Toxicity Following 3D Radiation Therapy for Prostate Cancer on RTOG 9406 Dose Level IV

Reviewer: William Levin, MD
Last Modified: October 11, 2002

Presenter: J.M. Michalski
Presenter's Affiliation: Dept. of Radiation Oncology, Washington University Medical School, St. Louis, MO, USA
Type of Session: Scientific


  • Numerous previous studies have suggested that there is a dose-response relationship with radiation therapy (RT) used in the treatment of prostate cancer.
  • This study is a toxicity report on dose level IV (74 Gy) on RTOG 9406 for stage I&II adenocarcinoma of the prostate.

Materials and Methods

  • At a dose of 74 Gy, 256 pts are analyzable for toxicity.
  • 2 Gy/day fractions were used and the dose was prescribed to the planning treatment volume (PTV).
  • Patients were stratified according to risk of seminal vesicle involvement (SVI).
  • For those pts with <15% risk of SVI (Group I), PTV included the prostate, while those with a 15% or greater risk (Group II) had an initial PTV that included the prostate and SV?s to 54 Gy followed by a conedown to the prostate-only.


  • Mean follow-up for Groups I &II, were 24 months and 20 months, respectively.
  • Acute toxicity at this dose level was remarkably low, with grade 3 effects seen in 1% of the Group I pts and 3% of the Group II pts.
  • Late grade 3 toxicity was much lower than expected when compared to historic controls on previous RTOG trials.
  • For Group I, 1 pt had a late grade 3 or higher toxicity, while 18 pts were predicted by the historical data. (p<.0001)
  • For Group II, 5 pts had toxicity, while 20 were predicted. (p=.001)
  • There was a trend for increased toxicity when fraction size was greater than 2 Gy.

Author's Conclusions

  • Toxicity at the 74 Gy dose level was better than predicted by the historical data.
  • Longer follow-up is necessary to better assess late toxicity.

Clinical/Scientific Implications

  • Information on toxicity is very important as radiation doses are escalated in the treatment of prostate cancer.
  • As the authors point out, longer follow-up is necessary to assess safety and efficacy of dose escalation.

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