A comparison of high-dose vs. moderate-dose SBRT for prostate cancer.

This study was carried out to assess different dosing regimens of hypofractionated stereotactic body radiotherapy (SBRT) in patients with prostate cancer. The study found that both doses were associated with high effectiveness and manageable side effects.

Radiotherapy is an effective treatment for early-stage PC. SBRT is a special type of radiotherapy that uses special equipment to position the patient for precise delivery of radiation to tumors. The goal of using SBRT is to achieve a low PSA nadir. PSA is a protein produced from the prostate gland and can be elevated in prostate cancer. PSA nadir is the lowest level that PSA drops to following treatment.

Previous studies have used a high dose of radiations (3800 cGy in 4 fractions) with good effectiveness. However, for certain patients, lower doses (3500 cGy in 5 fractions) can be used to limit side effects. It was unknown if the two dosages result in similar safety and effectiveness.

There were 289 patients enrolled in this study. 178 patients were assigned to a high dose regimen. 111 patients were assigned to a moderate dose regimen. Follow-up in the high-dose group was 58 months. Follow-up in the moderate-dose group was 27 months.

An initial PSA level was measured in both groups. PSA levels decreased in both groups over time. Levels of PSA reached 0.8 ng/mL (high-dose group) and 1.0 ng/mL (moderate-dose group) at year 1. At year 2, PSA levels were 0.4 ng/mL in the high-dose group vs. 0.5 ng/mL for the moderate-dose group. After 5 years, PSA levels were 0.034 ng/mL in the high-dose group vs. 0.1 ng/mL in the moderate-dose group. 

At 5 years, 98.3% in the moderate-dose group and 94.3% in the high-dose group still had low PSA levels indicating lack of cancer relapse. 

Medium severity side effects in the urinary and genital organs occurred in 11.6% of the high-dose group and 8.7% of the moderate-dose group at 5 years. 

The authors concluded that both dose regimens of SBRT were found to have high effectiveness and had reasonable safety. The authors also concluded that assigning an individualized SBRT treatment regimen based on factors relating to age and risk elements was reasonable. 

This trial was not randomized. The dosing of SBRT was determined by the treating radiation oncologist. Younger, intermediate-risk patients were more likely to be assigned a high-dose. Older, lower-risk patients were more likely to be assigned a moderate dose.