The impact of overranging on patient radiation dose in CT chest examinations utilising the VirtualDoseCT software
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Date
2024-02-19
Authors
Μαρκετάκης, Ιωάννης
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Abstract
The purpose of this study is to evaluate the additional effective dose and the organs’ doses, due to overranging for patients undergoing chest CT examination. Overranging can be defined as the difference between the image scan length and the exposed scan length. This additional scanning length is required for the image reconstruction in helical CT and increases the radiation dose patients receive without generating images in the overranging area.
The anatomical and demographic data were collected for 111 adult patients, 65 males and 46 females, along with the exposure parameters and the scanning lengths, from the picture archiving and communication system (PACS). The examinations were performed with an 80-detector row CT scanner (Toshiba Aquilion Prime 80) in the General University Hospital of Patras from July 2022 until February 2023. For the calculation of the effective dose and organ’s doses the software VirtualDoseCT has been utilized. The specific software uses a database of Monte Carlo simulations for various exposure parameters, phantoms and CT scanners.
The effective dose for the entire sample was calculated at 7.43 mSv without considering overranging and 8.27 mSv with the influence of overranging. For females the values are 6.66 and 7.49 mSv while for males 7.97 and 8.82 mSv. This leads to an increase of 11.47% to patients’ effective dose. The influence is greater for female (12.38%) than for male patients (10.82%). The percentage differences in the organs’ doses demonstrate a wide variation and depend on their spatial relation with the scanning field. The smallest percentage differences are observed for the organs inside the scanning field: Lungs (4.10%), Heart (3.88%) and Breasts (3.67%). The values rise significantly for organs at the field boundaries: Colon (48.24%), Thyroid (28.46%), Liver (19.53%), Kidneys (18.81%), Spleen (16.30%), Stomach (13.01%) and Oesophagus (7.04%). For organs outside the scanning field although the difference is high the total dose they receive is minimal: Uterus/Cervix (39.03%), Prostate (20.93%), Bladder (25.55%), gonads (20.45%) and lens of the eye (8.29%). The percentage differences for females are greater than males in all organs except the thyroid the bladder and the oesophagus. The findings indicate that the impact of overranging is significant in the effective dose and especially the organs’ doses at the field boundaries.
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Keywords
Overranging, Chest CT, VirtualDoseCT, Effective dose, Organ dose