Program Information
Influence of the Intrafraction Patient Repositioning On Spot Scanning Proton Therapy for Prostate Cancer
Y Fujii1,4*, T Matsuura1 , S Takao1 , Y Matsuzaki1 , T Yamada1,4 , N Miyamoto1 , S Shimizu2 , K Umegaki3 , H Shirato2 , (1) Hokkaido University Hospital, Sapporo, Hokkaido, (2) Hokkaido University Graduate School of Medicine, Sapporo, Hokkaido, (3) Faculty of Engineering, Hokkaido University, Sapporo, Japan, Sapporo, Hokkaido, (4) Hitachi Ltd., Hitachi-shi, Ibaraki
Presentations
SU-E-T-496 (Sunday, July 12, 2015) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose:
To verify the effect of intrafraction patient repositioning based on real time image guidance on the proton dose distribution for prostate cancer.
Methods:
Dose distributions were simulated using CT images of prostate cancer patients. Treatment plans were prepared using proton beam from left side of the patient with 3 and 6 mm lateral margins. During the beam delivery, prostate position was assumed to be shifted by 5 mm in anterior, posterior, superior and inferior directions. The dose distributions were calculated for two scenarios; (i) the patient position was readjusted by 5 mm just after the prostate shift occurs (ii) the patient position was not adjusted. Such a real time readjustment can be realized with real time image guidance. The differences of the values D₅ and D₉₅ in CTV (D₅₋₉₅) were compared between different sizes of the lateral margins and different scenarios.
Results:
D₅₋₉₅ values in the case of scenario (i) are smaller than scenario (ii). The differences between scenario (i) and (ii) were not depend on the directions of the prostate shift. In the case of scenario (ii), margin expansion makes D₅₋₉₅ values small. In the case of scenario (i), margin size is uncorrelated to D₅₋₉₅ values.
Conclusion:
These results indicate that the intrafraction patient repositioning is effective to minimize dose deterioration when the prostate moves during the irradiation. In the case without intrafraction patient repositioning, margin expansion is effective to reduce dose deterioration. In the case with intrafraction patient repositioning, 3 mm margin is enough to minimize dose deterioration.
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