First data from a RTC of proton beam radiation vs. conventional radiation therapy

When you go to large meetings with thousands of presentations, you miss things. And here’s one that a lot of people seem to have missed — your sitemaster included.

A report on the Medscape web site yesterday — several weeks after the ASCO meeting in Chicago at the beginning of the month — has publicized data from the very first randomized clinical trial (RCT) of three-dimensional proton beam radiation therapy (3D-PBRT) compared to intensity-modulated radiation therapy (IMRT) in the treatment of any type of cancer — non-small cell lung cancer (NSCLC). Obviously this is not prostate cancer, but the outcomes of this trial do seem to confirm the suggestions that PBRT is not necessarily any better than other modern forms of conventional radiation therapy in the treatment of at least some common forms of cancer.

Liao et al. (see abstract no. 8500) report data from a relatively small, randomized clinical trial of the two different types of radiation therapy, both with concurrent chemotherapy, for locally advanced NSCLC. Radiation + chemotherapy is a very standard type of treatment for this stage of NSCLC, so there is nothing controversial about such treatment.

The research group determined that IMRT could be expected to have a treatment failure rate of about 30 percent at 6 months and 40 percent at 12 months based on prior experience. They further hypothesized that 3D-PBRT might be able to reduce these treatment failure rates by 10 percent at 6 and 12 months compared to IMRT. Pairs of IMRT and 3D-PBRT treatment plans were created for each patient evaluated for inclusion in the trial, and patients were eligible for randomization only if both plans satisfied normal tissue constraints at the same radiation dose.

Patients who were not eligible for randomization were treated with the modality producing the better plan. Patients denied coverage for protocol treatment by their insurer were treated with the modality that was covered.

Treatment failure was defined as one or other of either grade ≥ 3 radiation pneumonitis or local recurrence within 12 months of completion of the treatment.

Liao et al. reported the following series of outcomes data:

  • 255 patients were enrolled as potential candidates for randomization, of whom
    • 149 patients were actually randomized to the trial.
      • 92 were randomized to IMRT.
      • 57 were randomized to 3D-PBRT.
    • 106 patients were not randomized to the trial for one or other of the reasons given above.
      • 70 were treated with IMRT
      • 36 were treated with 3D-PBRT
  • Among the randomized patients,
    • Patient characteristics were well balanced, but …
    • Target tissue volumes were larger (P = 0.071) in the 3D-PBRT group
    • More patients received higher doses to tumors and had larger lung volumes receiving ≥ 30 to 80 Gy in the 3D-PBR group.
  • Treatment failure rates at 12 months were
    • 20.7 percent overall
    • 15.6 percent in the IMRT group
    • 24.6 percent in the 3D-PBRT group
  • Average (median) times to treatment failure were 10.5 months for all patients and for the patients in the IMRT and 3D-PBRT groups specifically.
  • Rates of failure for radiation pneumonitis were
    • 8.7 percent overall
    • 7.2 percent in the IMRT group
    • 11.0 percent in the 3D-PBRT group
  • Average (median) times to failure for radiation pneumonitis were
    • 4.3 months overall
    • 4.5 months in the IMRT group
    • 4.0 months in the 3D-PBRT group
  • Local recurrences occurred in
    • 23.5 percent overall
    • 22.8 percent of the IMRT group
    • 24.6 percent of the 3D-PBRT group
  • Average (median) times to local recurrence were
    • 13.0 months overall
    • 12.7 months for the IMRT group
    • 13.4 months for the 3D-PBRT

Liao et al also report that

  • Among nonrandomized patients,
    • The IMRT group was younger (P = 0.013) and had higher-stage disease (P = 0.071)
    • Treatment failure rates and rates and time to treatment failure were no different for the IMRT and the 3D-PBRT patients.

The authors concluded that they could find no differences in outcome between patients treated with IMRT  and 3D-PBRT in this randomized trial.

This trial will clearly not end the debate about the potential value of PBRT compared to other forms of modern radiation therapy, but it is a potential sign of things to come.

One Response

  1. I think the researchers at MD Anderson and Mass General deserve a lot of credit for having the courage to publish this. However, what is of interest to prostate cancer patients is the toxicity to tissue outside of the treatment field. I don’t think that proton advocates argue that the oncological control is any better than IMRT, they argue that toxicity to surrounding tissue of the bladder and rectum is lower. As I understand it (and I may be mistaken), radiation pneumonitis is treatment limiting, so it is used as an indicator of treatment failure, rather than of toxicity to tissue outside of the treatment field. I hope they will continue with an RCT for prostate cancer.

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