CTDI Volume Measurement of CT Simulation and CT Effective Dose Calculation for Cervix and Prostate

Abstract

The accurate measurement of Computed Tomography Dose Index (CTDI) volume and the calculation of effective dose are crucial in optimizing patient safety and ensuring the efficacy of CT simulations in radiation therapy. This study focuses on evaluating the CTDI volume during CT simulations and calculating the effective dose for patients undergoing treatment for cervical and prostate cancers. By using phantoms and patient-specific data, this study aims to quantify the radiation dose distribution and assess the potential risks associated with these diagnostic procedures. The present retrospective study was conducted on 53 cervical and prostate cancer patients (6 prostate and 47 cervical) with ages ranging from 35 to 75 years. The examinations were carried out using a Philips Ingenuity Time-of-Flight (ToF) 64 slice PET/CT system (Philips Healthcare, Cleveland, OH, USA) at the Institute of Nuclear Medical Physics, Atomic Energy Research Establishment (AERE), Savar, Dhaka. The scans were performed according to institutional protocols. Dose measurements were carried out in terms of CTDI100. CTDI100 values for the center and periphery of the phantom were recorded, and the average value of the periphery doses was taken. Then, CTDIw was calculated using CTDI100 values. Since an axial CT scan was taken on the phantom, there was no patient table movement, making CTDIvol values the same as CTDIw values. The mean±SD CTDIvol was obtained as 18.879±5.914 mGy, ranging from 8.952 to 37.327 mGy. The CT effective doses were calculated using the dose conversion coefficient k=0.015 mSv.mGy-1.cm-1 for the pelvic region, as described in the American Association of Physicists in Medicine Report No. 96. The effective doses for the CT procedure were estimated using DLP values that represent radiation exposure over the entire scan length. The scan lengths were generated by the scanner, and the DLP values were measured as the product of CTDIvol and scan length. The DLP values ranged from 411.225 to 2030.96 mGy·cm, with a mean value of 1094.479±462.029 mGy·cm. The effective dose is the product of the DLP and the conversion coefficient k. The mean effective dose for the pelvic region was 16.271±7.180 mSv. The doses for prostate patients were 15.125±8.815 mSv, and for cervical patients, they were 16.417±8.930 mSv. The present study found these values to be moderately higher compared to the effective dose values of conventional diagnostic radiology examinations. This is because the CT scans were performed on the patients as part of radiotherapy treatment planning, and the scan lengths were longer than the pelvic region, resulting in higher effective doses. However, this study suggests that the risk-benefit ratio of any radiological scan should be clarified and carefully weighed.