| Abstract | Uporaba aktivnih elektroničkih osobnih dozimetara tema je velikog broja recentnih istraživanja. Razvili smo aktivni elektronički osobni dozimetar (AEPD) ALARA OD koji ima jedinstvenu funkciju mjerenja osobnog doznog ekvivalenta i njegove brzine u ovisnosti o vremenu dajući tako potpuno novi uvid u profesionalnu izloženost ionizirajućem zračenju AEPD je korišten za istraživanje profesionalne izloženosti ljudi koji rade uz rendgenske uređaje. Istraživanjem izloženosti sigurnosnih radnika koji rade uz rendgenske uređaje za kontrolu osobne prtljage na aerodromima po prvi je put prikazana vremenska raspodjela brzine doze raspršenog zračenja u okolini rendgenskog uređaja, dok je procjena maksimalne efektivne doze za sigurnosne radnike dala godišnju vrijednost do 428 µSv. U području intervencijske radiologije (IR) AEPD je korišten tijekom postupaka perkutane vaskularizacije zdjelice i gornjih arterija noge. Izmjerene maksimalne doze za radiologa operatera po postupku IR su bile u rasponu 4-7 µSv, a po prvi puta je zabilježen prikaz karakterističnog uzorka brzine doze u vremenu tijekom fluoroskopiranja u IR. Podaci izmjereni uporabom elektroničke i termoluminiscentne dozimetrije u IR, za 3 intervencijska radiologa tijekom 1 mjernog razdoblja, upotrijebljeni su za procjenu efektivne doze korištenjem konverzijskih koeficijenata baziranih na prikladnom matematičkom modelu. Dobivene vrijednosti efektivne doze su niže od vrijednosti dobivene na temelju modela drugih autora, ali ne bi trebalo doći do znatnog podcjenjivanja efektivne doze za intervencijske radiologe. |
| Abstract (english) | In regular personal dosimetry of individuals professionally exposed to ionizing radiation passive dosemeters such as film or termoluminiscent dosemeters (TLD) are widely used. However, passive dosemeters can provide information on total accumulated dose equivalent only, and not information on exposure dose rates or the actual duration of an exposure. On the other hand, modern technological trends and recently developed procedures, such as those used in medicine and technology, require upgraded and customized personal dosimetry. We have developed an active electronic personal dosemeter (AEPD) ALARA OD which has a unique capability of measuring and recording both total accumulated dose and dose rate as functions of time. The dosemeter can operate in two modes. In the “normal” (BG) mode, the instrument integrates impulses and records the dose/dose rate which originates only in the exposure to a local background radiation (LBG) over a certain preset time interval. The “event” (E) mode is activated when the actual dose rate exceeds a certain preset threshold. In the E mode the AEPD continuously measures and records dose, dose rate and exposure duration. This provides insight into time sequence of the accumulated dose and dose rate. The instrument has showed a good stability in dose and dose rate measurements, as well as a capability of measuring high dose rates up to 50 µSv/h. It could be used in pulsed fields of modern angiographic X-ray units. The AEPD ALARA OD was used to measure the levels and structure of the occupational exposure of workers that are predominantly exposed to scattered X-ray radiation. We investigated very low exposure of security workers that operated cabinet X-ray units for security screening on airports and were subjected to heavy workload conditions. The measurement setup consisting of a number of the AEPD’s enabled simultaneous measurements of both dose and dose rates at various positions in the radiation field. This revealed the spatial information of the scattered radiation in the area around a cabinet X-ray unit. Measurements of personal dose equivalent showed that the maximum effective dose for the security workers were still below from 1mSv/year even in heavy workload conditions. Due to an increasing number of fluoroscopy-guided procedures in interventional radiology (IR), interventional radiologists are among the most exposed professionals in medicine. The AEPD ALARA OD was used to quantify dose and dose rate levels of radiologists’ exposure to scattered X-ray radiation from the patient while performing percutaneous interventions. We obtained a new type of data – a characteristic pattern of dose rate versus time for any single IR intervention – which has so far not been reported in literature. Fluoroscopy guided procedures in urology use the same radiological equipment as in interventional radiology. Time dependent dose and dose rate data measured by an AEPD, worn by an urologist, have revealed that the exposures in interventional urology are usually shorter (up to a few seconds) and with lower maximum dose rates (up to 200 µSv/h) compared to those in IR. A further use of the AEPD was in investigation of the exposure to scattered hard X-ray radiation of workers that performed non-destructive testing in shipyards. These measurements have proven that the workers were exposed to dose rates up to 700 µSv/h, and in the conditions of a heavy workload, the effective doses could reach annual dose limits. Records of the accumulated dose measured by an AEPD, worn above a protective lead apron, together with TLD’s worn under and over apron, have been used to assess protective quantity effective dose for interventional radiologists. Due to specific factors which have to be considered in IR (energy spectrum of scattered radiation, field and operator-patient geometry, use of protective lead apron and thyroid shield, etc.), a set of appropriate conversion coefficients, based on a mathematical model which uses Monte Carlo methods by Siiskonen et al, was calculated. Effective doses were calculated for three interventional radiologists, using the conversion coefficients and data measured provided by the AEPD’s and TLD’s. A comparison of thus calculated effective doses with those obtained from algorithms of other authors has shown that in exposure conditions used in the measurements other models overestimate the effective dose. Results of this work have shown that effective doses in IR are, even for highly exposed radiologists, still below proposed annual dose limits; however, extensive use of IR procedures could lead to approaching these limits. AEPD ALARA OD has proved to be a good choice of a personal dosemeter for workers exposed to scattered X-ray radiation. The unique feature of time resolution in dose and dose rate measurements facilitates a new insight into radiation exposure burden for various professionally exposed workers particularly in interventional radiology and cardiology. Assessment of the effective dose using conversion coefficients and AEPD reading, worn over protective lead apron, has shown to be an appropriate method and it is therefore recommended for in routine use in dosimetry related to interventional radiology and cardiology. |
