Medical Imaging and Radiotherapy Journal (MIRTJ) 39 (Suppl. 1) 39 Medical Imaging and Radiotherapy Journal (MIRTJ) 39 (Suppl. 1) TIPIČNE CT DOZE PRI PET/CT PREISKAVH V SLOVENIJI TYPICAL ADULT CT DOSES OF PET-CT EXAMINATIONS IN SLOVENIA Jelena Perić 1, Nejc Mekiš 2, Dejan Žontar 3,4 1 Onkološki Inštitut Ljubljana, Oddelek za nuklearno medicino, Zaloška cesta 2, 1000 Ljubljana, Slovenija / Institute of Oncology Ljubljana, Department of Nuclear Medicine, Zaloška cesta 2, 1000 Ljubljana, Slovenia 2 Univerza v Ljubljani, Zdravstvena fakulteta, Oddelek za radiološko tehnologijo, Zdravstvena pot 5, 1000 Ljubljana, Slovenija / University of Ljubljana, Faculty of health sciences, Medical imaging and radiotherapy department, Zdravstvena pot 5, 1000 Ljubljana, Slovenia 3 Uprava Republike Slovenije za varstvo pred sevanji, Ajdovščina 4, 1000 Ljubljana, Slovenija / Slovenian Radiation Protection Administration, Ajdoviščina 4, 1000 Ljubljana, Slovenia 4 Inštitut Jožef Stefan, Jamova cesta 39, 1000 Ljubljana, Slovenija / Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia Korespondenca / Corresponding author: jelena.peric13@gmail.com Prejeto/Recived: 14. 3. 2022 Sprejeto/Accepted: 22. 3. 2022 IZVLEČEK Uvod: Hibridno slikanje, pri katerem pozitronsko emisijsko tomografi jo (PET) združimo z računalniško tomografi jo (CT), omogoča natančnejšo lokalizacijo in karakterizacijo bolezni, vendar pomembno poveča dozno obremenitev pacientov. Namen: Namen raziskave je bil določiti tipične izpostavljenosti pacientov zaradi CT slikanja pri najpogostejših PET-CT protokolih v Sloveniji. Metode: Na vseh treh PET-CT napravah v Sloveniji smo zbrali podatke za skupno 565 bolnikov, ki so v obdobju 11 mesecev opravili PET-CT preiskavo. Upoštevani so bili trije najpogostejši protokoli, ki obsegajo približno 2/3 vseh PET-CT preiskav, opravljenih v Sloveniji. Ker je število PET-CT naprav v Sloveniji prenizko za določitev nacionalnih DRL, smo sledili priporočilom ICRP in določili tipične vrednosti DRL količin kot mediane vrednosti združenega niza podatkov. Za vsako enoto smo določili povprečje, mediano in standardni odklon CT doznega indeksa (CTDIvol) ter produkta doze in dolžine preiskovalnega polja (DLP) za CT del izbranih protokolov. Da bi opredelili možna izstopanja, smo izvedli tudi primerjavo tipičnih izpostavljenosti med enotami. Rezultati: Ugotovljene tipične vrednosti skupnega DLP so 295 mGy∙cm za PET/CT slikanje od baze lobanje do sredine stegnenic, 359 mGy∙cm za PET/CT slikanje od vrha glave do sredine stegnenic in 676 mGy∙cm za PET/CT slikanje od vrha glave do vključno prstov na nogah. Pripadajoče vrednosti CTDIvol so 3,05 mGy, 3,22 mGy oziroma 3,60 mGy. Razprava in zaključek: Rezultati predstavljajo prve podatke o tipičnih vrednostih DRL količin za CT del najpogostejših PET- CT preiskav v Sloveniji. Primerjava podatkov med enotami je pokazala bistveno višje (p < 0,001) izpostavljenosti bolnikov v eni od enot, kar kaže na potrebo po optimizaciji. Ključne besede: pozitronska emisijska tomografi ja – računalniška tomografi ja, računalniška tomografi ja, diagnostično referenčne ravni, doze, optimizacija ABSTRACT Introduction: Hybrid imaging, which combines positron emission tomography (PET) with computed tomography (CT), allows more accurate localization and characterization of the disease but signifi cantly increases the dose load of patients. Purpose: The purpose of the study was to determine the typical dose exposures of patients due to CT imaging in the most common PET-CT protocols in Slovenia. Methods: Data on a total of 565 patients who underwent PET-CT examination over a period of 11 months were collected on all three PET-CT devices in Slovenia. The three most common protocols were taken into account, comprising approximately 2/3 of all PET- CT examinations performed in Slovenia. As the number of PET- CT devices in Slovenia is too low to determine national DRLs, we followed the ICRP recommendations and determined the typical values of DRL quantities as the median values of the combined data set. For each unit, we determined the mean, median, and standard deviation of the CT dose index (CTDIvol) and the dose and length of the test fi eld (DLP) product for the CT portion of the selected protocols. To identify possible deviations, we also performed a comparison of typical exposures between units. Results: Typical total DLP values are 295 mGy ∙ cm for PET / CT imaging from the base of the cranium to the middle of the femur, 359 mGy ∙ cm for PET / CT imaging from the top of the head to the middle of the femur and 676 mGy ∙ cm for PET / CT imaging from the top of the head up to and including the toes. The corresponding CTDIvol values are 3.05 mGy, 3.22 mGy and 3.60 mGy, respectively. Discussion and conclusion: The results represent the fi rst data on typical values of DRL quantities for CT as part of the most common PET-CT examinations in Slovenia. Comparison of data between units showed signifi cantly higher (p <0.001) patient exposures in one of the units, indicating the need for optimization. Keywords: positron emission tomography – computed tomography, computed tomography, diagnostic reference levels, doses, optimization 40 Medical Imaging and Radiotherapy Journal (MIRTJ) 39 (Suppl. 