Dose–Volume Constraints in Rectum in Patients with Prostate Cancer after 74-Gy 3-Dimensional Conformal Radiotherapy - Abstract
Purpose: To clarify the dose–volume relationship with late rectal toxicity (LRT) in prostate cancer patients after 74-Gy 3-dimensional conformal radiotherapy (3DCRT) using the 7-fields technique.
Materials and Methods: Between June 2004 and December 2011, 221 patients with localized prostate cancer [median age, 71 (48–89) years] were treated by 74-Gy 3DCRT using the coplanar 7-fields technique. Patients were classified according to the National Comprehensive Cancer Network risk group classification as low-risk, 20 patients (9%); intermediate-risk, 106 patients (48%); and high-risk, 95 patients (41.6%). Furthermore, 126 (57%) and 46 (20.9%) patients received androgen deprivation and anticoagulant therapy, respectively. For 3DCRT, the Clinical Target Volumes (CTV) included the prostate and at least half of the seminal vesicles in the intermediate and high-risk groups and the prostate alone in the low-risk group. We analyzed the relationship between the incidence rate of rectal bleeding and rectal wall Dose–Volume Histograms (DVHs). Late rectal bleeding (>90 days after radiotherapy) was evaluated according to the Common Terminology Criteria for Adverse Events v 4.0.
Results: The median follow-up period was 48 (range, 6–103) months, with a 4-year cumulative incidence rate for grade ?2 LRT of 11.0%. Univariate analysis (UA) determined the cutoff values of rectal wall DVHs for grade of ?2 LRT: V60 <38.9%, V65 <22.5%, V70 <17.8% and V72 <12.6%. UA also determined the cutoff values of rectal wall DVHs for grade of ?1 LRT: V10 <92.2%, V20 <76.7%, V30 <64.8%, V40 <66.5%, V50 <38.9%, V60 <22.5%, V70 <17.8, V72 <12.6%, Dmax <74.1Gy, Dmean <50.9Gy, Dmedian <47.6 Gy, and rectal wall volume of >23.6 cm3.
Conclusion: This study is the first to show a clear correlation between LRT and rectal DVHs after 74-Gy 3DCRT using the 7-fields technique and that it is acceptable.