Search

The use of positron emission tomography (PET) in radiation therapy (RT) is rapidly increasing in the areas of staging, segmentation, treatment planning, and response assessment. The most common radiotracer is 18F-fluorodeoxyglucose ([ 18F]FDG), a glucose analog with demonstrated efficacy in cancer diagnosis and staging. However, diagnosis and RT planning are different endeavors with unique requirements, and very little literature is available for guiding physicists and clinicians in the utilization of [ 18F]FDG-PET in RT. The two goals of this report are to educate and provide recommendations. The report provides background and education on current PET imaging systems, PET tracers, intensity quantification, and current utilization in RT (staging, segmentation, image registration, treatment planning, and therapy response assessment). Recommendations are provided on acceptance testing, annual and monthly quality assurance, scanning protocols to ensure consistency between interpatient scans and intrapatient longitudinal scans, reporting of patient and scan parameters in literature, requirements for incorporation of [ 18F]FDG-PET in treatment planning systems, and image registration. The recommendations provided here are minimum requirements and are not meant to cover all aspects of the use of [ 18F]FDG-PET for RT.

PURPOSE: Internal organ motion reduces the accuracy and efficacy of radiation therapy. However, there is a lack of tools to objectively (based on a medical or scientific task) assess the dosimetric consequences of motion, especially on an individual basis. We propose to use therapy operating characteristic (TOC) analysis to quantify the effects of motion on treatment efficacy for individual patients. We demonstrate the application of this tool with pancreatic stereotactic body radiation therapy (SBRT) clinical data and explore the origin of motion sensitivity. METHODS: The technique is described as follows. (1) Use tumor-motion data measured from patients to calculate the motion-convolved dose of the gross tumor volume (GTV) and the organs at risk (OARs). (2) Calculate tumor control probability (TCP) and normal tissue complication probability (NTCP) from the motion-convolved dose volume histograms. (3) Construct TOC curves from TCP and NTCP models. (4) Calculate the area under the TOC curve (AUTOC) and use it as a figure of merit for treatment efficacy. We used tumor motion data measured from patients to calculate the relation between AUTOC and motion magnitude for 25 pancreatic SBRT treatment plans. Furthermore, to explore the driving factor of motion sensitivity of a given plan, we compared the dose distribution of motion-sensitive plans and motion-robust plans and studied the dependence of motion sensitivity to motion directions. RESULTS: Our technique is able to recognize treatment plans that are sensitive to motion. Under the presence of motion, the treatment efficacy of some plans changes from providing high tumor control and low risks of complications to providing no tumor control and high risks of side effects. Several treatment plans experience falloffs in AUTOC at a smaller magnitude of motion than other plans. In our dataset, a potential indicator of a motion-sensitive treatment plan is that the duodenum is in close proximity to the tumor in the SI direction. CONCLUSIONS: The TOC framework can serve as a tool to quantify the effects of internal organ motion in radiation therapy. With pancreatic SBRT clinical data, we applied this tool to study the change in treatment efficacy induced by motion for individual treatment plans. This framework could potentially be used clinically to understand the effects of motion in an individual patient and to design a patient-specific motion management plan. This framework could also be used in research to evaluate different components of the treatment process, such as motion-management techniques, treatment-planning algorithms, treatment margins, etc.

Purpose Motion often hinders the safe delivery of ablative doses of radiation in the treatment of pancreatic tumors. Real-time tumor-tracking methods are an emerging technique to increase the accuracy of delivery. In this study, we report on a large, retrospective cohort of pancreatic patients treated with real-time, fiducial-based, kV-image guidance of stereotactic body radiation therapy (SBRT). The purpose of our study was to determine the impact of real-time tracking on treatment accuracy, tumor dose, and clinical workflow. Methods and Materials Real-time tracking data from 68 patients treated with pancreatic SBRT were analyzed. The kV images orthogonal to the treatment beam were acquired in real time during treatment to visualize the location of implanted fiducial markers. Positional corrections were made if the fiducial markers were observed >3 mm from the expected reference position. We recorded the frequency and nature of treatment interventions resulting from real-time tracking and derived a neural network–based dosimetric model to calculate the impact of these in-treatment interventions on target dose. Results Treatment pauses that required patient realignment because of real-time tumor tracking occurred during 32% of all fractions. The median magnitude of realignment shifts was 5.2 mm (range, 2.1-18.9 mm). Forty-five percent of shifts resulted in dosimetric differences to the tumor; of these, the median point dose difference was 23% ± 22% of prescription dose (maximum, 94%). The number of pauses per fraction was significantly higher in patients treated with respiratory gating (vs abdominal compression) and in patients with greater treatment time. Conclusion Fiducial-based, real-time target tracking is clinically feasible for pancreatic SBRT treatment. Our data indicate that real-time tumor tracking leads to patient realignment in 32% of cases and results in significant benefits to target coverage. The increased accuracy of real-time target tracking may potentially enable safe dose escalation in pancreatic SBRT.

