THE USE OF 3D CONFORMAL RADIOTHERAPY (3D CRT) TO SPARE THE COCHLEA INPATIENTS WITH MEDULLOBLASTOMA

Purpose: Radiation therapy in combination with cis-platinum chemothera py is associated with ototoxicity due to destruction of cochlear hair cells. This is a significant problem, especially in pediatric patients , because it may lead to difficulties with communication, speech, lang uage, and development of learning skills. The use of 3D conformal radi otherapy (3D CRT) may be useful in sparing auditory structures. This p aper discusses a technique using 3D CRT to spare the cochlea in patien ts with medulloblastoma. Methods and Materials: Five pediatric patient s with medulloblastoma were planned using 3D CRT, All had MRI and CT o btained specifically for treatment planning. Multiple structures mere contoured, including the cochlea and posterior fossa, and conformal be ams designed in beam's eye view and dose distribution analysis were ed ited to provide 3D dose coverage to the target while sparing the inner ear. Patients received 36 Gy to the craniospinal axis followed by an 18-20 Gy boost to the posterior fossa. Results: A 3D CRT cochlear spar ing technique was designed, using an axial pair of posterior oblique f ields to treat the posterior fossa while sparing the cochlea for all p atients in this analysis. Dose-volume information, obtained from 3D ca lculations, demonstrates that the average dose received by the cochlea was 65% of the prescribed dose using the cochlear sparing plan, as co mpared to 101% using standard opposed-lateral beams. Both plans delive red greater than or equal to 100% of the prescribed dose to the poster ior fossa. Conclusion: 3D CRT allows for cochlear sparing in the treat ment of medulloblastoma. Further follow-up is necessary to determine t he long-term benefit in these patients. (C) 1998 Elsevier Science Inc.