On-line correction of beam portals in the treatment of prostate cancer using an endorectal balloon device

Abstract

Background: Reproducible target volume assessment is required in order to optimize portal field margins in the treatment of prostate cancer. The benefits of an endorectal balloon on target volume assessment remain unclear. Material and methods: Nine patients were treated with a daily placed air filled rectal balloon. Portal films and computer-associated tomography during the treatment were used to determine the position of the structures of interest. Comparative planning with or without a balloon was performed in order to determine rectal wall exposure to radiation. Results: The range of movements during treatment predicting the position of the prostate in relation to the symphysis was 0.05–0.59 cm in the lateral direction, 0.27–2.2 cm in the antero-posterior direction, and 0.33–1.8 cm in the crano-caudal direction, as compared to the position of the prostate predicted by the balloon ranging from 0.18 to 0.76 cm in the lateral direction, 0.22–1.68 cm in the antero-posterior direction, and 0.58–2.99 cm in the crano-caudal direction. Planning target volumes (PTV) margins as defined by the position of the balloon were 10 mm in the antero-posterior direction, 6 mm in the lateral direction, and 16 mm in the crano-caudal direction. The volume of rectal wall exposed to radiation was reduced from 40 (±12%) to 25% (±19%) with an endorectal balloon ( P<0.05). Conclusions: Daily online correction with portal vision for external beam set-up is improved by an endorectal balloon device, leading to improved PTV margins and reduced radiation exposure of the rectal wall.