ESTABLISHMENT OF INSTITUTIONAL REFERENCE LEVEL OF RADIATION DOSE FOR RADIOTHERAPY COMPUTED TOMOGRAPHY SIMULATION PROCEDURES

Abstract

For the last two decades, diagnostic reference level (DRL) in medical imaging involving ionising radiation has become an essential tool for the optimisation of radiation exposure to the patients. A computed tomography (CT) simulator plays an important role in conformal radiotherapy to provide the volumetric information of the patient anatomy for the accurate delineation of the tumour and the critical structures. Optimization of radiation dose to patients during CT simulation procedures has not been a major concern in most countries; however, it cannot be ignored since the cancer patients may have a long life expectancy after their treatment. In addition, the As Low As Reasonably Achievable (ALARA) principle should be considered whenever ionising radiation is used. Therefore, this study aims to develop an institutional reference level of radiation dose for CT simulation procedures. Data from a total of 350 CT simulation procedures were accumulated from October 2022 to November 2022 at Apeksha Hospital-Maharagama, Sri Lanka. As per the ICRP recommendations, mostly performed CT simulations of anatomical regions were considered in this study, CT dose index (CTDI) volume and dose length product (DLP) were used as the DRL quantities, and the median values of the DRL quantities were calculated to define the DRL values. The established DRL values of the CTDI volume and DLP are 7.4 mGy, 394 mGy.cm for the abdomen region, 15.5 mGy, 454.5 mGy.cm for the chest region, 58.2 mGy, 2632 mGy.cm for the head region, and 9.3 mGy, 339 mGy.cm for the pelvis region, respectively. The developed DRLs for the thoracic region were higher compared to the other countries’ values, but the developed DRLs for all other anatomical regions are lower. This study highlights the importance of optimizing radiation dose to patients. Further, we recommend developing national DRLs for mostly performed CT simulation procedures in Sri Lanka.