Prostate Volume and Risk for Acute GU Side Effects After IMRT

There’s a new article in the radiation therapy literature suggesting a direct correlation between prostate volume and risk for severe, acute, genitourinary toxicity when prostate cancer patients with large-volume prostates are treated with intensity-modulated radiation therapy (IMRT).

Aizer et al. have carried out a retrospective analysis of data from 214 consecutive prostate cancer patients treated at one or other of two centers between 2004 and 2007. Prostate volumes were available for all 214 patients based on CT scan data from treatment planning, and patients received a median dose of 75.6 Gy delivered using IMRT.

Acute toxicity was defined as any toxicity that first occurred within 90 days of the completion of radiation therapy. Genitourinary toxicity was defined using the National Cancer Institute Common Terminology Criteria for Adverse Events Version 3.0 guidelines.

The authors categorized the patients into two groups — those with relatively small (volume < 50 cm3) or relatively large (volume > 50 cm3) prostates. They then compared the occurrence of genitourinary toxicity in the two groups of patients, with the following results:

• Patients with large prostates had a significantly higher rate of acute Grade 3 genitourinary toxicity.
• Prostate volume was predictive of the likelihood of developing acute Grade 3 genitourinary toxicity.
• Every 27.0 cm3 increase in prostate volume doubled the likelihood of acute Grade 3 genitourinary toxicity.

It would be interesting to see if other centers can replicate the results of this study, based on their experience. If they can, then there would appear to be some justification for use of a very short course of hormone therapy prior to IMRT in patients with larger prostates, to see if this would reduce the size of the prostate prior to treatment.

Unfortunately, there are no absolute data available in the abstract of this paper, so we do not know exactly how many cases of acute genitourinary toxicity were evident in these 214 patients, nor do we know whether the clinical stage, PSA level, or Gleason score of the patients was relevant to the risk for toxicity. Some of these data may be available in the full text of the article, since multivariate analysis of risk is mentioned in the abstract.

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