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Title: SU-F-T-586: Pre-Treatment QA of InCise2 MLC Plans On a Cyberknife-M6 Using the Delta4 System in SBRT

Abstract

Purpose: Performing pre-treatment quality assurance (QA) with the Delta4 system (ScandiDos Inc., Madison, WI) is well established for linac-based radiotherapy. This is not true when using a Cyberknife (Accuray Inc., Sunnyvale, CA) where, typically film-based QA is applied. The goal of this work was to test the feasibility to use the Delta4 system for pre-treatment QA for stereotactic body radiation therapy (SBRT) using a Cyberknife-M6 equipped with the InCise2 multileaf collimator (MLC). Methods: In order to perform measurements without accelerator pulse signal, the Tomotherapy option within the Delta4 software was used. Absolute calibration of the Delta4 phantom was performed using a 10×10 cm{sup 2} field shaped by the InCise2 MLC of the Cyberknife-M6. Five fiducials were attached to the Delta4 phantom in order to be able to track the phantom before and during measurements. For eight SBRT treatment plans (two liver, two prostate, one lung, three bone metastases) additional verification plans were recalculated on the Delta4 phantom using MultiPlan. Dicom data was exported from MultiPlan and was adapted in order to be compatible with the Delta4 software. The measured and calculated dose distributions were compared using the gamma analysis of the Delta4 system. Results: All eight SBRT plans were successfullymore » measured with the aid of the Delta4 system. In the mean, 98.0±1.9%, 95.8±4.1% and 88.40±11.4% of measured dose points passed the gamma analysis using a global dose deviation criterion of 3% (100% corresponds to the dose maximum) and a distance-to-agreement criterion of 3 mm, 2 mm and 1 mm, respectively, and a threshold of 20%. Conclusion: Pre-treatment QA of SBRT plans using the Delta4 system on a Cyberknife-M6 is feasible. Measured dose distributions of SBRT plans showed clinically acceptable agreement with the corresponding calculated dose distributions.« less

Authors:
; ; ; ; ;  [1]
  1. Division of Medical Radiation Physics and Department of Radiation Oncology, Inselspital, Bern University Hospital, and University of Bern (Switzerland)
Publication Date:
OSTI Identifier:
22649161
Resource Type:
Journal Article
Resource Relation:
Journal Name: Medical Physics; Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 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; 61 RADIATION PROTECTION AND DOSIMETRY; COMPUTER CODES; COMPUTERIZED TOMOGRAPHY; LINEAR ACCELERATORS; PHANTOMS; QUALITY ASSURANCE; RADIATION DOSE DISTRIBUTIONS

