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Study of a linac target activation
e120
Abstracts/Physica Medica 32 (2016) e116–e123
Results: Keeping in mind the obstinacy with which some still insist on use of E having regard to its adaptability to provide dosimetric information for all diagnostic modalities, it would be convenient to use it only as a quantity to compare different radiological exams of the same anatomic region or the same exam in different diagnostic centers. We could call it with a changed name like Effective Dose Index (EDI). Basically, EDI is precisely the effective dose that a standard patient would receive in the same exposure conditions of a real patient. For this reason, EDI is not defined for the individual patient, and so it cannot in any way be related to the individual risk. Conclusions: The dose indexes as PKA, CTDIvol, PKL, CT should be included in the dosimetric report to be communicated to patient. If the choice falls on E, it is appropriate to use it as an index to avoid wrong risk estimates of the patient. Here we propose the introduction of Effective Dose Index (EDI) closely related to a standard patient. http://dx.doi.org/10.1016/j.ejmp.2016.01.413
D.407 A WORK PROCESS-ORIENTED ANALYTICAL MODEL FOR THE CALCULATION OF DOSE AND RISK TO THE OPERATORS INVOLVED IN FLUOROSCOPIC PROCEDURES A. Valentini a, G. Miori b, A. Martignano *,a. a Department of Medical Physics, Azienda Provinciale per i Servizi Sanitari – APSS, Trento, Italy; b School of Medical Physics, University of Rome Tor Vergata, Roma, Italy Introduction: An analytical model for the calculation of dose and risk to the operators during fluoroscopic examinations was created and implemented in a homemade software. Materials and Methods: The model starts from the work processes of the single operator or homogenous group (set of comparable activity operators) to define the input data needed to calculate dose and risk. The software is divided into 3 parts: the 1st part consists of general data, number of operators in the group and technical setup parameters (output, kV, mAs, etc.). In the 2nd part complete radiological exams records are sampled over a certain period of time; the program estimates the 1-year projection of recorded data. In the 3rd part the cumulative charge, the entrance surface dose to the patient and the scatter dose to the operator are evaluated. The calculation is based on the annual cumulative exposure time, output of the fluoroscopic device at the correct duty cycle, mean patient thickness, source to surface distance, average tension and current. Results: The program estimates cumulative whole-body effective dose, hands dose and lens dose to the homogenous group. A 1.5 safety factor is introduced to account for incidents and malfunctions. The program takes into account the percentage of presence as 2nd operator, the percentage of use at three specific tube orientations, the transmission factors of X-ray protective equipment and the percentage of operator presence at four defined distance ranges. The X-ray tube orientation is of particular importance for hands and lens dose; for lens dose calculations the lens-torso distance is also considered. The classification of the operator is conservatively performed by comparing individual dose to half the legal limit levels. Conclusions: The implemented analytical model considers the radiological load and the work processes to give an adequately unbiased method to calculate operators doses that are consistent with personal dosimeters readings. http://dx.doi.org/10.1016/j.ejmp.2016.01.414
D.408 ATTENUATION OF PROTECTIVE EYEWEAR IN DIFFERENT GEOMETRIES: EXPERIMENTAL RESULTS R. De Vincolis *, V. La Monaca, D. Leanza, S. Mele, F. Platania, N. Romeo. Azienda Sanitaria Provinciale di Messina – UOC Radioterapia, Taormina, Italy Introduction: In April 2011, ICRP recommended lowering the equivalent dose limit for the lens of the eye to 20 mSv/year. The substantial limit reduction from the actual 150 mSv/y poses particular concern for certain workers especially interventional fluoroscopists.
