Posterior fossa: analysis of a popular technique for estimating the location in children with medulloblastoma.

Overview

PURPOSE: To quantify the accuracy of a popular technique of estimation of the borders of the posterior fossa in children with medulloblastoma by means of comparison with a magnetic resonance (MR) imaging estimation technique. MATERIALS AND METHODS: The borders of the posterior fossa on MR images were superimposed on simulation radiographs obtained in 10 children (eight boys, two girls; age range, 5-14 years) in accordance with a previously described MR imaging method. These borders were then quantitatively compared with the findings of the estimation method used in the Children's Cancer Group and Pediatric Oncology Group medulloblastoma trials. RESULTS: Use of the estimation method resulted in underestimation of the extent of the posterior fossa by an average area of 2.8 cm2 +/- 1.2. In five cases, it resulted in overestimation of the size of the posterior fossa in a separate region of the treatment field. CONCLUSION: MR imaging should be the preferred method of identification of the borders of the posterior fossa.