http://myjms.moe.gov.my/index.php/ptm
Effective Dose Estimation of Patients Administered with 18F-FDG and Ga-68 DOTATATE in PET/CT Examination Associated with Gender and Weight
1Kamal, I., 2Said, M. A., 3Bathumalai, J., 4Abdul Razak, H. R.
and5,*abdul karim, m. k.
ABSTRACT
The whole-body fluorodeoxyglucose F18 (18F-FDG) and gallium-68 (Ga-68 DOTATATE) are the most common radiopharmaceutical use in PET/CT imaging for cancer staging. Although radiopharmaceutical for PET/CT examination has been acknowledged for its safety and efficacy, the internal dosimetry and effective dose (ED) from the examinations are rarely discussed. Hence, this study aimed to evaluate radiation ED for whole-body radiopharmaceuticals PET/CT concerning patients’
gender and their weight. A total of 82 oncology patients (44 males and 38 females) were collected retrospectively from Institut Kanser Negara, Putrajaya. Data, such as 18F-FDG andGa-68 DOTATATE activity and patient demography (weight, height, age), were recorded and analyzed. Effective doses from both internal and external exposure were calculated using the coefficient provided by the International Commission on Radiological Protection (ICRP) report. The total ED of 18F-FDG for male patients was 20.2 ± 8.6 mSv and for female patients were 19.0 ± 8.2 mSv while total whole-body ED for Ga-68 DOTATATE for male patients was 18.5 ± 7.0 mSv and 17.0 ± 5.6 mSv for female patients. The ratio for ED between male and female were 1:1 for both examinations ranged from 12.0 – 23 mSv. From this study, it indicated that the ED of Ga-68 DOTATATE was far lower when compared to the ED of 18F-FDG by a factor of 0.7. Therefore, it is crucial to optimize the PET/CT protocol dose in order to uphold the dose as low as reasonably achievable (ALARA).
Keywords: Effective dose; PET/CT; 18F-FDG; Ga-68 DOTATATE
1,3School of Health Sciences, KPJ Healthcare University College, Persiaran Seriemas, Kota Seriemas, 71800 Nilai, Negeri Sembilan, Malaysia
2Department of Nuclear Medicine, Institut Kanser Negara, Ministry of Health Malaysia, Putrajaya, Malaysia
4Center of Diagnostic Nuclear Imaging, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
5*Department of Physics, Faculty of Science, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
*Corresponding Author: Abdul Karim, M. K.
Email: [email protected] Tel: +60192140612
Fax: +60397693237 Received: 29 March 2020
Accepted for publication: 29 May 2020
Publisher: Malaysian Association of Medical Physics (MAMP) http://mamp.org.my
https://www.facebook.com/MedicalPhysicsMalaysia
INTRODUCTION
PET/CT scanner is a hybrid imaging modality that combined positron emission tomography (PET) with computed tomography (CT) technology. In brief, PET gains simultaneous signals from the pairs of photons (with the energy of 511 keV) resulting from positron annihilation. Meanwhile, a CT scanner utilizes an X-ray to generate tomographic images and allows the visualization of morphological and anatomic structures with a high anatomical resolution. With the derivation of the anatomical area from CT images, the localization and characterization of lesions become more precise.
Since its inception, PET/CT has become acknowledged as an imaging tool that useful for diagnostic, staging, and monitoring malignancies (Musto et al. 2011; Yang et al. 2007). The combination of both PET and CT images increases the diagnostic value than a single scan of CT or PET (Townsend & Beyer 2002). PET/CT also known as a non-invasive quantitative assessment that acquires simultaneously morphological and functional information from one single imaging session (Konert et al. 2015)convened by the International Atomic Energy Agency (IAEA). Hence, the modality produces more accurate lesion localization and characterization than PET and CT alone.
