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

Abstract

Background and purposeThe 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 methodsThe injection of a spacer gel (10ml SpaceOAR™) 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 (78Gy prescription dose). ResultsIn 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 Dmean, and V78 for the PTV were reached with IMRT vs. 3D CRT plans, with a smaller rectum V76 but larger rectum V50. ConclusionsThe 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.