International Journal of Radiation Research, January 2020 Volume 18, No 1 Estimation of the visual system complication probability on children with Medulloblastoma after Craniospinal irradiation with three-dimensional conformal radiotherapy INTRODUCTION Medulloblastoma is a primitive neuroectoder- mal tumor (PNET) and originates from the cerebellum or fourth ventricle. It is one of the most common tumors of the central nervous system (CNS) in children (1, 2) . The main treatments for such patients are craniospinal irradiation (CSI) and chemotherapy. CSI technique consists of a pair of lateral parallel opposed fields to treat the brain and one or two posterior fields to the spinal axis with a boost consisting of four different gantry angle fields, two opposing fields of the posterior fossa (3, 4) . Three-dimensional conformal radiotherapy (3D-CRT) is a standard technique for treating this cancer nowadays (4) . The aim of radiation therapy is to deliver prescribed dose to the tumor (5) . It has been shown that head and neck external radiotherapy causes inevitably radiation doses delivered to healthy tissues and organs at risk (OAR), due to primary and stray beams. Brain radiotherapy has been reported to produce late effects in the visual system such as visual impairment, cataract, radiation retinopathy and optic neuropathy (2, 6-10) . It can be avoided blindness due to lens opacity by surgery, but there is no proven effective treatment for blindness due to retina, optic nerve and optic chiasm injury (6, 11) . P. Shoa 1 , I. Abedi 1,2 , M.B. Tavakoli 1* , A.R. Amouheidari 2 , K. Jabbari 1 ¹Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran 2 Department of Radiation-Oncology, Isfahan Milad Hospital, Isfahan, Iran ABSTRACT Background: The use of radiaton therapy for medulloblastoma can afect children’s visual system. We estmated children’s visual system complicaton probability in the craniospinal irradiaton (CSI) technique with three- dimensional conformal radiotherapy (3D-CRT). Materials and Methods: CSI of ffeen medulloblastoma patents and a phantom were planned with 6 MV photon beams and 23.4 Gy prescribed dose. The doses of lenses were measured using thermoluminescence dosimeters (TLD). The delivered doses and complicaton probabilites were calculated based on the equivalent uniform dose (EUD) model to each contoured organ, including the bilateral lenses, optc nerves, retnas and optc chiasm. Results: The received dose for each organ was less than the tolerance value (p<0.001), except for the eye lens. The normal tssue complicaton probability (NTCP) values for all of the organs at risk (OAR) were found insignifcant. The discrepancies of calculated and measured doses for the right and lef lenses were 6.35% and 6.23% (p<0.001), respectvely. Conclusion: The results of this study showed based on the Internatonal Commission on Radiological Protecton (ICRP) publicaton 118 that children with medulloblastoma cancer treated with CSI with 3D-CRT method are susceptble to cataract complicaton. Keywords: Visual System Complication Probability, Medulloblastoma, Craniospinal Irradiation, Three-dimensional conformal radiotherapy. *Corresponding authors: Mohammad B. Tavakoli, PhD., Fax: + 98 313 668 8597 E-mail: mohamadbtavakoli@gmail.com Revised: April 2019 Accepted: May 2019 Int. J. Radiat. Res., January 2020; 18(1): 117-123 ► Original article DOI: 10.18869/acadpub.ijrr.18.1.117 [ DOI: 10.18869/acadpub.ijrr.18.1.117 ] [ Downloaded from ijrr.com on 2021-12-15 ] 1 / 8