Generally, 18F-FDG has widely used in various types of cancer, e.g., bone cancer, while the Ga-68-
2016)but there are a number of clinical applications such as tumor imaging. Hence, PET/CT is vital to guide the diagnosis and treatment of cancer by obtaining accurate data on the location, size, nature, and extension of the disease. Although the use of PET/CT scanner has been proven for its advantages, the amount of radiation dose is higher when compared to other imaging modalities as patients receive from both, internal and external radiation exposure (Cho et al. 2012; Dhalisa et al. 2016;
Muhammad et al. 2019). Therefore, patient doses must be emphasized and monitored to balance the benefits of radiation exposure risk.
Although the number of references on PET / CT doses is available, the value of the dose may vary due to the different patient sizes and the techniques used (Andersson et al. 2014; Jiménez Londoño et al. 2014;
Mattsson et al. 2009). Periodical dosage monitoring allows the nuclear imaging staff to determine and alert of the danger level (ICRP 2008). The data on the radiation doses, especially effective dose (ED) of oncology patients who went through the PET/CT procedure, still lacks, especially in Malaysia. Hence the data for the most two common radiopharmaceutical compounds 18F-FDG and Ga-68 DOTATATE were collected and used for evaluation of ED in accords to patients’ weight. This research study may serve as a preliminary finding for Malaysian perspectives.
EXPERIMENTAL METHODS
STUDY DESIGN AND POPULATION
This retrospective study was conducted in a one-single institution from June 2018 to January 2019. Data, such as acquisition parameters and essential input for ED estimation, were collected and recorded in a standardized form. This study was approved by the Medical Research and Ethics Committee (MREC) of the Ministry of Health Malaysia (MOH) with an approval ID: NMRR-18-1176- 41991 which does not require patient consent.
DATA COLLECTION
After sample size was determined, 82 subjects with age ranged from 30 – 81 y/o (mean age ± SD, 62.5 ± 18.1) who underwent PET/CT examinations using DST Discovery (GE, USA) at Institut Kanser Negara (IKN) were analyzed. Two types of PET radiopharmaceuticals,
18F-FDG, and Ga-68 DOTATATE, were engaged and included in this study. Data, such as radioactivity and injection activity, were retrieved PET/CT archive
system. In addition, the dose from CT examination such as CT Dose Index (CTDI) and Dose Length Product (DLP) values were collected from the same workstation.
RADIATION DOSE ESTIMATION
It is notable that all protocols equipped with Automatic Tube Current Modulation protocols for the oncology patients to undergo the PET/CT procedure. The exposure that was being emitted from the radiopharmaceutical
18F-FDG and Ga-68 DOTATATE was known as the internal exposure. The 18F-FDG was a positron emitter with beta and gamma energies of 240 keV and 511 keV, respectively. Based on the ICRP publication 102, 103 and 106, the internal exposure was calculated using the equation (1) of absorbed dose (DT) to a tissue or organ (T) which defined as (ICRP 2007):
DT = A x Г18F or DT = A x Г68Ga (1) where A is the activity (MBq) of 18F-FDG and Ga-68 DOTATATE administered to the patient, and ГTFDG or ГTGa was dose coefficient provided by ICRP 106 for a variety of organs and tissues of the adult MIRD phantom.
The effective dose of internal exposure was determined based using the equation below:
E = ΣT WT x DT = A x ΣT WT x ГT18F or ГT68Ga (2) where ГT18F = 0.019 mSv/MBq and ГT68Ga= 0.0257 mSv/MBq is the dose coefficient for the ED of
18F-FDG and Ga-68-DOTATATE, and the WT is the tissue weighting factors, as stated in ICRP publication 128 (Mattsson et al. 2015)including biokinetic models, biokinetic data, dose coefficients for organ and tissue absorbed doses, and effective dose for major radiopharmaceuticals based on the radiation protection guidance given in Publication 60 (ICRP 1991). In order to determine the external exposure from the CT component, the dose length product values were used, which acquired from the CT control console. The ED of external exposure was calculated based on the following equation:
E= k x DLP (3) where k = 0.015 is the coefficient the empirical weighting factor (mSv.mGy-1.cm-1) based on ICRP 103 (ICRP, 2007).
