ESTRO 2025 - Abstract Book

S4386

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

Material/Methods:

A retrospective selection of 20 prostate cancer patients at this institution who underwent hypofractionated radiation therapy included 10 patients without SpaceOAR and 10 patients with SpaceOAR. Treatment plans were established using the Accuray Precision treatment planning system based on CT imaging. The target dose was planned at a total of 42.7 Gy, delivered in 7 fractions to the Planning Target Volume (PTV). Treatment plans were divided into groups based on the presence or absence of SpaceOAR insertion, and analyzed for distance between the prostate and rectum, target dose coverage and minimum dose, and rectal dose.

Results:

Analysis of median values (Mdn) for 20 treatment plans, grouped by the presence or absence of SpaceOAR insertion, revealed that the distance between the rectum and prostate at the base level increased in the SpaceOAR group by 11.05 mm on the right, 11.4 mm at the midline, and 11.55 mm on the left. At the midgland level, the group with SpaceOAR inserted showed an increase of 8.85 mm on the right, 9.4 mm at the midline, and 9.9 mm on the left. At the apex level, the group with SpaceOAR inserted showed an increase of 5.3 mm on the right, 6.9 mm at the midline, and 6.95 mm on the left. In terms of target dose coverage at V100%, the group with SpaceOAR inserted exhibited a 4.45% increase in Clinical Target Volume(CTV) and a 3.44% increase in PTV. For minimum target dose, the group with SpaceOAR inserted experienced an increase of 8.62% in CTV D100% and 6.1% in PTV D100%. For rectal dose, the group with SpaceOAR inserted showed reductions of 19.59% at D0.03cc, 29.67% at D2cc, 22.95% at D10cc, 17.76% at D20cc, and 27.6% at Dmean. Conclusion: The use of SpaceOAR in hypofractionated radiation therapy for prostate cancer physically increases the distance between the prostate and rectum, allowing for maximum dose delivery to the tumor and minimal dose to normal