Population Dose from General X-ray and Nuclear Medicine: 2010

Transcription

1 Population Dose from General X-ray and Nuclear Medicine: 2010 Medical Exposure Radiation Unit 1

2 Executive Summary of Results The Health Services Executive (HSE) has a legal obligation, under Article 12 of the European Commission Medical Exposures directive (1997) 1 and Article 22.6 of Statutory Instrument 478 (2002) 2, to collect and publish statistics on population dose levels from the use of medical ionising radiation. In 2008 the Population Dose Sub-Committee of the National Radiation Safety Committee 3 decided to select Computed Tomography (CT)as the first modality to survey in relation to population dose, followed by Dental Radiography. This survey is the third in the series and addresses both General X-ray imaging and Nuclear Medicine Scans. The survey commenced in All X-ray and Nuclear Medicine holders,both public and private, on the HSE register of ionising radiation installationswere surveyed. A 100% response rate was achieved for Nuclear Medicine holders, while the response rate amongst holders of x-ray installations was 64%. Of those that responded 14% provided partial information citing resource issues. A subset of examinations was selected for survey in line with recommendations from the European Commission 4, and the 2008 UK Population dose survey. Additional information was obtained from the 2008 Baseline clinical audit questionnaire,as carried out by the Health Service Executive s Taskforce on the Implementation of the SI An estimate of 2,575,180 x-rays for 2010 was extrapolated from the information returned. The collective dose (total dose to the population) from General X-ray was found to be 255manSv with a dose per caput (dose per head of population) of 0.056mSv per annum. The comparable dose per caput for other countries recently surveyed ranges from 0.08mSv in the UK ( ) to 0.3mSv in France ( ). There were 29,993 nuclear medicine scans performed in the year. The collective dose from Nuclear Medicine scans was found to be 112manSv, with a dose per caput of 0.02mSv per annum. The comparable dose per caput for other countries recently surveyed ranges from 0.03mSv in the UK (2003) to 0.11mSv in Germany ( ). These results can be compared to that of CT where a Collective Dose of 1368manSv was reported by the HSE in Taking the RPII data for interventional procedures into account this suggests a total collective dose to the population from all diagnostic ionising radiation procedures of 2076manSv. The collective dose from all diagnostic ionising radiation procedures equates to a total annual dose per caput of 0.5mSv. This compares to an estimate of 0.54mSv in RPII 2006 data for Ireland and to the dose per caput in the UK (2008) of 0.4msv (excluding Nuclear Medicine), the USA where the dose per caput is 2.2mSv (NCRP ) and France where the dose per caput is 1.3mSv (2007) 2

3 Introduction The Health Services Executive (HSE) has a legal obligation, under Article 12 of the European Commission Medical Exposures directive (1997) and Article 22.6 of Statutory Instrument 478 (2002), to collect and publish statistics on population dose levels from the use of medical ionising radiation. One benefit from constructing an estimate of the population dose is that it allows comparison of the contributions from different types of X-ray examination. Such information can provide guidance on where best to concentrate efforts on dose reduction. Another benefit is the capability to monitor and trend in annual per caput effective dose associated with changes in radiology practice. In 2008 the Population Dose Sub-Committee of the National Radiation Safety Committee decided to select Computed Tomography (CT)as the first modality to survey in relation to population dose, followed by Dental Radiography. This survey is the third in the series and addresses both General X-ray imaging and Nuclear Medicine Scans. This report presents the results of a new study of frequency and collective dose from X-ray examination. It follows the recommended methods published by the European Commission for estimating population dose from medical X-ray procedures. Diagnostic nuclear medicine procedures were analysed following the recommendations of the Health Protection Agency produced for the Administration of Radioactive Substances Advisory Committee 11 Methodology To assist member states with the implementation of Article 12, the European Commission published European Guidance on Estimating Population Doses from Medical X-ray Procedures. This document has been useful to the Population Dose Sub-Committee in formulating methodology and in reporting on population dose. Phase one of the projects started in May In this phase the HSE contacted and invited 136 public hospitals, private hospitals and chiropractors to complete a survey form following the requested criteria: - Dose data can be collected retrospectively from January Dose data may also be collected prospectively - Enter the frequency for all the examinations carried out at the facility - Collate dose data for examinations carried out regularly at the facility - Data for ten or twenty patients is to be averaged, and the averaged values for DAP recorded (where a DAP meter is available) - Only average size adult patients are to be included in the adult dataset - Dose for the full examination is to be averaged For the nuclear medicine survey, 19 hospitals were contacted and invited to complete a survey form following the requested criteria: - The average injected activity per scan is to be recorded in MBq - If the injected activity is varied by patient an average value from average patients is to be recorded 3

