DESIGN AND IMPLEMENTATION OF THE RADIATION DOSE CALCULATION METHOD TO PATIENTS IN CT EXAMINATION

• Main Author: ANAM (NIM: 30213017), CHOIRUL
• Format: Dissertations
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/26246
• Institution: Institut Teknologi Bandung

Since 2011, size-specific dose estimates (SSDE) have been used to estimate the radiation dose received by patients during CT exams. However, SSDE measurements are still carried out manually. SSDE calculation methods have not been standardized and optimized and their accuracy still has shortcomings that need to be improved. This research aims to automate SSDE calculations, standardize and optimize the parameters in the SSDE calculations and improve the accuracy of the SSDE calculation. The automation of SSDE calculations begins with patient contouring. Based on the results of auto-contouring, calculation of the effective diameter (Deff) and water-equivalent diameter (Dw) were performed. After that, the conversion factor as a function of size was determined. The value of this size conversion factor was then multiplied by the value of the CT dose index (CTDIvol) to obtain the SSDE value. In this study, CTDIvol values were obtained from DICOM headers and ImPACT software, while conversion factors were obtained from AAPM report No. 204. The results of automated calculations were compared with manual methods. An estimation of Dw from Deff was also conducted. Standardization of the SSDE calculations was carried out by considering the selection of positions in the size calculations and optimization was carried out by evaluating the number of slices in the SSDE calculations. Increasing the accuracy of the calculation of SSDE was carried out by using contouring that fitted well to the patient border and applying a correction factor due to the truncation of CT images. The automated radiation dose calculation was successfully developed with fairly accurate results. The difference between automated and manual calculation of SSDE, Deff and Dw values, was less than 2%. This study found that in the chest, Deff was 4.5% greater than Dw, while in the head Deff was 8.6% smaller than Dw. There was a linear relationship between Deff and Dw, so that Dw can be estimated from Deff. The determination of the lateral (LAT) and anterior-posterior (AP) diameter position in the Deff calculation was evaluated. It was found that Deff values calculated on the basis of maximum LAT and maximum AP (Deff, m) did not differ significantly (p> 0.05) from the Deff values calculated directly from the image area of the patient (Deff, A). Deff values calculated on the basis of central LAT and AP (Deff, c) differed significantly (p <0.05) from Deff, A for the chest, but did not differ <br /> significantly for the head. The calculated SSDE values using nine slices were similar (to within 1%) to the value using the average of all slices. Furthermore, it was found that SSDE calculated using the contours fitted to the patient border differed significantly from the values using circular contours (&#916; = 5.5%, p <0.05) for chest examinations than, but, did not significantly differ (&#916; = 1.1%, p &#707; 0.05) for head examinations. This study revealed that the axial images from clinical examinations are typically truncated around the edges (~86% in chest image and ~9% in head image). It is found that the required correction factor increases with an increase in the value of truncated percentage (TP). In conclusion, a novel system to calculate the patient's radiation dose automatically based on the concept of SSDE has been developed. In addition, standardization of parameters such as the diameter position in size calculation and optimization the number of slices used to compute SSDE has been achieved. This system provides a higher accuracy (by up to 5%) than the previous system.