Search

Objectives: Spatially fractionated radiation therapy (SFRT) intentionally delivers a heterogeneous dose distribution characterized by alternating regions of high and low doses throughout a tumor. This modality may enhance response to subsequent whole tumor radiation in bulky and radioresistant lesions that are historically less responsive to conventional radiation doses alone. The current study presents a single institution experience with modern era SFRT using predominantly a volumetric modulated arc therapy (VMAT) lattice technique., Methods: Patients treated with SFRT between 10/2019 and 6/2022 were included for analysis. Patient characteristics, tumor characteristics, and dosimetric parameters were collected retrospectively as part of an institutional review board approved registry and protocol. Descriptive statistics were used to collate patient data and Kaplan Meier analysis were generated for overall survival and local control. Univariate analyses were used to investigate factors associated with outcomes., Results: A total of 176 patients with 186 sites treated were included. Median age was 64 and the most commonly treated histologies were non-small cell lung cancer and sarcoma. The most common SFRT dose was 20 Gy in 1 fraction with 88% of patients receiving follow-up whole tumor radiotherapy to a median EQD2 dose of 32.5 Gy (=10). Median gross tumor volume (GTV) was 480.5 cc (7.8-10,897.8). Median follow-up was 322 days with 1 year overall survival 37% and 1 year local control 81%. Local control was available in 138 treated sites (131 patients. SFRT factors including dose to 10% (D10%), dose to 90% (D90%), equivalent uniform dose, and mean dose were highly predictive of local control. Grade 3 toxicity occurred in 9 patients. All of these patients received follow-up whole tumor radiation and at least two of these were attributable to unexpected rapid regression of tumor., Conclusions: SFRT is a promising technique that appears to confer good local control across a disparate group of patients with bulky and radioresistant tumors. Dosimetric parameters of SFRT treatment plans may be independent predictors of local control. Further investigation is warranted as are prospective trials to evaluate the role of SFRT in both the palliative and definitive setting., (Copyright © 2024 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.)

Purpose: Our purpose was to dosimetrically compare volumetric modulated arc therapy (VMAT) lattice radiation therapy (LRT), brass, and proton grid therapy planning techniques and suggest potential clinical applications for each., Methods and Materials: Four plans delivering 20 Gy in 1 fraction were created for each of 22 patients. Brass and proton grid plans used a single static field and the same beam angle. Proton grid plans used the same beam size and spacing as the brass block. Two VMAT LRT plans were generated for each patient: one with 1-cm diameter lattice points spaced 2-cm center-to-center (2-cm VMAT) and another with 1.5-cm diameter lattice points spaced 3-cm center-to-center (3- cm VMAT). Maximum, minimum, mean, and equivalent uniform dose and the dose to 90%, 50%, 20%, 10%, and 5% (D90%[%], D50%[%], etc) of gross tumor volume (GTV) were reported. D10%/D90% characterized dose heterogeneity. Normal tissue dose was generalized by the maximum dose and volume in cubic centimeters of tissue outside the GTV receiving 30% and 50% of prescription (body-GTV V30%[cm 3 ]; body-GTV V50%[cm 3 ])., Results: VMAT LRT plans delivered the highest maximum GTV doses while brass and proton plans delivered higher D5%(%), D10%(%), and D20%(%) values. D50%(%), D90%(%), and minimum dose varied little between plan types. Proton and brass plans had the highest dose heterogeneity. Two-centimeter VMAT and brass grid plans had the highest mean GTV doses. Two-centimeter VMAT plans had the highest equivalent uniform dose, followed by 3-cm VMAT, brass, and proton plans. VMAT LRT plans exhibited the lowest normal tissue maximum and body GTV V30%(cm 3 ) and body GTV V50%(cm 3 ) values., Conclusions: An in-depth comparison of target and normal tissue dosimetric parameters for common photon and proton grid therapy planning techniques was made. Strengths of each plan type were noted leading to general recommendations on usage., (Copyright © 2022 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.)

