Radiation Protection Issues in a PET/CT Installation M. Coronado 1, R. Plaza 2, R. Couto 1, MD. Marin 1, C. Huerga 2, J. Coya 1, LM Martin Curto 1, M. Téllez de Cepeda 2 1 Servicio de Medicina Nuclear, Hospital Universitario La Paz, Paseo de la Castellana 261, 28046 Madrid, Spain E-mail: lmartin.hulp@salud.madrid.org 2 Servicio de Radiofísica-Radioprotección, Hospital Universitario La Paz, Madrid, Spain E-mail: radprotec.hulp@salud.madrid.org Abstract. In the recent past years, positron emission tracers are being extended in the clinical practice. [ 18 F]fluoro-2-deoxi-D-glucose ( 18 FDG) is the most widely used radiopharmaceutical in Positron Emission Tomography (PET) imaging, and characteristically produces 511 KeV gamma rays in the positron annihilation reaction. This physical feature makes radiation dose very important in the work place [1]. The recent installation of a PET/CT scanner in our Nuclear Medicine Department, lead us to make some modifications in the radioactive installation (RI) as well as to apply different radiation protection measures adapted to the new system. We describe the consecutive stages that have been done in the Nuclear Medicine Department of La Paz University Hospital, alluding to the most relevant radiation protection aspects. Description of the consecutive stages (which took place from December 2002 to July 2003) 1. Draft of application for modifying the radioactive installation. It was presented in December of 2002 and included the following items: 1.1. Design of the PET/CT installation and location plan adapted to the Nuclear Medicine Department (FIG 1), contemplating the distribution of new rooms and reorganization of diagnostic equipment (which included four gammacameras, two densitometers and a treadmill). The new rooms included the entries for patients and working staff; a hot room equipped with a storage and dose preparation cell, a 18 FDG automatic extraction and transportation system, an air radiation detector and a radionuclide dose calibrator (activimeter); two injection and rest rooms; a toilet for injected patients; the PET-CT room and a control room. 1.2. A security study. This included calculation of shielding, 18 FDG confinement systems, management of wastes, estimation of the professionally exposed workers (PEW) doses and incident and accident prevention measures [2], [3]. Shielding calculation was realized according to the DIN6844, taking into account the source to room distance, the room occupation factor (200 working hours/year), and the occupational dose rate (1 µsv/h for PEW, 0.4 µsv/h for the general population and 0.02 1 µsv/h for scintigraphy rooms). The necessary lead shielding of the PET/CT, hot and injection rooms is shown in Tables I and II. Estimated annual doses were of 2.0 msv for PEW, 0.4 msv for members of public and 0.02 msv for conventional nuclear medicine imaging equipment. Calculation of estimated annual doses for PET studies were of 1.2 msv/6 working months for the hot room technicians handling without the automatic 18 FDG dispenser), 1.6/4 working months for nurses, 13.8 msv/working year for nurse assistants and 0.8 msv/4 working months for the nuclear medicine technicians. 1.3. Elaboration of RI regulations for operating staff, radiation protection and proceeding manuals. 1
2. Conditioning work It was started once the draft and its budget was finished. It took from February to April of 2003, shielding being the most arduous part (FIG 2, 3). Simultaneously, application for the Nuclear Medicine staff accreditation to work with X-Ray equipment was done to the Nuclear Security Council. 3. Installation and assembly of the PET/CT (Discovery LS) Frame up of the Discovery LS took less than a week (FIG. 4). System tests and fitting of computer systems took up four weeks. After Ge-68 attenuation correction sources were installed, 18 FDG another tests were done. 4. Acceptance tests and staff training 4.1. Acceptance tests were done during the first week of July 2003, including tests for PET (attenuation correction accuracy, scatter correction accuracy, sensitivity, uniformity, count rate losses and randoms, count rate correction accuracy) and for CT (geometric parameters, image and beam quality, dosimetry). 4.2. A GE training program for the operating staff was then imparted. It included the first studies with patients and 18 FDG management optimization protocols. Results Equipment conditioning was finished by the end of July 2003, being the applicable radioprotection standards fulfilled (RD 1841/1997). Table I. Shielding of PET/CT room Location Lead thickness (cm) Wall next to hospital passage 1.2 Wall next to Nuclear Medicine passage 2.5 Control room, ceiling, Nuclear Medicine office 1 Table II. Shielding of hot lab and injection rooms Location Lead thickness (cm) Wall next to Nuclear Medicine passage 3.2 Wall next to control room 2 Doors 0.5 Ceiling and wall next to elevators Not necessary (30 and 50 cm of concrete) 2
References 1. Chiesa C, De Sanctis V, Crippa F, et al. Radiation dose to technicians per nuclear medicine procedure: comparison between Tc-99m, Ga-67, and i-131 radiotracers and F-18-FDG. Eur J nucl Med 1997;24(11):1380-1389. 2. Kearfott K.J. et al. Radiation Protection design for a clinical positron emission tomography imaging suite. Health Phys. 63(5): 581-589;1992 3. Ostertag H.J. et al. Measurement and calculation of local radiation doses in the vicinity of a positron emission tomography (PET). Radiation Protection Dosimetry. Vol. 36 Nº 1. 37-41. 1991 FIG 1. Design of the Nuclear Medicine Department FIG 3. Outside wall 3
FIG 4. Detail of shielding FIG 5. Image of assembly of Discovery LS 4
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