A comparison between high dose rate brachytherapy and stereotactic body radiotherapy boost after elective pelvic irradiation for high and very high-risk prostate cancer

PURPOSE: To compare biochemical recurrence-free survival (BRFS) and toxicity outcomes of high dose rate brachytherapy (HDRB) and stereotactic body radiotherapy (SBRT) boost after elective nodal irradiation for high/very high-risk prostate cancer. MATERIALS AND METHODS: A retrospective analysis was performed in 149 male patients. In 98 patients, the boost to the prostate was delivered by HDRB as 2 fractions of 10 Gy (EQD(2) for α/β = 1.5; 66 Gy) or 1 fraction of 15 Gy (EQD(2) for α/β = 1.5; 71 Gy). In 51 male patients, SBRT was used for the boost delivery (3 fractions of 7 Gy; EQD(2) for α/β = 1.5; 51 Gy) because brachytherapy equipment was out of order. RESULTS: In 98 patients that received HDRB boost, 3- and 5-year BRFS were 74.6% and 66.8%. Late grade-II genitourinary toxicity was detected in 27, grade-III in 1 case. Grade-II (maximum) rectal toxicity was diagnosed in nine patients. For 51 male patients that received SBRT boost, 3- and 5-year BRFS was 76.5% and 67.7%. Late grade-II (maximum) genitourinary toxicity was detected in five cases, late grade-II rectal toxicity in four cases. Other three patients developed late grade-III–IV rectal toxicity that required diverting colostomy. SBRT boost was associated with higher maximum dose to 2 cm(3) of anterior rectal wall (D(2cm³rectum)) compared to HDRB: 92% versus 55% of dose to prostate. Severe rectal toxicity was negligible at EQD(2) D(2cm³rectum) <85 Gy and EQD(2) D(5cm³ rectum) <75 Gy. CONCLUSION: Our results indicate similar 3- and 5-year BRFS in patients with high/very high-risk prostate cancer who received HDRB or SBRT boost, but SBRT boost is associated with higher rate of severe late rectal toxicity.