Purpose: To describe a novel and practical volumetric modulated arc therapy (VMAT) planning approach for grid therapy., Methods and Materials: Dose is prescribed to 1.5-cm diameter spherical contours placed throughout the gross tumor volume (GTV). Placement of spheres is variable, but they must maintain at least a 3-cm (center to center) separation, and the edge of any sphere must be at least 1 cm from any organ at risk (OAR). Three concentric ring structures are used during optimization to confine the highest doses to the center of the spheres and maximize dose sparing between them. The end result is alternating regions of high and low dose throughout the GTV and minimal dose to OARs. High-intensity flattening filter-free (FFF) modes are used to efficiently deliver the plans, and entire treatments typically take only 15 to 20 minutes., Results: The approach is illustrated with 2 examples treated at our institution. Patient #1 had a 1703-cm 3 mediastinal mass and was prescribed 20 Gray (Gy) to 24 spherical regions within the GTV. Patient #2 had a 3680-cm 3 abdominal tumor and was prescribed 18 Gy to 32 spherical regions within the GTV. Both patients received additional consolidative radiation approximately 1 week after the initial VMAT grid treatment. Each patient experienced marked reduction in tumor size and symptomatic relief without treatment-related complications., Conclusions: We have described in detail a planning approach for VMAT grid therapy treatments that can typically be delivered in a clinically practical time span. The VMAT approach is especially useful for tumors that are surrounded by sensitive critical structures. As many centers offer VMAT treatments, the approach is widely accessible and can be readily implemented once appropriate patient selection and delivery processes are established., (Copyright © 2020 The Author(s). Published by Elsevier Inc. All rights reserved.)

Purpose: This study aimed to evaluate dose calculation accuracy for the Eclipse Analytical Anisotropic Algorithm (AAA) and Acuros XB algorithm for various lung tumor sizes and to investigate dosimetric changes associated with treatment of regressing tumors., Methods and Materials: A water phantom with cylindrical cork inserts (lung surrogates) was fabricated. Large (202 cm 3 ), medium (54 cm 3 ), and small (3 cm 3 ) solid water tumors were implanted within cork inserts. A plain cork insert was used to simulate a lung without a tumor. The cork inserts and tumors were cut along the long axis, and Gafchromic film was placed between the sections to measure dose distributions. Three-dimensional conformal plans were created using 6 MV and 10 MV beams, and volumetric modulated arc therapy plans were created using 6 MV beams for each tumor size. Doses were calculated using Eclipse AAA and Acuros XB. The measured and calculated dose distributions were compared for each tumor size and treatment algorithm. To simulate a regressing tumor, the original plans created for the large tumor were separately delivered to the phantom that contained a small, medium, or no tumor. The dosimetric effects were evaluated using gamma passing rates with a 2%/2 mm criterion and dose profile comparisons., Results: Agreement between the measurements and AAA calculations decreased as tumor size decreased, but Acuros XB showed better agreement for all tumor sizes. The largest difference was observed for a 6 MV volumetric modulated arc therapy plan created to treat the smallest tumor. The gamma passing rate was 89.7% but that of Acuros was 99.5%. For the tumor regression evaluation, the gamma passing rates ranged from 53% to 99% for AAA. For Acuros XB, the gamma passing rates were >98% for all scenarios., Conclusion: Both AAA and Acuros XB calculated the dose accurately for the largest lung tumor. For the smallest and regressing tumors, Acuros XB more accurately modelled the dose distribution compared with AAA., (Copyright © 2018 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.)

Purpose: To assess the accuracy of the Eclipse Analytical Anisotropic Algorithm when calculating dose for spine stereotactic body radiation therapy treatments involving surgically implanted titanium hardware., Methods and Materials: A human spine was removed from a cadaver, cut sagittally along the midline, and then separated into thoracic and lumbar sections. The thoracic section was implanted with titanium stabilization hardware; the lumbar section was not implanted. Spine sections were secured in a water phantom and simulated for treatment planning using both standard and extended computed tomography (CT) scales. Target volumes were created on both spine sections. Dose calculations were performed using (1) the standard CT scale with relative electron density (RED) override of image artifacts and hardware, (2) the extended CT scale with RED override of image artifacts only, and (3) the standard CT scale with no RED overrides for hardware or artifacts. Plans were delivered with volumetric modulated arc therapy using a 6-MV beam with and without a flattening filter. A total of 3 measurements for each plan were made with Gafchromic film placed between the spine sections and compared with Eclipse dose calculations using gamma analysis with a 2%/2 mm passing criteria. A single measurement in a homogeneous phantom was made for each plan before actual delivery., Results: Gamma passing rates for measurements in the homogeneous phantom were 99.6% or greater. Passing rates for measurements made in the lumbar spine section without hardware were 99.3% or greater; measurements made in the thoracic spine containing titanium were 98.6 to 99.5%., Conclusions: Eclipse Analytical Anisotropic Algorithm can adequately model the effects of titanium implants for spine stereotactic body radiation therapy treatments using volumetric modulated arc therapy. Calculations with standard or extended CT scales give similarly accurate results., (Copyright © 2016 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.)

