This latter finding – the non-superiority of proton therapy to IMRT for prostate treatment – has been disputed by ProCure, a US healthcare company that develops and operates full-service proton therapy centres. According to Eugen Hug, chief medical officer of ProCure Treatment Centers, this conclusion is contradicted by several peer-reviewed studies, which found that proton therapy reduced gastrointestinal side effects. Hug has released a statement to this effect.
An abridged version of Hug's statement follows:
"A controversial conclusion reached in the study Comparative effectiveness of intensity modulated radiation therapy, proton therapy and conformal radiation therapy in the treatment of localized prostate cancer is firmly contradicted by a number of well regarded peer-reviewed studies that found protons reduce – not increase – gastrointestinal side effects. The University of North Carolina (UNC) study runs counter to what we know from these studies, from research being carried out by ProCure and other proton centres and from our first-hand experience treating hundreds of patients with this important cancer therapy.
"Proton Therapy has consistently and for multiple disease sites reported a low incidence of side effects.
"In the treatment of prostate cancer, proton therapy has been shown to decrease the radiation dose to gastrointestinal structures, including the bowel, by at least 59% compared to X-rays. Several prospective clinical studies, including a randomized study enrolling 393 patients with prostate cancer and published in JAMA, reported very low gastrointestinal (2%) and genitourinary (1%) severe side effects, as might be expected from the favourable dose distributions of proton therapy. This is reinforced by a study presented by Massachusetts General Hospital at the same meeting and session as the UNC study, which reported significantly better bowel and bladder outcomes in prostate cancer patients treated with protons versus IMRT. The UNC data analysis is further contradicted by studies that have patients self-report their medical condition before treatment and then again after treatment, using accepted, validated evaluation tools. These self-reported studies also have found fewer gastrointestinal side effects with proton therapy versus radiation, as well as fewer genitourinary side effects.
"Prospective studies like these are in general considered "higher level" evidence than retrospective studies like the UNC study. The low incidence of side effects in prospective proton therapy studies is in stark contrast to the high number of gastrointestinal events reported in the UNC study.
"We support the conduct of rigorous prospective studies that control for variables to further define benefits and limitations of the various radiation modalities offered to patients with prostate cancer. Those clinical trials are either already in progress or in development within the network of the Proton Collaborative Group and other proton therapy centres worldwide.
"Some of the more notable peer-reviewed published and presented studies that contradict Dr Chen's paper:
• The Red Journal published an important study (Mendenhall et al 2012 Int. J. Radiat. Oncol. Biol. Phys. 82 213) on the early outcomes of image-guided proton therapy for prostate cancer. Study findings suggest high efficacy and minimal toxicity for proton therapy, with low rates of genitourinary symptoms and gastrointestinal toxicities.
• Three published studies from the PROG 95-09 trial, reporting on 5- and 10-year follow-up for prostate patients (Zietman et al 2008 JAMA 299 898; Zietman et al 2010 JCO 28 1106) and quality-of-life outcomes (Talcott et al 2010 JAMA 303 1046), reporting low levels of gastrointestinal and bowel toxicity and side effects.
• A 2009 meta-analysis (Viani et al 2009 Int. J. Radiat. Oncol. Biol. Phys. 74 1405) of randomized controlled dose escalation trials reported higher levels of radiation and toxicity with X-rays versus protons.
• The Massachusetts General Hospital study reported at the ASCO Genitourinary Cancers Symposium in February 2012reported "significantly" better bowel and bladder outcomes with protons compared to IMRT, using validated measurement instruments."