Application of a spacer gel to optimize three-dimensional conformal and intensity modulated radiotherapy for prostate cancer

Background and purpose: The aim was to evaluate the impact of a spacer gel on the dose distribution, applying three-dimensional conformal (3D CRT) and intensity modulated radiotherapy (IMRT) planning techniques. Material and methods: The injection of a spacer gel (10 ml SpaceOAR (TM)) was performed between the prostate and rectum under transrectal ultrasound guidance in 18 patients with prostate cancer. 3D CRT and IMRT treatment plans were compared based on CT before and after injection (78 Gy prescription dose). Results: In contrast to the PTV and bladder, significant advantages (p < 0.01) resulted in respect of all analysed rectal dose values comparing pre spacer with post spacer plans for both techniques. Rectal NTCP (normal tissue complication probability) reached the lowest percentage after spacer injection irrespective of the technique, with a mean reduction of >50% for both IMRT and 3D CRT. Significantly (p < 0.01) higher D(mean), and V(78) for the PTV were reached with IMRT vs. 3D CRT plans, with a smaller rectum V(76) but larger rectum V(50). Conclusions: The injection of a spacer gel between the prostate and anterior rectal wall is associated with considerably lower doses to the rectum and consequentially lower NTCP values irrespective of the radiotherapy technique. (C) 2011 Elsevier Ireland Ltd. All rights reserved. Radiotherapy and Oncology 100 (2011) 436-441