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Radiation Therapy for Glioblastoma: What Is New and What Is Missing in the ASCO-Endorsed ASTRO Guidelines



It is a positive trend to see two major medical societies come together on such important guidelines and align their approaches to improving the outcome of patients with this difficult malignancy.
— William J. Curran, Jr, MD

An ASCO Special Article in the Journal of Clinical Oncology by Sulman et al,1 reviewed in this issue of The ASCO Post, issued ASCO’s endorsement of the American Society for Radiation Oncology (ASTRO) guidelines on radiation therapy for adult patients diagnosed with glioblastoma. It is a positive trend to see two major medical societies come together on such important guidelines and align their approaches to improving the outcome of patients with this difficult malignancy.

Most of the content in the ASTRO guidelines and the ASCO endorsement is straightforward and noncontroversial; in fact, much of the content has changed very little over the past 20 years. The landmark trials defining the survival benefit of radiation over no radiation and the value of image-guided partial-brain radiation over whole-brain radiation were primarily conducted in the 1970s and 1980s. A few confirmatory trials in these realms have been reported since then.

What Is New

The newer information in these guidelines relates to two themes: (1) the use of hypofractionated, shorter-course radiation regimens for patients over the age of 65 or 70 years and the lack of apparent inferiority in outcome when compared with a 6-week regimen; and (2) the use of hypofractionated small-field re-irradiation for patients with progressive or recurrent glioblastoma. The data in support of hypofractionated regimens for elderly patients are much stronger than the re-irradiation data, but both issues are well addressed in this report.

Several other important developments are touched on briefly in the endorsement, including the testing of proton-beam therapy as the initial radiotherapeutic approach to patients with glioblastoma. There is an active National Cancer Institute–sponsored trial under the auspices of NRG Oncology (NRG BN001) that is currently testing this approach and randomizing patients between proton and conventional photon therapies.

What Is Missing

What is glaringly absent in these guidelines is evidence of progress in applying the tools of advanced imaging to improving target delineation and response assessment in brain tumor therapeutics. There have been significant advances in brain tumor imaging in terms of higher-resolution magnetic resonance imaging and the regular use of magnetic resonance spectroscopy to differentiate tumor from nontumor regions both before and after radiation. Despite this progress, there is insufficient evidence to introduce these tools as useful and necessary in planning and assessing a glioblastoma radiation treatment plan. Although research in this work continues, particularly under the auspices of the National Cancer Institute Quantitative Imaging Network, it remains unclear how best to design a clinical trial to test the value of these new tools.

There is a final caveat in the “bottom line” summary of these endorsed guidelines, which states: “Cancer clinical trials … improve cancer care and all patients should have the opportunity to participate.” There is no group of patients for whom this statement is more true than those afflicted with glioblastoma. ■

Disclosure: Dr. Curran reported no potential conflicts of interest.

Reference

1. Sulman EP, Ismaila N, Armstrong TS, et al: Radiation therapy for glioblastoma: American Society of Clinical Oncology clinical practice guideline endorsement of the American Society for Radiation Oncology guideline. J Clin Oncol. November 28, 2016 (early release online).


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