1) Medical Imaging and Radiotherapy Journal (MIRTJ) 39 (Suppl. 1) LITERATURA / REFERENCES Abe K, Hosono M, Igarashi T, Iimori T, Ishiguro M, Ito T, Nagahata T, Tsushima H and Watanabe H 2020 The 2020 national diagnostic reference levels for nuclear medicine in Japan Ann. Nucl. Med. 34 799–806. Alkhybari E M, McEntee M F, Brennan P C, Willowson K P, Hogg P and Kench P L 2018 Determining and updating PET/CT and SPECT/CT diagnostic reference levels: a systematic review Radiat. Prot. Dosim. 182 532–45. Australian Radiation Protection and Nuclear Safety Agency 2017 Nuclear medicine diagnostic reference levels (DRLs). Avramova-Cholakova S, Shalamanov S, Dogandzhiyska D, Ivanova S, Kostova-Lefterova D, Marinov V and Mihaylova P 2017 Second national survey of patient doses from PET/ CT examinations in Bulgaria Int. Conf. Radiation Protection in Medicine. Bacher K and Verfaillie G 2019 Report on the Current use of Multi-modality Systems in Nuclear Medicine MEDIRAD: D2.8. Bailey D L, Townsend D W, Valik P E and Maisey M N 2005 Positron Emission Tomography Basic Science (Berlin: Springer) (https://doi.org/10.1126/science.1113530). Etard C, Celier D, Roch P and Aubert B 2012 National survey of patient doses from whole-body FDG PET-CT examinations in France in 2011 Radiat. Prot. Dosim. 152 334–8. Fareed A et al 2017 Impact of iterative reconstruction vs. fi ltered back projection on image quality in 320-slice CT coronary angiography: insights from the CORE320 multicenter study Medicine 96 e8452–e8452. IAEA (International Atomic Energy Agency) 2014 Radiation Protection and Safety of Radiation Sources: International Basic Safety Standards (Vienna: International Atomic Energy Agency). Iball G R, Bebbington N A, Burniston M, Edyvean S, Fraser L, Julyan P, Parkar N and Wood T 2017 A national survey of computed tomography doses in hybrid PET-CT and SPECT- CT examinations in the UK Nucl. Med. Commun. 38 459–70. Khamwan K, Krisanachinda A and Pasawang P 2010 The determination of patient dose from 18FFDG PET/CT examination Radiat. Prot. Dosim. 141 50–55. Kuo Y, Lin -Y-Y, Lee R-C, Lin C-J, Chiou -Y-Y and Guo W-Y 2016 Comparison of image quality from fi ltered back projection, statistical iterative reconstruction, and model- based iterative reconstruction algorithms in abdominal computed tomography Medicine 95 e4456. Kwon H W, Kim J P, Lee H J, Paeng J C, Lee J S, Cheon G J, Lee D S, Chung J K and Kang K W 2016 Radiation dose from whole-body F-18 fl uorodeoxyglucose positron emission tomography/- computed tomography: nationwide survey in Korea J. Korean Med. Sci. 31 S69–74. Lima T V M, Gnesin S, Ryckx N, Strobel K, Stritt N and Linder R Swiss Workgroup on Nuclear Medicine DRLs 2018 Swiss survey on hybrid imaging CTs doses in nuclear medicine and proposed national dose reference levels Z. Med. Phys. 28 265–75. Roch P, Célier D, Dessaud C and Etard C 2018 Using diagnostic reference levels to evaluate the improvement of patient dose optimisation and the infl uence of recent technologies in radiography and computed tomography Eur. J. Radiol. 98 68–74. Southard R N, Bardo D M E, Temkit M H, Thorkelson M A, Augustyn R A and Martinot C A 2019 Comparison of iterative model reconstruction versus fi ltered back-projection in pediatric emergency head CT: dose, image quality, and image-reconstruction times Am. J. Neuroradiol. 40 866–71. Townsend D W 2011 Design and operation of combined PET- CT scanners Clinical PET-CT in Radiology ed P Shreve and D W Townsend (Berlin: Springer) pp 29–39. Vanaudenhove T, Van Muylem A, Howarth N, Gevenois P A and Tack D 2019 CT diagnostic reference levels: are they appropriately computed? Eur. Radiol. 29 5264–71. Vañó E, Miller D L, Martin C J, Rehani M M, Kang K, Rosenstein M, Ortiz-López P, Mattsson S, Padovani R and Rogers A 2017 ICRP publication 135: diagnostic reference levels in medical imaging Ann. ICRP 46 1–144. Willemink M J and Noël P B 2019 The evolution of image reconstruction for CT-from fi ltered back projection to artifi cial intelligence The fi rst clinical CT scan took about Eur. Radiol. 29 2185–95.