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) x Y(SI) x X(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 cm3) than in the Conv-RT group (1036 +/- 223 cm3) (p < 0.0001). Acute side-effects in urological tracts (GU) were associated with XRL (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 (GI) toxicity was associated with X(RL) (p = 0.02), X(AP) (p = 0.03). Late GU toxicities were associated with YAP (p = 0.02) and X(RL) (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.