4 The survey return required the approval by the Practitioner-in-charge, the Radiation Safety Officer, Clinical Specialist in Nuclear Medicine and the Radiation Protection Advisor/Medical Physics Expert. The survey form is reported in Appendix A. In the second phase of the project, started in June 2011, all the contacted X-ray machines holders were invited to submit on-line the collected data by the end of July Survey design For the plain radiography survey, a set of examinations for adults was included in the survey. The set of examinations was chosen based on the recommendations of the European Commission in RP-154. In total 23 examinations were selected for survey of the adult population: Chest PA, Chest AP, Cervical Spine AP, Cervical Spine Lat, Thoracic Spine AP, Thoracic Spine Lat, Lumbar Spine AP, Lumbar Spine Lat, Lumbar sacral junction, Full Spine (T+L), Full Spine (C+T+L), Abdomen AP, Abdomen Barium follow through, Pelvic AP, Single Hip AP, Double Hip, Femur AP, Femur Lat, Mammography Screening, Mammography Symptomatic, Feet/Ankles/Wrist/Hand, Knees (AP and Lateral), Arthrography. Data for Barium follow through and Arthrography was held over for analysis until a more detailed survey of fluoroscopic examinations was completed. The survey form (Appendix A) was sent to the CEO, Clinical Specialist Radiographer and the Practitioner in Charge at each location, and data on patient and examination frequency, DAP were requested. For the Nuclear Medicine Survey, a set of examinations for adult was included in the survey. The following 15 examinations were taken into account: 99mTc Bone Scan, 99mTc Thyroid Scan, 131-I Thyroid Uptake Scan, 123-I Thyroid Uptake Scan, 131-I Thyroid metastases, 99mTc V/Q Perfusion Scan, 99mTc Aerosol V/Q Ventilation Scan, 99mTc TechneGas V/Q Ventilation Scan, 99mTc DTPA Renogram Scan, 99mTc MAG3 Renogram Scan, 123-I DAT Scan, 123-I MIBG Scan, 111-In OctreoScan, 99mTc Myocardial Scan, 99mTc Cerebral blood flow. In order to ensure that the data returned was validated internally before submission the survey required the signature of the Practitioner-in-charge, the Radiation Safety Officer, Clinical Specialist in Nuclear Medicine and the Radiation Protection Advisor/Medical Physics Expert. Further verification of the average dose data submitted was made with the participating site where the submission indicated a dose significantly lower or higher than the Medical Council approved dose reference level. In a small number of cases the holder altered the average dose submitted following query, and the altered average dose was used for analysis of population dose. Collection of data on examination frequency was found to be problematic with no centralised system for recording examination frequency. The survey relied on 4

