ESTRO 2021 Abstract Book

S1509

ESTRO 2021

Fig 1. Results of MOSFET detectors characteristic for 6 MV FF beam.

Fig 2. Results of radiation doses from imaging with 2D-MV protocols in selected organs of the pelvic area.

Conclusion After proper characterization and calibration, MOSFET detectors are a suitable tool for measuring doses from MV imaging. The highest doses were measured for the 6 MV HQ protocol due to energy used. The lowest doses characterize the 2.5 MV HQ protocol. Thus, taking into account the obtained image quality, it can be considered as a method of optimizing doses from fiducial marker 2D-MV image-guided prostate radiotherapy. PO-1783 Competitive study between estimation of lung dose using different methods for the patient size A. Abuhaimed 1 , C. Martin 2 1 King Abdulaziz City for Science and Technology (KACST), The National Center for Applied Physics , Riyadh , Saudi Arabia; 2 University of Glasgow, Department of Clinical Physics and Bioengineering, Glasgow, United Kingdom Purpose or Objective Assessment of organ doses from CT scans is an essential requirement for the radiation protection practice. It allows performing dose optimization for a scan of interest and making comparisons between different scan protocols and procedures. Several approaches are used for organ dose assessment, one of which is based on utilizing size-specific and scanner-independent dose conversion coefficients (DCCs). This approach is applied by determination of a DCC that is based on the patient size and multiply it by CTDI vol of the scan of interest. The aim of this study is to compare between two methods used for determination of the patient size and hence DDCs to assess size-specific lung dose. Materials and Methods The two methods considered in this work are effective diameter (ED) and water-equivalent diameter (D w ). The main difference between these methods is that the ED is determined by the lateral and the anterior-posterior dimensions of the patient in the region of interest, whereas the D w method is affected by attenuation of the scan region, thus the photon energy plays a major role on determination of the patient size. This impact is expected to be notable in the chest region, specifically for lungs. This is because lungs have large areas, but low attenuation tissues. The ICRP reference paediatric and adult phantoms were involved to assess lung doses. The reference paediatric phantoms represent paediatric patients by ten phantoms that are categorized into five age groups: new-born, 1-year, 5-years, 10-years, and 15-years. Lung dose was assessed for three scan protocols, chest, chest-abdomen, and the trunk scan (CAP). The NCICT software was used to assess lung dose