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Title: SU-E-T-24: A Dose Volume Comparison in Stereotactic Body Radiation Therapy Using Flattened and Un-Flattened Photon Beams

Abstract

Purpose: Aim of this study is to compare the dose volume characteristics of 6X FFF (flattening Free Filter) Arc and 6X FB (flattened Beam) arc photon plans in SBRT technique. Methods: Eight patients who received linear Accelearator-based SBRT were retrospectively included in this study. A dose of 50 Gy was given to the target in five fractions. Same data set was used to generate plans for both FFF and FB. ITV was generated using maximum intensity projection and critical structures were derived using average intensity projection. PTV obtained by giving 0.5cm margin to ITV. Results: While both modalities can provide satisfactory target dose coverage, the dose to PTV was more heterogeneous in FFF than 6X FB plans in all cases. The doses in all plans were well below institutional constraints for both modalities. Comparing the results of Homogeneity Index(HI), Conformity Index(CI), PTV-D80% volume, D50% volume and D20% volume (Table-1 ) for both techniques, found all the indices are within limits of RTOG guidelines but the 6X FFF is superior in sparing normal tissues in compare with FB. In all cases studied, more treatment time was required for FB treatment delivery for a given prescription. The results indicate that for largemore » dose delivery FFF is preferable as volumetric parameters like HI and CI are better and dose can be delivered in a short span of time. Conclusion: Both Flattened and Unflattened beam SBRT systems can provide adequate dose coverage for target tumor. While the unflattened beams deliver less normal tissue dose than Flattened beams in all cases. The magnitude of differences in normal tissue dose between both modalities was due to beam characterization of the beams. Flattened beam requires more Monitor Units to deliver similar target prescription to the tumor than unflattened beam SBRT systems. The results of this study may provide a general guideline for patient and treatment modality selection based on volumetric, tumor control and normal tissue sparing considerations.« less

Authors:
 [1]
  1. American Oncology Institute, Hyderabad, Telangana (India)
Publication Date:
OSTI Identifier:
22545159
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 42; Journal Issue: 6; Other Information: (c) 2015 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; ANIMAL TISSUES; LIMITING VALUES; NEOPLASMS; PATIENTS; PHOTON BEAMS; RADIATION DOSES; RADIOTHERAPY; RECOMMENDATIONS