5 each holder to determine frequency locally and return on-line along with the average dose data. Some inconsistency of frequency data returned was noted. A copy of this report, along with recommendations, will be forwarded to each holder and they will be asked for verify their methodology of collating examination frequency. This may assist locations in compiling data for future surveys. Where participating sites were able to provide examination frequency but unable to provide information on the number of patients irradiated an estimate of patient frequency was made, based on the ratio of patient to examination frequency from other similar participating sites. Effective Dose Determination Irish statutory instruments SI 125(2000) 12 and SI478 (2002) enact the European Council Directives 96/299 and 97/43/EURATOM1 which take into account the 1990 recommendations of the International Commission on Radiological Protection (ICRP) 13 on protection against the risks associated with ionising radiation. However, in recent years the ICRP have revised their view of the radiosensitivity of some organs, most notably Breast and Gonads and published their most recent recommendations ICRP-103 in The European Commission is revisiting the Directive 97/43/EURATOM in light of these revised recommendations. The effective dose E is defined by ICRP [ICRP, 1990] as the weighted sum of the mean doses to a number of radiosensitive tissues or organs in the body. ICRP Publication 60 specifies 12 tissues or organs with reasonably well established sensitivities for the stochastic effects of radiation and a further 10 (the so-called remainder organs ) which might be susceptible to cancer induction but with a lower and individually undetermined sensitivity. Ideally estimates of the mean absorbed dose to each of the 12 specified organs and to as many of the remainder organs as possible are required to estimate the effective dose. Since it is impossible to make direct measurements of most of these organ doses in living patients, it has been common practice to resort to the use of computational dosimetry techniques to model x-ray examinations on phantoms representing typical patients. Most of the computational dosimetry techniques use Monte Carlo radiation transport codes to simulate medical x-ray exposures on the phantoms and to calculate the energy deposited in each organ. A number of radiation protection organisations around the world have performed these Monte Carlo calculations and have published organ and effective dose coefficients for a large number of types of x-ray examination under a wide range of exposure conditions [Rosenstein , Stern , Drexler , Zankl , Jones , Tapiovaara ]. The recommended tissue weighting factors for effective dose changed with the publication of the new Recommendations of ICRP in 2007 [ICRP Publication 103, 2007a]. In this survey the conversion factors, to calculate the effective dose from the DAP, were taken from the ICRP

6 When calculating the effective dose from a mammography examination, it is reasonable to assume that the breast is the only exposed organ, so that only the dose to the radiosensitive tissues in the breast and the tissue weighting factor for the breast need to be taken into account. In this case the effective dose was calculated from the Mean Glandular Dose, measured in mgy. The effective dose calculation for Nuclear Medicine procedures was based on the methodology of the ICRP 21, with conversion factors taken from the ARSAC Guidance notes of2006. Population Dose The Average Effective Dose per examination was used to contribute to the determination of Population Dose. Population dose is reported as the annual Collective Effective Dose mansv and Dose per Caput, as recommended by RP-154. The collective dose is defined as the sum of the average effective dose for each Examination multiplied by the frequency of each examination. The Dose per Caput is defined as the collective dose average over the whole population. The population for 2010 has been taken from the 2011 Census4,588,252 Results The survey commenced in May 2011 and a final reminder was sent in February A 100% response rate was achieved for Nuclear Medicine holders, while the response rate amongst holders of x-ray installations was 64%. Based on the received data a total number of 2,575,180 x-rays for the year 2010 was extrapolated. There were 29,993 nuclear medicine scans performed in the same year. Frequency of examinations for the plain radiography survey The number of studies and the relative frequency of X-ray examinations surveyed, from all health care sectors in Ireland in 2010, is shown in Table 1 and the distribution of frequency is shown in figure 1. Some anomalies were noted in the frequency data returned for a large number of locations. For example it would appear that some locations are not routinely carrying out a Lateral lumbar spine when carrying out an AP lumbar spine, and there are significant numbers of Lumbar sacral junction x-rays. Locations will be asked to further verify the frequency data and their methology of collating during the feedback process. The main X-ray examinations performed are Chest PA (24.8%) and extremities (15.2%), followed by Chest AP (6%), Pelvic AP (4.9%), and Abdominal AP (4.2%). 6

7 Examination Extrapolated number of studies Examination frequency Chest PA % Chest AP % Cervical Spine AP % Cervical Spine Lat % Thoracic Spine AP % Thoracic Spine Lat % Lumbar Spine AP % Lumbar Spine Lat % Lumbar Sacral Junction % Full Spine (T+L) % Full Spine (C+T+L) % Skeletal Survey % Abdominal AP % Pelvic AP % Single Hip AP % Both Hips % Femur AP % Femur Lat % Mammography Screening % Mammography Symptomatic % Feet/Ankles/Wrist/Hand % Knees AP/Lateral % Table 1 Number of studies extrapolated for the year 2010 and relative frequency Figure 1: Contribution by examination type to the total number of examination performed in 2010for the subset surveyed 7

