Radiation Protection Dosimetry Advance Access published April 5, 2015 Radiation Protection Dosimetry (2015), pp. 1–4

doi:10.1093/rpd/ncv071

LOOKING INTO FUTURE: CHALLENGES IN RADIATION PROTECTION IN MEDICINE M. M. Rehani* Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA *Corresponding author: [email protected] Radiation protection in medicine is becoming more and more important with increasing wider use of X-rays, documentation of effects besides the potential for long-term carcinogenic effects. With computed tomography (CT) likely to become sub-mSv in coming years, positron emission tomography (PET), single photon emission computed tomography (SPECT) and some of the nuclear medical examination will become focus of attraction as high-dose examinations, even though they are less-frequent ones. Clarity will be needed on radiation effects at levels of radiation doses encountered in a couple of CT scans and if effects are really cumulative. There is challenge to develop radiation metrics that can be used as easily as units of temperature and length and avoidance of multiple meaning of a single dose metric. Other challenges include development of biological indicators of radiation dose, transition from dose to a representative phantom to dose to individual patient, system for tracking of radiation exposure history of patient, avoidance of radiation-induced skin injury in patients and radiation cataract in staff, cutting down inappropriate referrals for radiological examinations, confidence building in patient and patient safety in radiotherapy.

While the Bonn call for action(1) provides comprehensive recommendations, upcoming challenges need to be addressed from time to time. The International Conference on Radiation Protection in Medicine held at Varna, Bulgaria from 30 May to 2 June 2014 provided the opportunity to discuss upcoming challenges. This conference was second in series, the first one being in 2010 at the same place. An article in this journal following the 2010 conference listed issues for the next decade(2). There is a need to see what has changed and what not.

WITH CT LIKELY BECOMING SUB-MSV IN COMING YEARS, WHAT NEXT? The media reports on cancer risks from computed tomography (CT) with increasing use and multiple CT scans that many patients undergo created impact on public and gave rise to situation where industry is striving towards sub-mSv CT. CT has been centre of attraction when it comes to radiation protection for the past almost a decade. It is a matter of imagination what will the situation be when CT for any body part can be done with effective dose of sub-mSv. Already sub-mSv cardiac CT is a reality. It is not difficult to see that many of the nuclear medical imaging examinations in particular positron emission tomography (PET) or single photon emission computed tomography (SPECT) and also some nuclear cardiology studies will still likely be in the range of 5 mSv per study. This is going to be challenge number one in coming years for nuclear medical community and manufacturers not to be found at the level of around 5 mSv and compete for sub-mSv. Another area where radiation doses are likely to be in the rage of few mSv

of effective dose is interventional procedures. The therapeutic benefits associated with interventional procedures should not create alarm with few mSv, but radiation-induced skin injuries are continuing to occur(3). Thus, the focus will have to be on avoidance of skin injuries and of course minimising exposure to children in interventional procedures.

CONTROVERSIES ON RADIATION EFFECTS IN CHILDREN UNDERGOING CT SCANS In recent years, while radiation risks from CT scans have received wide media attention, some colleagues have taken upon themselves the task of propagating that there is lack of scientific basis for cancer risk with few mSv involved in a CT scan. One can certainly cast doubt on the validity of extrapolation of dose–effect relationship curve from high dose to low dose, but can the opposite be proved? Is there a scientific basis of no effect being there? The situation is similar to adverse effects or no effect from a single or couple of pills that one takes daily for blood pressure or lowering of lipids. At least there one can document improvement associated, if not adverse effect. Is the hypothesis of radiation hormesis accepted widely or only by few involved? Major organisations like United Nations Scientific Committee on Effects of Atomic Radiation (UNSCEAR), International Atomic Energy Agency (IAEA), International Commission on Radiological Protection (ICRP), Biological Effects of Ionizing Radiation (BEIR) and National Council on Radiation Protection and Measurements (NCRP) argue that there is no evidence for hormesis in humans. As a result, there is need to conduct large-scale epidemiological studies on humans to give direction. Three

