Identification of a rectal subregion highly predictive of rectal bleeding in prostate cancer IMRT.
BACKGROUND AND PURPOSE To identify rectal subregions at risks (SRR) highly predictive of 3 year rectal bleeding (RB) in prostate cancer IMRT. MATERIALS AND METHODS Overall, 173 prostate cancer patients treated with IMRT/IGRT were prospectively analyzed, divided into "training" (n=118) and "validation" cohorts (n=53) Dose volume histograms (DVHs) were calculated in three types of rectal subregions: "geometric" intuitively defined (hemi rectum, "personalized" obtained by non rigid registration followed by voxel wise statistical analysis (SRRp) "generic" mapped from SRRps, located within 8x8 rectal subsections (SRRg) DVHs from patients with and without RB were compared and used for toxicity prediction. RESULTS Training cohort SRRps were primarily within the inferior anterior hemi rectum and upper anal canal, with 3.8Gy mean dose increase for Grade1 RB patients. The SRRg, representing 15% of the absolute rectal volume, was located in 10 inferior anterior rectal subsections. V18 V70 for SRRps and V58 V65 for SRRg were significantly higher for RB patients than non RB. Maximum areas under the curve (AUCs) for SRRp and SRRg RB prediction were 71% and 64% respectively. The validation cohort confirmed the predictive value of SRRg for Grade1 RB. The total cohort confirmed the predictive value of SRRg for Grade2 RB. Geometrical subregions were not RB predictors. CONCLUSION The inferior anterior hemi anorectum was highly predictive of RB.
Radiotherapy and oncology journal of the European Society for Therapeutic Radiology and Oncology