Radiation Dose Limits PDF

HEALTH SCIENCES PROGRAM 27 Dose reference Average radiation dose per examination used as a guide for general practice, for the safety of patients against unnecessarily high radiation dose and negligence from radiology technologists.​  HEALTH SCIENCES PROGRAM...

HEALTH SCIENCES PROGRAM 27 Dose reference Average radiation dose per examination used as a guide for general practice, for the safety of patients against unnecessarily high radiation dose and negligence from radiology technologists.​  HEALTH SCIENCES PROGRAM 28 Dose Limits ▪ Effective dose of 1 mSv in a year. ▪ In special circumstances, effective dose of 5 mSv in a single year, provided that the average over five consecutive years in less than 1mSv per year. ▪ Equivalent dose to lens of the eye 15 mSv in a year. ▪ Equivalent dose to skin of 50 mSv in a year.  HEALTH SCIENCES PROGRAM 29 Dose Limits ▪ Because the basis of the DL assumes a linear, non-threshold response, all unnecessary radiation must be avoided. ▪ The NCRP has assessed risks based upon the BEIR Committee and the National Safety Council. ▪ State and federal government agencies routinely adopt the recommended dose limits as law. ▪ They are developed for whole body and various organs and for various working conditions. 29  HEALTH SCIENCES PROGRAM 30 Dose Limits ▪ The dose limits are set to prevent deterministic effects and to limit stochastic effects ▪ The DL is specified for occupational exposures ▪ Particular care must be taken to make certain that no radiation worker receives a radiation dose in excess of the DL ▪ Dose limits are not applicable for the patient in medical exposures. In this case a direct risk versus benefit assessment can be made. Patient exposure is kelp as low as possible but there is no limit or DL for patients.(ALARA)  HEALTH SCIENCES PROGRAM 31 Radiation Dose Limits ▪ The NCRP limits established in 1987 is 50 mSv per year (5000 mrem) Cumulative 10 mSv x age ▪ The International Commission on Radiation Protection limits established in 1991 limits of 20 mSv per year (2000 mrem). ▪ Skin Some organs have a higher DL than the whole body DL. The DL for skin is 500 mSv/year. ▪ Eyes The DL for eyes is 15mSv/year. ▪ Individuals in the general population are limited to 5mSv/year(500 mrem/year) if the exposure is infrequent. If the exposure is frequent as with a hospital employee who may visit radiology, the limit is 1 mSv/year (100 mrem/year). ▪ The 1mSv/year DL is what physicist use to compute thickness of protective barriers 31  HEALTH SCIENCES PROGRAM 32 Radiation Dose Limits ▪ Student under the age of 18 may their course of educational activities. ▪ For this reason, student technologists under 18 may be engaged in x-ray imaging but their exposure is limited to 1mSv/year. ▪ It is a general practice to not accept underage students for RT (Radiation Technology) programs. not receive more than 1 mSv/year during  HEALTH SCIENCES PROGRAM 33 Radiation Dose Limits and Pregnancy ▪ Two situations in diagnostic radiology require particular care and action. Both are associated with pregnancy. Their importance is obvious from both a physical and emotional stand point. ▪ The severity of potential response to radiation in utero is both ▪ Time and ▪ Dose related  Responsibilities to the patient ▪ Estimate the fetal dose. ▪ The fetal dose would rarely exceed 5 rad after a series of x-ray examinations. ▪ Determine stage of gestation that the exposure happened. ▪ This can be done by the radiologist and referring doctor. ▪ Determine which alternative to recommend to the patient. ▪ Continue to term ▪ Terminate the pregnancy.  HEALTH SCIENCES PROGRAM 35 Responsibilities to the patient ▪ Continue to term ▪ Rarely would an abortion be indicated from diagnostic x-ray exposure. Because the natural incidence of congenital abnormalities is about 5%, no such event can be reasonably considered from diagnostic exposure. ▪ Damage to the fetus is unlikely below 25 rad fetal exposure though some suggest that lower exposure may cause mental developmental abnormalities. ▪ Therapeutic Abortion ▪ Below 10 rad, exposure a therapeutic abortion is not indicated unless there are other risk factors involved. ▪ Above 25 rad, the risks of latent injury may justify termination of the pregnancy. ▪ Between 10 and 25 rad, the precise time of irradiation, the emotional state of the patient.  HEALTH SCIENCES PROGRAM 36 Radiation Dose Limits and Pregnancy ▪ One should never knowingly examine a pregnant patient with x-rays unless a documented decision to do so is made. ▪ Discuss the need for the exam with a radiologist before performing X-ray examinations. ▪ Should radiography be anticipated, determine the patient’s menstrual cycle and withhold the exam until any question about pregnancy is answered. ▪ The ten day rule can be a guide. We want to take the radiograph before ovulation.  