Phase I dose-escalation study of stereotactic body radiation therapy for low- and intermediate-risk prostate cancer

Abstract

Purpose: To evaluate the tolerability of escalating doses of stereotactic body radiation therapy in the treatment of localized prostate cancer.

Patients and methods: Eligible patients included those with Gleason score 2 to 6 with prostate-specific antigen (PSA) ≤ 20, Gleason score 7 with PSA ≤ 15, ≤ T2b, prostate size ≤ 60 cm(3), and American Urological Association (AUA) score ≤ 15. Pretreatment preparation required an enema and placement of a rectal balloon. Dose-limiting toxicity (DLT) was defined as grade 3 or worse GI/genitourinary (GU) toxicity by Common Terminology Criteria of Adverse Events (version 3). Patients completed quality-of-life questionnaires at defined intervals.

Results: Groups of 15 patients received 45 Gy, 47.5 Gy, and 50 Gy in five fractions (45 total patients). The median follow-up is 30 months (range, 3 to 36 months), 18 months (range, 0 to 30 months), and 12 months (range, 3 to 18 months) for the 45 Gy, 47.5 Gy, and 50 Gy groups, respectively. For all patients, GI grade ≥ 2 and grade ≥ 3 toxicity occurred in 18% and 2%, respectively, and GU grade ≥ 2 and grade ≥ 3 toxicity occurred in 31% and 4%, respectively. Mean AUA scores increased significantly from baseline in the 47.5-Gy dose level (P = .002) as compared with the other dose levels, where mean values returned to baseline. Rectal quality-of-life scores (Expanded Prostate Cancer Index Composite) fell from baseline up to 12 months but trended back at 18 months. In all patients, PSA control is 100% by the nadir + 2 ng/mL failure definition.

Conclusion: Dose escalation to 50 Gy has been completed without DLT. A multicenter phase II trial is underway treating patients to 50 Gy in five fractions to further evaluate this experimental therapy.

Fig 1.

Isodose distribution of a patient receiving 50 Gy of radiation in the axial plane (A), coronal plane (B), and sagittal plane (C). (D) is a dose-volume histogram showing coverage of the planning target volume (PTV)/prostate and low dose to surrounding organs. Ant., anterior.

Fig 2.

Means and SEs for Expanded Prostate Cancer Index Composite (EPIC) scores for (A) bowel, (B) sexual, and (C) urinary quality of life. (D) American Urological Association (AUA) mean scores with SEs that were normalized using a given patient's baseline score as the denominator. Data points with a single measurement are not shown.

Fig 3.

Mean prostate-specific antigen (PSA) with SEs. PSA was normalized using a given patient's baseline as the denominator.