Monte Carlo Study Of Organ Doses And Related Risks For Secondary Cancer From Radiation Treatments Of Cervical And Retinoblastoma Patients Involving Co-60 Source

The use of Co-60 radiation therapy for the treatments of unilateral retinoblastoma(Rb)and cervical cancer(CxCa)patients is a widespread procedure in many developing countries including Tanzania.There is a critical and growing concern about radiation treatment increased the risks of secondary cancer incidence and late radiation tissue injury.This research aims to assess the organ doses from external beam radiation therapy(EBRT)and high dose rate(HDR)brachytherapy(BT)involving Co-60 source for unilateral Rb and CxCa and to evaluate the secondary cancer risks for the patient exposed to secondary radiation undergoing radiotherapy.This is achieved by Monte Carlo simulations of validated radiotherapy models and anatomically-realistic models of patients to estimate organ-absorbed doses and the lifetime attribute cancer risks.The evaluation of organ dose is based on the Monte Carlo(MC)method and a set of age-dependent USTC computational male and female phantoms.The estimated doses are used to calculate the secondary cancer risks in non-target organs by using the biological effects of ionizing radiation(BEIR)VII methodology.The survival information and baseline cancer risks are based on relevant statistics for the Tanzanian population.The results for EBRT of unilateral Rb show that organs which are near to the target volume such as the brain,salivary glands,and thyroid glands received a very high absorbed dose from scattered photons.The results also show that the resulting photon doses to non-target organs depend on the patient's age.Younger patients are more sensitive to radiation and received higher dose contributions from the treatment head due to a larger part of the body exposed to radiation.The higher lifetime attribute risks(LARs)per 100,000 populations for 5 years old child is found in the brain(3.58 × 102)located along the beam direction and thyroid glands(2.81)close to the target volume.For 10 years old and an adult male the highest LARs per 100,000 population in the brain are 2.83 × 102 and 2.14 × 102,and in the thyroid glands are 1.86 and 2.33×10-1,respectively.In the case of CxCa treatment,the highest absorbed doses of 6.98 × 10-2 and 5.74 × 10-2 Sv/Gy are recorded in the bladder for BT and EBRT.Doses to the bladder are 6.4%higher for BT and 5.7%higher for EBRT when comparing with the colon.The highest risk is found in the colon at 1.06 × 10-3 in the HDR-BT and 9.75 × 10-5 in the EBRT per 100,000 population at exposure age of 35 years.In general,the secondary cancer risks in all sites considered in the treatments for CxCa and unilateral Rb patient are lower than the baseline risks.This results can help to provide a database about the effect of radiotherapy-induced secondary cancer risks during CxCa and unilateral Rb treatment in Tanzania and other developing countries.