SBRT has equivalent toxicity when given with 5 and 12 treatments


Data reported at the recent Genitourinary Cancers Symposium have shown that the toxicities associated with stereotactic body radiation therapy (SBRT) are acceptable and similar whether the radiation is give as 5 or 12 doses.

Lukka et al. (abstract no. 27; “Patient reported outcomes in NRG Oncology/RTOG 0938, evaluating two ultrahypofractionated regimens (UHR) for prostate cancer (CaP)”) presented early outcome data from the RTOG 0938 trial, which was a multi-institutional US/Canadian study among 240 low-risk men.

The patients 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 2½ 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-year quality-of-life analysis, with future analyses to be performed after 2 and 5 years. The EPIC questionnaire was used to assess bowel and urinary 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.

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

  • Bowel changes: 23.5 percent in Arm 1 and 23.1 percent in Arm 2
    • The difference is not statistically different from each other.
  • Urinary changes: 35.3 percent in Arm 1 and 34.7 percent in Arm 2
    • The difference is not statistically different from each other.

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)

So both treatment regimens 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 can compare IMRT and SBRT.

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

 

2 Responses

  1. One does, of course, have to note that all the 240 men enrolled in this study were low-risk patients, which raises questions about how many of them really needed treatment at all at the time that they were actually treated. Many of these men might have been just as well off if they had just been carefully monitored.

  2. I just wanted to thank both of you for the excellent summaries you provide on this forum!

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