AIM: SBRT effectiveness unproven
Evidence showing the effectiveness of stereotactic body radiation therapy (SBRT) relative to other radiotherapy techniques is sorely lacking, with no comparative effectiveness trials published on SBRT and the majority of trials investigating thoracic tumors, leaving a paucity of data on treatment of all other tumors, according to a literature review published May 2 in the Annals of Internal Medicine.

Dating back to 1896, the use of radiation to treat cancer has expanded significantly as PET, CT and MRI have advanced radiotherapy planning and accuracy. External-beam radiation therapy stands as the most common radiation therapy technique, with image-guided procedures further progressing treatment.

Several studies and researchers have promoted SBRT as a less expensive radiation therapy method that improves patient survival and tumor control, all with fewer fractions than other methods. Meanwhile, a 2010 study published in the American Journal of Clinical Oncology found that four fractions of SBRT cost an average of approximately $52,000, compared with $55,000 for 3D conformal radiation therapy (35 fractions) and $147,000 for intensity-modulated radiation therapy (also 35 fractions). At the same time, the authors noted that Medicare reimbursements for the therapies came in at just $11,000 for SBRT, $23,000 for intensity-modulated radiotherapy and $14,000 for conformal therapy.

The authors of the present review concentrated on composing a technical brief of the current state of SBRT for solid malignant tumors. Solicited by the Agency for Healthcare Research and Quality Effective Health Care Program, three investigators identified 124 relevant SBRT studies published between 2000 and 2010.

Sixty-eight of the 124 studies investigated SBRT’s use in thoracic tumors. A total of 27 studies were conducted on the treatment of pancreatic, liver and colon cancers, and fewer than 10 studies each investigated SBRT of the uterus, pelvis, kidneys, thyroid and prostate.

The authors identified 67 prospective single-group studies and 57 retrospective single-group studies. No studies compared SBRT with another form of radiation treatment, according to Kelley Tipton, MPH, and co-authors from the ECRI Institute Evidence-based Practice Center, part of Plymouth Meeting and Temple University Hospital in Philadelphia.

Treatment planning was commonly facilitated by CT, MRI and PET, Tipton and colleagues found, while image guidance usually consisted of CT, cone-beam CT and orthogonal x-ray. The most frequently used systems included modified linacs, CyberKnife (Accuray), Novalis Shaped Beam or Clinac (Varian Medical Systems), TomoTherapy Hi-ART (TomoTherapy), as well as a fusion of CT and linac and the Synergy system (Elekta).

The most regularly studied endpoints included tumor response (55 studies), local control (55 studies), overall survival (48 studies) and toxicity (42 studies). Adverse events were reported by 113 studies and commonly included pain, fatigue, nausea, bleeding and diarrhea.

SBRT is an increasingly attractive cancer therapy in large part due to the convenience of fewer treatments, argued Tipton et al. They noted that the decision by radiation oncologists on how to proceed with treatment varied according to numerous factors, including a patient’s prior radiation history, proposed treatment volume, the functioning of nearby organs, the capacity of patients to recover, the number of tumor sites and patient preference.

“Although many published studies describe SBRT, several limitations in the available literature raise concerns about the widespread use of SBRT. To date, no published comparative studies (either randomized or nonrandomized prospective studies) address the relative effectiveness and safety of SBRT versus other forms of external-beam radiation therapy,” offered Tipton and colleagues.

The authors did add that 50 SBRT trials are currently under way; however, only one of these compares SBRT with another form of radiotherapy.

“The general consensus among these reviews is that although single-group studies show potentially promising results for various cancer sites, prospective studies are necessary to determine the efficacy of SBRT compared with other available treatment options (for example, surgery or radiation therapy),” concluded Tipton and co-authors.