Radiology_Aug04 ORIGINAL ARTICLE 24 SA JOURNAL OF RADIOLOGY • August 2004 Abstract This study determined the correlation between radiation doses absorbed by health care workers and dose area product meter (DAP) measurements at Universitas Hospital, Bloemfontein. The DAP is an instrument which accurately measures the radiation emitted from the source. The study included the interventional radiolo- gists, radiographers and nurses associ- ated with radiological intervention procedures during the period 1 August 2003 - 31 August 2003. The amount of radiation produced during every procedure was measured by a dose area product meter (DAP) and routinely recorded. The absorbed doses received by health care workers were measured using a thermolumi- nescent dose meter (TLD). The TLDs were analysed and recorded at the end of each week. Health care workers wore TLDs on the following areas: forehead, thyroid (attached under thyroid guard), and abdomen (worn under lead jacket). A strong positive correlation (r = 0.9, p = 0.0374) was found between the radiographers’ head TLD and DAP meter readings. All other correlations between TLD and DAP readings were not statistical- ly significant. Strong positive correla- tions were found between the TLD readings of the radiologists’ and nurs- es’ bodies, the nurses’ and radiogra- phers’ bodies and the radiologists’ and the radiographers’ bodies, all of which were statistically significant. Introduction Interventional radiology is often the preferred treatment procedure, but is associated with a certain amount of radiation to the health care workers performing the procedure.1 The resulting health care worker con- cern for the risk of ionising radiation has prompted research into radiologi- cal procedures2 and is of importance to the hospital radiation protection sections.3 Fluoroscopic procedures are the main source of radiation because high scatter levels are emitted and the body does not uniformly absorb the doses. The head and limbs receive higher doses because a lead jacket protects the body. The yearly effective dose received by interventional radiologists is approximately equal to the natural background effective dose (average 3m SV), but may be higher.4 Except for the thyroid, the lead jacket protects all or a portion of the 12 organs and tissue the International Commission on Radiological Protection deter- mined as most sensitive to radiation. The use of a thyroid guard also decreases the effective dose by approx- imately a factor of 2.5 Health care workers may receive primary and secondary radiation. Primary radiation refers to when any body part is placed directly in front of the X-ray and secondary radiation refers to radiation received from ray scatter from the patient or X-ray tube leakage.6 Adequate training, procedure optimisation and use and availability of protective measures all contribute to decreasing radiation doses received by health care workers.3 Do dose area product meter measurements reflect radiation doses absorbed by health care workers? R Raubenheimer B Spangenberg G van Jaarsveld A Koller C de Vries MMedRad (D) Department of Diagnostic Radiology University of the Free State Bloemfontein C P Herbst PhD C A Willemse PhD Department of Medical Physics University of the Free State Bloemfontein G Joubert BA, MSc Department of Biostatistics University of the Free State Bloemfontein Regular monitoring of profession- al radiation is necessary. Thermo- luminescent dosimetry is used to measure radiation and the apparatus is placed on various parts of the body, namely under the lead jacket to deter- mine radiation on the entire body, on the shoulder or thyroid guard, and on the hand.7 Radiologists receive larger radia- tion doses during abdominal studies than during cerebral studies, even though the average fluoroscopic time is longer for cerebral angiography. This may be because of the increased diffraction from the patient tissue and the shorter distance between the radiologist and the X-ray tube during abdominal studies. The radiologist’s hands receive the highest absorbed dose with an average of 7.1 mRad for cerebral angiography and 39.9 mRad for abdominal and peripheral vascu- lar angiography. The thyroid absorbs the second highest dose.5 During cerebral arteriography, health care workers wear lead jackets and the radiation monitor is often placed beneath the jacket. Radio- sensitive areas such as the eyes, thyroid and hands are not protected