Citation Formats

Schmidhalter, D, Henzen, D, Malthaner, M, Frauchiger, D, Fix, M K, and Manser, P. SU-F-T-586: Pre-Treatment QA of InCise2 MLC Plans On a Cyberknife-M6 Using the Delta4 System in SBRT. United States: N. p., 2016. Web. doi:10.1118/1.4956771.
Schmidhalter, D, Henzen, D, Malthaner, M, Frauchiger, D, Fix, M K, & Manser, P. SU-F-T-586: Pre-Treatment QA of InCise2 MLC Plans On a Cyberknife-M6 Using the Delta4 System in SBRT. United States. doi:10.1118/1.4956771.
Schmidhalter, D, Henzen, D, Malthaner, M, Frauchiger, D, Fix, M K, and Manser, P. 2016. "SU-F-T-586: Pre-Treatment QA of InCise2 MLC Plans On a Cyberknife-M6 Using the Delta4 System in SBRT". United States. doi:10.1118/1.4956771.
@article{osti_22649161,
title = {SU-F-T-586: Pre-Treatment QA of InCise2 MLC Plans On a Cyberknife-M6 Using the Delta4 System in SBRT},
author = {Schmidhalter, D and Henzen, D and Malthaner, M and Frauchiger, D and Fix, M K and Manser, P},
abstractNote = {Purpose: Performing pre-treatment quality assurance (QA) with the Delta4 system (ScandiDos Inc., Madison, WI) is well established for linac-based radiotherapy. This is not true when using a Cyberknife (Accuray Inc., Sunnyvale, CA) where, typically film-based QA is applied. The goal of this work was to test the feasibility to use the Delta4 system for pre-treatment QA for stereotactic body radiation therapy (SBRT) using a Cyberknife-M6 equipped with the InCise2 multileaf collimator (MLC). Methods: In order to perform measurements without accelerator pulse signal, the Tomotherapy option within the Delta4 software was used. Absolute calibration of the Delta4 phantom was performed using a 10×10 cm{sup 2} field shaped by the InCise2 MLC of the Cyberknife-M6. Five fiducials were attached to the Delta4 phantom in order to be able to track the phantom before and during measurements. For eight SBRT treatment plans (two liver, two prostate, one lung, three bone metastases) additional verification plans were recalculated on the Delta4 phantom using MultiPlan. Dicom data was exported from MultiPlan and was adapted in order to be compatible with the Delta4 software. The measured and calculated dose distributions were compared using the gamma analysis of the Delta4 system. Results: All eight SBRT plans were successfully measured with the aid of the Delta4 system. In the mean, 98.0±1.9%, 95.8±4.1% and 88.40±11.4% of measured dose points passed the gamma analysis using a global dose deviation criterion of 3% (100% corresponds to the dose maximum) and a distance-to-agreement criterion of 3 mm, 2 mm and 1 mm, respectively, and a threshold of 20%. Conclusion: Pre-treatment QA of SBRT plans using the Delta4 system on a Cyberknife-M6 is feasible. Measured dose distributions of SBRT plans showed clinically acceptable agreement with the corresponding calculated dose distributions.},
doi = {10.1118/1.4956771},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: To implement the new EBT-XD Gafchromic films for accurate dosimetric and geometric validation of stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) CyberKnife (CK) patient specific QA. Methods: Film calibration was performed using a triplechannel film analysis on an Epson 10000XL scanner. Calibration films were irradiated using a Varian Clinac 21EX flattened beam (0 to 20 Gy), to ensure sufficient dose homogeneity. Films were scanned to a resolution of 0.3 mm, 24 hours post irradiation following a well-defined protocol. A set of 12 QA was performed for several types of CK plans: trigeminal neuralgia, brain metastasis, prostate andmore » lung tumors. A custom made insert for the CK head phantom has been manufactured to yield an accurate measured to calculated dose registration. When the high dose region was large enough, absolute dose was also measured with an ionization chamber. Dose calculation is performed using MultiPlan Ray-tracing algorithm for all cases since the phantom is mostly made from near water-equivalent plastic. Results: Good agreement (<2%) was found between the dose to the chamber and the film, when a chamber measurement was possible The average dose difference and standard deviations between film measurements and TPS calculations were respectively 1.75% and 3%. The geometric accuracy has been estimated to be <1 mm, combining robot positioning uncertainty and film registration to calculated dose. Conclusion: Patient specific QA measurements using EBT-XD films yielded a full 2D dose plane with high spatial resolution and acceptable dose accuracy. This method is particularly promising for trigeminal neuralgia plan QA, where the positioning of the spatial dose distribution is equally or more important than the absolute delivered dose to achieve clinical goals.« less
  • Purpose: Patient-specific quality assurance (QA) is necessary to accurately deliver high dose radiation to the target, especially for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT). Unlike previous 2 dimensional (D) array QA devices, Delta{sup 4} can verify the dose delivery in 3D. In this study, the difference between calculated and measured dose distribution was compared with two QA devices (MATRIXX and Delta{sup 4}) to evaluate the delivery accuracy. Methods: Twenty-seven SRS/SBRT plans with VMAT were verified with point-dose and dose-map analysis. We use an ion chamber (A1SL, 0.053cc) for point-dose measurement. For verification of the dose map, themore » differences between the calculated and measured doses were analyzed with a gamma index using MATRIXX and Delta{sup 4} devices. The passing criteria for gamma evaluation were set at 3 mm for distance-to-agreement (DTA) and 3% for dose-difference. A gamma index less than 1 was defined as the verification passing the criteria and satisfying at least 95% of the points. Results: The mean prescribed dose and fraction was 40 ± 14.41 Gy (range: 16–60) and 10 ± 2.35 fractions (range: 1–8), respectively. In point dose analysis, the differences between the calculated and measured doses were all less than 5% (mean: 2.12 ± 1.13%; range: −0.55% to 4.45%). In dose-map analysis, the average passing rates were 99.38 ± 0.96% (range: 95.31–100%) and 100 ± 0.12% (range: 99.5%–100%) for MATRIXX and Delta{sup 4}, respectively. Even using criteria of 2%/2 mm, the passing rate of Delta{sup 4} was still more than 95% (mean: 99 ± 1.08%; range: 95.6%–100%). Conclusion: Both MATRIXX and Delta{sup 4} offer accurate and efficient verification for SRS/SBRT plans. The results measured by MATRIXX and Delta{sup 4} dosimetry systems are similar for SRS/SBRT performed with the VMAT technique.« less