The aim of this work is to evaluate the attenuation properties, in different exposure geometries, of two protective eyewear manufactured by EUROPROTEX, mod. 9941 Ultralite and mod. Fitover. Material and Methods: The patient was simulated by 15 cm thick water equivalent RW3 slab; two different interventional fluoroscopy procedures were considered (femoral access and gastro-intestinal), positioning the operator phantom like looking at the image display, during x-ray exposure, and not at the scattered radiation source (patient). For the femoral access procedure the operator’s eye is around 60 cm far from the scattered radiation source and the eye-display line form an angle of 45° with the eye-source line; similarly for the gastro-intestinal procedure there is around 75 cm distance and 90° angle. For each protective device 4 dosimeters were used: 1 in front and 1 behind the eyewear lens both for left and right eye. For measurements TLD dosimeters, calibrated in Hp(0.07), were adopted. Results: The eyewear protection factor is strongly influenced by the radiation source location. When the described angle is small (source in front of the fluoroscopist) the device effectiveness is important; however, when the source was to fluoroscopist’s side, the reduced cross section of the side shield show significant reduction in protection. In our experiment transmission factors were evaluated in the range 50–75%. Conclusions: The use of protective eyewear may provide a false sense of safety when radiation does not strike from the front direction since a lot of radiation can slip through the gap created between cheek and eyewear. This effect could be reduced by raising the bed and positioning the image display in front of operator’s eye. http://dx.doi.org/10.1016/j.ejmp.2016.01.415
D.409 STUDY OF A LINAC TARGET ACTIVATION A. Mitillo *, S. Anglesio. AOU San Luigi Gonzaga, SS. Radioterapia, Orbassano, Italy Introduction: The head components of a linear accelerator, operating with potential greater than 8–10 MV, exhibit an induced radioactivity, as expected. Our Elekta Synergy Platform target was replaced on 14/7/2015, because of a technical intervention on the target mechanical support. The linac had been in use since January 2010; 50% of the Monitor Units (MU) were delivered with 10 and 18 MV photon beams. A study of the target radiation emission was carried out in order to identify the activation products. The study was also performed to approximately estimate the target activity in view of its disposal. Materials and Methods: The study started just one day after the target replacement, in order to identify radionuclides with very short half-lives. The target emission has been studied, during the elapsed 6 months, with a NaI scintillation detector equipped with a digiBase (Ortec) base. The bad geometrical conditions, due to our sample shape and size, were partially overcome keeping constant the sample-detector distance and position. The dose-rate at different measured distances from the target was also evaluated in terms of μSv/h using a Victoreen 451 Ionization Chamber (600 cm3). The evaluation of target activity, performed immediately after the replacement, was obtained starting from the dose-rate, using the Gamma constant, and from the spectra counts. Results: The main identified radioactive components are Ta-183 (T1/ 2 = 5.1 d), Re-184 (T1/2 = 38 d), Au-196 (T1/2 = 6.2 d), Au-198 (T1/2 = 2.7 d). From these components, it has been possible to recognize the originating nuclides, mainly W-183 and Au-197. Both the methods, used to estimate the target activity, provide approximately the same result of about 300 kBq. Conclusions: The identified components are those expected from literature. The main identified radionuclides half-lives are lower than 75 days; however, the study will continue to verify the absence of long-lives radionuclides and to more accurately assess the target activity. http://dx.doi.org/10.1016/j.ejmp.2016.01.416
Abstracts/Physica Medica 32 (2016) e116–e123
Results: Keeping in mind the obstinacy with which some still insist on use of E having regard to its adaptability to provide dosimetric information for all diagnostic modalities, it would be convenient to use it only as a quantity to compare different radiological exams of the same anatomic region or the same exam in different diagnostic centers. We could call it with a changed name like Effective Dose Index (EDI). Basically, EDI is precisely the effective dose that a standard patient would receive in the same exposure conditions of a real patient. For this reason, EDI is not defined for the individual patient, and so it cannot in any way be related to the individual risk. Conclusions: The dose indexes as PKA, CTDIvol, PKL, CT should be included in the dosimetric report to be communicated to patient. If the choice falls on E, it is appropriate to use it as an index to avoid wrong risk estimates of the patient. Here we propose the introduction of Effective Dose Index (EDI) closely related to a standard patient. http://dx.doi.org/10.1016/j.ejmp.2016.01.413
D.407 A WORK PROCESS-ORIENTED ANALYTICAL MODEL FOR THE CALCULATION OF DOSE AND RISK TO THE OPERATORS INVOLVED IN FLUOROSCOPIC PROCEDURES A. Valentini a, G. Miori b, A. Martignano *,a. a Department of Medical Physics, Azienda Provinciale per i Servizi Sanitari – APSS, Trento, Italy; b School of Medical Physics, University of Rome Tor Vergata, Roma, Italy Introduction: An analytical model for the calculation of dose and risk to the operators during fluoroscopic examinations was created and implemented in a homemade software. Materials and Methods: The model starts from the work processes of the single operator or homogenous group (set of comparable activity operators) to define the input data needed to calculate dose and risk. The software is divided into 3 parts: the 1st part consists of general data, number of operators in the group and technical setup parameters (output, kV, mAs, etc.). In the 2nd part complete radiological exams records are sampled over a certain period of time; the program estimates the 1-year projection of recorded data. In the 3rd part the cumulative charge, the entrance surface dose to the patient and the scatter dose to the operator are evaluated. The calculation is based on the annual cumulative exposure time, output of the fluoroscopic device at the correct duty cycle, mean patient thickness, source to surface distance, average tension and current. Results: The program estimates cumulative whole-body effective dose, hands dose and lens dose to the homogenous group. A 1.5 safety factor is introduced to account for incidents and malfunctions. The program takes into account the percentage of presence as 2nd operator, the percentage of use at three specific tube orientations, the transmission factors of X-ray protective equipment and the percentage of operator presence at four defined distance ranges. The X-ray tube orientation is of particular importance for hands and lens dose; for lens dose calculations the lens-torso distance is also considered. The classification of the operator is conservatively performed by comparing individual dose to half the legal limit levels. Conclusions: The implemented analytical model considers the radiological load and the work processes to give an adequately unbiased method to calculate operators doses that are consistent with personal dosimeters readings. http://dx.doi.org/10.1016/j.ejmp.2016.01.414
D.408 ATTENUATION OF PROTECTIVE EYEWEAR IN DIFFERENT GEOMETRIES: EXPERIMENTAL RESULTS R. De Vincolis *, V. La Monaca, D. Leanza, S. Mele, F. Platania, N. Romeo. Azienda Sanitaria Provinciale di Messina – UOC Radioterapia, Taormina, Italy Introduction: In April 2011, ICRP recommended lowering the equivalent dose limit for the lens of the eye to 20 mSv/year. The substantial limit reduction from the actual 150 mSv/y poses particular concern for certain workers especially interventional fluoroscopists.
