Reduction of Irradiation Volume and Toxicities with 3-D Radiotherapy Planning over Conventional Radiotherapy for Prostate Cancer Treated with Long-term Hormonal Therapy

Background: As hormonal therapy has an influence not only on outcome but also on toxicities, we compare the efficacy of three-dimensional radiotherapy planning (3D-RTP) and of conventional radiotherapy (Conv-RT) in association with long-term hormonal therapy in reducing toxicity of treatment. Patients and Methods,: A retrospective case-control study was performed comparing the frequency of radiation toxicity between 63 Conv-RT and 52 3D-RTP patients with locally advanced prostate cancer (intermediate to high risk) treated with combined hormonal therapy. The average duration of neoadjuvant treatment was 7 months (1-38 months) and that of adjuvant treatment was 38 months (4-94 months). Patients were treated with 70 Gy of box field radiotherapy for the same clinical target volume (60 Gy prostate + seminal vesicle and 10 Gy boost to prostate). Results: Treatment volumes (=X(RL)xY(SI)xX(AP), where X-RL=right left length of anterior-posterior portals, X-Ap=anterior posterior length of lateral portals and Y-SI=superior inferior length of anterior-posterior portals) were significantly smaller in the 3D-RTP group (630 +/- 130 cm(3)) than in the Conv-RT group (1036 +/- 223 cm(3)) (p<0.0001). Acute side-effects in urological tracts (GU) were associated with X-RL (p=0.02), Y-SI (p=0.008) and treatment technique (Conv-RT vs. 3D-RTP: p=0.01). The frequency of acute gastrointestinal tract (61) toxicity was associated with XRL (p=0.02), X-AP (p=0.03). Late GU toxicities were associated with YAP (p=0.02) and XRL (p=0.03). Treatment technique was the determinant of late GI toxicities (p=0.03). Frequency of late GI toxicities of G2 or more was reduced from 35% in the Conv-RT group to 15% in the 3D-RTP group (p=0.03, odds ratio=0.43). Patients with late GI toxicity received longer periods (39 +/- 19 months) of adjuvant hormonal therapy than the patients without (31 +/- 18 months, p=0.04). Prostate-specific antigen (PSA) failure-free survival rates at 3 years were 92% for the 3D-RTP group and 90% for the Conv-RT group (73% at 5 years, 67% at 10 years). Overall survival rates were 97% (3-year), 91% (5-year), and 91% (10-year) in the Conv-RT group, compared to 100% at 3 years in the 3D-RTP group. Conclusion: Long-term hormonal therapy has the potential to improve outcome but induce late GI toxicity),. 3D-RTP simultaneously reduced treatment volume and frequency of acute urinary and late GI toxicities even with long-term hormonal therapy