September 19, 2009 - Particle beam radiation therapy (PBRT) is safe and may provide effective tumor control, but "there are not enough comparative studies to base an evaluation of the clinical or cost effectiveness of [the technology] compared with other treatments," concluded investigators at the Tufts Medical Center Evidence-based Practice Center in Boston, which did the review for the Agency for Healthcare Research and Quality (AHRQ).
PBRT delivers radiation with electrically charged atomic particles. It is believed to provide superior depth-dose distribution, delivering maximum radiation to the target with minimal impact on surrounding tissue. Seven U.S. centers have PBRT facilities, and the investigators reported at least four more are being built at costs ranging from $100 million to $250 million.
The Tufts investigators conducted a Medline search to identify studies of any design that described clinical outcomes or adverse events in 10 or more patients with cancer who received PBRT. For purposes of the review, the investigators defined charged-particle radiation therapy as irradiation with protons, helium ions, or heaver ions; they explicitly excluded radiation therapy with neutrons or other particles. Conventional radiation therapy was defined as external photon-beam radiation guided by 2D or 3D imaging with or without the use of treatment-planning computers or older technologies and without beam intensity modulation.
Of 243 eligible articles in which charged-particle radiation therapy was used alone or in combination with other interventions for various cancer types, 185 (76%) were retrospective studies and 35 (14%) were prospective single-group trials. Only 8 randomized controlled trials were found; 13 comparative studies were not randomized.
The size of the trials ranged from 10 to 2,645 patients (median, 63). Follow-up ranged from 5 months to more than 10 years in two studies. Three-fourths of the studies assessed adverse events, but established scales were not always used.
Methodologic limitations of the various studies hindered useful comparisons, the authors noted. For example, "typically, studies did not provide detailed information on cancer staging or explicit descriptions of the clinical context," they wrote.
Additionally, when the treatment was used in combination with other therapies, the studies often assessed the treatment strategies as a whole and did not evaluate each specific strategy individually. Inconsistencies in reporting criteria, patient characteristics, and outcome definitions further diluted the value of the data for comparison.
Only three randomized, comparative studies explicitly stated primary outcomes, and no trial was designed to have a sufficiently large sample size or follow-up duration to demonstrate statistically significant differences in overall or cancer-specific survival, according to the report.
The authors wrote: "four trials reported statistically significant differences in various other outcomes...In 3 of 4 trials, the results favored the charged-particle radiation therapy group."
The researchers agreed with previous reviewers that PBRT is a viable alternative to conventional radiation therapy for certain types of cancer, such as head and neck cancer, where risk to critical structures is greater.
For more information: www.ahrq.gov