RESULTS
PATIENT DEMOGRAPHIC AND ADMINISTERED ACTIVITY
Table 1 summarized the whole data recorded, including patient demography for both types of administered radiopharmaceuticals. Mean value for patient’s body weight, height and patient body mass index (BMI) for 18F-FDG examination were 66.9 ± 17.5 kg, 160.1
± 18.4 cm and 29.7 ± 4.9 kg/m2, respectively. There was no significant difference observed between patient demography except for BMI (p<0.05). CTDIvol for the
18F-FDG study were ranged from 4.4 to 17.5 (8.8 ± 3.9) mGy, and for the Ga-68 examination ranged from 4.4 to 15.9 (7.3 ± 2.8) mGy. Notably, there was no significant difference between examinations as CT dosimetry is independent of patient habitus except for DLP, which depends on the scanning range.
The mean value of whole-body effective dose from CT scan for 18F-FDG and Ga-68 was 12.8 ± 6.5 mSv and 10.6 ± 4.4, respectively. Fig. 1 illustrates the frequency
of patients’ weight, which categorized into 30 - 60 kg, 60 - 90 kg, and 90 – 120 kg that represent 45.0%, 49%, and 6% of the samples, respectively. Fig. 2 shows a scatter chart for the distribution of administered activity given to the type of radiopharmaceuticals for 82 patients.
The mean value of the 18F-FDG and Ga-68 DOTATATE administered activity was 424.8 ± 125.9 MBq and 213.9
± 45.3 MBq, respectively. Both were found to have differed significantly with p-value < 0.05.
ESTIMATION OF EFFECTIVE DOSE
Table 2 tabulates the total ED of patients based on gender and type of examinations. The total mean value of ED whole-body has differed significantly, where 18F-FDG and Ga-68 DOTATATE were 20.8 ± 8.3 mSv and 16.1 ± 4.5 mSv, respectively.
Specifically, the ratio whole-body ED of 18F-FDG to Ga-68 DOTATATE for male and female patients was 1.1 and 1.2, respectively. Fig. 3 summarizes the total whole-body ED for both examinations in accordance with patients’ weight.
TABLE 1 Subjects’ demography and dose estimation from both radiopharmaceuticals study
Features Radiopharmaceuticals (mean ± SD) (min – max)
18FDG Ga-68
Demography Weight/kg Height/cm BMI/kgm-2
66.9 ± 17.5 (38 – 102) 160.1 ± 18.4 (66 - 188) 29.7 ± 4.9 (16.8 – 34.5)
60.2 ± 12.5 (38 – 94) 161.5 ± 8.6 (144 – 178) 23.0 ± 4.1 (16.4 – 33.7) CT dosimetry
CTDIvol/mGy åDLP/mGy.cm
CT ED/mSv
8.8 ± 3.9 (4.4 – 17.5) 850.9 ± 433.4 (124.9 – 1821.7) 12.8 ± 6.5 (1.9 – 27.3)
7.3 ± 2.8 (4.4 – 15.9) 708.8 ± 290.9 (401.9 – 1654.1) 10.6 ± 4.4 (6.0 – 24.8) PET dosimetry
Activity/MBq
PET ED/mSv 424.8 ± 125.9 (205.7 – 675.9)
8.1 ± 2.4 (3.9 – 12.8) 213.9 ± 45.3 (126.9 – 304.8) 5.5 ± 1.2 (3.3 – 7.8)
Total ED (PET + CT)/mSv 20.8 ± 8.3 (9.9 – 39.3) 16.1 ± 4.5 (10.2 – 31.1)
TABLE 2 The total whole-body effective dose of PET/CT based on gender Radiopharmaceutical Total whole body effective dose/mSv
18 F-FDG 20.8 ± 8.3
Male 20.2 8.6
Female 19.0 8.2
FIGURE 2 Distribution of patients’ weight according to administered activity in MBq
FIGURE 1 Frequency of patients in this study based on three categorized weights
(a)
(b)
FIGURE 3 (a) The total whole-body effective dose of CT (external exposure) and (b) PET (internal exposure) based on patients' weight.