Citation Formats

Pangam, S. SU-E-T-24: A Dose Volume Comparison in Stereotactic Body Radiation Therapy Using Flattened and Un-Flattened Photon Beams. United States: N. p., 2015. Web. doi:10.1118/1.4924385.
Pangam, S. SU-E-T-24: A Dose Volume Comparison in Stereotactic Body Radiation Therapy Using Flattened and Un-Flattened Photon Beams. United States. doi:10.1118/1.4924385.
Pangam, S. Mon . "SU-E-T-24: A Dose Volume Comparison in Stereotactic Body Radiation Therapy Using Flattened and Un-Flattened Photon Beams". United States. doi:10.1118/1.4924385.
@article{osti_22545159,
title = {SU-E-T-24: A Dose Volume Comparison in Stereotactic Body Radiation Therapy Using Flattened and Un-Flattened Photon Beams},
author = {Pangam, S},
abstractNote = {Purpose: Aim of this study is to compare the dose volume characteristics of 6X FFF (flattening Free Filter) Arc and 6X FB (flattened Beam) arc photon plans in SBRT technique. Methods: Eight patients who received linear Accelearator-based SBRT were retrospectively included in this study. A dose of 50 Gy was given to the target in five fractions. Same data set was used to generate plans for both FFF and FB. ITV was generated using maximum intensity projection and critical structures were derived using average intensity projection. PTV obtained by giving 0.5cm margin to ITV. Results: While both modalities can provide satisfactory target dose coverage, the dose to PTV was more heterogeneous in FFF than 6X FB plans in all cases. The doses in all plans were well below institutional constraints for both modalities. Comparing the results of Homogeneity Index(HI), Conformity Index(CI), PTV-D80% volume, D50% volume and D20% volume (Table-1 ) for both techniques, found all the indices are within limits of RTOG guidelines but the 6X FFF is superior in sparing normal tissues in compare with FB. In all cases studied, more treatment time was required for FB treatment delivery for a given prescription. The results indicate that for large dose delivery FFF is preferable as volumetric parameters like HI and CI are better and dose can be delivered in a short span of time. Conclusion: Both Flattened and Unflattened beam SBRT systems can provide adequate dose coverage for target tumor. While the unflattened beams deliver less normal tissue dose than Flattened beams in all cases. The magnitude of differences in normal tissue dose between both modalities was due to beam characterization of the beams. Flattened beam requires more Monitor Units to deliver similar target prescription to the tumor than unflattened beam SBRT systems. The results of this study may provide a general guideline for patient and treatment modality selection based on volumetric, tumor control and normal tissue sparing considerations.},
doi = {10.1118/1.4924385},
journal = {Medical Physics},
number = 6,
volume = 42,
place = {United States},
year = {Mon Jun 15 00:00:00 EDT 2015},
month = {Mon Jun 15 00:00:00 EDT 2015}
}
  • Purpose: To evaluate performance of three commercially available treatment planning systems for stereotactic body radiation therapy (SBRT) of lung cancer using the following algorithms: Boltzmann transport equation based algorithm (AcurosXB AXB), convolution based algorithm Anisotropic Analytic Algorithm (AAA); and Monte Carlo based algorithm (XVMC). Methods: A total of 10 patients with early stage non-small cell peripheral lung cancer were included. The initial clinical plans were generated using the XVMC based treatment planning system with a prescription of 54Gy in 3 fractions following RTOG0613 protocol. The plans were recalculated with the same beam parameters and monitor units using AAA and AXBmore » algorithms. A calculation grid size of 2mm was used for all algorithms. The dose distribution, conformity, and dosimetric parameters for the targets and organs at risk (OAR) are compared between the algorithms. Results: The average PTV volume was 19.6mL (range 4.2–47.2mL). The volume of PTV covered by the prescribed dose (PTV-V100) were 93.97±2.00%, 95.07±2.07% and 95.10±2.97% for XVMC, AXB and AAA algorithms, respectively. There was no significant difference in high dose conformity index; however, XVMC predicted slightly higher values (p=0.04) for the ratio of 50% prescription isodose volume to PTV (R50%). The percentage volume of total lungs receiving dose >20Gy (LungV20Gy) were 4.03±2.26%, 3.86±2.22% and 3.85±2.21% for XVMC, AXB and AAA algorithms. Examination of dose volume histograms (DVH) revealed small differences in targets and OARs for most patients. However, the AAA algorithm was found to predict considerable higher PTV coverage compared with AXB and XVMC algorithms in two cases. The dose difference was found to be primarily located at the periphery region of the target. Conclusion: For clinical SBRT lung treatment planning, the dosimetric differences between three commercially available algorithms are generally small except at target periphery. XVMC and AXB algorithms are recommended for accurate dose estimation at tissue boundaries.« less
  • Purpose: Flattening Filter Free (FFF) beams offer the potential for higher dose rates, short treatment time, and lower out of field dose. Therefore, the aim of this study was to investigate the dosimetric effects and out of field dose of Volumetric Modulated Arc Therapy (VMAT) plans using FFF vs Flattening Filtering (FF) beams for partial brain irradiation. Methods: Ten brain patients treated with a 6FF beam from a Truebeam STX were analyzed retrospectively for this study. These plans (46Gy at 2 Gy per fraction) were re-optimized for 6FFF beams using the same dose constraints as the original plans. PTV coverage,more » PTV Dmax, total MUs, and mean dose to organs-at-risk (OAR) were evaluated. In addition, the out-of-field dose for 6FF and 6FFF plans for one patient was measured on an anthropomorphic phantom. TLDs were placed inside (central axis) and outside (surface) the phantom at distances ranging from 0.5 cm to 17 cm from the field edge. Paired T-test was used for statistical analysis. Results: PTV coverage and PTV Dmax were comparable for the FF and FFF plans with 95.9% versus 95.6% and 111.2% versus 111.9%, respectively. Mean dose to the OARs were 3.7% less for FFF than FF plans (p<0.0001). Total MUs were, on average, 12.5% greater for FFF than FF plans with 481±55 MU (FFF) versus 429±50 MU (FF), p=0.0003. On average, the measured out of field dose was 24% less for FFF compared to FF, p<0.0001. A similar beam-on time was observed for the FFF and FF treatment. Conclusion: It is beneficial to use 6FFF beams for regular fractionated brain VMAT treatments. VMAT treatment plans using FFF beams can achieve comparable PTV coverage but with more OAR sparing. The out of field dose is significant less with mean reduction of 24%.« less
