ESTRO meets Asia 2024 - Abstract Book

S312

Physics – Detectors, dose measurement and phantoms

ESTRO meets Asia 2024

Luca Capone 1 , Giorgio Hamid raza 1 , Chiara D'Ambrosio 1 , Francesca Cavallo 2 , Debora Di Minico 2 , Simona Borrelli 2 , Valeria Denotti 3 , Silvia Lo Cascio 4 , Barbara Ragonese 4 , Piercarlo Gentile 1 1 Radiotherapy, UPMC Hillman Cancer Center San Pietro, Rome, Italy. 2 Radiotherapy, UPMC Hillman Cancer Center Villa Maria, Mirabella Eclano, Italy. 3 Quality, UPMC Italy, Rome, Italy. 4 Quality, UPMC Italy, Palermo, Italy

Purpose/Objective:

In recent years, there has been growing concern about the potential risks associated with exposure to ionizing radiation from medical imaging procedures, particularly from repeated Computed Tomography (CT) scans. The diagnostic reference levels (DRLs) are values used as a reference for comparing the radiation dose in medical imaging exams in order to optimize the procedures applying the ALARA principle. The fundamental CT dose quantities in the CT control console are the dose-length product (DLP) and the volumetric CT dose index (CTDIvol). To optimize CT simulation for radiotherapy treatments, our purpose is to monitor the DLP and CTDIvol of UPMC Hillman Cancer Centers in Italy, compare that with the available data in literature and define a new method to collect DLP and CTDIvol values with respect to different the radiotherapy techniques. To our knowledge this kind of comparison is being made for the first time. A retrospective analysis was performed on CT scans to established DLP and CTDI values for procedures of different anatomical regions (Head&Neck; Brain; Pelvis; Thorax). To facilitate categorization, breast cancer patients were included in the Thorax district, along with patients who had radiation therapy of the lung or mediastinum. Treatments of the abdomen such as liver or lymph nodes were placed, along with treatments of the prostate or rectum, in the Pelvis district. A separate category was reserved for simulation CTs that involved the use of the respiratory motion management technique to treat supra and sub diaphragmatic targets. Data on the dose received by each patient undergoing simulation CT and the scan range were extrapolated using DICOM Radiation Dose Structured reports automatically recorded at the end of each examination. In order to compare our data with literature, the median values of DLP and CTDIvol for each anatomical district were chosen to be used. CTDIvol and DLP values collected on a sample of 358 patients from January 2023 to December 2023 were divided according to the main irradiation techniques used: 3D-CRT, IMRT, RA, SBRT/SRS and 4D-RT for the most treated districts in the cancer center (Brain, Lung, Breast, Metastases and Pelvis). Material/Methods:

Results:

The median values for the simulation CT were: CTDI vol 19.17 mGy, 27.63 mGy, 24.03 mGy, 24.9 mGy, 79.78 mGy and DLP 723.32 mGy*cm, 1104.58 mGy*cm, 989.99 mGy*cm, 993.73 mGy*cm, 2552.98 mGy*cm respectively for 3D-CRT, IMRT, RA, SBRT/SRS, 4D-RT techniques. The median scan range was 388.75 mm.

Conclusion:

In conclusion, CTDIvol and DLP values in radiotherapy appear to be higher than the values found by Radiology and internationally defined as standard. This is because larger FOVs and bigger scan range are needed in Radiotherapy for the acquisition of the whole immobilization system in different body districts.