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Dose Evaluation From Scattered Protons in Passive Scattering Proton Therapy

C Kim1*, N Lee1 , S Lee1 , J Jeong1 , H Kim1 , D Shin1 , Y Lim1 , W Shin2 , C Min2 , (1) National Cancer Center Korea, Goyang-si, Gyeonggi-do, (2) Yonsei University, Wonju, Gangwon-do


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To investigate the potential dose variation from scattered protons in passive scattering proton therapy, which is not included on dose calculation with TPS (Eclipse v13.7).

Methods: Dose distributions from the TPS calculation, Monte Carlo simulation and measurement were compared and the difference was analyzed. The simple imaginary target on the solid water phantom and a patient case were chosen for the study. The previously verified TOPAS (v3.0) Monte Carlo simulation model was used. 2 dimensional dose distributions were measured at several depths, using radiochromic films and MatriXX. Differing from previous studies which cover an aperture only, both aperture and range compensator were included in this study for investigation of variation of patient dose during actual treatment.

Results: The dose distribution calculated with the TOPAS model showed close results to the measured dose distribution in every respect. On the other hand, the calculated dose distribution on TPS showed the good approximation but it had clear differences on the shallow region of a range compensator. This dose variation on the shallow region of a range compensator was mainly due to scattered protons from the snout and aperture, and could be 2-10% depending on the depth and region. In the following study, selection of the proper thickness of a range compensator was shown to help reduce this dose variation.

Conclusion: In this study, the dose variation from scattered protons on the current TPS in the passive scattering proton therapy was evaluated with the aperture and compensator. TPS dose calculation showed the considerable difference compared to the MC calculation and measurement, and it was mainly due to scattered protons from the snout and aperture. This potential dose variation should be considered in the treatment planning and the proper thickness of a range compensator can reduce this dose variation.


Protons, Scatter, Dose


Not Applicable / None Entered.

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