Comparison of late rectal toxicity from conventional versus three-dimensional conformal radiotherapy for prostate cancer: analysis of clinical and dosimetric factors.
OBJECTIVE
To compare late rectal toxicity (LRT) after definitive radiotherapy (DR) and salvage radiotherapy (SR) in prostate cancer using conventional (CONV) or three-dimensional conformal (3-D) techniques.


METHODS
The outcomes and clinical factors of 212 patients with Stage T1a-T4 prostate cancer were evaluated (separated into DR and SR groups). The median prescribed dose was 66, 74, 66, and 70 Gy, for the CONV-DR, 3-D-DR, CONV-SR, and 3-D-SR groups, respectively. LRT was scored using both Radiation Therapy Oncology Group (RTOG) and modified RTOG and Late Effects Normal Tissue (mRTOG/LENT) scales.


RESULTS
The 4-year biochemical relapse-free survival rate was 83% for all patients, with a trend toward improvement in the 3-D groups (78% CONV and 85% 3-D, P = 0.12). One patient (1%) in the CONV group and 24 (24%) in the 3-D group experienced grade 2 or worse LRT by the mRTOG/LENT scale. Patients undergoing DR experienced grade 2 or worse LRT of 1% versus 21% (P = 0.003) for the CONV and 3-D groups, respectively. Patients undergoing SR experienced grade 2 or worse LRT of 0% versus 40% for the CONV and 3-D groups, respectively. The following variables correlated significantly with LRT on both univariate and multivariate analyses: prescribed radiation dose (P <0.0001), percentage of rectal volume receiving 60 Gy (P <0.005), and percentage of rectal volume receiving 70 Gy (P <0.001). The pretreatment clinical factors, when added to the dosimetric data, were not statistically significant on multivariate analysis (P >0.05).


CONCLUSIONS
The prescribed radiation dose and percentage of rectal volume treated to 60 or 70 Gy had statistically significant correlations with increased LRT. The rate of grade 2 or worse LRT was greater for patients undergoing SR than for those undergoing DR. We believe that continued close attention to dosimetric variables is imperative for future studies of dose escalation.
Lee
Christopher M
CM
Department of Radiation Oncology, LDS Hospital, Salt Lake City, Utah 84143, USA.
Lee
R Jeffrey
RJ
Handrahan
Diana L
DL
Sause
William T
WT
D000230:Adenocarcinoma / Q000188:drug therapy / Q000532:radiotherapy*; D000368:Aged; D018931:Antineoplastic Agents, Hormonal / Q000627:therapeutic use; D003131:Combined Modality Therapy; D003967:Diarrhea / Q000209:etiology*; D018572:Disease-Free Survival; D005500:Follow-Up Studies; D006471:Gastrointestinal Hemorrhage / Q000209:etiology; D006801:Humans; D015993:Life Tables; D008297:Male; D008875:Middle Aged; D016016:Proportional Hazards Models; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000009:adverse effects*; D011882:Radiotherapy, High-Energy / Q000009:adverse effects*; D012007:Rectum / Q000528:radiation effects*; D012189:Retrospective Studies; D012306:Risk; D016879:Salvage Therapy; D013997:Time Factors; D016896:Treatment Outcome
D018931:Antineoplastic Agents, Hormonal