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M. M.REHANI

reports so far although having some lacunae have shown slight increase in cancer incidence among those who underwent CT scans in childhood(4 – 6). Further studies are in pipeline(7). This is an important area for future research that will have impact on radiation protection in medicine. DOSE METRIC AND PATIENT DOSE Multiple representation of a single dose metric poses problem not only among physicians, radiologists and radiographers but also among medical physicists. The dose quantity millisievert can be used for effective dose and equivalent dose and milligray for absorbed dose, incident kerms and energy imparted. There is a need to develop new system where each unit immediately brings to mind the corresponding dose to which it refers, somewhat like degrees Celsius for temperature, kilometre for distance and so on(8). Although patient dose is often used, this term has never been defined. It is considered so far to be a dose to a representative phantom, and thus invariably dose to an adult of 60 kg is same as dose to person with double the weight of 120 kg, which is certainly not true. There have been attempts to develop mathematical phantom that can simulate patients of different sizes(9). There is need to achieve clarity on patient dose, and it should represent dose to the particular patient. Similarly, risk estimations are fraudulent as they are not applicable to individual person. Also, the utility of estimating cumulative dose to an individual needs to be elucidated. The correlation of eye lens opacity with radiation absorbed dose to eye lens(10) is paving the way for biological indicators for absorbed dose. Further, there is need to develop biomarkers to depict radiation absorbed dose and radiation damage. Means for individual radiosensitivity testing will be very helpful in radiation protection. EDUCATION, TRAINING AND TECHNOLOGICAL DEVELOPMENTS Education and training actions for doctors using fluoroscopy outside imaging departments such as in operation theatres need strengthening as there is still absence of training in radiation protection for such doctors in very many countries around the world. Training actions need to be tailored to target audience, and a recent publication from ICRP(11) provides a useful resource as also material available on radiation protection of patients website of IAEA(12). While education and training (E&T) have their own place, there are situations where no amount of E&T can accomplish what can be accomplished through technology. For example, the collision avoidance mechanism that was initially implemented by the automobile industry and later implemented in imaging and therapy machines makes gantry stop as

soon as the rotating gantry touches any object (13). The results achieved cannot match with any amount of operator training. Automatic exposure control (AEC) and tube current modulation are similar examples. Following over exposures in CT that resulted in skin injuries to nearly 400 patients, the National Electrical Manufacturers Association (NEMA) published the NEMA CT Dose Check Standard (XR 25)(14). The purpose is to notify and alert the operator before a scan whenever the estimated dose index is above 1 or more of 2 defined values. The first, the ‘Notification Value,’ is a facility-defined value for volume CT dose index (CTDIvol ) or dose length product (DLP) for a specific scan protocol. If the Notification Value is exceeded, a pop-up warning appears on the operator’s console that prompts the technologist to review the scan settings before proceeding with the examination, and to either verify that they are correct or change them. The second value, the ‘Alert Value,’ is higher. It is associated with a complete examination protocol not with individual scan sequences. It is a warning that the radiation dose index for all of the completed scans, plus the estimated radiation dose index for the planned scan, exceeds a previously set value and warrants more stringent review before proceeding(15). The purpose of the Alert Value is to avoid acute tissue reactions, such as erythema or epilation. It is hoped that wider adoption of this approach by the industry will ensure patients safety. There are some actions underway to provide alert for higher doses that may lead to deterministic injuries such as what happened with CT in 2008. There seems to be good progress with actions to create awareness on cataract risks to interventionists, on effectiveness of protective tools and on implementation of protection with this group. These approaches control upper value of exposure, but optimisation requires obtaining image at minimal radiation dose. The concept of acceptable quality dose (AQD) as described by the author elsewhere provides a mean for clinically acceptable image quality at doses that are based on patients of different weight ranges (in kg) like 41– 50, 51 –60, 61–70, . . ., 91– 100, etc.(16). There is need to develop imaging equipment that minimise and optimise radiation exposure automatically for achieving clinical purpose. There is need to develop equipment that can provide safe imaging for patients that justifiably require few tens of imaging procedures in lifetime for an individual patient. PATIENT PROTECTION IN RADIOTHERAPY Advances in radiotherapy have been tempered by important questions of risks of subsequent malignancies, and this gained importance recently with proton therapy as with earlier new therapies(17). Is proton