  • Purpose: The purpose of this study is to evaluate the dosimetric and radiobiological impact of Acuros XB (AXB) and Anisotropic Analytic Algorithm (AAA) dose calculation algorithms on prostate stereotactic body radiation therapy plans with both conventional flattened (FF) and flattening-filter free (FFF) modes. Methods: For thirteen patients with prostate cancer, SBRT planning was performed using 10-MV photon beam with FF and FFF modes. The total dose prescribed to the PTV was 42.7 Gy in 7 fractions. All plans were initially calculated using AAA algorithm in Eclipse treatment planning system (11.0.34), and then were re-calculated using AXB with the same MUsmore » and MLC files. The four types of plans for different algorithms and beam energies were compared in terms of homogeneity and conformity. To evaluate the radiobiological impact, the tumor control probability (TCP) and normal tissue complication probability (NTCP) calculations were performed. Results: For PTV, both calculation algorithms and beam modes lead to comparable homogeneity and conformity. However, the averaged TCP values in AXB plans were always lower than in AAA plans with an average difference of 5.3% and 6.1% for 10-MV FFF and FF beam, respectively. In addition, the averaged NTCP values for organs at risk (OARs) were comparable. Conclusion: This study showed that prostate SBRT plan were comparable dosimetric results with different dose calculation algorithms as well as delivery beam modes. For biological results, even though NTCP values for both calculation algorithms and beam modes were similar, AXB plans produced slightly lower TCP compared to the AAA plans.« less
  • Purpose: SBRT shows excellent tumor control and toxicity rates for patients with locally advanced pancreatic cancer (PCA). Herein, we evaluate the feasibility of using VMAT with ABC for PCA SBRT. Methods: Nine PCA patients previously treated via SBRT utilizing 11-beam step-and-shoot IMRT technique in our center were retrospectively identified, among whom eight patients received 3300cGy in 5 fractions while one received 3000cGy in 5 fractions. A VMAT plan was generated on each patient’s planning CT in Pinnacle v9.8 on Elekta Synergy following the same PCA SBRT clinical protocol. Three partial arcs (182°–300°, 300°-60°, and 60°-180°) with 2°/4° control-point spacing weremore » used. The dosimetric difference between the VMAT and the original IMRT plans was analyzed. IMRT QA was performed for the VMAT plans using MapCheck2 in MapPHAN and the total delivery time was recorded. To mimic the treatment situation with ABC, where patients hold their breath for 20–30 seconds, the delivery was intentionally interrupted every 20–30 seconds. For each plan, the QA was performed with and without beam interruption. Gamma analysis (2%/2mm) was used to compare the planned and measured doses. Results: All VMAT plans with 2mm dose grid passed the clinic protocol with similar PTV coverage and OARs sparing, where PTV V-RxDose was 92.7±2.1% (VMAT) vs. 92.1±2.6% (IMRT), and proximal stomach V15Gy was 3.60±2.69 cc (VMAT) vs. 4.80±3.13 cc (IMRT). The mean total MU and delivery time of the VMAT plans were 2453.8±531.1 MU and 282.1±56.0 seconds. The gamma passing rates of absolute dose were 94.9±3.4% and 94.5±4.0% for delivery without and with interruption respectively, suggesting the dosimetry of VMAT delivery with ABC for SBRT won’t be compromised. Conclusion: This study suggests that PCA SBRT using VMAT with ABC is a feasible technique without compromising plan dosimetry. The combination of VMAT with ABC will potentially reduce the SBRT treatment time.« less
  • Purpose: To measure the CT density model variations between different CT scanners used for treatment planning and impact on the accuracy of MC dose calculation in lung SBRT. Methods: A Gammex electron density phantom (RMI 465) was scanned on two 64-slice CT scanners (GE LightSpeed VCT64) and a 16-slice CT (Philips Brilliance Big Bore CT). All three scanners had been used to acquire CT for CyberKnife lung SBRT treatment planning. To minimize the influences of beam hardening and scatter for improving reproducibility, three scans were acquired with the phantom rotated 120° between scans. The mean CT HU of each densitymore » insert, averaged over the three scans, was used to build the CT density models. For 14 patient plans, repeat MC dose calculations were performed by using the scanner-specific CT density models and compared to a baseline CT density model in the base plans. All dose re-calculations were done using the same plan beam configurations and MUs. Comparisons of dosimetric parameters included PTV volume covered by prescription dose, mean PTV dose, V5 and V20 for lungs, and the maximum dose to the closest critical organ. Results: Up to 50.7 HU variations in CT density models were observed over the baseline CT density model. For 14 patient plans examined, maximum differences in MC dose re-calculations were less than 2% in 71.4% of the cases, less than 5% in 85.7% of the cases, and 5–10% for 14.3% of the cases. As all the base plans well exceeded the clinical objectives of target coverage and OAR sparing, none of the observed differences led to clinically significant concerns. Conclusion: Marked variations of CT density models were observed for three different CT scanners. Though the differences can cause up to 5–10% differences in MC dose calculations, it was found that they caused no clinically significant concerns.« less