Stereotactic radiosurgery better for spinal metastases
By Mary Ann Porucznik
Musculoskeletal metastases are common in patients with renal cell carcinoma, developing in approximately 30 percent of patients. With the advent of systemic treatment modalities that allow longer patient survival, local recurrence of musculoskeletal metastases, especially in the spine, is common.
For many of these individuals, particularly those for whom prior radiation treatment or surgery has failed, stereotactic radiosurgery may provide more and longer-lasting pain relief than conventional radiotherapy, according to poster exhibit P524.
Stereotactic radiosurgery has in the past been available only for intracranial tumors, but now frameless robotic computer controlled hypofractionated high dose radiation can be delivered anywhere in the body with submillimeter accuracy. The use of image guidance technology allows the system to continuously track, detect and correct for tumor and patient movement throughout the treatment. The high-dose radiation is generally delivered in one to three treatment sessions, utilizing 150 to 200 beams—all coming from different directions and all targeted on the tumor (Figure 1).
External beam radiation treatment of musculoskeletal metastases from renal cell carcinoma commonly results in a relatively low response rate (50 percent) and durability (50 percent recurrence at six months) unless the dose is greater 50Gy. But such high doses are difficult to deliver in the spine and pelvis without significant toxicity and prolonged treatments. Researchers hoped that stereotactic radiosurgery would improve results.
The poster reports on an institutional review board-approved prospective registry protocol, conducted from April 2003 to November 2005. The study involved 24 patients with extracranial lesions (15 spine and 9 others). Patients were treated with stereotactic radiosurgery of 2550 cGy at the 80 percent isodose line in three one-hour stages. Pain response was monitored by both patient assessment and narcotic analgesic use. Tumor response was monitored by magnetic resonance imaging (MRI) and/or computerized axial tomography (CAT) scan evaluations done every three months.
Nearly half (7 of 15) of the patients with spinal metastases had failed priorexternal beam radiation (Figure 2). They had recurrence of symptoms and growth of the tumor with a mean volume at the time of presentation of 70.4 cc.
After sterotactic radiosurgery, 14 of the 15 patients had complete initial pain relief; most experienced marked improvement within five days of treatment. Radiologically, three of the patients experienced a complete regression of the tumor (Figure 3) and five experienced a partial regression. The disease process stabilized in the remaining seven patients.
In addition, the results lasted much longer with stereotactic radiosurgery than with conventional radiotherapy. The mean survival among these patients is 12.3 months (median: 14 months) with 6 of the 15 patients alive at the time of analysis.
Twelve of the 15 patients with spinal metastases have had durable results. In one patient, symptoms returned after 17 months; a second patient had an asymptomatic recurrence at 12 months. Both were again treated with stereotactic radiosurgery, and experienced relief of symptoms and tumor regression at a minimum 12 month follow-up after the second treatment.
Of the group of nine bone and soft tissue lesions which had a mean volume of 183 cc, two had failed to get relief from prior external beam radiation treatment. Stereotactic radiosurgery provided complete initial pain relief in eight of the nine; the last patient experienced partial relief.
One patient experienced complete regression; five had partial regression, and the size of the lesions stabilized in three patients. Among this group, three are alive with mean survival of 10 months and no recurrence or exacerbation of symptoms.
Although the biologically equivalent dose of the radiation delivered by stereotactic radiosurgery is at least double that of the external beam radiation therapy used for palliation of skeletal metastases, patients can receive additional treatment even in spinal lesions because of the extreme precision of the delivery, which spares the surrounding normal tissue to a far greater degree than external beam. This has allowed successful retreatment of two of the patients in the series with spinal lesions.
Authors of the poster include Alan M. Levine, MD, of Baltimore; Mark E. Brenner, MD, of Pinehurst, N.C.; Cardella Coleman, MD, of Baltimore and Charles Lee, PhD, of San Diego. Dr. Lee serves as a consultant to Accuray; researchers have received nonresearch support from Accuray.