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Title: SU-F-T-275: A Correlation Study On 3D Fluence-Based QA and 2D Dose Measurement-Based QA

Abstract

Purpose: The aim of this paper was to demonstrate the feasibility and creditability of computing and verifying 3D fluencies to assure IMRT and VMAT treatment deliveries, by correlating the passing rates of the 3D fluence-based QA (P(ά)) to the passing rates of 2D dose measurementbased QA (P(Dm)). Methods: 3D volumetric primary fluencies are calculated by forward-projecting the beam apertures and modulated by beam MU values at all gantry angles. We first introduce simulated machine parameter errors (MU, MLC positions, jaw, gantry and collimator) to the plan. Using passing rates of voxel intensity differences (P(Ir)) and 3D gamma analysis (P(γ)), calculated 3D fluencies, calculated 3D delivered dose, and measured 2D planar dose in phantom from the original plan are then compared with those from corresponding plans with errors, respectively. The correlations of these three groups of resultant passing rates, i.e. 3D fluence-based QA (P(ά,Ir) and P(ά,γ)), calculated 3D dose (P(Dc,Ir) and P(Dc,γ)), and 2D dose measurement-based QA (P(Dm,Ir) and P(Dm,γ)), will be investigated. Results: 20 treatment plans with 5 different types of errors were tested. Spearman’s correlations were found between P(ά,Ir) and P(Dc,Ir), and also between P(ά,γ) and P(Dc,γ), with averaged p-value 0.037, 0.065, and averaged correlation coefficient ρ-value 0.942, 0.871more » respectively. Using Matrixx QA for IMRT plans, Spearman’s correlations were also obtained between P(ά,Ir) and P(Dm,Ir) and also between P(ά,γ) and P(Dm,γ), with p-value being 0.048, 0.071 and ρ-value being 0.897, 0.779 respectively. Conclusion: The demonstrated correlations improve the creditability of using 3D fluence-based QA for assuring treatment deliveries for IMRT/VMAT plans. Together with advantages of high detection sensitivity and better visualization of machine parameter errors, this study further demonstrates the accuracy and feasibility of 3D fluence based-QA in pre-treatment QA and daily QA. Research reported in this study is supported by the Agency for Healthcare Research and Quality (AHRQ) under award 1R01HS0222888. The senior author received research grants from ViewRay Inc. and Varian Medical System.« less

Authors:
; ; ; ; ; ;  [1]
  1. Washington University School of Medicine, Saint Louis, MO (United States)
Publication Date:
OSTI Identifier:
22648889
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; CORRELATIONS; ERRORS; RADIATION DOSES; RADIOTHERAPY; RATS