DISCUSSION
In this study, the effective dose from PET/CT examinations was evaluated for pre-determined risk to oncologic patients. Even though the radiation exposure risk to the population with cancer has less impact due to the reduced life expectancy but the query is upstretched when it derives to the importance of evaluating the risk or benefit for justification and relevant protocol optimization and personnel protection (Brenner, 2012;
Brenner and Hall, 2007; N. A. Muhammad et al., 2019).
It is because the doses that being given to the patients for the same type of examination differ widely between centers suggesting that there is considerable scope for management of patient dose (Guttikonda et al., 2014).
The use of the most common radiopharmaceutical compound, which is the 18F-FDG and Ga-68-DOTATATE for the assessment of oncology patients, was known for the detection of all types of cancer cells using whole- body scanning technique.
The age of the patient plays a significant role in the
whose age was between the age group of 31-50-year- old and above 50-year-old had the highest estimation of whole-body ED of PET/CT. It is because the individuals who are exposed at early ages are the most radiosensitive as the primary damage has a longer latent phase to erupt into cancer (Halid et al., 2018; Schrevens et al., 2004).
Afterward, sensitivity to radiation reduces till middle age, nonetheless upsurges yet again at older ages. The radiation doses that were received after the age of 45 displayed a greater association with cancer fatality than those received at younger ages and prove that the radiation sensitivity increases with age among adults after the age of 40 years (Einstein et al., 2007). The weight of the oncology patients may influence radiation exposure from PET/CT examinations. The patient who weight between 31-50 kg and 50-70 kg being estimated of receives ED within the range of 5 mSv and 6-10 mSv.
Meanwhile, patients who weighted in the category above 70 kg receive ED within 11-15 mSv. It is because in regular weighted patients there will be an increase in the relative radiation dose however in overweight patients
the low relative injected dose (Heismann et al., 2008;
Karim et al., 2019; Seco et al., 2014).
The ED of the oncology patients who undergo whole body 18F-FDG PET/CT imaging in this study was 11.5
± 5.0 mSv, which was less compared to the previously reported values ranging from 21.46 to 25 mSv. Indeed, the result of this research was within the mean value of the whole-body ED values in Huang et al. 2009 study where both male and female receives ED of 20.6 mSv and 19.3 mSv, respectively (Huang et al., 2009).
Therefore, the estimated PET/CT ED of this study was considerably lesser as compared to the previous studies, which apprehensions the estimation of radiation dose that is given to the patient in the PET/CT imaging procedure.
T h e P E T / C T w h o l e - b o d y E D o f t h e radiopharmaceutical Ga-68-DOTATATE in this study was 6.1 ± 2.9 mSv, which turn out to be lesser compared to 18F-FDG PET/CT as stated in the previous study (Sandström et al., 2013; Walker et al., 2013). This also can be fortified by the study conducted by The American College of Radiology, which affirms that the total ED from a typical 68Ga DOTATATE PET (~5 mSv) is less than 18F-FDG (~7 mSv) scans (Coleman et al., 2005).
According to Boellaard R et al. 2008, the Ga-68 labeled somatostatin analogs provide higher quality images with less total radiation exposure to the patient than 18F-FDG (Boellaard et al., 2008). Indeed, the Ga-68-DOTATATE dose coefficient is higher compared to the 18F-FDG due to the average positron energy where the 68Ga is 0.83 MeV, and the 18F is 0.25 MeV. Since the given activity for 18F-FDG was set to 5 MBq per patient's body weight in kg, while Ga-68 DOTATATE was set at an almost fixed value of 185 MBq per patient, thus the Ga-68 DOTATATE ED is higher than the ED of 18F-FDG. The main reason for Ga-68 that contributes lesser radioactivity to the patients is because this radiopharmaceutical only targets the specific organs that being related to neuroendocrine tumours while the 18F is to provide information on the glucose uptake throughout the body. Thus, the patients' weight is a crucial factor in PET dosimetry for 18F compared to the Ga-68.