8 The frequency of 4 examinations (Chest/thorax, Cervical Spine, Abdomen and Pelvis/Hip), in terms of number of examination for 1000 inhabitants is compared in figure 2 with results of other European surveys. The year (s) in which the frequency data were obtained are indicated below the Country symbol. Results are taken from DD Report 1 of Radiation Protection n.154. For most of the exams the maximum annual frequencies per head of population occur in Belgium or Germany. The minimum annual frequencies per head of population occur in Denmark, Netherland and UK. Ireland s frequencies are in the middle. Figure 2 Frequencies of 4 main exams in 11 European Countries Frequency of examinations for the Nuclear Medicine survey The number of scans performed in 2010 in Ireland and the examination frequencies for the subset of scans surveyed are reported in Table 2. The distribution of frequencies is reported in figure 2. Among the scans selected in this survey, the bone scan represents the vast majority (73.06%) followed by 99mTc Thyroid Scan (5.54%) and 99mTc V/Q Perfusion Scan (4.57%). All other scans represent a small percentage around 2% r less. 8

9 Exam Extrapolated number of studies Examination frequency 99mTc Bone Scan % 99mTc Thyroid Scan % 131-I Thyroid Uptake Scan % 131-I Thyroid metastases % 99mTc V/Q Perfusion Scan % 99mTc Aerosol V/Q Ventilation Scan % 99mTc TechneGas V/Q Ventilation Scan % 99mTc DTPA Renogram Scan % 99mTc MAG3 Renogram Scan % 123-I DAT Scan % 123-I MIBG Scan % 111-In OctreoScan % 99mTc Myocardial Scan % 99mTc Cerebral blood flow % Table 2 Number of scans performed in 2010 and relative frequency calculated for the subset of scans included in the survey Figure 2: Contribution by scan type to the total number of scans performed in 2010 for the subset of examinations surveyed The contribution of different groups of examinations (bone, heart, thyroid, lung and kidney) to the total annual number of nuclear medicine examinations is reported in figure 3 and compared with results of other European Countries. The year (s) in which the frequency data were obtained are indicated beside the Country symbol. Results are taken from DD Report 1a 22 of Radiation Protection n.154. In all countries the five categories contribute more than 80% to the total, except for Ireland which contribute to 67%. This result presumably depends on the choice of the scans selected for this survey. In 7 countries bone scans are the most frequently performed examination. Only in Germany thyroid examinations occur more frequently. Thyroid examinations are also often carried out in Luxemburg and Belgium contrary to the United Kingdom and Ireland where they are relatively rare. 9

10 Relative contribution of five groups of examinations to the total frequency of nuclear medicine examinations UK CH 2004 SE 2005 NO 2004 Bone Hearth Thyroid Lung Kidney NL 2002 LU 2002 GE 2002 BE IRE Frequency distribution (%) Figure 3 relative contributions of 5 groups of examinations to the total frequency of nuclear medicine examinations Population Dose for plain radiography Table 3 shows the Mean Effective dose for all the 24 examinations included in the survey, based on the average of typical DAP measurements. Examinations Mean Effective Dose(mSv) Chest PA 0.02 Chest AP 0.04 Cervical Spine AP 0.04 Cervical Spine Lat 0.03 Thoracic Spine AP 0.22 Thoracic Spine Lat 0.17 Lumbar Spine AP 0.35 Lumbar Spine Lat 0.22 Lumbar sacral junction 0.19 Full Spine (T+L) 1.22 Full Spine (C+T+L) 0.92 Skeletal Survey 0.80 Abdominal AP 0.40 Pelvic AP 0.29 Single Hip AP 0.18 Double Hip 0.27 Femur AP 0.03 Femur Lat Mammography Screening 0.57 Mammography Symptomatic 0.54 Feet/Ankles/Wrist/Hand Knees AP/Lateral Table 3 Mean effective dose calculated for the 24 examinations included in the survey 10

11 Taking into account the typical projections for solely radiographic examinations, the effective doses have been summed and results compared to the results of other European surveys. Results are shown in figure 4. Due to the diversity between countries, three sets of typical effective doses have been defined: 1. A higher exposure group (Germany and Switzerland) 2. An average exposure group (all Countries) 3. A lower exposure group (Netherland and UK) The dose data from Germany, Switzerland, Netherlands and United Kingdom, all comes from relatively large surveys that were fairly representative of national practice at the time of the survey. The effective dose values in these surveys was computed using the tissue weighting factors of ICRP-60. For the purposes of comparison the Irish doses presented in Figure 4 have also been computed with ICRP-60 tissue weighting factors, rather than ICRP-103 as used elsewhere in this report. Figure 4 Comparison of the Mean Effective doses with other European countries doses Ireland s effective doses are comparable with the lower exposure group. In addition Ireland s effective doses are comparable with UK doses reported in 2008, and illustrated in figure 5 (both datasets based on the tissue weighting factors of ICRP-103) 11

