Anal wall sparing effect of an endorectal balloon in 3D conformal and intensity-modulated prostate radiotherapy

Background and purposeTo investigate the anal wall (Awall) sparing effect of an endorectal balloon (ERB) in 3D conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) for prostate cancer.Materials and methodsIn 24 patients with localized prostate carcinoma, two planning CT-scans were performed: with and without ERB. A prostate planning target volume (PTV) was defined, and the Awall was delineated, using two different methods. Three-field and 4-field 3D-CRT plans, and IMRT plans were generated with a prescription dose of 78 Gy. In 144 treatment plans, the minimum dose (Dmin), maximum dose (Dmax), and mean dose (Dmean) to the Awall were calculated, as well as the Awall volumes exposed to doses ranging from ⩾20 Gy to ⩾70 Gy (V20 − V70, respectively).ResultsIn the 3D-CRT plans, an ERB significantly reduced Dmean, Dmax, and V30 − V70. For IMRT all investigated dose parameters were significantly reduced by the ERB. The absolute reduction of Dmean was 12 Gy in 3D-CRT and was 7.5 Gy in IMRT for both methods of Awall delineation.ConclusionsApplication of an ERB showed a significant Awall sparing effect in both 3D-CRT and IMRT. This may lead to reduced late anal toxicity in prostate radiotherapy.