against radiation and are seldom monitored. Tryhus et al.8 found that during cere- bral angiograms the radiographer and technician received respectively 3 mREM and 2 mREM radiation doses on areas not covered by the lead jack- et. The dosage received is much lower than the maximum radiation dose of 5.0 REM. The patient, however, received much higher doses, with radiation near the eyes measuring 20 REM with the maximum recom- mended dose being 0.5 REM.8 The dose area product (DAP) meter is an instrument mounted on the X-ray tube, which accurately mea- sures the radiation emitted from the source after calibration. This study determined the correlation between radiation doses absorbed by health care workers and DAP measurements at Universitas Hospital, Bloemfontein. If strong correlations exist, health care workers’ radiation exposure could be derived from the DAP readings. Methods The study included the interven- tional radiologists, radiographers and nurses associated with radiological intervention procedures that took place from 1 August 2003 to 31 August 2003 at Universitas Hospital, Bloem- fontein. The amount of radiation pro- duced during every procedure was measured by a DAP (PTV Dianometer M2 model) and routine- ly recorded. The absorbed doses received by health care workers were measured using a thermoluminescent dose (TLD) meter. Health care work- ers wore TLDs on the following areas: forehead (worn around head with specially designed headband), thyroid (attached under thyroid guard), and abdomen (worn under lead jacket). The respective health care workers’ TLDs were colour coded to enable identification. The TLDs were analysed and recorded at the end of every week. Per week, three TLDs were used for calibration and three TLDs measured background radiation in the storage place. Radiation was measured in cGy and cGycm2 for the TLD and DAP meters, respectively. The TLD and DAP readings that were recorded per week represent all the procedures that took place at the interventional unit during the week. The following Spearman’s rank correlations were calculated: DAP meter readings and TLD meter read- ing for each health care worker’s body area (head, thyroid and body); and TLD head, thyroid and body readings compared between radiologist, nurse and radiographer. Results The correlation between the DAP and radiologists’ TLD readings are given in Table I and Fig. 1. There was a positive correlation between the DAP and TLD head reading, a negative cor- relation with TLD thyroid reading, and no correlation with the TLD body reading. No correlation was statistical- ly significant. The correlation between the DAP and radiographers’ TLD readings are given in Table I and Fig. 2. There was a ORIGINAL ARTICLE 25 SA JOURNAL OF RADIOLOGY • August 2004 Table I. Correlation between TLD and DAP readings Health care worker Area Correlation coefficient p-value Radiologist Head 0.7 0.1881 Thyroid -0.7 0.1881 Body -0.2 0.7471 Radiographer Head 0.9 0.0374 Thyroid 0.4 0.5046 Body -0.2 0.7471 Nurse Head 0.3 0.6238 Thyroid 0.2 0.7471 Body -0.4 0.5046 statistically significant positive corre- lation between the DAP and TLD head reading, no correlation with TLD body reading, and a positive cor- relation with the TLD thyroid read- ing. The correlation between the DAP and nurses’ TLD readings are given in Table I and Fig. 3. There was a positive correlation between the DAP and TLD head reading, a negative correla- tion with TLD body reading, and no correlation with the TLD thyroid reading. No correlation was statistical- ly significant. The correlations between the doses absorbed by the radiologists, radiographers and nurses are given in Table II. Although not statistically sig- nificant, a positive correlation was found between the TLD readings of the radiologists’ and nurses’ heads, as well as between the radiologists’ and radiographers’ heads. No correlation was found between the TLD readings of the radiographers’ and nurses’ heads. A negative correlation coeffi- cient was found between the radiolo- gists’ and nurses’ TLD thyroid read- ings, but there was a positive correla- tion between those of the radiogra- phers and nurses, and no correlation between those of the radiologists and radiographers. A strong positive cor- relation was found between the TLD readings of the radiologists’ and nurs- es’ bodies, the nurses’ and radiogra- phers’ bodies, as well as the radiolo- gists’ and the radiographers’ bodies, all of