Citation Formats

Liu, S, Mazur, T, Li, H, Green, O, Sun, B, Mutic, S, and Yang, D. SU-F-T-275: A Correlation Study On 3D Fluence-Based QA and 2D Dose Measurement-Based QA. United States: N. p., 2016. Web. doi:10.1118/1.4956415.
Liu, S, Mazur, T, Li, H, Green, O, Sun, B, Mutic, S, & Yang, D. SU-F-T-275: A Correlation Study On 3D Fluence-Based QA and 2D Dose Measurement-Based QA. United States. doi:10.1118/1.4956415.
Liu, S, Mazur, T, Li, H, Green, O, Sun, B, Mutic, S, and Yang, D. 2016. "SU-F-T-275: A Correlation Study On 3D Fluence-Based QA and 2D Dose Measurement-Based QA". United States. doi:10.1118/1.4956415.
@article{osti_22648889,
title = {SU-F-T-275: A Correlation Study On 3D Fluence-Based QA and 2D Dose Measurement-Based QA},
author = {Liu, S and Mazur, T and Li, H and Green, O and Sun, B and Mutic, S and Yang, D},
abstractNote = {Purpose: The aim of this paper was to demonstrate the feasibility and creditability of computing and verifying 3D fluencies to assure IMRT and VMAT treatment deliveries, by correlating the passing rates of the 3D fluence-based QA (P(ά)) to the passing rates of 2D dose measurementbased QA (P(Dm)). Methods: 3D volumetric primary fluencies are calculated by forward-projecting the beam apertures and modulated by beam MU values at all gantry angles. We first introduce simulated machine parameter errors (MU, MLC positions, jaw, gantry and collimator) to the plan. Using passing rates of voxel intensity differences (P(Ir)) and 3D gamma analysis (P(γ)), calculated 3D fluencies, calculated 3D delivered dose, and measured 2D planar dose in phantom from the original plan are then compared with those from corresponding plans with errors, respectively. The correlations of these three groups of resultant passing rates, i.e. 3D fluence-based QA (P(ά,Ir) and P(ά,γ)), calculated 3D dose (P(Dc,Ir) and P(Dc,γ)), and 2D dose measurement-based QA (P(Dm,Ir) and P(Dm,γ)), will be investigated. Results: 20 treatment plans with 5 different types of errors were tested. Spearman’s correlations were found between P(ά,Ir) and P(Dc,Ir), and also between P(ά,γ) and P(Dc,γ), with averaged p-value 0.037, 0.065, and averaged correlation coefficient ρ-value 0.942, 0.871 respectively. Using Matrixx QA for IMRT plans, Spearman’s correlations were also obtained between P(ά,Ir) and P(Dm,Ir) and also between P(ά,γ) and P(Dm,γ), with p-value being 0.048, 0.071 and ρ-value being 0.897, 0.779 respectively. Conclusion: The demonstrated correlations improve the creditability of using 3D fluence-based QA for assuring treatment deliveries for IMRT/VMAT plans. Together with advantages of high detection sensitivity and better visualization of machine parameter errors, this study further demonstrates the accuracy and feasibility of 3D fluence based-QA in pre-treatment QA and daily QA. Research reported in this study is supported by the Agency for Healthcare Research and Quality (AHRQ) under award 1R01HS0222888. The senior author received research grants from ViewRay Inc. and Varian Medical System.},
doi = {10.1118/1.4956415},
journal = {Medical Physics},
number = 6,
volume = 43,
place = {United States},
year = 2016,
month = 6
}
  • Purpose: To investigate the efficacy of exit-fluence-based dose computation for prostate radiotherapy by determining if it estimates true dose more accurately than the original planning dose. Methods: Virtual exit-fluencebased dose computation was performed for 19 patients, each with 9–12 repeat CT images. For each patient, a 78 Gy treatment plan was created utilizing 5 mm CTV-to-PTV and OAR-to-PRV margins. A Monte Carlo framework was used to compute dose and exit-fluence images for the planning image and for each repeat CT image based on boney-anatomyaligned and prostate-centroid-aligned CTs. Identical source particles were used for the MC dose-computations on the planning andmore » repeat CTs to maximize correlation. The exit-fluence-based dose and image were computed by multiplying source particle weights by FC(x,y)=FP(x,y)/FT(x,y), where (x,y) are the source particle coordinates projected to the exit-fluence plane and we denote the dose/fluence from the plan by (DP,FP), from the repeat-CT as (DT,FT), and the exit-fluence computation by (DFC,FFC). DFC mimics exit-fluence backprojection through the planning image as FT=FFC. Dose estimates were intercompared to judge the efficacy of exit-fluence-based dose computation. Results: Boney- and prostate-centroid aligned results are combined as there is no statistical difference between them, yielding 420 dose comparisons per dose-volume metric. DFC is more accurate than DP for 46%, 33%, and 44% of cases in estimating CTV D98, D50, and D2 respectively. DFC improved rectum D50 and D2 estimates 54% and 49% respectively and bladder D50 and D2 47 and 49% respectively. While averaged over all patients and images DFC and DP were within 3.1% of DT, they differed from DT by as much as 22% for GTV D98, 71% for the Bladder D50, 17% for Bladder D2, 19% for Rectum D2. Conclusion: Exit-fluence based dose computations infrequently improve CTV or OAR dose estimates and should be used with caution. Research supported in part by Varian Medical Systems.« less