HEALTH SCIENCES PROGRAM 37 10 Day Rule: Pregnancy ▪ The safest time to x-ray a female of child bearing age is within ten to fourteen days of the onset of menses ▪ The 10-day rule is recommended for certain high dose examinations where the dose to the uterus is likely to exceed 10 mGy. ▪ High dose examinations are performed within 10 days of the start of the period to ensure the patient is not pregnant  HEALTH SCIENCES PROGRAM 38 The 28 Day Rule ▪ All requests for radiological examinations of female patients of reproductive capacity, which place the uterus in or near the primary X-ray beam, ▪ i.e. irradiation between the diaphragm and pubis, ▪ If the patient has missed a period, the request will be referred back to the doctor for discussion.  HEALTH SCIENCES PROGRAM 39 The 28 Day Rule 39  HEALTH SCIENCES PROGRAM 41 Objective of radiation protection ▪ 1- to prevent any clinically important radiation induced deterministic effect from occurring by adhering to dose limits that are below threshold level ▪ 2- to limit the risk of stochastic response to a conservative level as weighted against societal needs, values, benefits acquired, and economic consideration ▪ ALARA concept: national council on radiation protection and measurements (NCRP) put this principle that radiation exposure should be kept as low as reasonably achievable with consideration for economic and social factors. ▪ The continuation of good radiation protection program and practices which traditionally have been effective in keeping the average and individual exposures for monitored workers well below the limit. ▪ For the radiographer and the radiologist the ALARA concept should serve as a guide for the selection of technical radiographic and fluoroscopic exposure factors for all patient imaging procedure. ▪ The reason for this concept in radiologic practice is to keep radiation exposure and consequent dose to the lowest possible level.  HEALTH SCIENCES PROGRAM 43 Responsibility for Maintaining ALARA ▪ It is the responsibility of the employer to provide the necessary resources and appropriate environment in which to execute an ALARA program. ▪ To determine that proper lowered radiation exposure are being applied, management should perform periodic exposure audits. ▪ Radiation workers with appropriate education and work experience must function with awareness of rules governing the work situations.  HEALTH SCIENCES PROGRAM 44 Optimisation of a practice (ALARA) ▪ The main goal of the ALARA program is to reduce both the external and internal radiation doses to a level that is As Low As Reasonably Achievable. ▪ It is a philosophy and not a number ▪ The three basic protective measures used to reduce external exposure are (Cardinal Principles of Radiation Protection): ▪ Minimizing time in a field of radiation ▪ Maximizing the distance from a source of radiation ▪ Using shielding.Insert shielding material between the radiation source and the exposed person, whenever possible. 44  HEALTH SCIENCES PROGRAM 45 ALARA ▪ Assume that any radiation exposure carries with it some risk. ▪ ALARA effort is related to balancing the assumed risks of radiation exposure against the benefit of performing the work. So "reasonable" in this context means that the risk from receiving the exposure is "worth" the net benefit of the activity. An extension of this philosophy would be the statement that "There should not be any occupational exposure of workers to ionizing radiation without the expectation of an overall benefit from the activity causing the exposure." 45  HEALTH SCIENCES PROGRAM 46 ALARA ▪ ALARAmeans preventing unnecessary exposure as well as overexposure. ▪ The implementation of the ALARA concept is the responsibility of all employees. The success of the ALARA program depends on each radiological worker's attitude and actions. 46  HEALTH SCIENCES PROGRAM 47 Minimize Time ▪ Exposure = Exposure rate x exposure time ▪ During radiography the exposure time is reduced to reduce motion blur. ▪ During fluoroscopy exposure time is reduced to reduce patient and personnel exposure. Radiologists are trained to switch the exposure on and off rather than continuous on to lower exposure. Pulsed progressive fluoroscopy reduces patient exposure by a factor of 0.1 or less ▪ Fluoroscopy machine have a 5 minute reset timer. ▪ Time should be optimized. 47  HEALTH SCIENCES PROGRAM 48 METHODS OF MINIMIZING TIME ▪ Pre-plan and discuss the task thoroughly prior to entering the area. ▪ Use only the number of workers actually required to do the job. ▪ Have all necessary tools before entering the area. ▪ Take the most direct route to the job site. ▪ Work efficiently but swiftly. ▪ Do the job right the first time