Rectal wall sparing effect of three different endorectal balloons in 3D conformal and IMRT prostate radiotherapy

Purpose: To investigate the dosimetric consequences and rectal wall (Rwall) sparing effect of three different endorectal balloons (ERBs) for three-dimensional conformal radiotherapy (3D-CRT) and intensity-modulated radiotherapy (IMRT) for prostate cancer. Methods and Materials: In 20 patients, 4 planning computed tomography scans were made: 1 without ERB and 3 with ERB1, ERB2, or ERB3 inserted. Two different planning target volumes were defined: prostate only, and prostate plus seminal vesicles. The 3D-CRT and IMRT planning techniques were used, and the prescription dose was 78 Gy. In 284 treatment plans, the Rwall mean dose, the Rwall normal tissue complication probability, and the absolute Rwall volumes exposed to ≥50 Gy (V50) and ≥70 Gy (V70) were calculated. For spatial dose distribution analysis, inner rectal wall dose maps and dose surface histograms were generated. Results: Each ERB was tolerated well. In the case of 3D-CRT, each ERB showed a statistically significant reduction of all the measured parameters. ERB2 and ERB3 performed better than ERB1. In IMRT, a statistically significant reduction in the Rwall dose parameters could not be demonstrated for any of the ERBs. For 3D-CRT and IMRT, as a result of the rectal dilation, ranging from 8 to 20 cm in circumference, the ERBs resulted in a reduction of the relative inner Rwall surface exposed to intermediate and high doses. Conclusions: In 3D-CRT, any ERB showed a significant rectal wall sparing effect. ERB2 and ERB3 were superior to ERB1. For both 3D-CRT and IMRT, a reduction of the relative inner Rwall surface exposed to intermediate and high doses was found, which may lead to reduced late rectal toxicity. Development of user- and patient-friendly ERBs is warranted to increase their acceptability