The local field in infratentorial ependymoma: does the entire posterior fossa need to be treated?

INTRODUCTION: In the past decade, there have been multiple reports indicating that the predominant problem in the curative treatment of intracranial ependymoma is local failure. As a result, many have recommended local field radiotherapy. For infratentorial ependymoma, there is controversy regarding what constitutes the local field. Some radiation oncologists advocate coverage of the entire posterior fossa, whereas others recommend radiotherapy to the tumor bed and a safety margin. METHODS AND MATERIALS: From 1984 to 1998, 28 patients with posterior fossa ependymoma were diagnosed at our institution. There were 18 males and 10 females with a median age of 12 years (range, 2-81 years). Four patients (14%) had high-grade ependymoma and 3 (11%) had M+ disease at initial diagnosis. Gross total resection was achieved in 17 (61%) and postoperative radiotherapy (RT) was given to 22 (77%). Radiotherapy fields were craniospinal in 10, whole brain in 1, posterior fossa in 2, and tumor bed with a 2-cm. margin in 9. Median dose to the primary site was 54 Gy (range, 45-55 Gy). All 4 patients with high-grade ependymoma received craniospinal RT. Six patients did not receive RT after surgery. Magnetic resonance imaging (MRI) or computed tomography (CT) scans of the brain at initial diagnosis were compared to MRI or CT scans of patients at relapse to determine if the local relapse was in the tumor bed or nontumor bed posterior fossa. Median follow-up was 127 months (range, 14-188 months).
RESULTS: Six patients have relapsed. For the 11 patients who had craniospinal or whole brain radiotherapy (RT), 3 recurred (tumor bed 1, spine 1, nontumor bed posterior fossa + spine 1). Both patients who failed in the spine had high-grade tumors. Neither of the 2 treated with posterior fossa fields relapsed. For the 9 patients who had tumor bed RT alone and the 6 who did not receive RT, there were 3 relapses; all were in the tumor bed. There were no relapses in the nontumor bed posterior fossa.
CONCLUSION: For nondisseminated, low-grade infratentorial ependymoma, the radiotherapy volume does not need to include the entire posterior fossa. This information can be used to minimize late effects of RT in the era of three-dimensional (conformal) radiotherapy. No conclusion can be reached regarding the appropriate local field for high-grade infratentorial ependymoma because of the small number of patients.