SBRT has equivalent toxicity with 5 treatments and 12 treatments: an update


We first reported data from the results of the RTOG 0938 trial in January 2016 when they were presented at the Genitourinary Cancers Symposium in that year. These results have now been formally published, and there are some changes to the data on publication, so Allen Edel has provided an update.

Lukka et al. have now published the short-term 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 2½ weeks
  • Arm 2: 51.6 Gy delivered in 12 fractions 5 days a week for 2 ½ weeks

These doses are approximately equivalent in biological 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-year 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.
    • Any such change affecting ≤ 35 percent of men was considered to be acceptable.
    • Any such change affecting ≥ 55 percent of men was judged to be unacceptable.
  • Urinary changes  > 2 points are considered clinically significant.
    • Any such change affecting ≤ 40 percent of men was considered to be acceptable.
    • Any such change affecting ≥ 60 percent of men was considered to be unacceptable.
  • Sexual score changes ≥ 11 points are considered clinically significant

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

  • Bowel changes were acceptable: 29.8 percent in Arm 1 and 28.4 percent in Arm 2.
  • Urinary changes were borderline acceptable: 45.7 percent in Arm 1 and 42.2 percent in Arm 2.
  • Sexual score changes: 32.9 percent in Arm 1 and 30.9 percent in Arm 2.

Disease-free survival at 2 years was 93.3 percent in Arm 1 and 88.3 percent in Arm 2.

None of these differences between Arm 1 and 2 were statistically significant

Physician-reported toxicities were as follows:

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

Both treatment regimens substantially met the study’s toxicity requirements so far, 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.

Editorial note: This revised commentary was written by Allen Edel for The “New” Prostate Cancer InfoLink.

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