물흡수선량 표준에 기반한 $^{192}Ir$ 근접치료 선원 교정 시 원통형 이온함의 이온함 간 변화 Chamber to Chamber Variations of a Cylindrical Ionization Chamber for the Calibration of an $^{192}Ir$ Brachytherapy Source Based on an Absorbed Dose to Water Standards원문보기
본 논문은 물 흡수선량 표준에 기반하여 근접치료 선원인 $^{192}Ir$을 교정하는 것에 대한 예비적 연구를 위한 것이다. 이온함을 사용하여 물흡수선량 표준에 기반하여 근접치료 선원을 교정하기 위해선, 빔 선질 교정인자인 $k_{Q,Q_0}$가 필요하다. 본 연구에선 일차 표준을 사용하여 지정된 거리에서의 흡수선량를 측정하는 데 있어서의 현실적인 어려움 때문에 몬테칼로 전산모사와 반실험적인 방법을 통하여 $k_{Q,Q_0}$를 결정하였다. 본 연구를 위해 PTW30013 이온함 5개를 선택하였다. 포괄적 $k^{gen}_{Q,Q_0}$ 값의 경우엔 이온함간 변화가 최대 4.0%에 이른 반면, 개별적 $k^{ind}_{Q,Q_0}$ 경우엔 이온함간 변화가 최대 0.5% 이내였다. 이 결과는 물 흡수선량에 기반하여 근접치료 선원인 $^{192}Ir$을 교정시에 이온함을 왜 개별적으로 교정해야 하는지, 개별적인 교정이 얼마나 중요한 지를 보여 준다. 가까운 장래에 공기커마 세기 대신에 사용자가 근접치료 선원을 고에너지 광자빔과 전자빔의 교정에서처럼 치료에서 관심있는 물리량인 물흡수선량의 관점에서 교정할 수 있기를 희망한다.
본 논문은 물 흡수선량 표준에 기반하여 근접치료 선원인 $^{192}Ir$을 교정하는 것에 대한 예비적 연구를 위한 것이다. 이온함을 사용하여 물흡수선량 표준에 기반하여 근접치료 선원을 교정하기 위해선, 빔 선질 교정인자인 $k_{Q,Q_0}$가 필요하다. 본 연구에선 일차 표준을 사용하여 지정된 거리에서의 흡수선량를 측정하는 데 있어서의 현실적인 어려움 때문에 몬테칼로 전산모사와 반실험적인 방법을 통하여 $k_{Q,Q_0}$를 결정하였다. 본 연구를 위해 PTW30013 이온함 5개를 선택하였다. 포괄적 $k^{gen}_{Q,Q_0}$ 값의 경우엔 이온함간 변화가 최대 4.0%에 이른 반면, 개별적 $k^{ind}_{Q,Q_0}$ 경우엔 이온함간 변화가 최대 0.5% 이내였다. 이 결과는 물 흡수선량에 기반하여 근접치료 선원인 $^{192}Ir$을 교정시에 이온함을 왜 개별적으로 교정해야 하는지, 개별적인 교정이 얼마나 중요한 지를 보여 준다. 가까운 장래에 공기커마 세기 대신에 사용자가 근접치료 선원을 고에너지 광자빔과 전자빔의 교정에서처럼 치료에서 관심있는 물리량인 물흡수선량의 관점에서 교정할 수 있기를 희망한다.
This work is for the preliminary study for the calibration of an $^{192}Ir$ brachytherapy source based on an absorbed dose to water standards. In order to calibrate brachytherapy sources based on absorbed dose to water standards using a clyndirical ionization chamber, the beam quality cor...
This work is for the preliminary study for the calibration of an $^{192}Ir$ brachytherapy source based on an absorbed dose to water standards. In order to calibrate brachytherapy sources based on absorbed dose to water standards using a clyndirical ionization chamber, the beam quality correction factor $k_{Q,Q_0}$ is needed. In this study $k_{Q,Q_0}s$ were determined by both Monte carlo simulation and semiexperimental methods because of the realistic difficulties to use primary standards to measure an absolute dose at a specified distance. The 5 different serial numbers of the PTW30013 chamber type were selected for this study. While chamber to chamber variations ran up to maximum 4.0% with the generic $k^{gen}_{Q,Q_0}$, the chamber to chamber variations were within a maximum deviation of 0.5% with the individual $k^{ind}_{Q,Q_0}$. The results show why and how important ionization chambers must be calibrated individually for the calibration of $^{192}Ir$ brachytherapy sources based on absorbed dose to water standards. We hope that in the near future users will be able to calibrate the brachytherapy sources in terms of an absorbed dose to water, the quantity of interest in the treatment, instead of an air kerma strength just as the calibration in the high energy photon and electron beam.
