Toxicity Limits Potential for Cheaper Prostate Ca Tx

Stereotactic body radiotherapy (SBRT) for prostate cancer led to significantly lower initial cost of care versus intensity-modulated radiotherapy (IMRT), but increased toxicity offset most of the savings, a review of 4,000 cases showed.

Treatment cost averaged $13,645 for SBRT and $21,023 for IMRT. Beginning 6 months post treatment and continuing out to 2 years, SBRT-treated patients had significantly higher rates of toxicity, especially urinary complications.

The findings add to conflicting results from previous studies of SBRT-associated toxicity, James B. Yu, MD, of Yale University, and colleagues reported online in the Journal of Clinical Oncology.

"Despite conflicting reports, given the potentially high doses of radiation delivered to the urethra and bladder neck by SBRT, our finding of greater genitourinary toxicities for SBRT remains plausible," the authors concluded.

Some patients and clinicians might still consider SBRT preferable to IMRT because of shorter treatment duration, lower cost in spite of the higher complication rate, and evidence that SBRT might be superior to IMRT in terms of curative treatment, they added.

The finding of increased GU toxicity with SBRT is a "concerning but testable hypothesis" that is being examined in an ongoing randomized trial comparing SBRT and IMRT in patients with prostate cancer, Anthony V. D'Amico, MD, PhD, of Brigham and Women's Hospital in Boston, said in an accompanying editorial.

SBRT has characteristics that make it an appealing alternative to conventional IMRT. SBRT delivers a higher dose of radiation per visit, and a treatment plan can be completed in as few as five visits. In contrast, the typical IMRT course requires 7 to 9 weeks to complete.

The accelerated treatment period has the potential to reduce the cost of radiation therapy compared with IMRT. Moreover, the higher radiation dose per fraction may increase the potential for cure, the authors noted.

A hypofractionated protocol may also confer an increased risk of toxicity, particularly as SBRT has expanded beyond the institutions where the technique was developed and into the community.

Initial reports from developers suggest SBRT has acceptable acute toxicity and offers cancer control comparable to that of IMRT, the authors continued. Nonetheless, late GU symptoms have led some investigators to alter their technique in an effort to reduce exposure of susceptible normal tissue.

Emerging cost data for SBRT have provided another stimulus for evaluating the technique as an alternative to the more expensive IMRT. However, no cost studies had examined SBRT from the Medicare perspective, a dominant payer in the age group affected by prostate cancer.

Yu and colleagues undertook a retrospective comparison of SBRT and IMRT as primary treatment for prostate cancer. For the analysis they queried the Chronic Conditions Warehouse, a database containing 100% of Medicare fee-for-service claims related to specific conditions, including prostate cancer.

The authors identified claims from January 2008 through June 2011, submitted for treatment of early stage-prostate cancer in men, ages 66 to 94. They limited the search to patients who received IMRT or SBRT as primary treatment.

The search identified 1,335 patients treated with SBRT and 53,841 treated with IMRT, all of whom had at least 6 months of follow-up. Investigators matched each patient treated with SBRT to two treated with IMRT. The primary outcomes of interest were toxicity and cost.

The analysis showed higher rates of GU toxicity for SBRT at all time points analyzed, suggesting increased rates of acute and late toxicity.

At 6 months post treatment, 15.6% had a claim related to treatment of GU toxicity compared with 12.6% of the IMRT patients (odds ratio 1.29, P=0.009). By 12 months, the proportion of patients with toxicity-related claims had risen to 27.1% in the SBRT group and 23.2% in the IMRT group (OR 1.23, P=0.01). By 24 months, claims related to GU toxicity had been submitted for 43.9% and 36.3% of SBRT and IMRT patients, respectively (OR 1.38, P=0.001).

On the basis of claims submitted, SBRT was associated with significantly more diagnostic procedures for urinary incontinence and obstruction at 6, 12, and 24 months and significantly more claims related to diagnosis or treatment of urethritis, urethral strictures, and obstruction at 12 and 24 months (P=0.003 for all comparisons versus IMRT). Analysis of the same toxicities limited to 13 to 24 months after treatment showed more toxicity with SBRT (OR 1.33, P=0.005).

Gastrointestinal toxicity occurred more often with SBRT at 6 months but not thereafter.

The mean cost of diagnostic procedures to investigate incontinence, obstruction, urethritis, urethral strictures, and bladder outlet obstruction was $145 with SBRT and $69 for IMRT (P<0.001). The SBRT group also had a higher cost for cancer-related nonradiation care in the year following treatment ($2,963 versus $1,978 for IMRT, P<0.001).

In the editorial, D'Amico pointed out several limitations of the study.

The authors did not clarify the circumstances of androgen deprivation therapy when it was used with radiation therapy, an issue that could influence toxicity. The toxicity rates in the study were high for SBRT and IMRT and do not reflect clinical experience with either technique, D'Amico continued. The authors included diagnostic tests (cystourethroscopy, complex uroflowmetry) in their assessment of toxicity, which may have been performed for issues unrelated to treatment.

"Therefore, when treating men with prostate cancer is it acceptable to recommend a more convenient treatment that takes less time and is less expensive despite the possibility of increased toxicity and unknown comparative efficacy to current standards of practice?" D'Amico asked. "I do not think so.

"Despite the potential limitations of the study ... the results of the current study should raise our awareness that the potential for an increase in clinically significant GU toxicity with SBRT as compared with IMRT exists."

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