Purpose: We present preliminary results of a nonrandomized comparison of three-dimensional conformal radiation therapy (3D CRT) and standard radiation therapy (SRT) in localized carcinoma of the prostate in two groups of patients with comparable prognostic factors treated during the same period.
Methods and materials: Between January 1992 and December 1997, 146 patients were treated with 3D CRT and 131 with SRT alone for clinical stage T1c or T2 histologically confirmed carcinoma of the prostate. None of these patients received hormonal therapy. Mean follow-up for all patients is 3 years (range, 1-6 years). For 3D CRT, 7 intersecting fields were used (Cerrobend blocking or multileaf collimation) to deliver 68-73.8 Gy to the prostate; 3D dose distributions and dose-volume histograms (DVHs) of the planning target volume, bladder, and rectum were obtained. SRT consisted of bilateral 120 degrees rotational arcs, with portals with 2-cm margins around the prostate to deliver 68-70 Gy to the prostate. The criterion for chemical disease-free survival was a postirradiation prostate-specific antigen (PSA) (Tandem-R, Hybritech) value following the American Society for Therapeutic Radiology and Oncology guidelines. Symptoms during treatment were quantitated weekly, and late effects were assessed every 4-6 months.
Results: DVHs showed a two-thirds reduction in normal bladder or rectum receiving 70 Gy or more with 3D CRT. Higher 5-year chemical disease-free survival was observed with 3D CRT (91% for T1c and 96% for T2 tumors) compared with SRT (53% and 58%, respectively). There was no statistically significant difference in chemical disease-free survival in patients with Gleason score of 4 or less (p = 0.83), but with Gleason score of 5-7, the 5-year survival rates were 96% with 3D CRT and 53% with SRT (p < or = 0.01). In 111 patients with pretreatment PSA of 10 ng/mL or less, treated with 3D CRT, the chemical disease-free rate was 96% vs. 65% in 94 patients treated with SRT (p < or = 0.01). In patients with PSA of 10. 1-20 ng/mL, the chemical disease-free survival rate for 26 patients treated with 3D CRT was 88% compared with 40% for 20 patients treated with SRT (p = 0.05). The corresponding values were 71% and 26%, respectively, for patients with PSA levels of greater than 20 ng/mL (p = 0.30). On multivariate analysis, the most important prognostic factors for chemical failure were pretreatment PSA (p = 0. 023), nadir PSA (p = 0.001), and 3D CRT technique (p = 0.033). Moderate dysuria and difficulty in urinating were reported by 2-5% of patients treated with 3D CRT in contrast to 6-9% of patients treated with SRT; moderate urinary frequency and nocturia were reported by 18-24% treated with 3D CRT and 18-27% of patients in the SRT group. The incidence of moderate loose stools/diarrhea, usually after the 4th week of treatment, was 3-5% in the 3D CRT patients and 8-19% in the SRT group. Late intestinal morbidity (proctitis, rectal bleeding) was very low (1.7%) in the 3D CRT group in contrast to the SRT patients (8%).
Conclusion: Three-dimensional CRT spares more normal tissues, yields higher chemical disease-free survival, and results in less treatment morbidity than SRT in treatment of Stage T1-T2 prostate cancer. Longer follow-up is needed to confirm these preliminary observations.