Development of a program for estimation of patient exposure in mammography

Transcription

1 Developmt of a program for estimation of patit exposure in mammography Y. Asada 1, S. Suzuki, M. Kobayashi, S. Koga 1 Faculty of radiological technology, Fujita Health University, School of Health Scices, Japan to : asada@fujita-hu.ac.jp Fujita Health University, School of Medicine, Aichi, , Japan Abstract. The average glandular dose, which is used as an index of the dose of exposure to radiation in mammography, is obtained by multiplying the in-air exposure on the trance surface by the absorbed dose conversion factor. Sobol et al. reported a method of calculating the absorbed dose conversion factor that is determined by x-ray quality (tube voltage and half-value layer), compressed breast thickness, and breast composition. A method of calculating average glandular dose, however, has established, and no software for estimation of the dose of exposure to radiation in mammography has be developed. Rectly, the authors developed software for the estimation of exposure dose that can be easily used in a facility without a dosimeter. We confirmed that the use of this new software abled the calculation of average glandular dose based on the breast composition. In a facility without measuremt equipmt such as a dosimeter, a user can estimate the exposure dose without difficulty simply by tering the exposure conditions. Furthermore, half-value layer, in-air exposure, and conversion factor can be calculated by using the newly developed software. The other hand, a facility with a dosimeter can ter the value measured at its facility wh they choose a half value layer and/or in-air exposure by the option command and it can compute average glandular dose. Also, the calculation result can save by the CSV method. This technique seemed to be sufficitly useful if a user simply estimates exposure dose. 1. Introduction The average glandular dose, which is used as an index of the dose of exposure to radiation in mammography, is obtained by multiplying the in-air exposure on the trance surface by the absorbed dose conversion factor. Sobol et al. [1] repoted a method of calculating the absorbed dose conversion factor that is determined by x-ray quality (tube voltage and half-value layer), compressed breast thickness and breast composition. A method of calculating average glandular dose, however, has established, and no software for estimation of the dose of exposure to radiation in mammography has be developed. Rectly, the authors developed software for the estimation of exposure dose that can be easily used in a facility without a dosimeter. We confirmed that the use of this new software abled the calculation of average glandular dose based on the breast composition. In a facility without measuremt equipmt such as a dosimeter, a user can estimate the exposure dose without difficulty simply by tering the exposure conditions.. Materials and Methods -1 Measuremt of the foundation data -1-1 Measuremt of radiation output A radiation monitor (Radcal Corporation, model 9015) with a 6cc 10X5-6M ionization chamber was used for measuremt of radiation output (incidt exposure in the air), according to mammographic quality control manual in Japanese society of radiological technology []. The used mammographic equipmts were HFQ-450, DM-1500(Bnett Corporation), Sographe 800T, 500T, DMR (GE Medical Systems), M-4(Lorad Corporation), Mammodiagnostic UC (Philips Corporation), Mammorex (Toshiba Medical Corporation) and Sepio (Shimadzu Corporation). The combination of target/filter Prest address: Kutukake-cho Dgakugakubo, Toyoake, 1-98, Aichi (Japan). 1

2 was molybdum/molybdum (Mo/Mo), molybdum/rhodium (Mo/Rh), and rhodium/rhodium (Rh/Rh). The kvs were 4, 8 and 3 kv, the milliampere second (mas) were 50 or 30 mas. The incidt exposure of each tube voltage was made per the mas value. The number of measured target/filter combination of Mo/Mo, Mo/Rh and Rh/Rh were 10, 36, and 11, respectively. -1- Mesuremt of HVL A radiation monitor with a 6cc 10X5-6M ionization chamber and the high purity aluminum attuators were used for measuremt of HVL (half-value layer). HVLs were obtained by interpolating betwe the two exposure measuremt bounding the HVL, according to mammographic quality control manual in Japanese society of radiological technology []. The combination of target/filter was Mo/Mo, Mo/Rh, and Rh/Rh. The kv were 4, 8 and 3 kv, the mas value were 50 or 30 mas. The number of measured target/filter combination of Mo/Mo, Mo/Rh and Rh/Rh were as well as -1-1 Measuremt of radiation output []. - Developing software of estimation patit exposure From -1 foundation data, the software estimated patit exposure in mammography using the developmt software (Microsoft Corp, Visual Basic Ver.6.0) was developed. This developing software can be estimated average glandular dose and trance surface dose automatically. The average glandular dose is calculated as: where D g = X air D gn (1) D g average glandular dose (mgy); X air incidt exposure per mas (C kg 1 / mas) measured in -1-1 took advantage of mas (C kg 1 ); D gn an average absorbed dose in the mammary gland resulting from an incidt exposure in-air of Ckg -1 reported Sobol et al. data [1] (Gy kg / C); The trance surface dose is calculated as: where D m = X air Wair ( Đ / ĕ) m FCD B. S. F. e ( Đ / ĕ) FSD air () Dm trance surface dose (mgy); Xair incidt exposure per mas (C kg 1 / mas) measured in -1-1 took advantage of mas (C kg 1 ); B.S.F. back scatter factor from B.Grosswdt data [3]; Wair / e (J / C) ( Đ / ĕ ergy absorption cofficit in medium (cm / g); ) m ( Đ / ĕ ergy absorption cofficit in air (cm / g); SCD SSD ) air 3. Result source chamber distance (cm); source skin distance (cm); 3-1 Measuremt of the foundation data Measuremt of radiation output The result of measuremt of radiation output was shown in Table I.