The activity dose of administered activity 18F-FDG is higher due to the patient's weight, as suggested by several established publications (EANM/SNMMI). The formula being used as a disadvantage for obese patients because the fat in the patient's body also included in the calculation and has another formulation (Quinn et al., 2016). However, the bodyweight formula is acceptable for clinical purposes. The outcome of the CT scan completely depends on the Automatic Tube Current Modulation;
nonetheless, the CT scan dose is variable according to the patient's body weight (Karim et al., 2019; Sabarudin
There is some limitation in this study. First, the study was a retrospective analysis from one single institution only, which might have biased. Second, this study unable to evaluate the performance in term of image quality. The acquisition parameters also were not discussed, which was necessary to verify the organ dose and evaluate patient risk systematically.
CONCLUSION
The estimation of the total whole-body PET/CT ED for male patients is moderately higher when compared to female patients. The main reason for this was due to the influence of the patient habitus, which has been the main contributor to the ED as the weight of the patient is directly proportional to the total whole-body PET/
CT ED. From this study, it also indicated that the ED of Ga-68-DOTATATE was lower compared to the ED of 18F-FDG. Besides, it is also essential to optimize the PET/CT protocol dose in order to uphold the dose as low as reasonably achievable (ALARA). Thus, it is necessary to conduct studies based on the estimation of radiation dose in order to create awareness of the long-term risk among medical professionals and patients.
ACKNOWLEDGMENT
The author wishes to acknowledge the support and cooperation given by the staff at the Nuclear Medicine Department of Institut Kanser Negara and KPJ University College for granting the ethics to conduct this research
REFERENCES
Andersson, M., Johansson, L., Minarik, D., Leide- Svegborn, S. and Mattsson, S. 2014. Effective Dose to Adult Patients from 338 Radiopharmaceuticals Estimated using ICRP Biokinetic Data, ICRP/
ICRU Computational Reference Phantoms and ICRP 2007 Tissue Weighting Factors. EJNMMI Phys. 1(1): 9.
Boellaard, R., Oyen, W. J. G., Hoekstra, C. J., Hoekstra, O. S., Visser, E. P., Willemsen, A. T., Arends, B., Verzijlbergen, F. J., Zijlstra, J., Paans, A. M., Comans, E. F. I. and Pruim, J. 2008. The Netherlands Protocol for Standardisation and Quantification of FDG Whole Body PET Studies in Multi-centre Trials. Eur. J. Nucl. Med. Mol. Imaging. 35(12):
2320 - 2333.
Brenner, D. J. 2012. Minimising Medically Unwarranted Computed Tomography Scans. Ann. ICRP 41:
161–169.
Brenner, D. J. and Hall, E. J. 2007. Computed Tomography-An Increasing Source of Radiation Exposure. N. Engl. J. Med. 357: 2277–2284.
Budäus, L., Leyh-Bannurah, S.-R., Salomon, G., Michl, U., Heinzer, H., Huland, H., Graefen, M., Steuber, T.
and Rosenbaum, C. 2015. Initial Experience of (68) Ga-PSMA PET/CT Imaging in High-risk Prostate Cancer Patients Prior to Radical Prostatectomy. Eur.
Urol. 69: 393–396.
Cho, S. Y., Gage, K. L., Mease, R. C., Senthamizhchelvan, S., Holt, D. P., Jeffrey-Kwanisai, A., Endres, C. J., Dannals, R. F., Sgouros, G., Lodge, M., Eisenberger, M. A., Rodriguez, R., Carducci, M. A., Rojas, C., Slusher, B. S., Kozikowski, A. P. and Pomper, M.
G. 2012. Biodistribution, Tumor Detection and Radiation Dosimetry of 18F-DCFBC, a Low- molecular-weight Inhibitor of Prostate-specific Membrane Antigen, in Patients with Metastatic Prostate Cancer. J. Nucl. Med. 53: 1883–1891.
