin, a significant amount of normal tissue may be irradiated unnecessarily. The issue of respiratory compensation becomes more important for hypofractionated treatments and even more so for single‐fraction extracranial radiosurgery applications. CyberKnife is an image‐guidedradiosurgery system that consists of a 6‐MV LINAC mounted to a robotic arm coupled through a control loop to a digital diagnostic x‐ray imaging system. The robotic arm can point the beam anywhere in space with six degrees of freedom, without being constrained to a conventional isocenter. The CyberKnife has been recently upgraded with a real‐time respiratory tracking and compensation system called Synchrony. Using external markers in conjunction with diagnostic x‐ray images, Synchrony helps to guide the robotic arm to move the radiation beam in real time such that the beam always remains aligned with the target. With the aid of the Synchrony, the tumor motion can be tracked in three dimensional space, and the motion induced dosimetric change to target can be minimized without an increase in margin. The working principles, advantages, limitations and our clinical experience with this new technology will be discussed.

full 3D motion of CTV. A prototype Hexamotion 6D motion platform was used in the validation study. It was used to simulate patient specific tumor motion pattern. The platform moves with input at every 20 ms. Three different VMAT plans were delivered with movement and compared with static measurements. In addition, each of the VMAT plans was also delivered with a sinusoidal motion pattern with peak to peak amplitudes of 1, 2 and 3 cm and target period of 3.5 seconds. All the measurements were performed using a 3D dosimeter with each of the VMAT plan irradiated 3 times, each irradiation starting at a random point in respiratory cycle. The average monitor units (MU) per plan was 2910 MU, the average number of segments per plan was 191 with 2 MU being minimum MU per control point. Results: All static plans passed with local gamma at 99.6% and 96.8% at 3%, 3mm and 2%, 2mm threshold criteria respectively. The average passing rate for local gamma with patient specific tumor motion was 96.7 % and 90% at 3%, 3mm and 2%, 2mm threshold criteria respectively. The average passing rate at 3% 3mm threshold criteria was 97.2% with 2cm peak to peak sinusoidal motion in the superior-inferior (SI) direction and 76.7% for the 3 cm peak to peak SI amplitude sinusoidal motion pattern. Conclusion: Dosimetry measurements using 3D and Hexamotion 6D platform indicate that single arc VMAT plans can be accurately delivered and that interplay effect is not significant for target amplitudes less than or equal to 2cm. The interplay effect is low because of the larger averaging effect associated with increased dose per fraction (1000 cGy) delivered during at least 90 breathing cycles. Author Disclosure: R. Varadhan: None. S. Way: None. C. Overbeck: None. K. Nisi: None.

Purpose: To investigate the feasibility of RapidArc technique on intracranial radiosurgery for multiple lesions. Methods: Six patients who were previously treated using cone‐based technique, Cyberknife were included in this study. These patients have multiple lesions (6–9, mostly metastasis). In our current clinical practice, each lesion was planned and treated individually. The prescription was 15–21 Gy at 80% with single fraction. These cases were replanned with RapidArc on the platform of Varian Truebeam STx equipped with high resolution MLC leaves of 2.5mm at center. The maximum dose rate is 1400 MU/min at 6 MV for flattering filter free mode. Because of long span of multiple lesions, the targets were divided into two groups with two isocenters. Each plan with one isocenter contains 4 non‐coplanar arcs, and dose optimization was performed with the two plans combined. Critical organs, such as eyes, brainstem and brain were constrained. The individual Cyberknife plans were summed to compare with the RapidArc plan. Scenarios of setup error were simulated during RapidArc treatment. Results: RapidArc plans can achieve comparable target coverage and normal tissue avoidance to Cyberknife plans. The brain dose volume histogram (DVH) curves of the two techniques are similar in spite of different appearance of their 3D dose distributions. MU is much higher for summed Cyberknife plan. Because RapidArc can treat several lesions together, the complete treatment time for all lesions is significantly reduced. However RapidArc treatment is susceptible to setup error, which may cause increase in normal tissue dose and decrease in target dose coverage. The level of discrepancy depends on the magnitude of setup error, location and dose distribution of the target. Conclusion: Multiple brain lesions treatment with RapidArc radiosurgery is clinically feasible with setup error fully accounted. It can provide dose performance comparable to cone‐based Cyberknife treatment.

Purpose: Management of recurrent presacral rectal cancer is often not amenable to curative surgery. The goal of this study is to evaluate the safety and efficacy of cyberknife stereotactic body radiotherapy (SBRT) in the management of presacral recurrences. Materials and Methods: Between April 2003 and October 2008, 14 patients with presacral tumors from rectal adenocarcinoma were SBRT treated. Eleven patients were treated with 36 Gy in 3 fractions and 3 patients were treated with single fraction of 12, 16 or 18 Gy. Tumor response was assessed using response evaluation and criteria in solid tumor (RECIST) criteria. Toxicities were assessed with common terminology criteria adverse events v 3.0. Pain control was assessed. Results: One patient (6.7%) received SBRT as boost therapy. All patients had prior radiotherapy [median 50.4 Gy (20 - 81 Gy)]. Median tumor volume was 52.5 cc (19 - 110 cc). At initial follow-up of a median 4.9 months (1 - 16.3 months), treatment responses were complete response (n=3) and stable disease (n=8). With a median follow-up of 16.5 months (6 - 69 months), the one- and two-year LC rates were 90.9 and 68.2%, respectively, and the one- and two-year OS rates were 90 and 78.8%, respectively. No factors were significantly predictive of LC and OS. There were no grade 3 or 4 toxicities. Fifty percent (n=7) of our patients experienced pain with recurrence before treatment and 4 (57.1%) of them reported no pain after completion of their SBRT. Conclusions: Stereotactic body radiotherapy for presacral recurrence of rectal adenocarcinoma is an efficacious and well-tolerated treatment modality which allows for palliation of pain.