Source:Practical Radiation Oncology
Author(s): Glenn Bauman, Jeff Chen, George Rodrigues, Melanie Davidson, Andrew Warner, Andrew Loblaw
BackgroundWe explored the association of dosimetric parameters with late rectal bleeding among high risk prostate cancer patients treated with hypofactionated simultaneous in-field boost (H-SIB) to prostate with nodal treatment..MethodologyRectal toxicity results and dose volume histogram (DVH) information from patients treated on TRIAL 1 and TRIAL 2 were combined. Patients in both trials received long term androgen deprivation and H-SIB with prescription dose 40Gy to the prostate and proximal seminal vesicles and 25Gy to the lymph nodes delivered over 5 weekly fractions using image guidance with cone-beam CT. Mean rectal DVH values at 5Gy intervals and mean DVH curves were compared between patients with rectal bleeding (B) versus no bleeding (NB).ResultsThere were 12 B and 33 NB patients in the pooled group. Rectal bleeding was more frequent and of higher grade among TRIAL 1 patients (8/15, 5 Grade 2 or higher) than TRIAL 2 patients (4/30, all Grade 1). For any bleeding (Grade≥1) individual dose volume points in the 20–40Gy range were significantly different (two-sided p<0.05) between the B and NB groups with the 40Gy point being the most significant: V40=1.53%, SD 1.32 (B) vs. 0.69%, SD 1.46 (NB), p=0.006. For Grade≥2 bleeding, the V20Gy was most significant with 68.4%, SD 4.76 (B) vs. 40.4 5%, SD 13.9 (NB), p<0.001.ConclusionsThe higher relative dose volumes to the rectum (V20-V40) were most strongly associated with clinically significant bleeding in this analysis and is consistent with findings of series using H-SIB to treat prostate only. Differences in the prostate target volumes and planning margins likely account for different rates and grades of rectal bleeding observed between trials.
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