For the first time, some 15 years after proton beam radiation therapy (PBRT) was initially popularized as a potential treatment for prostate cancer by the group at Loma Linda, we have an independent assessment of the risk for side effects associated with this form of radiation therapy … and the comparative data are not good.
Sheets et al. will be presenting these data tomorrow at the Genitourinary Cancer Symposium in San Francisco, but the American Society for Clincial Oncology (ASCO) has already issued a media release, and the abstract of the presentation is available on line.
The study by Sheets et al. also compared outcomes of traditional (three-dimensional, conformal) external beam radiation therapy (3D-CRT) to intensity-modulated radiation therapy (IMRT). Data from the study suggest that IMRT is more effective than 3D-CRT — although there are indications that IMRT is associated with a greater risk for sexual dysfunction post-treatment (probably because it can be carried out with higher levels of total radiation dose for greater efficacy).
The research team, under the leadership of Dr. Chen at the University of North Carolina, Chapel Hill, carried out a careful study of Medicare records from > 12,000 men treated for non-metastatic prostate cancer between 2000 and 2009. Follow-up data was available on patients for an average of about 4 years.
The results of the study (shown in terms of “propensity scores”) are as follows:
- Use of intensity-modulated radiation therapy (IMRT) increased from 0.15 percent in 2000 to 95.9 percent in 2008.
- Men treated with IMRT as opposed to 3D-CRT were
- Less likely to be diagnosed with gastrointestinal morbidity (13.4 vs. 14.7 per 100 person-years, p < 0.001)
- Less likely to have subsequent hip fractures (0.8 vs. 1.0 per 100 person-years, p = 0.006)
- More likely to be diagnosed with erectile dysfunction (5.9 vs. 5.3 per 100 person-years, p = 0.006).
- Less likely to need additional cancer therapy (2.5 vs. 3.1 per 100 person-years, p < 0.001).
- Men treated with PBRT as opposed to IMRT (between 2002 and 2007) were
- More likely to be diagnosed with gastrointestinal morbidity (17.8 vs. 12.2 per 100 person-years, p < 0.001).
- Equally likely to have other complications and side effects
- Equally likely to need additional cancer therapy
The study suggests that patients treated with PBRT had about a 30 percent greater likelihood of bowel problems, such as bleeding and blockages, than similar men given IMRT. This result is in complete contrast to claims from some of the PBRT centers (and their “boosters”) that PBRT is associated with a lower risk for complications than other forms of radiation therapy.
The results of this study by Chen and his colleagues adds compelling evidence in support of the argument (supported by The “New” Prostate Cancer InfoLink) that some form of independent, well-designed study is needed to compare the outcomes of well-characterized patients treated with PBRT as opposed to IGRT/IMRT — and perhaps stereotactic body radiation therapy (SBRT) too. It does need to be recognized that this type of study, based on Medicare records, is fraught with all sorts of limitations, but it is clear, finally, that the advocates for PBRT as being “safer” than other modern forms of radiation therapy for the treatment of localized prostate cancer are no longer standing on anything approaching solid ground. (It has long been accepted that PBRT was likely to be superior to the much older 3D-CRT.)
According to Dr. Chen, quoted in a report in The Boston Globe, “There’s no clear evidence that proton therapy is better’’ for prostate cancer. He went on to add that “We found that patients who were treated with IMRT required fewer additional treatments after radiation which indicates better cancer control.’’