محاسبه دز اوليه و ثانويه در پروتون تراپي تومور مغز با روش مونت كارلو

چكيده انگليسي :

Calculation of Primary and Secondary Dose in Proton Therapy of Brain Tumors Using Monte Carlo Method Author fatemeh moghbel Esfahani Moghbel fatemeh@yahoo com Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language farsi Date 19 September 2012 Supervisors Dr M Alamatsaz Dr A Karimian Abstract High energy beams of protons offer significant advantages for the treatment of deep seated local tumors Their physical depth dose distribution in tissue is characterized by a small entrance dose and a distinct maximum Bragg peak near the end of range with a sharp fall off at the distal edge When protons travel through matter secondary particles are created by the interactions of protons and matter en route to and within the patient It is believed that secondary dose can lead to secondary cancer especially in pediatric cases Therefore a lot researches must be done to investigate the possible negative and positive effects of using proton therapy Therefore the focus of this work is determining both primary and secondary dose A mono energetic proton source like a pencil beam has been used in this simulation Dose calculations were performed in two stages In the first stage the head was simulated by a cylindrical water phantom with length of 19cm and diameter of 19cm with 0 5 cm thickness of plexiglass Then proton characteristics such as depth dose distribution were investigated In the next stage to evaluate the effect of variation of target density on depth dose distribution density of phantom materials varied Increasing tissue density by 5 proton dose was decreased Then a spherical tumor with diameter of 1cm in the phantom was considered and calculation of dose performed in the tumor and phantom We have applied the MCNPX version of 2 6 0 code for proton beam energies ranging from 150 to 160 MeV with steps of 1MeV to obtain the ionization values which are related to the cell damage or dose in the target MCNPX code is a general purpose radiation transport simulation code which is capable to simulate proton beams This code requires an input file data that defines the geometry the physical parameters and the tallies of the simulated problem The results show that energies of 152 to 154 MeV are appropriate for treatment of tumor Children are particularly difficult population to treat as they are more sensitive to radiation The treatment of pediatric brain tumors using radiation can lead to severe side effects such as endocrine abnormalities hindrance of growth but clinical studies reported that patients with cancer of head and neck treated by proton had less side effects comparison with radiation induced side effect Proton therapy is an important component of pediatric brain tumors treatment So in order to estimate the dose in pediatric brain tumor the head phantom of MIRD age 5 is made of brain skull head and skin was simulated The elemental compositions of each tissue type were derived from data in ICRP publication 23 and a tumor with 10 mm diameter was considered inside of brain Primary and secondary dose were calculated The results of the simulation show that the best proton energy interval to cover completely the brain tumor is from energy of 123 to 125 MeV Secondary neutron dose was found to be 100 orders lower than primary proton dose Further providing evidence that secondary dose is relatively small in proton therapy Simulations were initially validated with packages such as SRIM TRIM Keywords proton therapy brain tumors MCNPX TRIM

مقبل اصفهاني، فاطمه

محاسبه دز اوليه و ثانويه در پروتون تراپي تومور مغز با روش مونت كارلو

پرتودرماني با باريكه يوني , فانتوم MIRD