Radiation Dose Concepts (PDF)

HEALTH SCIENCES PROGRAM 3 The concept of radiation dose Medical Exposure Dose Limits Occupational Exposure  HEALTH SCIENCES PROGRAM 4 Radiation measures 01 02 03 According to ICRP a...

HEALTH SCIENCES PROGRAM 3 The concept of radiation dose Medical Exposure Dose Limits Occupational Exposure  HEALTH SCIENCES PROGRAM 4 Radiation measures 01 02 03 According to ICRP and Dose limits are not Investigation of BSS, two basic principles applicable, but a exposures is strongly of radiation protection Guidance is given on recommended are to be complied with: dose levels justification and optimization  HEALTH SCIENCES PROGRAM 6 Types of radiation ▪ Medical Exposure (principally the exposure of persons as part of their diagnostic or treatment) ▪ Occupational Exposure (exposure incurred at work, and practically as a result of work) ▪ Public Exposure (including all other exposures)  HEALTH SCIENCES PROGRAM 7 Medical Exposure Exposure of persons as part of their diagnostic or treatment Exposures (other than occupational) incurred knowingly and willingly by individuals such as family and close friends helping What is medical exposure? either in hospital or at home in the support and comfort of patients Exposures incurred by volunteers as part of a program of biomedical research  HEALTH SCIENCES PROGRAM 10 Guidance level for medical exposure ▪ Comparison with DRL shall be only made using mean values of a sample of patients ▪ Quantities used as guidance (or reference) levels should be easily measured ▪ Quantities used as guidance (or reference) levels should be understood by radiologists and radiographers ▪ DRL should always be used in parallel to image quality evaluation (enough information for diagnosis shall be obtained) ▪ DRL can mean several quantities (such as DAP) and parameters (such as fluoro time and number of images)  HEALTH SCIENCES PROGRAM 11 Guidance level for medical exposure ▪ DRL should be ‘flexible’ (tolerances should be established: different patient sizes, different pathologies, etc). DRL are not a border line between good and bad medicine ▪ Values BELOW guidance levels could not be optimized. ▪ Values ABOVE reference levels should require an investigation and optimization of X Ray system or protocols. ▪ The main objective of DRL is their use in a dynamic and continuous process of optimization.  HEALTH SCIENCES PROGRAM 12 Guidance level for medical exposure ▪ The guidance levels are intended: a) to be a reasonable indication of doses for average sized patients b) to be established by relevant professional bodies in consultation with the Regulatory Authority c) to provide guidance on what is achievable with current good practice rather than on what should be considered optimum performance d)to be applied with flexibility to allow higher exposures if these are indicated by sound clinical judgement e) to be revised as technology and techniques improve  HEALTH SCIENCES PROGRAM 13 Typical effective dose from medical exposure ▪ Registrants and licensees shall promptly investigate: ▪ Any diagnostic exposure substantially greater than intended or resulting in doses repeatedly and substantially exceeding the established guidance levels. ▪ Any equipment failure, accident error, mishap or other unusual occurrence with the potential for causing a patient exposure significantly different from that intended.  HEALTH SCIENCES PROGRAM 14 Dose constraints for medical exposure ▪ For medical exposure dose constraints should only be used in optimizing the protection of persons exposed for medical research purposes, or of persons, other than workers, who assist in the care, support or comfort of exposed patients. ▪ for medical research purposes. ▪ for individuals helping in care, support or comfort of patients, and visitors ▪ 5 mSv during the period of the examination or treatment ▪ 1 mSv for children visiting ▪ maximum activity in patients discharged from hospitals ▪ Iodine 131-1100 MBq  HEALTH SCIENCES PROGRAM 15 Radiological protection for medical exposure ▪ Justification ▪ Optimization ▪ The use of doses limits is NOT APPLICABLE ▪ Dose constraints and guidance (or reference) levels ARE RECOMMENDED ▪ The decision to adopt or continue any human activity involves a review of benefits and disadvantages of the possible options ▪ E.g.: choosing between the use of X Rays or ultrasound ▪ Often, the radiation detriment will be only a small part of the total detriment ▪ Most of the assessments needed for the justification of a practice are made on the basis of experience, professional judgement, and common sense.  HEALTH SCIENCES PROGRAM 16 Generic justification ▪ It is a matter for national professional bodies, sometimes in conjunction with national regulatory authorities. ▪ The exposures to staff (occupational) and to members of the public should be taken into account. ▪ The possibility of accidental or unintended exposures (potential exposure) should also be considered. ▪ The decisions should be reviewed from time to time as new information becomes available.  