This work is for the preliminary study for the calibration of an $^{192}Ir$ brachytherapy source based on an absorbed dose to water standards. In order to calibrate brachytherapy sources based on absorbed dose to water standards using a clyndirical ionization chamber, the beam quality correction factor $k_{Q,Q_0}$ is needed. In this study $k_{Q,Q_0}s$ were determined by both Monte carlo simulation and semiexperimental methods because of the realistic difficulties to use primary standards to measure an absolute dose at a specified distance. The 5 different serial numbers of the PTW30013 chamber type were selected for this study. While chamber to chamber variations ran up to maximum 4.0% with the generic $k^{gen}_{Q,Q_0}$, the chamber to chamber variations were within a maximum deviation of 0.5% with the individual $k^{ind}_{Q,Q_0}$. The results show why and how important ionization chambers must be calibrated individually for the calibration of $^{192}Ir$ brachytherapy sources based on absorbed dose to water standards. We hope that in the near future users will be able to calibrate the brachytherapy sources in terms of an absorbed dose to water, the quantity of interest in the treatment, instead of an air kerma strength just as the calibration in the high energy photon and electron beam.
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문제 정의
The protocols based on the absorbed dose to water aim to provide directly the absorbed dose to water, which is just the quantity of interest in the clinical treatment, instead of air kerma. This work is for the preliminary study for the calibration of an brachytherapy source based on an 192Ir absorbed dose to water standards.
제안 방법
For this work the multipurpose brachytherapy phantom (MPBP) was home-made, which was designed to enable both sources and chambers positioned at the exact distance you want from the Ir-192 source in water phantom (Fig. 4). Ir-192 source moves through the fixed catheter and the chamber is positioned at the distance of 5 cm from the center of Ir-192 source.
이론/모형
For the calculation of ND,W,cobalt and ND,W,Ir192, Eldorado8 cobalt therapy machine was modeled using BEAM code and the PTW30013 Chamber and the Ir-192 source were coded using EGSnrcCPP code.
The DW and Dair determined by Monte Carlo simulation were used to calculate ND,W,cobalt and ND,W,Ir192 in equation (8) and (9).
The geometry of both the Ir-192 source and the PTW30013 ionization chamber was modeled using EGSnrcCPP code. The absorbed doses in both the Co-60 sysetm an the Ir-192 source system were determined by EGSnrcCPP code.
Phase space file was obtained at the plane of SSD 100 cm and used as the source file of the cobalt beam. The geometry of both the Ir-192 source and the PTW30013 ionization chamber was modeled using EGSnrcCPP code. The absorbed doses in both the Co-60 sysetm an the Ir-192 source system were determined by EGSnrcCPP code.
The model of Eldorado8 as the Cobalt teletherapy machine was chosen and modeled using BEAM code (Fig. 3). Phase space file was obtained at the plane of SSD 100 cm and used as the source file of the cobalt beam.
후속연구
Nevertheless, the result shown in the Table 2 gives users hopeful hints that this kind of trials done in this work might be an alternative for the calibration of 192Ir brachytherapy sources based on absorbed dose to water standards in the situation where primary standards are nonavailable and stresses how important the individual calibrations of ionization chambers are for the calibration of 192Ir brachytherapy sources.
참고문헌 (8)
Arman Sarfehnia, Kristin stewart, Jan Seuntjens: An absorbed dose to water standard for HDR $^{192}Ir$ brachytherapy sources based on water calorimetry: Numerical and experimental proof- of-priciple. Med Phys 34:4957-4961 (2007)
Austerlitz C, Mota HC, Sempau J, et al: Determination of absorbed dose in water at the reference point D( $r_0,\;{\theta}_0$ ) for an $^{192}Ir$ HDR brachytherapy source using a Fricke system. Med Phys 35:5360-5365 (2008)
Peter R.Almond, Peter J.Biggs, Coursey BM, et al: AAPM’s TG-51 Protocol for clinical reference dosimetry of high energy photon and electron beams. Med Phys 26:1847-1870 (1999)
Ballester F, Hernandez C, Perez-Calatayud J, Lliso F: Monte Carlo calculation of dose rate distributions around $^{192}Ir$ wires. Med Phys 24:1221-1228 (1997)
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