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therapy associated with increased subsequent malignancies compared with photon therapy as a result of increased neutron scatter, or is proton therapy actually associated with decreased subsequent malignancies compared with photon therapy as a result of dose reductions to normal tissue? For patient protection, this question remains valid for all new therapies and will need to be continuously addressed. Doses to nontarget areas from image-guided radiotherapy need increasing attention. Dose verification in new modalities and strengthening in vivo dosimetry are foreseen.

(2) (3) (4) (5) (6)

OTHER CHALLENGES Development of methods of strengthening justification, increased emphasis on optimisation, development of newer effective regulatory mechanisms and accounting for repeated examination of an individual patient all still remain challenges to meet. Continuing to repeat something in which success in implementation during decades has been minimal means lack of new ideas. Use of appropriateness criteria for justification has been one such example. Newer approaches are needed to handle issue of inappropriate examination. The controls at the level of source (referrer) are likely to be more effective than at the level of those who are performing examination. Clinical decisionbased electronic referrals are one such good example. Creating a system of accountability for referrer for any examination that involves radiation dose to the patient of more than a defined value say 2 mSv could be another way(2). Increasing individual patient doses will need tracking of radiation exposure history as already pointed out (18 – 20), but there may be a need to consider development of dose constraints, not limits, for patients— an area that is taboo currently. Changing situations require changing approaches, and constraints will increase awareness on the part of referring physicians to consider radiation dose in addition to clinical considerations. Alternatively or additionally, mechanisms shall need to be developed for referrers to make them look into previous exams for clinical information. A tendency has been emerging on passing on radiation dose values in an examination like a CT scan to patients in the report of the examination, and it has led to a law in a state in USA. The challenge lies in confidence building in the patient. Displays in patient waiting areas depicting system of regular monitoring of patient doses, comparing them with standards and ensuring that doses are maintained minimal without affecting quality shall be more assuring that providing mGy or other units of radiation dose figures to patients. Summarising current challenges, they are: (1) With CT likely to become sub-mSv in coming years, PET, SPECT and some of the nuclear medical examinations will become focus of

(7) (8) (9) (10)

attraction as high-dose examinations, even though they are less-frequent ones. Clarity on radiation effects at levels of radiation doses encountered in a couple of CT scans and if effects are really cumulative. Development of radiation quantities that can be used as easily as units of temperature and length and there is no multiple usage of one dose quantity. Development of biological indicators of radiation dose. Transition from dose to a representative phantom to dose to individual patient. Pop-up warning on the operator’s console that prompts the radiographer to review the scan settings before proceeding with the examination and alerts when dose is high enough to lead to tissue reactions. Cutting down inappropriate referrals for radiological examinations that use ionising radiation. Development of imaging equipment those minimise and optimise radiation exposure automatically for achieving clinical purpose. Avoidance of radiation-induced skin injury in patients and radiation cataract in staff. Confidence building in patient on safety and efficacy of medical radiological examination and therapies.