HEALTH SCIENCES PROGRAM 17 Generic justification ▪ The resources in a country or region should be considered (fluoroscopy for chest imaging could be the procedure chosen instead of radiography for economical reasons). ▪ The justification of diagnostic investigations for which the benefit to the patient is not the primary objective needs special consideration (e.g. radiography for insurance purposes. ▪ Any radiological examination for occupational, legal or health insurance purposes undertaken without reference to clinical indications is deemed to be not justified unless it is expected to provide useful information on the health of the individual examined or unless the specific type of examination is justified by those requesting it in consultation with relevant professional bodies.  HEALTH SCIENCES PROGRAM 19 Occupational Exposures ▪ In radiologic technology, 95% of the occupational exposure comes from fluoroscopy and mobile radiography. ▪ The worst case scenario is that you would receive 5% of the exposure that a technologist would receive. ▪ During radiography, the operator should be behind a protective barrier. ▪ These barriers are usually considered as secondary barriers so protection would be from tube leakage and scatter from the patient. The tube should never be pointed toward this type barrier. ▪ If the barrier can have the tube angled toward the barrier. It must be a primary barrier. ▪ Staying behind the barrier effectively eliminates the source of occupational exposure if the shielding is adequate 19  HEALTH SCIENCES PROGRAM 20 Occupational Exposures Medical Imaging Exposures ▪ Fluoroscopy: All personnel will wear protective apron. If extremities get into the beam lead gloves can be worn. ▪ The radiologist will usually be close to the machine during fluoroscopy so their exposure will be higher than that the technologist. Aprons between the Image intensifier and Bucky Slot covers reduce radiologist exposure. ▪ The technologist should stand as far away from the table as possible during the exam and move closed only when necessary. ▪ The radiologist will use short burst of exposure and keep the exposure time as short as possible. The 5 minute clock timer will alarm when 5 minutes of fluoroscopy has been used. 20  HEALTH SCIENCES PROGRAM 21 Occupational Exposures Medical Imaging Exposures ▪ Mobile radiography: ▪ The technologist must wear a lead apron during mobile plain film or fluoroscopy examinations. ▪ An apron must be assigned to each portable machine. ▪ The exposure cord for portable radiographic machines must be 2 meters long to maximize distance from the tube during exposures. ▪ Radiology Ancillary Staff ▪ Assuming the rooms are adequately shielded, the receptionist, file room and darkroom staff should not receive any occupational exposure. ▪ Radiology ancillary staff should not be used to hold patients during radiography. 21  HEALTH SCIENCES PROGRAM 22 Occupational Exposures ▪ Lead apron used for operator or patient protection must be the equivalent of 0.5mm of lead. ▪ They must be worn when in a room during the exposure or during fluoroscopy. ▪ Half aprons are effective means to provide gonad protection during radiography. ▪ 0.25 mm of lead aprons should be avoided as they only attenuate 66% of the beam at 76 kVp. ▪ The whole body badge is typically worn at collar level so it can be outside the lead apron. ▪ Fetal monitoring badges used during pregnancy are worn at waist level under the apron. 22  HEALTH SCIENCES PROGRAM 23 Occupational Exposures ▪ During fluoroscopy radiologic technologist should stand as far as possible from the machine. ▪ Standing behind the radiologist offers added protection. ▪ If you must be in the room, position your body as far away from the primary beam as possible. ▪ Patient holding ▪ Radiology or office staff should never hold a patient. Family or friends may be called upon to assist the patient. ▪ The person assisting the patient must wear a lead apron and if their hands will be in the beam lead gloves. ▪ Position the person as far away from the primary beam as possible. ▪ Since the person holding the patient may be a parent, make sure they are not pregnant 23  HEALTH SCIENCES PROGRAM 24 Dose Measurements 1 DAP (Dose Area Product) = D x Area the SI unit of DAP is Gy.cm2  HEALTH SCIENCES PROGRAM 25 To check that the required information is not yet available JUSTIFICATION OF AN Once the procedure is generically justified, no additional justification is INDIVIUAL needed for simple diagnostic investigations PATIENT For complex procedures (such as CT, IR, etc) an individual justification should be taken into account by medical practitioner (radiologist, referral doctor..)  HEALTH SCIENCES PROGRAM 26 RADIATION DOSE LIMITS