  • Purpose: Developing a fast and accurate calculation model to reconstruct the applied photon fluence from an external photon radiation therapy treatment based on an image recorded by an electronic portal image device (EPID). Methods: To reconstruct the initial photon fluence the 2D EPID image was corrected for scatter from the patient/phantom and EPID to generate the transmitted primary photon fluence. This was done by an iterative deconvolution using precalculated point spread functions (PSF). The transmitted primary photon fluence was then backprojected through the patient/phantom geometry considering linear attenuation to receive the initial photon fluence applied for the treatment.The calculation modelmore » was verified using Monte Carlo simulations performed with the EGSnrc code system. EPID images were produced by calculating the dose deposition in the EPID from a 6 MV photon beam irradiating a water phantom with air and bone inhomogeneities and the ICRP anthropomorphic voxel phantom. Results: The initial photon fluence was reconstructed using a single PSF and position dependent PSFs which depend on the radiological thickness of the irradiated object. Appling position dependent point spread functions the mean uncertainty of the reconstructed initial photon fluence could be reduced from 1.13 % to 0.13 %. Conclusion: This study presents a calculation model for fluence reconstruction from EPID images. The{sup Result} show a clear advantage when position dependent PSF are used for the iterative reconstruction. The basic work of a reconstruction method was established and further evaluations must be made in an experimental study.« less
  • Purpose: To compare the dose-volume histogram (DVH) parameters obtained by three-dimensional gynecologic brachytherapy planning with the rectosigmoid mucosal changes observed by flexible sigmoidoscopy. Methods and Materials: Between January 2004 and July 2005, 71 patients with International Federation of Gynecology and Obstetrics Stage IB-IIIB uterine cervical cancer underwent computed tomography-based high-dose-rate intracavitary brachytherapy. The total dose (external beam radiotherapy [RT] plus intracavitary brachytherapy) to the International Commission of Radiation Units and Measurements rectal point (ICRU{sub RP}) and DVH parameters for rectosigmoid colon were calculated using the equivalent dose in 2-Gy fractions ({alpha}/{beta} = 3 Gy). Sigmoidoscopy was performed every 6 monthsmore » after RT, with the 6-scale scoring system used to determine mucosal changes. Results: The mean values of the DVH parameters and ICRU{sub RP} were significantly greater in patients with a score of {>=}2 than in those with a score <2 at 12 months after RT (ICRU{sub RP}, 71 Gy{sub {alpha}}{sub /{beta}}{sub 3} vs. 66 Gy{sub {alpha}}{sub /{beta}}{sub 3}, p = 0.02; D{sub 0.1cc}, 93 Gy{sub {alpha}}{sub /{beta}}{sub 3} vs. 85 Gy{sub {alpha}}{sub /{beta}}{sub 3}, p = 0.04; D{sub 1cc}, 80 Gy{sub {alpha}}{sub /{beta}}{sub 3} vs. 73 Gy{sub {alpha}}{sub /{beta}}{sub 3}, p = 0.02; D{sub 2cc}, 75 Gy{sub {alpha}}{sub /{beta}}{sub 3} vs. 69 Gy{sub {alpha}}{sub /{beta}}{sub 3}, p = 0.02). The probability of a score of {>=}2 showed a significant relationship with the DVH parameters and ICRU{sub RP} (ICRU{sub RP}, p = 0.03; D{sub 0.1cc}, p = 0.05; D{sub 1cc}, p = 0.02; D{sub 2cc}, p = 0.02). Conclusion: Our preliminary data have shown that DVH values of the rectosigmoid colon obtained by computed tomography-based three-dimensional brachytherapy planning are reliable and predictive of score {>=}2 rectosigmoid mucosal changes.« less
  • We find a strong correlation between the peak energy at zero fluence (E{sub peak,0}) and the isotropic energy (E{sub {gamma},iso}) of the 22 pulses of nine gamma-ray bursts (GRBs) detected by the Fermi satellite. The correlation holds for the individual pulses of each GRB, which shows the reality of the correlation. The derived correlation (Spearman correlation coefficient, r, which is 0.96) is much stronger compared to the correlations using E{sub peak} (in place of E{sub peak,0}) determined from the time-integrated spectrum (r = 0.8), the time-resolved spectrum without accounting for broad pulse structures (r = 0.37), or the pulsewise spectrummore » (r = 0.89). Though the improvement in the E{sub peak}-E{sub {gamma},iso} relation (the Amati relation) for a pulsewise analysis is known earlier, this is the first time a parameter derived from a joint spectral and timing fit to the data is shown to improve the correlation. We suggest that E{sub peak,0}, rather than E{sub peak}, is intrinsic to a GRB pulse and a natural choice as the parameter in pulsewise correlation studies.« less
  • Purpose: Systematic radiotherapy plan quality assessment promotes quality improvement. Software tools can perform this analysis by applying site-specific structure dose metrics. The next step is to similarly evaluate the quality of the dose delivery. This study defines metrics for acceptable doses to targets and normal organs for a particular treatment site and scores each plan accordingly. The input can be the TPS or the measurement-based 3D patient dose. From this analysis, one can determine whether the delivered dose distribution to the patient receives a score which is comparable to the TPS plan score, otherwise replanning may be indicated. Methods: Elevenmore » neuroblastoma patient plans were exported from Eclipse to the Quality Reports program. A scoring algorithm defined a score for each normal and target structure based on dose-volume parameters. Each plan was scored by this algorithm and the percentage of total possible points was obtained. Each plan also underwent IMRT QA measurements with a Mapcheck2 or ArcCheck. These measurements were input into the 3DVH program to compute the patient 3D dose distribution which was analyzed using the same scoring algorithm as the TPS plan. Results: The mean quality score for the TPS plans was 75.37% (std dev=14.15%) compared to 71.95% (std dev=13.45%) for the 3DVH dose distribution. For 3/11 plans, the 3DVH-based quality score was higher than the TPS score, by between 0.5 to 8.4 percentage points. Eight/11 plans scores decreased based on IMRT QA measurements by 1.2 to 18.6 points. Conclusion: Software was used to determine the degree to which the plan quality score differed between the TPS and measurement-based dose. Although the delivery score was generally in good agreement with the planned dose score, there were some that improved while there was one plan whose delivered dose quality was significantly less than planned. This methodology helps evaluate both planned and delivered dose quality. Sun Nuclear Corporation has provded a license for the software described.« less