3 Table I. The relation betwe tube voltage and radiation output. Target/Filter Approximate curve Decision cofficit R Mo/Mo y = 0.116e 0.119x Mo/Rh y = e x Rh/Rh y = e x Measuremt of HVL data The result of measuremt of HVL was shown in Table II. Table II. The relation betwe tube voltage and HVL. Target/Filter Approximate type Decision cofficit R Mo/Mo y = x Mo/Rh y = x 0.8 Rh/Rh y = x Developing software of estimation patit exposure The input and output scre were shown in Fig1 and. The combination of the target/filter is chos, and tube voltage, mas value, SID, compressed breast thickness and breast composition are inputted. FIG.1. Input display of the software The input of the breast composition is with fatty (under 10%), a promint duct pattern to a minimal degree (0-30%), a promint duct pattern to a moderate to severe degree (50-60%), dse (80-90%) as judgmt [4]. The inside of the parthesis is a breast glandular fraction. Wh it clicks on the mu of Cal and Exe(practice) is chos, the HVL, effective ergy [5], back scatter factor [3], 3

4 FIG.. Output display of the software incidt exposure in the air, conversion factor, the average glandular dose and trance surface dose are outputted (Fig.). Wh it clicks on the mu of Edit and HVL or Exposure is checked, the measuremt value can be inputted in the H.V.L. and the incidt exposure in the air, and the average glandular dose and trance surface dose are calculated. As follows, a calculation result is outputted in the bottom table wh it clicks on the mu of Edit and Disp (indication) is chos. (Fig.3). It is kept with the CSV form wh it clicks on the mu of File and Save (preservation) is chos. FIG.3. List of input / output results obtained by the software. 4

5 4. Discussion The average glandular dose that the computation of the conversion factor that a table was caught till now could cope with a result, a change in the compressed breast thickness and in the breast glandular fraction handily could be estimated by developing of this software. Therefore, the simulation of the patit exposure becomes possible in the change in the compressed breast thickness or in the breast glandular fraction. And, this software, as for the facilities to own a dosimeter, using edit command function by inputting measured HVL and the incidt exposure in the air, is possible to use as the calculator. Furthermore, the average glandular dose is the most useful measure of radiation risk at mammography, however, as the index of investigating the maximum dose, the trance surface dose is important. Such the trance surface dose can be estimated at the same time. 5. Conclusion In a facility without measuremt equipmt such as a dosimeter, a user can estimate the exposure dose without difficulty simply by tering the exposure conditions. Furthermore, half-value layer, incidt exposure in the air, and conversion factor can be calculated by using the newly developed software. The other hand, a facility with a dosimeter can ter the value measured at its facility wh they choose a HVL and/or incidt exposure in the air by the option command and it can compute average glandular dose and trance surface dose. Also, the calculation result can save by the CSV form. This technique seemed to be sufficitly useful if a user simply estimates exposure dose. Refferces 1. Sobol, W.T. and Wu, X., Parametrization of mammography normalized average glandular dose tables, Med. Phys., 4: , (1997).. Horita, k. (Ed.), Mammographic quality control manual, Japanese society of radiological technology, Kyoto (1999) 3. Grosswedt, B., Depdce of the photon backscatter factors for x-rays gerated at voltages betwe 16 and 140kVPhys.Med.Biol., 35: (1990). 4. Ohuchi,N. (Ed.), The guide of the breast cancer medical examination ofmammography - precision managemt manual-, Nipponijishinpousya, Tokyo (001). 5. Maekoshi, H. (Ed.), photon attuation databook, Japanese society of radiological technology, Kyoto (1995) 5