12 Figure 5 Comparison between Ireland and UK effective doses Once the number of studies performed for every kind of examinationwas known, the collective dose was then calculated. Figure 6 and 7 show the collective doses values for each examination surveyd, along with the percentage distribution Figure 6Collective 6 dose (mansv) for all the examinations included in the survey 12

13 Figure 7 Distribution of the collective dose (mansv) for the examinations included in the survey The total annual collective dose from all X-ray examinations in Ireland in 2010 amounts to 255manSv. With anireland population of 4,588,252 in 2011 the annual per caput effective dose is 0.056mSv Population Dose for Nuclear Medicine Table 4 shows the Mean Effective dose for all the 15 examinations included in the survey, based on the average of typical activity (MBq). From the frequency, and the effective dose per examination, the annual collective dose has been calculated and results are reported in figure 8 and 9. Exam 99mTc Bone Scan mTc Thyroid Scan I Thyroid Uptake I Thyroid metastases mTc V/Q Perfusion Scan mTc Aerosol V/Q Ventilation Scan mTc TechneGas V/Q Ventilation Scan mTc DTPA Renogram Scan mTc MAG3 Renogram Scan I DAT Scan I MIBG Scan In OctreoScan mTc Myocardial Scan mTc Cerebral blood flow 6.65 AverageEffectiveDose (msv) 13

14 The reported dose for 131-I uptake has been subject to further review with regard to justification and optimisation in the small number of organisations that carry out this examination. These scans account for just 0.55% of the frequency distribution for nuclear medicine. Figure 8 Collective dose (mansv) for all the scans included in the survey Figure 9 Distribution of the collective dose (mansv) for the scans included in the survey For the nuclear medicine scans it is quite difficult to make a comparison with other Countries in terms of effective doses. In fact the average effective dose to patients from a nuclear medicine examination depends mostly on typical amount of activity administred and the radionuclide used.there are substantial differences in the mean administrated activities between some countries for particular examinations. For example, the mean administrated activity for a bone 14

15 scan in Ireland is MBq while in the rest of Europe it ranges from 505 MBq in Sweden and 720 MBq in Belgium. The total annual collective dose from all nuclear medicine scans in Ireland in 2010 amounts to 112manSv. With an Ireland population of in 2011the annual per caput effective dose is 0.02mSv. Figure 10 show the comparison of Ireland annual per caput effective dose in Ireland with other Countries. Annual effective dose per caput for all nuclear medicine examinations 0.25 Effective dose per caput (msv) IRE 2010 BE GE 2002 LU 2002 NL 2002 NO 2004 SE 2005 CH 2004 UK Survey Figure 10Annual effective dose per caput for all nuclear medicine examinations Conclusions A second survey, approved by the Population Dose Sub-committee of the National Radiation Safety Committee, related to the calculation of the total collective dose to the population from the use of General Radiography and Nuclear Medicine has been carried out by HSE. A total number of X-ray examinations carried out in Ireland in 2010 is estimated to be 2,556,388. In the same year nuclear medicine scans were performed. The Collective Dose from Nuclear Medicine scans was found to be 112manSv, leading to a dose per caput of 0.02mSv per annum, while the Collective Dose from General X-ray was found to be 255manSv with a dose per caput of 0.056mSv per annum. These results can be compared to that of CT where a Collective Dose of 1368manSv and a dose per caput of 0.32mSv per annum. 15