Coleman, R. E., Delbeke, D., Guiberteau, M. J., Conti, P. S., Royal, H. D., Weinreb, J. C., Siegel, B. A., Federle, M. P., Townsend, D. W. and Berland, L.
L. 2005. Concurrent PET/CT with an Integrated Imaging System: Intersociety Dialogue from the Joint Working Group of the American College of Radiology, the Society of Nuclear Medicine and the Society of Computed Body Tomography and Magnetic Resonance. J. Am. Coll. Radiol. 2:
568–584.
Dhalisa, H., Mohamad, A. S. and Rafidah, Z. 2016.
Radiation Assessment to Paediatric with F-18-FDG Undergo Whole-body PET/CT Examination, in: AIP Conference Proceedings. 1704: 030004.
Einstein, A. J., Henzlova, M. J. and Rajagopalan, S.
2007. Estimating Risk of Cancer Associated with Radiation Exposure from 64-slice Computed Tomography Coronary Angiography. JAMA 298:
317–323.
Groheux, D., Mankoff, D., Lemarignier, C., Cochet, A., Humbert, O., Champion, L., Alberini, J. -L.
and Hindié, E. 2016. Impact of Molecular and Histological Subtype of Breast Cancer on 18FDG- PET/CT Imaging: Knowledge Gained from Recent Studies. Médecine Nucléaire 40: 65–71.
Guttikonda, R., Herts, B. R., Dong, F., Baker, M. E., Fenner, K. B. and Pohlman, B. 2014. Estimated Radiation Exposure and Cancer Risk from CT and PET/CT Scans in Patients with Lymphoma. Eur. J.
Radiol. 83: 1011–1015.
Halid, B., Karim, M. K. A., Sabarudin, A., Bakar, K.
A. and Shariff, N. D. 2018. Assessment of Lifetime
During Abdominal CT Examinations Based on Monte Carlo Simulation. In: Vo Van T., Nguyen Le T., Nguyen Duc T. (eds.) 6th. International Conference on the Development of Biomedical Engineering in Vietnam (BME6). BME 2017.
IFMBE Proceedings, 63. Springer: Singapore Heismann, B. J., Bätz, L., Pham-Gia, K., Metzger,
W., Niederlöhner, D. and Wirth, S. 2008. Signal Transport in Computed Tomography Detectors.
Nucl. Instrum. Meth. A 591(1): 28–33.
Huang, B., Law, M. W. M. and Khong, P. L. 2009. Whole- body PET/CT Scanning: Estimation of Radiation Dose and Cancer Risk. Radiology 251(1):166-174.
ICRP Publication 103. 2007. The 2007 Recommendations of the International Commission on Radiological Protection. Ann. ICRP 37(2-4).
ICRP Publication 106. 2008. Radiation Dose to Patients from Radiopharmaceuticals - Addendum 3 to ICRP Publication 53. Ann. ICRP 38(1-2).
ICRP Publication 128. 2015. Radiation Dose to Patients from Radiopharmaceuticals: A Compendium of Current Information Related to Frequently Used Substances. Ann. ICRP 44(2 Suppl.): 7–321.
Jiménez Londoño, G. A., García Vicente, A. M., Sánchez Pérez, V., Jiménez Aragón, F., León Martin, A., Cano Cano, J. M., Domínguez Ferreras, E., Gómez López, O. Van Espinosa Arranz, J. and Soriano Castrejón, A. M. 2014. 18F-FDG PET/
Contrast Enhanced CT in the Standard Surveillance of High Risk Colorectal Cancer Patients. Eur. J.
Radiol. 83: 2224–2230.
Karim, M. K. A., Rahim, N. A., Mustafa, S. N. S., Sabarudin, A. and Ibahim, M. J. 2019. Assessment of Radiation Effective Dose from Lung Cancer Screening Pilot Project in Institut Kanser Negara:
A Preliminary Finding. J. Phys. Conf. Ser. 1248:
012012.
