Room: AAPM ePoster Library
Purpose: investigate the gamma testing results of the IMPT PB plans vs MC plans for breast treatment.
Methods: breast patients were consecutively selected for this study. For each patient, two plans were retrospectively generated using the RayStation TPS: 1) the PB plan was calculated using PB algorithm and 2) the MC plan was calculated using MC algorithm with the same MUs and beam parameters as those in the PB plan. 2 en-face beams were used for each plan. Patient-specific QA was performed for each patient, which measured 2D dose distributions beam-by-beam using MatriXX PT. For each beam, two different depths were measured. As each plan contained 2 beams, 4 measurements were conducted for each patient. In total 80 measurements were performed for this study. The 3%/3mm gamma analysis was conducted to compare the TPS calculated planner dose distribution with the measured 2D dose. The PB plan gamma passing rate was compared with the MC plan.
Results: the 80 measurements in our study, for PB plans, 47.5%, 27.5%, and 20% of the measurements had a 3%/3mm gamma passing rate =95%, =90% but <95%, and <90%,respectively. For MC plans, 92.5% of the measurements had a gamma passing rate >95%, only 7.5% had a gamma passing rate in between 90% and 95%, and none had a gamma passing rate <90%. The PB plan had a significant lower gamma passing rate (P = 3.3E-14) compared with the MC plan. The median (range) of the 3%/3mm gamma passing rate were 94.7% (75.3%-99.8%) and 99.1% (90.9% -100%) for the PB plans and MC plans, respectively.
Conclusion: PB plan had a lower patient-specific QA gamma passing rate compared with the MC plan. The PB algorithm dose calculation error is, to some degree, reflected by the lower gamma testing rate.
Protons, Breast, Quality Assurance
Not Applicable / None Entered.