SBRT has equivalent toxicity with 5 treatments and 12 treatments

Lukka et al. reported one-year outcomes of the RTOG 0938 trial designed to test whether SBRT done in 5 treatments of fractions has equivalent and acceptable toxicity compared to SBRT in 12 fractions.

This was a multi-institutional US /Canadian study among 246 low risk men. They were randomly assigned to one of two SBRT treatment regimens:

• Arm 1: 36.25 Gy delivered in 5 fractions twice a week for 2 ½ weeks.
• Arm 2: 51.6 Gy delivered in 12 fractions 5 days a week for 2 ½ weeks.

These doses are approximately equivalent in biologically effect for cancer control and in their expected effect on healthy tissues. Men were allowed to be treated on several different SBRT platforms, including CyberKnife, VMAT and protons.

This is the planned 1-yr quality-of-life analysis, with future analyses to be performed after 2 and 5 years.  The EPIC questionnaire was used to assess bowel, urinary, and sexual quality-of-life.

•     Bowel changes > 5 points are considered clinically significant.

o   Any such change affecting ≤ 35% of men was considered to be acceptable.

o   Any such change affecting ≥ 55% of men was judged to be unacceptable.

•   Urinary changes  > 2 points are considered clinically significant.

o   Any such change affecting ≤ 40% of men was considered to be acceptable.

o   Any such change affecting ≥ 60% of men was considered to be unacceptable.

• Sexual score changes ≥ 11 points are considered clinically significant

After 1 year of follow-up, patient-reported clinically significant changes were noted in:

• Bowel changes were acceptable: 29.8% in Arm 1 and 28.4% in Arm 2
• Urinary changes were borderline acceptable: 45.7% in Arm 1 and 42.2% in Arm 2
• Sexual score changes: 32.9% in Arm 1 and 30.9% in Arm 2
• Disease-free survival at two years: 93.3% in Arm 1 and 88.3% in Arm 2
• None of the differences between Arm 1 and 2 were statistically significant

Physician-reported toxicities were as follows:

• Acute urinary: Grade 3 – 2 patients (1.7%)
• Acute rectal: Grade 3 – 2 patients (1.7%), Grade 4 – 1 patient (1.1%)
•  Late urinary: Grade 3 – 1 patient (0.8%)
•  Late rectal: Grade 3 – 2 patients (1.7%)

Both treatment regimens substantially met the study’s toxicity requirements, and confirm that 5 fractions are as toxicity-free as 12 fractions. These outcomes are in line with historical controls based on conventional IMRT treatment regimens. Of course, only a randomized clinical trial (like this one, which proved there were no differences in oncological or toxicity outcomes) can compare IMRT and SBRT.