Karim, M. K. A., Sabarudin, A., Muhammad, N. A., Ng, K. H. 2019. A Comparative Study of Radiation Doses Between Phantom and Patients Via CT Angiography of the Intra-/Extra-Cranial, Pulmonary and Abdominal/Pelvic Arteries. Radiol. Phys.
Technol. 12: 374–381.
Konert, T., Vogel, W., MacManus, M. P., Nestle, U., Belderbos, J., Grégoire, V., Thorwarth, D., Fidarova, E., Paez, D., Chiti, A., and Hanna, G. G., 2015.
PET/CT Imaging for Target Volume Delineation in Curative Intent Radiotherapy of Non-Small Cell Lung Cancer: IAEA Consensus Report 2014.
Radiother. Oncol. 116: 27–34.
Mattsson, S., Johansson, L., Liniecki, J., Nosske, D., Stabin, M., Leide-Svegborn, S. and Taylor, D. 2009. Radiation Dose to Patients from Radiopharmaceuticals. In: Dössel O., Schlegel W.
Biomedical Engineering, September 7 - 12, 2009, Munich, Germany. IFMBE Proceedings, vol 25/3.
Springer, Berlin, Heidelberg
Muhammad, N. A., Karim, M. K. A., Hassan, H. A., Kamarudin, M. A., Wong, J. H. D. and Ibahim, M.
J. 2019. Estimation of Effective Dose and Organ Cancer Risk from Paediatric Computed Tomography Thorax – Abdomen - Pelvis Examinations. Radiat.
Phys. Chem. 165: 108438.
Musto, A., Rampin, L., Nanni, C., Marzola, M. C., Fanti, S. and Rubello, D. 2011. Present and Future of PET and PET/CT in Gynaecologic Malignancies. Eur. J.
Radiol. 78(1):12-20.
Quinn, B., Dauer, Z., Pandit-Taskar, N., Schoder, H., Dauer, L. T. 2016. Radiation Dosimetry of 18F-FDG PET/CT: Incorporating Exam-Specific Parameters in Dose Estimates. BMC Med. Imaging 16(1): 41.
Sabarudin, A., Siong, T. W., Chin, A. W., Hoong, N. K., and Karim, M. K. A. 2019. A Comparison Study of Radiation Effective Dose in ECG-Gated Coronary CT Angiography and Calcium Scoring Examinations Performed with a Dual-Source CT Scanner. Sci. Rep.
9(1): 4374.
Sandström, M., Velikyan, I., Garske-Román, U., Sörensen, J., Eriksson, B., Granberg, D., Lundqvist, H., Sundin, A. and Lubberink, M. 2013. Comparative Biodistribution and Radiation Dosimetry of 68Ga- DOTATOC and 68Ga-DOTATATE in Patients with Neuroendocrine Tumors. J. Nucl. Med. 54(10):1755- 1759.
Schrevens, L., Lorent, N., Dooms, C. and Vansteenkiste, J., 2004. The Role of PET Scan in Diagnosis, Staging and Management of Non-Small Cell Lung Cancer.
Oncologist 9(6): 633-643.
Seco, J., Clasie, B. and Partridge, M. 2014. Review on the Characteristics of Radiation Detectors for Dosimetry and Imaging. Phys. Med. Biol. 59:
R303–R347.
Townsend, D. W. and Beyer, T. 2002. A Combined PET/
CT Scanner: The Path to True Image Fusion. Br. J.
Radiol. 75 Spec No(suppl. 9): S24-30.
Walker, R. C., Smith, G. T., Liu, E., Moore, B., Clanton, J. and Stabin, M. 2013. Measured Human Dosimetry of 68Ga-DOTATATE. J. Nucl. Med. 54(6):855-860.
Yang, S. K., Cho, N. and Moon, W. K. 2007. The Role of PET/CT for Evaluating Breast Cancer. Korean J.
Radiol. 8(5): 429 - 437.