PURPOSE: To quantitatively evaluate published experiences with hepatic stereotactic body radiation therapy (SBRT), to determine local control rates after treatment of primary and metastatic liver tumors and to examine whether outcomes are affected by SBRT dosing regimen. METHODS AND MATERIALS: We identified published articles that reported local control rates after SBRT for primary or metastatic liver tumors. Biologically effective doses (BEDs) were calculated for each dosing regimen using the linear-quadratic equation. We excluded series in which a wide range of BEDs was used. Individual lesion data for local control were extracted from actuarial survival curves, and data were aggregated to form a single dataset. Actuarial local control curves were generated using the Kaplan-Meier method after grouping lesions by disease type and BED (100 Gy(10)). Comparisons were made using logerank testing. RESULTS: Thirteen articles met all inclusion criteria and formed the dataset for this analysis. The 1-, 2-, and 3-year actuarial local control rates after SBRT for primary liver tumors (n = 431) were 93%, 89%, and 86%, respectively. Lower 1- (90%), 2- (79%), and 3-year (76%) actuarial local control rates were observed for liver metastases (n = 290, logerank P = .011). Among patients treated with SBRT for primary liver tumors, there was no evidence that local control is influenced by BED within the range of schedules used. For liver metastases, on the other hand, outcomes were significantly better for lesions treated with BEDs exceeding 100 Gy(10) (3-year local control 93%) than for those treated with BEDs of 100 Gy(10) (3-year local control 65%, P < .001). CONCLUSIONS: Stereotactic body radiation therapy for primary liver tumors provides high rates of durable local control, with no clear evidence for a doseeresponse relationship among commonly utilized schedules. Excellent local control rates are also seen after SBRT for liver metastases when BEDs of >100 Gy(10) are utilized.

Documentation is a required component of a residency program, but can be difficult to collect and disseminate, resulting in minimal utilization by residents and faculty. The purpose of this work is to adapt a commercially‐available Web‐based medical residency management system to improve the learning experience by efficiently distributing program information, documenting resident activities, and providing frequent monitoring and timely feedback of resident progress. To distribute program information, program requirements and rotation readings were uploaded. An educational conference calendar was created with associated files and attendance records added. To document resident progress, requirements for over 37 different clinical procedures were added, for which the resident logged the total number of procedures performed. Progress reports were created and automatically distributed. To provide feedback to the resident, an extensive electronic evaluation system was created. Results are shown for the initial 21 months of program existence, consisting of a single resident for the first 12 months and two residents for the subsequent 9 months. The system recorded that 130 documents were uploaded and 100% of required documents were downloaded by the resident. In total, 385 educational conferences and meetings were offered, of which the residents attended 95%. The second‐year and first‐year residents logged 1030 and 522 clinical procedures, respectively. The residents submitted a total of 116 status reports detailing weekly activities, 100% of which were reviewed by faculty within an average of 11.3 days. A total of 65 evaluations of the residents were submitted. The residents reviewed 100% of respective evaluations within an average of 1.5 days. We have successfully incorporated a paperless, Web‐based management system in a medical physics residency program. A robust electronic documentation system has been implemented, which has played a central role in enhancing the training experience. PACS number: 01

