Abstract and Introduction
Abstract
Purpose: To assess the efficacy and safety in average-risk pediatric medulloblastoma (MB) receiving tumor bed boost irradiation compared to a posterior fossa (PF) boost.
Patients and methods: Thirty patients were enrolled in the study and divided evenly into two treatment arms of 15. Both arms received 23.4 Gy craniospinal irradiation (CS) and a 32.4 Gy boost. Patients in arm 1 were given PF boosts, and those in arm 2 were given boosts to the gross target volume (GTV). Weekly oncovin was given throughout all radiotherapy (RT). Eight cycles of adjuvant chemotherapy of CCNU, oncovin and platinol were given to all patients after RT. MRI, pure tone audiogram (PTA) and intelligence quotient (IQ) tests were performed before and after RT and every three months thereafter.
Results: There were significant differences in the sparing dose to the cochlea and brain stem as well as the volume of the normal brain receiving a 100% dose. There was a significant initial improvement of hearing function in patients given the target volume boost after RT, which was lost after chemotherapy. With a median follow up of 23 months, there was no difference in progression free survival or overall survival between the two arms.
Conclusions: Irradiation of the tumor bed after 23.4 Gy craniospinal irradiation for average-risk MB results in similar disease control as a PF boost. Dosimetric sparing for the cochleae and normal tissue is evident in patients receiving tumor bed boosts. The hearing improvement and cognitive function preservation effects of the treatment need more follow up.
Introduction
Medulloblastoma (MB) is the most common malignant brain tumor in children and constitutes 20–25% of CNS neoplasms.[1] Cerebrospinal fluid metastasis accounts for 30% of cases at diagnosis.[2] This metastatic feature was the cause of treatment failure for several decades following the original description of MB in 1925 by Bailey and Cushing.[3]
Since the mid-1990s, the risk classification for the relapse and treatment of MB patients has remained strictly clinical, with cases stratified into two risk groups, 'average risk' and 'high risk', based on age, extent of resection, and Chang metastasis staging.[4] Accordingly, average-risk patients are those older than three years of age with non-metastatic disease and totally or near totally resected tumors (<1.5 cm of residual tumor on postoperative MRI). Patients not fulfilling these criteria are regarded as high-risk. This clinical staging can be used in predicting prognosis, but it does not differentiate high- from low-risk patients within the same clinical stage as they may have biological differences within the same tumor.[5]
The overall 5-year survival rate for patients with MB is 60% with surgery, CSI, and chemotherapy but is much higher for standard-risk disease. Debilitating side effects occur in almost all patients that survive radiotherapy (RT) despite the use of protons as opposed to photons. Late side effects include cognitive impairment, psychiatric disorders, endocrine dysfunction, and skeletal growth retardation.[6]
The standard treatment for average-risk MB includes postoperative CSI with a dose of 23.4 Gy, irradiation of the anatomic posterior fossa (PF) to 55.8 Gy and 12 months of combination chemotherapy according to the Children's Oncology Group.[7] Reducing the neuraxis dose in the absence of chemotherapy has had limited success.[8]
Despite the use of chemotherapy and neuraxis radiation dose reductions, decline in cognitive function continues to be a significant issue.[9] Conventional treatment of the entire PF irradiates 35% of the brain and 60% of either temporal lobe. As a result, investigators have attempted to reduce the effects of irradiation by using new techniques to limit the boost volume to the tumor bed.[10]
Our primary goal is to cure MB as we are located in a developing country with limited resources. Intensity-modulated radiation therapy (IMRT) is not widely used due to a lack of both facilities and experience. This is the first study in Egypt to consider quality of life and cognitive function in pediatric MB by reducing the volume of RT in an attempt to limit the serious late side effects of radiation.
Chin Clin Oncol. 2014;3(1) © 2014 AME Publishing Company
