Prostate Dose-painting Radiotherapy and Radiobiological Guided Optimisation Enhances the Therapeutic Ratio.

AIMS: To describe the treatment of 11 patients with radiobiologically guided dose-painting radiotherapy and report on toxicity. MATERIALS AND METHODS: Boost volumes were identified with functional magnetic resonance imaging scans in 11 patients with high-risk prostate cancer. Patients were treated using a dose-painting approach; the boost dose was limited to 86 Gy in 37 fractions, while keeping the rectal normal tissue complication probability to 5-6%. Rotational intensity-modulated radiotherapy was used with daily image guidance and fiducial markers. RESULTS: The median dose to the prostate (outside the boost volume) and urethra was 75.4 Gy/37 fractions (range 75.1-75.8 Gy), whereas the median boost dose was 83.4 Gy (range 79.0-87.4 Gy). The tumour control probability (TCP) (Marsden model) increased from 71% for the standard plans to 83.6% [76.6-86.8%] for the dose-painting boost plans. The mean (Lyman-Kutcher-Burman) normal tissue complication probability for rectal bleeding was 5.2% (range 3.3-6.2%) and 5.2% for faecal incontinence (range 3.6-7.8%). All patients tolerated the treatment well, with a low acute toxicity profile. At a median follow-up of 36 months (range 24-50) there was no grade 3 late toxicity. Two patients had grade 2 late urinary toxicity (urethral stricture, urinary frequency and urgency), one patient had grade 1 and one grade 2 late rectal toxicity. The mean prostate-specific antigen at follow-up was 0.81 ng/ml after stopping hormone therapy; one patient relapsed biochemically at 32 months (2.70 ng/ml). CONCLUSIONS: The toxicity for this radiobiological guided dose-painting protocol was low, but we have only treated a small cohort with limited follow-up time. The advantages of this treatment approach should be established in a clinical trial.