To study the risk factors for radiation-induced lung toxicity (RILT) after stereotactic body radiation therapy (SBRT) of the thorax.Published studies on lung toxicity in patients with early-stage non-small cell lung cancer (NSCLC) or metastatic lung tumors treated with SBRT were pooled and analyzed. The primary endpoint was RILT, including pneumonitis and fibrosis. Data of RILT and risk factors were extracted from each study, and rates of grade 2 to 5 (G2+) and grade 3 to 5 (G3+) RILT were computed. Patient, tumor, and dosimetric factors were analyzed for their correlation with RILT.Eighty-eight studies (7752 patients) that reported RILT incidence were eligible. The pooled rates of G2+ and G3+ RILT from all 88 studies were 9.1% (95% confidence interval [CI]: 7.15-11.4) and 1.8% (95% CI: 1.3-2.5), respectively. The median of median tumor sizes was 2.3 (range, 1.4-4.1) cm. Among the factors analyzed, older patient age (P=.044) and larger tumor size (the greatest diameter) were significantly correlated with higher rates of G2+ (P=.049) and G3+ RILT (P=.001). Patients with stage IA versus stage IB NSCLC had significantly lower risks of G2+ RILT (8.3% vs 17.1%, odds ratio = 0.43, 95% CI: 0.29-0.64, P.0001). Among studies that provided detailed dosimetric data, the pooled analysis demonstrated a significantly higher mean lung dose (MLD) (P=.027) and V20 (P=.019) in patients with G2+ RILT than in those with grade 0 to 1 RILT.The overall rate of RILT is relatively low after thoracic SBRT. Older age and larger tumor size are significant adverse risk factors for RILT. Lung dosimetry, specifically lung V20 and MLD, also significantly affect RILT risk.

The objective of this work is to evaluate the interfractional biological effective dose (BED) variation in MammoSite high dose rate (HDR) brachytherapy. Dose distributions of 19 patients who received 34 Gy in 10 fractions were evaluated. A method was employed to account for nonuniform dose distribution in the BED calculation. Furthermore, a range of α/β values was utilized for specific clinical end points: fibrosis, telangiectasia, erythema, desquamation and breast carcinoma. Two scenarios were simulated to calculate the BED value using: i) the same dose distribution of fraction 1 over fractions 2–10 (constant case, CC), and ii) the actual delivered dose distribution for each fraction 1–10 (interfraction dose variation case, IVC). Although the average BED difference (IVC – CC) was

During Stereotactic Body Radiotherapy (SBRT) for the treatment of prostate cancer, an inflatable endorectal balloon (ERB) may be used to reduce motion of the target and reduce the dose to the posterior rectal wall. This work assessed the dosimetric impact of manual interventions on ERB position in patients receiving prostate SBRT and investigated the impact of ERB interventions on prostate shape. Daily kilovoltage (kV) cone-beam computed tomography (CBCT) imaging was performed to localize the PTV, and an automated fusion with the planning images yielded displacements required for PTV re-localization. When the ERB volume and/or position were judged to yield inaccurate repositioning, manual adjustment (ERB re-inflation and/or repositioning) was performed. Based on all 59 CBCT image sets acquired, a deformable registration algorithm was used to determine the dose received by, displacement of, and deformation of the prostate, bladder, and anterior rectal wall. This dose tracking methodology was applied to images taken before and after manual adjustment of the ERB (intervention), and the delivered dose was compared to that which would have been delivered in the absence of intervention. Interventions occurred in 24 out of 35 (69%) of the treated fractions. The direct effect of these interventions was an increase in the prostate radiation dose that included 95% of the PTV (D95) and an increase in prostate coverage. Additionally, ERB interventions reduced prostate deformation in the anterior-posterior (AP) direction, reduced errors in the sagittal rotation of the prostate, and increased the similarity in shape of the prostate to the radiotherapy plan. Image-guided interventions in ERB volume and/or position during prostate SBRT were necessary to ensure the delivery of the dose distribution as planned., 10 pages, 7 figures

Purpose: To propose a novel method to determine α/β from post radiation CT scans for different fractionations that does not rely on binary endpoint analysis. Methods: Pre‐and post‐RT (12mo) CT images from patients with lung cancer treated at 3 institutions, using conventional RT (Duke/North Carolina, VU Medical center Netherlands) and hypofractionated RT (VU and University of Colorado) were compared. Changes in normal lung tissue density were assessed and related to the regional RT dose (considered as a continuous variable) to generate a dose‐density response curves (DRC). Principal Component Analysis was used to characterize the deviation of each of the 449 DRCs to the mean DRC. In the low dose region ( 6 mo was 3.9 at (173 Conv‐fx / 131 Hypo‐fx). Restricted to the two VU fractionation sets, α/β was 2.3 (12 Conv‐fx/ 50 Hypo‐fx) at < 6mo. Adding the CU data to the VU data, α/β ratio became 2.8 (12 Conv‐fx/102 Hypo‐fx) indicating relative Result stability with regard to sample size. To be consistent with other institutions, the Duke/North Carolina data needed to be corrected by the density value in non‐irradiated regions. Conclusion: The estimated α/β value of 3.7 based on CT density changes is endpoint independent and compatible with published values for clinical endpoints. Despite inter‐institution processing variations, values from different subsets were consistent suggesting tolerance to noise.