craniospinal irradiation in medulloblastoma using high energy medical linear accelerator: an innovative approach to planning technique

Background: craniospinal irradiation (csi) of medulloblastoma poses technologicalchallenges due to the involvement of large treatment volume. commonly, thewhole treatment length is covered with two different isocentric plans in which thejunction is shifted after every five fractions to overcome the possibility of hot andcold spot.objective: this study aims to evaluate dosimetrically and clinically the innovativeplanning technique for the csi which doesn’t need re-planning and re-setup ofpatients after every five fractions.material and methods: computed tomography was done for fifteen (tenchildren and five adults) patients diagnosed with medulloblastoma. treatment planningfor 36 gray (gy) in 20 fractions (#) at the rate of 1.8gy/# was done on thetreatment planning system. a single plan for children was created with two bilateralfields of 6 mega voltage (mv) energy for cranium and one posterior field of 6 mvfor spinal cord (c1-s2). two plans for adult patients were created, first plan was withtwo bilateral fields of 6 mv for cranium and two posterior oblique fields of 6 mv forcervical and the part of thoracic spinal cord (up to t8-t9). the second plan was witha single posterior field of 15 mv covering remaining thoracic (t8-t9 to t12), lumbarand sacrum (up to lower border of s2) spine. after careful evaluation of all the plans,treatment was delivered; acute toxicities were recorded.results: 95% of prescribed dose was received by more than 95% of planningtarget volume in all the plans with the acceptable hot spot and good homogeneityindex. all the patients reported common radiation induced acute toxicities (headache,vomiting, weakness) during radiotherapy.conclusion: the new planning technique for csi has acceptable dosimetric andacute clinical possibilities; therefore it can be used for csi for improved homogeneousdose delivery.