16 References 1. Council Directive 97/43/Euratom June 1997 on the health protection of individuals against the dangers of ionisng radiation in relation to medical exposure and repealing Directive 84/466/Euratom. 2. S.I No. 478 of European Communities (Medical Ionising Radiation Protection) Regulations EEC Directive 97/43/Euratom. Health Protection of Individuals against the danger of Ionising Radiation in relation to Medical Exposures. 3. Annual Report HSE National Radiation Safety Committee 4. European Guidance on estimating population doses from medical x-rays. Radiation Protection No European Commission Quality Assurance Reference Centre (UK). Formal Baseline Clinical Audit of Current Practice in Medical Ionising Radiation Protection as required under Statutory Instrument 478 (2002). HSE National Radiation Safety Committee. 6. D. Hart, B F Wall, M C Hillier, P C Shrimpton, Frequency and Collective dose for Medical and Dental X-ray examinations in the UK, 2008, HPA (2010) 7. Cecile Etard et al. Medical Exposure of the French Population in Proceedings of the third European IRPA congress European Guidance on estimating population doses from medical x-rays. Radiation Protection No Annex 2 DD Report 1a Review of national surveys of population exposure from Nuclear Medicine examinations in eight European Countries 9. Radiation Doses Received by the Irish Population. Radiological Protection Institute of Ireland May Recommendations of the National Council on Radiation Protection and Measurements. Ionizing Radiation Exposure of the Population of the United States, NCRP Report 160, Notes for Guidance on the Clinical Administration of Radiopharmaceuticals and Use of Sealed Radioactive Sources, Administration of Radioactive Substances Advisory Committee. HPA (2006), revised 2007, S.I. No 125 of Radiological Protection Act, 1991 (Ionising Radiation)Order, The 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, Annals of the ICRP, Vol 21, No The 2007 recommendations of the International Commission on Radiological Protection ICRP Publication 103, Annals of the ICRP Vol Rosenstein M, Suleiman OH, Burkhart RL, Stern SH, and Williams G. (1992) Handbook of Selected Tissue Doses for the Upper Gastrointestinal Fluoroscopic Examinations. HHS Publication FDA (Rockville, USA: Center for Devices and Radiological Health). 16

17 16. Stern SH, Rosenstein M, Renauld L and Zankl M. (1995) Handbook of Selected Tissue Doses for Fluoroscopic and Cineangiographic Examination of the Coronary Arteries. HHS Publication FDA (Rockville, USA: Center for Devices and Radiological Health) 17. Drexler G, Panzer W, Widenmann L, Williams G and Zankl M. (1990) The Calculation of Dose from External Photon Exposures Using Reference Human Phantoms and Monte Carlo Methods. Part III: Organ Doses in X-ray Diagnosis. GSF-Bericht 11/90 (Neuherberg, D: GSF-National Research Centre for Environment and Health). 18. Zankl M, Panzer W and Drexler G. (1991) The Calculation of Dose from External Photon Exposures Using Reference Human Phantoms and Monte Carlo Methods. Part VI: Organ Doses from Computed Tomography Examinations. GSF-Bericht 30/91 (Neuherberg, D: GSF: National Research Centre for Environment and Health). 19. Jones DG and Shrimpton PC. (1993) Normalised Organ Doses for X-ray Computed Tomography Calculated Using Monte Carlo Techniques. NRPB- SR250 (Chilton, UK: National Radiological Protection Board) 20. Tapiovaara M, Lakkisto M and Servomaa A. (1997) PCXMC A PC Based Monte Carlo for Calculating Patient Doses in Medical X-ray Examinations. Report STUK-A139. (Helsinki: Finnish Centre for Radiation and Nuclear Safety (STUK)). 21. International Commission on Radiological Protection Radiation dose to patients from radiopharmaceuticals. ICRP Publication 80, Annals of the ICRP, vol. 28 No. 3, European Guidance on estimating population doses from medical x-rays. Radiation Protection No Annex 1 DD Report 1 Review of recent national surveys of population exposure from medical X-rays in Europe, European Commission

18 Appendix A 18

19 Nuclear Medicine Dose Survey Data Collection Range Submitted By Contact Name Contact Tel. Total Number of Scans Performed Year Exam 99mTc Bone Scan 99mTc Thyroid Scan 131-I Thyroid Uptake Scan 123-I Thyroid Uptake Scan 131-I Thyroid metastates 99mTc V/Q Perfusion Scan 99mTc Aerosol V/Q Ventilation Scan 99mTc TechneGas V/Q Ventilation Scan 99mTc DTPA Renogram Scan 99mTc MAG3 Renogram Scan 123-I DAT Scan 123-I MIBG Scan 111-In OctreoScan 99mTc Myocardial Scan 99mTc Cerebral blood flow Average Injected Dose Total Exams for the Year 19