Craniospinal Irradiation in Medulloblastoma using High Energy Medical Linear Accelerator: an Innovative Approach to Planning Technique

Background: Craniospinal irradiation (CSI) of medulloblastoma poses technological challenges due to the involvement of large treatment volume. Commonly, the whole treatment length is covered with two different isocentric plans in which the junction is shifted after every five fractions to overcome the possibility of hot and cold spot.Objective: This study aims to evaluate dosimetrically and clinically the innovative planning technique for the CSI which doesn’t need re-planning and re-setup of patients after every five fractions. Material and Methods: Computed tomography was done for fifteen (ten children and five adults) patients diagnosed with medulloblastoma. Treatment planning for ۳۶ Gray (Gy) in ۲۰ fractions (#) at the rate of ۱.۸Gy/# was done on the treatment planning system. A single plan for children was created with two bilateral fields of ۶ Mega Voltage (MV) energy for cranium and one posterior field of ۶ MV for spinal cord (C۱-S۲). Two plans for adult patients were created, first plan was with two bilateral fields of ۶ MV for cranium and two posterior oblique fields of ۶ MV for cervical and the part of thoracic spinal cord (up to T۸-T۹). The second plan was with a single posterior field of ۱۵ MV covering remaining thoracic (T۸-T۹ to T۱۲), lumbar and sacrum (up to lower border of S۲) spine. After careful evaluation of all the plans, treatment was delivered; acute toxicities were recorded. Results: ۹۵% of prescribed dose was received by more than ۹۵% of planning target volume in all the plans with the acceptable hot spot and good homogeneity index. All the patients reported common radiation induced acute toxicities (headache, vomiting, weakness) during radiotherapy. Conclusion: The new planning technique for CSI has acceptable dosimetric and acute clinical possibilities; therefore it can be used for CSI for improved homogeneous dose delivery.