Hypofractionated stereotactic body radiation therapy as monotherapy for intermediate-risk prostate cancer

Abstract

Background: Hypofractionated stereotactic body radiation therapy (SBRT) has been advanced as monotherapy for low-risk prostate cancer. We examined the dose distributions and early clinical outcomes using this modality for the treatment of intermediate-risk prostate cancer.

Methods: Forty-one sequential hormone-naïve intermediate-risk prostate cancer patients received 35-36.25 Gy of CyberKnife-delivered SBRT in 5 fractions. Radiation dose distributions were analyzed for coverage of potential microscopic ECE by measuring the distance from the prostatic capsule to the 33 Gy isodose line. PSA levels, toxicities, and quality of life (QOL) measures were assessed at baseline and follow-up.

Results: All patients completed treatment with a mean coverage by the 33 Gy isodose line extending >5 mm beyond the prostatic capsule in all directions except posteriorly. Clinical responses were documented by a mean PSA decrease from 7.67 ng/mL pretreatment to 0.64 ng/mL at the median follow-up of 21 months. Forty patients remain free from biochemical progression. No Grade 3 or 4 toxicities were observed. Mean EPIC urinary irritation/obstruction and bowel QOL scores exhibited a transient decline post-treatment with a subsequent return to baseline. No significant change in sexual QOL was observed.

Conclusions: In this intermediate-risk patient population, an adequate radiation dose was delivered to areas of expected microscopic ECE in the majority of patients. Although prospective studies are needed to confirm long-term tumor control and toxicity, the short-term PSA response, biochemical relapse-free survival rate, and QOL in this interim analysis are comparable to results reported for prostate brachytherapy or external beam radiotherapy.

Trial registration: The Georgetown Institutional Review Board has approved this retrospective study (IRB 2009-510).

Figure 1

Example treatment plan showing an axial view. The volumes represent the GTV (red), PTV (blue) and rectum (light green). The prescription isodose line (79%) is denoted by the thick light blue line.

Figure 2

Coverage of potential ECE. Radar plots of the mean distance (solid red line) in millimeters of the 33 Gy isodose line from an idealized prostate GTV (solid black line). The 95% confidence interval of the mean is shown in dashed blue lines. The distances are shown on (a) the axial plane 1 cm caudal to base, (b) the axial plane in mid-prostate, and (c) the axial plane 0.5 cm cranial to apex.

Figure 3

(a-e) Mean quality of life measures at baseline and follow-up. Analysis of the QOL data included all time points that had at least an 80% patient response rate, which was up to 15 months for all QOL measures. Shown are plots for IPSS (a), EPIC urinary irritation/obstruction domain (b), EPIC urinary incontinence domain (c), EPIC bowel domain (d), and EPIC sexual domain (e). The thresholds for clinically significant changes in scores (½ standard deviation above and below the baseline) are marked with dashed lines. IPSS scores range from 0–35 with higher values representing worsening urinary symptoms. EPIC scores range from 0–100 with higher values representing a more favorable health-related QOL.