A case-matched study of toxicity outcomes after proton therapy and intensity-modulated radiation therapy for prostate cancer, "Beyond the Abstract," by Neha Vapiwala, MD

BERKELEY, CA (UroToday.com) - The relative merits of proton beam therapy (PT) compared to so-called “conventional” (photon) therapy for cancer treatment is a “hot topic” of great interest in recent years, a debate almost entirely driven by the higher up-front costs and technical reimbursements associated with the former. Prostate cancer is a common disease for which both PT and photon-based intensity-modulated radiation therapy (IMRT) have been used for some time, yet the literature that has been published to date directly comparing these technologies with data derived from actual medical records (as opposed to databases of insurance claims or billing codes) has been notably lacking. With this study, we really wanted to provide a meaningful and robust comparison of side effects between these two modalities of external beam radiation using prospectively collected data from patient charts, stringent patient-matching criteria, and very rigorous statistical analyses. In order to achieve very tight case-matching, we markedly reduced the number of cases eligible for analysis, a tradeoff favoring adjustment for potential confounders at the expense of sample size. Although a randomized trial would be the ideal way to compare 2 treatments, and such a study is currently accruing, it will be a while before we have any results from it. In the meantime, this study provides some data where there is currently a dearth.

In our study thus far, with a follow-up period of approximately 2.5 years after PT and 4 years after IMRT, there do not appear to be statistically significant differences in genitourinary or gastrointestinal side effects among patients who received PT and IMRT for prostate cancer. Having said this, it will be critical for us to continue to observe these patients and analyze chronic side effect rates, as well as important cancer outcomes such as disease-free survival. Potential clinical advantages resulting from PT’s generally superior radiation dose distributions and lower integral dose (defined as total amount of energy absorbed by a patient or object during exposure to radiation) compared to IMRT can take many years to manifest. Thus ongoing follow up and greater numbers of patients may well reveal differences with time. In particular, PT may confer a lower risk of late toxicities occurring 5-10 years after treatment and/or a reduced risk of radiation-induced cancers, a phenomenon believed to be directly related to integral dose and the low-dose radiation “baths” associated with IMRT. As an increasing proportion of the men we treat for prostate cancer are under the age of 65 and otherwise generally healthy, these late endpoints of organ damage and secondary cancers carry greater import than ever before.

Written by:
Neha Vapiwala, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.

Associate Professor
Vice Chair of Education, Radiation Oncology
Advisory Dean, Perelman School of Medicine
University of Pennsylvania
Philadelphia, PA USA

A case-matched study of toxicity outcomes after proton therapy and intensity-modulated radiation therapy for prostate cancer - Abstract

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