Acute toxicity of three-dimensional conformal radiotherapy in prostate cancer patients eligible for implant monotherapy

Abstract

Purpose: To assess the acute toxicity of three-dimensional conformal radiotherapy (3D-CRT) in prostate cancer patients eligible for implant monotherapy. Methods and Materials: Between December 1991 and June 1998, 198 prostate cancer patients were treated with 3D-CRT at the University of California Davis Medical Center. Fifty-two of these patients had a prostate-specific antigen (PSA) level ≤ 10.0 ng/ml, Gleason score ≤ 6, and a 1997 AJCC clinical stage T1bN0–T2bN0. Eleven (21%) patients received radiotherapy to the prostate and seminal vesicles; the remaining patients were treated to the prostate only. The 3D-CRT treatment planning guidelines in Radiation Therapy Oncology Group (RTOG) 9406 were followed after 1994 (similar treatment planning was used before the protocol became available). Typically, 4 oblique and 2 lateral fields were treated. All patients were seen at least weekly while under treatment, 1 month postirradiation and then every 3 months. Total radiation doses ranged from 66.0–79.2 Gy, with a median dose of 73.8 Gy in 41 fractions over 8 weeks. Acute toxicity is described according to the RTOG acute toxicity scoring system. Results: Overall, 3D-CRT was well-tolerated: 29% of patients experienced RTOG Grade 1 and 27% experienced Grade 2 acute lower gastrointestinal (GI) toxicity. Forty percent and 33% of patients experienced Grade 1 and 2 acute genitourinary (GU) toxicity, respectively. As expected, more acute morbidity, especially GI, was observed with a larger clinical target volume (prostate and seminal vesicles versus prostate only; p = 0.05). Neoadjuvant hormonal therapy did not increase the incidence or severity of radiation-induced side effects. No acute toxicity ≥ Grade 3, e.g., hourly nocturia, gross hematuria, diarrhea requiring parenteral support, narcotics for pain control, or catheterization for acute urinary retention, was observed. Conclusion: Although relatively high doses of radiation are delivered to prostate cancers with 3D-CRT compared with conventional radiotherapy, 3D-CRT is surprisingly well-tolerated. No patients in the cohort eligible for implant monotherapy experienced acute toxicity ≥ Grade 3.