Purpose: To separate the dosimetric consequences of changing tumor volume from positional uncertainty for patients undergoing conventionally fractionated lung radiation therapy (RT) and to quantify which factor has a larger impact on dose to target volumes and organs at risk (OAR)., Methods and Materials: Clinical treatment plans from 20 patients who had received conventionally fractionated RT were retrospectively altered by replacing tumor and atelectasis with lung equivalent tissue in the treatment planning system calculations. To simulate positional uncertainty, the isocenter was shifted in both the altered and original plans by 2 and 5 mm in 6 directions. Rotational uncertainty was introduced by rotating each computed tomographic image set by ± 3 degrees about a superior-inferior axis extending through patient center. Additionally, after rotation the isocenter was translated back to its original point within the patient to evaluate whether purely translational corrections could minimize dosimetric consequences due to rotations., Results: Dosimetric statistics for each altered plan were compared with the original. Average changes in the planning target volume (PTV) receiving 95% of prescription dose (PTV V95%) resulting from changing tumor anatomy alone were approximately 0.1%. Average changes in PTV V95% resulting from positional uncertainty were greater (0.2%-4.2%) but were largely independent of whether or not the original tumor volume was present. For 3 patients, increases in volumes receiving 110% of the prescription dose were seen but were largely limited to within the PTV. Translational corrections for patient rotations were effective in minimizing differences in target coverage but had less effect on reducing the maximum spinal cord dose., Conclusions: Anatomic changes alone, such as reductions in tumor volume and atelectasis, had minimal effect on the overall dose distribution. Greater dosimetric consequences were seen with positional uncertainty. With accurate patient localization, replanning during the course of treatment for conventionally fractionated lung cancer patients may not be necessary.

Purpose: To evaluate the dependence of an automatic match process on the size of the user-defined region of interest (ROI), the structure volume of interest (VOI), and changes in tumor volume when using cone-beam computed tomography (CBCT) for tumor localization and to compare these results with a gold standard defined by a physician's manual match., Methods and Materials: Daily CBCT images for 11 patients with lung cancer treated with conventionally fractionated radiation therapy were retrospectively matched to a reference CT image using the Varian On Board Imager software (Varian, Palo Alto, CA) and a 3-step automatic matching protocol. Matches were performed with 3 ROI sizes (small, medium, large), with and without a structure VOI (internal target volume [ITV] or planning target volume [PTV]) used in the last step. Additionally, matches were performed using an intensity range that isolated the bony anatomy of the spinal column. All automatic matches were compared with a manual match made by a physician., Results: The CBCT images from 109 fractions were analyzed. Automatic match results depend on ROI size and the structure VOI. Compared with the physician's manual match, automatic matches using the PTV as the structure VOI and a small ROI resulted in differences ≥ 5 mm in 1.8% of comparisons. Automatic matches using no VOI and a large ROI differed by ≥ 5 mm in 30.3% of comparisons. Differences between manual and automatic matches using the ITV as the structure VOI increased as tumor size decreased during the treatment course., Conclusions: Users of automatic matching techniques should carefully consider how user-defined parameters affect tumor localization. Automatic matches using the PTV as the structure VOI and a small ROI were most consistent with a physician's manual match, and were independent of volumetric tumor changes., (Copyright © 2014 American Society for Radiation Oncology. Published by Elsevier Inc. All rights reserved.)