Results of multiparametric transrectal ultrasound-based focal high-dose-rate dose escalation combined with supplementary external beam irradiation in intermediate- and high-risk localized prostate cancer patients.

Purpose: Clinical results of a biologic information-based focused dose escalation combined with dose de-escalation for the whole organ in external beam radiotherapy + high-dose-rate brachytherapy (HDR-BT) boost application for localized prostate cancer in a consecutively treated patient cohort.

Methods And Materials: One hundred thirty patients were treated with external beam radiotherapy (50 Gy) complementary to two multiparametric transrectal ultrasound-guided 15 Gy HDR-BT fractions. Real-time multiparametric transrectal ultrasound-based biologic planning for high-dose-rate boost dose planning used the summation of gray scale and Doppler sonography imaging + biopsy information. Target subvolumes received HDR-BT dose escalation up to 60 Gy/fraction. Dose-volume histogram parameters, organ at risks doses, and toxicity results were investigated.

Results: The median followup was 4.3 years, the median age was 68.62 years, and the mean initial prostate-specific antigen was 18.69 ng/mL. Low-, intermediate-, and high-risk constituted 69%, 21%, and 10% of the patients, respectively. The mean peripheral dose was 3.9 Gy per fraction. Prostate-specific antigen nadir was in 93% of the patients ≤1 ng/mL. Quality parameters were as follows: D: 6.58 Gy, V: 30.36%, V: 9.96%, V: 3.16%, uD: 7.34 Gy, uD: 9.34 Gy, rD: 10.56 Gy, and rD: 8.32 Gy, respectively. We observed G1, G2, G3 urinary toxicity in 17/130, 11/130, and 2/130 patients, respectively. Rectal toxicity: G1 and G2 occurred in 19/130 and 2/130 patients with mean dose values G1: 8.2 Gy and G2: 8.76 Gy. Analysis of variance test resulted in no correlation between toxicities and any other investigated factors.

Conclusions: Focused extreme dose escalation with low prostate mean peripheral dose results in excellent long-term outcome data and very high focal boost doses and is causing no enhancement in late treatment toxicity.