which were statistically significant. Discussion A positive correlation indicates that an increase in the DAP reading is reflected by an increase in the TLD reading. The radiologist stands near- est to the DAP meter during each pro- cedure and receives a large amount of scattered radiation. The correlation is not statistically significant, possibly because the radiologist’s head is mov- ing constantly and each radiologist has a different physical build, which will result in a variable radiation read- ing. A negative correlation indicates an increased DAP reading, but a decreased TLD reading. The radiolo- gist’s body is covered with a lead jack- et and by the table, both of which will absorb radiation. The height of the table and the radiologist’s physical build also determine whether the TLD is situated under the table. The radio- logist may move around during the procedure. These factors would influ- ence the amount of radiation that reaches the TLD. The significant correlation between the DAP and radiographer’s TLD head reading may be because the radiographer’s head is not protected and he/she is more static than the nurse or the radiologist. The radiogra- pher sits or stands at the bottom end of the patient, wears lead jackets and is shielded by the table, which may explain the poor correlation between the DAP and radiographer’s TLD ORIGINAL ARTICLE 26 SA JOURNAL OF RADIOLOGY • August 2004 Fig. 1. Correlation between the DAP meter and radiologists’ TLD meter readings. Fig. 2. Correlation between the DAP meter and radiographers’ TLD meter readings. Fig. 3. Correlation between the DAP meter and nurses’ TLD meter readings. body reading. The sitting position and the radiographer’s physical build would also influence the reading. An ineffective thyroid guard, openings on the side of incorrectly fastened guards, and the radiographer’s physical build all contribute to variable TLD thyroid readings. The nurse moves around or sits during procedures. As a result the radiation may have moved through the patient, bed and lead jacket before a reading is registered. The TLD meter receives scattered radiation whereas the DAP meter receives direct radia- tion escaping from the apparatus. The TLD body readings of the radiologists, radiographers and nurses showed a strong correlation. The radi- ation only reaches the TLD meter after passing through other members, the patient, bed, equipment and lead jacket. Conclusion The only statistically significant correlation between the DAP and TLD readings was that of the positive correlation between the radiograph- er’s head TLD and DAP meter read- ing. It is not possible to determine health care worker radiation from the DAP reading because of the general lack of correlation between the DAP and TLD readings. References 1. Thomson KR. Interventional radiology. Lancet 1997; 350: 354-358. 2. Janssen RJJN, Hadders RH, Henkelman MS, Bos AJJ. Exposure to operating staff during car- diac catheterisation measured by thermolumi- nescence. Radiation Protection Dosimetry 1992; 43: 175-177. 3. Vano E, Gonzalez L, Guibelalde E, Fernandez JM, Ten JI. Radiation exposure to medical staff in interventional and cardiac radiology. Br J Radiol 1998; 71: 954-960. 4. McEwan AC. The UNSCEAR 2000 report cited 15 April 2003. Available from: http://www.arps.org.au/UNSCEAR2000.htm 5. Niklason LT, Marx MV, Chan HP. Inter- ventional radiologists: occupational radiation doses and risks. Radiology 1993; 187: 729-733. 6. McParland BJ, Nosil J, Burry B. A survey of the radiation exposures received by the staff at two cardiac catheterization laboratories. Br J Radiol 1990; 63: 885-888. 7. Marshall NW, Noble J, Faulkner K. Patient and staff dosimetry in neuroradiological proce- dures. Br J Radiol 1995; 68: 495-501. 8. Tryhus M, Mettler FA Jr, Kelsey C. The radiolo- gist and angiographic procedures. Absorbed radiation dose. Invest Radiol 1987; 22: 747-750. ORIGINAL ARTICLE 27 SA JOURNAL OF RADIOLOGY • August 2004 Table II. Correlations between the doses absorbed by the radiologists, radiogra- phers and nurses Area Comparison Correlation coefficient p-value Head Radiologist with nurse 0.3 0.6238 Radiologist with radiographer 0.4 0.5046 Nurse with radiographer 0 1.000 Thyroid Radiologist with nurse -0.3 0.6238 Radiologist with radiographer 0.1 0.8729 Nurse with radiographer 0.6 0.2848 Body Radiologist with nurse 0.9 0.0374 Radiologist with radiographer 1.0 < 0.0001 Nurse with radiographer 0.9 0.0374