REFERENCES 1. International Atomic Energy Agency and World Health Organization. Bonn Call For Action. https://rpop.iaea. org/RPOP/RPoP/Content/Documents/Whitepapers/ Bonn-Call-for-Action.pdf. 2. Rehani, M. M. and Vano, E. Radiation protection in medicine in next decade. Radiat. Prot. Dosim. 147, 52– 53 (2011). 3. Rehani, M. M. and Srimahachota, S. Skin injuries in interventional procedures. Radiat. Prot. Dosim. 147, 8–12 (2011). 4. Miglioretti, D. et al. The use of computed tomography in pediatrics and the associated radiation exposure and estimated risk of cancer. JAMA Pediatr. 167, 700– 707 (2013). doi: 10.1001/jamapediatrics.2013.311. 5. Pearce, M. S. et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumors: a retrospective cohort study. Lancet. 380, 499–505 (2012). 6. Mathews, J. D. et al. Cancer risk in 680,000 people exposed to computed tomography scans in childhood or adolescence: data linkage study of 11 million Australians. BMJ. 346, f2360 (2013). doi: 10.1136/bmj.f2360. 7. Thierry-Chef, I. et al. Assessing organ doses from paediatric CT scans—a novel approach for an epidemiology study (the EPI-CT study). Int. J. Environ. Res. Public Health. 10(2), 717–728 (2013). 8. Rehani, M. M. Challenges in radiation protection of patients for the 21st century. AJR Am. J. Roentgenol. 200(4), 762– 764 (2013). 9. Zhang, Y., Li, X., Segars, W. P. and Samei, E. Comparison of patient specific dose metrics between chest

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radiography, tomosynthesis, and CT for adult patients of wide ranging body habitus. Med. Phys. 41(2), 023901 (2014). doi: 10.1118/1.4859315. Ciraj-Bjelac, O., Rehani, M. M., Sim, K. H., Liew, H. B., Vano, E. and Kleiman, N. J. Risk for radiation induced cataract for staff in interventional cardiology: Is there reason for concern? Catheterization Cardiovasc. Interventions. 76, 826– 834 (2010). Van˜o´, E., Rosenstein, M., Liniecki, J., Rehani, M. M., Martin, C. J. and Vetter, R. J. ICRP Publication 113. Education and training in radiological protection for diagnostic and interventional procedures. Ann. ICRP. 39(5), 7– 68 (2009). doi: 10.1016/j.icrp.2011.01.002. Radiation protection of patients website of the International Atomic Energy Agency. https://rpop.iaea.org/RPOP/ RPoP/Content/AdditionalResources/Training/1_Training Material/index.htm. Rehani, M. M. Patient dose management in CT and CBCT. Proceedings of the Second ICRP Symposium on the International System of Radiological Protection. Ann. ICRP. 44(s2) (2015). in press. NEMA. CT Dose Check. NEMA Standards Publication XR 25-2010. National Electrical Manufacturers Association (2010).

15. American Association of Physicists in Medicine (AAPM). AAPM recommendations regarding notification and alert values for CT scanners: guidelines for use of the NEMA XR 25 CT Dose Check standard. Available at http://www.aapm.org/pubs/CTProtocols/ documents/NotificationLevelsStatement.pdf. 16. Rehani, M. M. Limitations of diagnostic reference level (DRL) and introduction of acceptable quality dose (AQD). Br. J. Radiol. 88(1045), 20140344 (2015). doi: 10.1259/bjr.20140344. 17. Bekelman, J. E., Schultheiss, T. and Berrington De Gonzalez, A. Subsequent malignancies after photon versus proton radiation therapy. Int. J. Radiat. Oncol. Biol. Phys. 87(1), 10–12. (2013). doi: 10.1016/j.ijrobp. 2013.05.016. 18. Rehani, M. M. and Frush, D. P. Patient exposure tracking – the IAEA smart card project. Radiat. Prot. Dosim. 47(1–2), 314–316 (2011). 19. Rehani, M. and Frush, D. Tracking radiation exposure of patients. Lancet. 376(9743), 754–755 (2010). 20. Seuri, R., Rehani, M. M. and Kortesniemi, M. How tracking patients radiological procedures and dose helps? Experience from Finland. AJR Am. J. Roentgenol. 200(4), 771– 775 (2013).

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Looking into future: challenges in radiation protection in medicine.

Radiation protection in medicine is becoming more and more important with increasing wider use of X-rays, documentation of effects besides the potenti...
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