The aim of this work is to evaluate the attenuation properties, in different exposure geometries, of two protective eyewear manufactured by EUROPROTEX, mod. 9941 Ultralite and mod. Fitover. Material and Methods: The patient was simulated by 15 cm thick water equivalent RW3 slab; two different interventional fluoroscopy procedures were considered (femoral access and gastro-intestinal), positioning the operator phantom like looking at the image display, during x-ray exposure, and not at the scattered radiation source (patient). For the femoral access procedure the operator’s eye is around 60 cm far from the scattered radiation source and the eye-display line form an angle of 45° with the eye-source line; similarly for the gastro-intestinal procedure there is around 75 cm distance and 90° angle. For each protective device 4 dosimeters were used: 1 in front and 1 behind the eyewear lens both for left and right eye. For measurements TLD dosimeters, calibrated in Hp(0.07), were adopted. Results: The eyewear protection factor is strongly influenced by the radiation source location. When the described angle is small (source in front of the fluoroscopist) the device effectiveness is important; however, when the source was to fluoroscopist’s side, the reduced cross section of the side shield show significant reduction in protection. In our experiment transmission factors were evaluated in the range 50–75%. Conclusions: The use of protective eyewear may provide a false sense of safety when radiation does not strike from the front direction since a lot of radiation can slip through the gap created between cheek and eyewear. This effect could be reduced by raising the bed and positioning the image display in front of operator’s eye. http://dx.doi.org/10.1016/j.ejmp.2016.01.415
D.409 STUDY OF A LINAC TARGET ACTIVATION A. Mitillo *, S. Anglesio. AOU San Luigi Gonzaga, SS. Radioterapia, Orbassano, Italy Introduction: The head components of a linear accelerator, operating with potential greater than 8–10 MV, exhibit an induced radioactivity, as expected. Our Elekta Synergy Platform target was replaced on 14/7/2015, because of a technical intervention on the target mechanical support. The linac had been in use since January 2010; 50% of the Monitor Units (MU) were delivered with 10 and 18 MV photon beams. A study of the target radiation emission was carried out in order to identify the activation products. The study was also performed to approximately estimate the target activity in view of its disposal. Materials and Methods: The study started just one day after the target replacement, in order to identify radionuclides with very short half-lives. The target emission has been studied, during the elapsed 6 months, with a NaI scintillation detector equipped with a digiBase (Ortec) base. The bad geometrical conditions, due to our sample shape and size, were partially overcome keeping constant the sample-detector distance and position. The dose-rate at different measured distances from the target was also evaluated in terms of μSv/h using a Victoreen 451 Ionization Chamber (600 cm3). The evaluation of target activity, performed immediately after the replacement, was obtained starting from the dose-rate, using the Gamma constant, and from the spectra counts. Results: The main identified radioactive components are Ta-183 (T1/ 2 = 5.1 d), Re-184 (T1/2 = 38 d), Au-196 (T1/2 = 6.2 d), Au-198 (T1/2 = 2.7 d). From these components, it has been possible to recognize the originating nuclides, mainly W-183 and Au-197. Both the methods, used to estimate the target activity, provide approximately the same result of about 300 kBq. Conclusions: The identified components are those expected from literature. The main identified radionuclides half-lives are lower than 75 days; however, the study will continue to verify the absence of long-lives radionuclides and to more accurately assess the target activity. http://dx.doi.org/10.1016/j.ejmp.2016.01.416