POSTERIOR-FOSSA - ANALYSIS OF A POPULAR TECHNIQUE FOR ESTIMATING THE LOCATION IN CHILDREN WITH MEDULLOBLASTOMA

PURPOSE: To quantify the accuracy of a popular technique of estimation of the borders of the posterior fossa in children with medulloblastom a by means of comparison with a magnetic resonance (MR) imaging estima tion technique. MATERIALS AND METHODS: The borders of the posterior fo ssa on MR images were superimposed on simulation radiographs obtained in 10 children (eight boys, two girls; age range, 5-14 years) in accor dance with a previously described MR imaging method. These borders wer e then quantitatively compared with the findings of the estimation met hod used in the Children's Cancer Group and Pediatric Oncology Group m edulloblastoma trials. RESULTS: Use of the estimation method resulted in underestimation of the extent of the posterior fossa by an average area of 2.8 cm(2) +/- 1.2. In five cases, it resulted in overestimatio n of the size of the posterior fossa in a separate region of the treat ment field. CONCLUSION: MR imaging should be the preferred method of i dentification of the borders of the posterior fossa.