  • Purpose: To illustrate 25% reduction in CyberKnife prostate SBRT treatment times using a water filled rectal balloon. Methods: We perform prostate SBRT using a 3800cGy in 4 fraction regimen prescribed between 51% 59% iso-dose lines to 95% of PTV using a CyberKnife System. The resultant heterogeneous dosimetry is analogous to HDR dosimetry. Our patients are treated in a feet first supine position to decrease treatment couch sag and also to position the prostate anatomy closer to the robot. CT imaging is performed with a Radiadyne Immobiloc rectal balloon filled with 45-50cc water placed firmly inside the patient's rectum. A treatmentmore » plan is developed from this CT study using Multiplan. The patient is treated every other day for 4 days using the rectal balloon for each fraction. Gold fiducials previously implanted inside the prostate are used for tracking by the CyberKnife system. Results: Critical structures comprise the usual GU anatomy of bladder, rectum, urethra, femoral-heads along with emphasis on doses to anterior rectal wall and rectal mucosa. The water filled rectal balloon localizes the rectum, which enables the physician to accurately contour both anterior rectal wall, and rectal mucosa. The balloon also has a gas release valve enabling better patient comfort. Rectum localization enables the CyberKnife system to make fewer corrections resulting in fewer treatment interruptions and time lost to re-adjustment for rectal motion, bowel filling and gas creation. Effective treatment times are reduced by 25% to approximately 45 minutes. Adoption of the balloon has required minimal change to our planning strategy and plan evaluation process. Conclusion: Patient follow-up comparisons show no difference in effectiveness of treatment with and without balloons We conclude that rectal balloons enhance patient comfort and decrease effective treatment times.« less
  • Purpose: To investigate the influence of respiratory motion on the delivered dose in lung stereotactic body radiotherapy (SBRT) using Cyberknife (CK) 0-View tracking mode. Methods: CT scans at inspiration and expiration of an anthropomorphic motion phantom were fused base on the spine and an internal target volume (ITV) was created. A 5mm expansion around the ITV resulted in the planning target volume. Three CK plans were generated in Accuray MultiPlan using Lung Optimization Tracking 0-View technique with the minimum MU per beam set to (a) 5MU, (b) 15MU and (c) 30MU, respectively. Doses were calculated on the expiration CT usingmore » Monte-Carlo algorithm. Each plan was delivered 5 times with a range of different starting phases in the respiratory cycle to assess the dose variation due to interplay effect. The delivered dose was measured with EBT3 Gafchromic film which was inserted in the moving target of the phantom. The target motion range is 3 cm in superior-inferior (SI) direction with the breathing period of 5 seconds. Results: The gamma analysis (5%/2mm) of the dose with the films in the transverse plane resulted in average passing rate of 95.5±4.1%, 96.7±2.6%, and 96.2±2.5% for plan (a), (b), and (c), respectively. For the sagittal films, the average passing rate was 91.1±4.9%, 92.1±3.6%, and 92.3±2.9% for the three plans, respectively. The disagreement between measurement and dose calculations were mostly on the target edges in SI direction. The mean measured versus calculated dose differences at the edge of target in SI direction were (a) 3.9±4.8%, (b) 2.4±3.3%, and (c) 2.2±3.2% for the three plans, respectively. Conclusions: The plans with low-MU beams (below 10MU) tend to cause slightly larger dose variation. However in terms of target coverage, the overall clinical dosimetric impact of the intrafraction respiratory motion in lung SBRT is insignificant when averaged over 3∼5 fractions.« less
  • Purpose: The latest publications indicate that the Ray Tracing algorithm significantly overestimates the dose delivered as compared to the Monte Carlo (MC) algorithm. The purpose of this study is to quantify this overestimation and to identify significant correlations between the RT and MC calculated dose distributions. Methods: Preliminary results are based on 50 preexisting RT algorithm dose optimization and calculation treatment plans prepared on the Multiplan treatment planning system (Accuray Inc., Sunnyvale, CA). The analysis will be expanded to include 100 plans. These plans are recalculated using the MC algorithm, with high resolution and 1% uncertainty. The geometry and numbermore » of beams for a given plan, as well as the number of monitor units, is constant for the calculations for both algorithms and normalized differences are compared. Results: MC calculated doses were significantly smaller than RT doses. The D95 of the PTV was 27% lower for the MC calculation. The GTV and PTV mean coverage were 13 and 39% less for MC calculation. The first parameter of conformality, as defined as the ratio of the Prescription Isodose Volume to the PTV Volume was on average 1.18 for RT and 0.62 for MC. Maximum doses delivered to OARs was reduced in the MC plans. The doses for 1000 and 1500 cc of total lung minus PTV, respectively were reduced by 39% and 53% for the MC plans. The correlation of the ratio of air in PTV to the PTV with the difference in PTV coverage had a coefficient of −0.54. Conclusion: The preliminary results confirm that the RT algorithm significantly overestimates the dosages delivered confirming previous analyses. Finally, subdividing the data into different size regimes increased the correlation for the smaller size PTVs indicating the MC algorithm improvement verses the RT algorithm is dependent upon the size of the PTV.« less