Journal Article Variation in patient position and impact on carbon-ion scanning beam distribution during prostate treatment

Mori, Shinichiro  ,  Inaniwa, Taku  ,  Miki, Kentaro  ,  Tanimoto, Katsuyuki  ,  Tajiri, Minoru  ,  Kuroiwa, Daigo  ,  Shiraishi, Yurika  ,  Shibayama, Kouichi  ,  Tsuji, Hiroshi

88 ( 1051 )  , pp.20140623-1 - 20140623-7 , 2015-05 , The British Institute of Radiology
Purpose: We assessed the impact of changes in patient position on carbon-ion scanning beam distribution during treatment for prostate cancer.Methods: Sixty-eight patients were selected. Carbon-ion scanning dose was calculated. Two different planning target volumes (PTVs) were defined: PTV1 was the clinical target volume plus a setup margin for the anterior/lateral sides and posterior side, while PTV2 was the same as PTV1 minus the posterior side. Total prescribed doses of 34.4Gy (RBE) and 17.2Gy (RBE) were given to PTV1 and PTV2, respectively. To estimate the influence of the geometric variations on dose distribution, the dose was recalculated on the rigidly shifted single planning CT based on the 2D-3D rigid registration of the orthogonal X-ray images before and after treatment for the fraction of maximum positional changes.Results: Intrafractional patient positional change values average over all patients throughout the treatment course were less than target registration error = 2.00 mm and angular error = 1.27 deg. However, these maximum positional errors did not occur in all twelve-treatment fractions. Even though large positional changes occurred during irradiation in all treatment fractions, D95-PTV1 was over 98 % of the prescribed dose.Conclusions: Intrafractional patient positional changes occurred during treatment beam irradiation and degraded carbon-ion beam dose distribution. Our evaluation was not considered non-rigid deformations, albeit that, distribution was still within levels considered clinically acceptable.Advances in knowledge: Inter- and intra-fractional changes did not affect carbon-ion beam prostate treatment accuracy.

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