[논문]Gafchromic EBT2필름과 다양한 검출기를 이용하여 <tex>$3cm^2$</tex> 이하의 소조사면에서 출력비율의 선량검증

오세안; 예지원; 이레나; 박헌보; 김성규

doi:10.14316/pmp.2014.25.4.218

Gafchromic EBT2필름과 다양한 검출기를 이용하여 $3cm^2$ 이하의 소조사면에서 출력비율의 선량검증
Dosimetric Verifications of the Output Factors in the Small Field Less Than $3cm^2$ Using the Gafchromic EBT2 Films and the Various Detectors 원문보기

Progress in Medical Physics = 의학물리, v.25 no.4, 2014년, pp.218 - 224

오세안 (영남대학교의료원 방사선종양학과) , 예지원 (영남대학교의료원 방사선종양학과) , 이레나 (이화여자대학교 의과대학 이대목동병원 방사선종양학교실) , 박헌보 (건국대학교의료원 신경외과) , 김성규 (영남대학교의료원 방사선종양학과)

초록
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소조사면의 선량검증은 고선량을 1회에 치료하는 정위적방사선수술(Stereotactic radiosurgery, SRS)과 고선량을 소분할 하여 치료하는 소분할방사선치료(hypo-fractionated radiotherapy)에서 작은 크기의 종양을 치료하기 위해서 자주 사용되기 때문에 현대의 방사선치료에서 있어서 매우 중요하다. 그러나, $3cm^2$ 이하의 소조사면에 대한 선량검증은 방사선치료에서 있어서 대단한 도전이다. 소조사면의 선량검증은 (a) 측방전자균형(lateral electronic equilibrium)의 부족, (b) 급격한 선량 기울기(steep dose gradient), (c) 선원의 부분적 차폐 때문에 어렵다. 이 연구의 목적은 6 MV 광자선의 $3cm^2$ 이하의 소조사면에서 출력비율을 다양한 검출기로 측정하고 검증하는 것이다. 출력비율은 CC13 이온함, CC01 이온함, EDGE 검출기, 열발광선량계(thermoluminescence dosimeters, TLD), Gafchromic EBT2 필름을 이용하여 $0.5{\times}0.5cm^2$, $1{\times}1cm^2$, $2{\times}2cm^2$, $3{\times}3cm^2$, $5{\times}5cm^2$, $10{\times}10cm^2$의 다양한 조사면에서 측정하였다. 출력비율의 차이는 조사면의 크기가 작아질수록 검출기간의 차이는 증가하였다. 본 연구의 결과는 $3cm^2$ 이하의 소조사면의 선량측정은 CC01 이온함, EDGE 검출기와 같은 작은 크기의 방사부부피(active volume)를 가지는 검출기를 사용해야 한다는 것을 입증하였다. 또한, $3cm^2$ 이하의 소조사면에서 EDGE 검출기의 출력비율은 Gafchromic EBT2 필름의 결과와 잘 일치하였다.

Abstract ▼ AI-Helper

The small field dosimetry is very important in modern radiotherapy because it has been frequently used to treat the tumor with high dose hypo-fractionated radiotherapy or high dose single fraction stereotactic radiosurgery (SRS) with small size target. But, the dosimetry of a small field (< $3{\times}3cm^2$) has been great challenges in radiotherapy. Small field dosimetry is difficult because of (a) a lack of lateral electronic equilibrium, (b) steep dose gradients, and (c) partial blocking of the source. The objectives of this study were to measure and verify with the various detectors the output factors in a small field (<3 cm) for the 6 MV photon beams. Output factors were measured using the CC13, CC01, EDGE detector, thermoluminescence dosimeters (TLDs), and Gafchromic EBT2 films at the sizes of field such as $0.5{\times}0.5$, $1{\times}1$, $2{\times}2$, $3{\times}3$, $5{\times}5$, and $10{\times}10cm^2$. The differences in the output factors with the various detectors increased with decreasing field size. Our study demonstrates that the dosimetry for a small photon beam (< $3{\times}3cm^2$) should use CC01 or EDGE detectors with a small active volume. And also, Output factors with the EDGE detectors in a small field (< $3{\times}3cm^2$) coincided well with the Gafchromic EBT2 films.

주제어

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문제 정의

The aim of this study was to examine the output factors for various detector in a small fields (＜3 cm) in a medical LINAC. The beam characteristics was examined using a range of detectors, such as CC13 (IBA Dosimetry, Schwarzenbruck, Germany) ion chamber, CC01 (IBA Dosimetry, Schwarzenbruck, Germany) ion chamber, edge (Sun Nuclear Inc.

제안 방법

4. Calibration curve for the 6 MV photon beam with R, G, B channel (0, 10, 20, 30, 50, 70, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 700, and 1000 cGy).
The EBT2 films were calibrated with #1∼#16, #24, and #25 for the 0, 10, 20, 30, 50, 70, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 700, and 1000 cGy, respectively, and #17∼#22 of the films exposed with 5 mm×5 mm, 10 mm×10 mm, 20 mm×20 mm, 30 mm×30 mm, 50 mm×50 mm and 100 mm×100 mm for the output factor measurements, respectively.
The aim of this study was to examine the output factors for various detector in a small fields (＜3 cm) in a medical LINAC. The beam characteristics was examined using a range of detectors, such as CC13 (IBA Dosimetry, Schwarzenbruck, Germany) ion chamber, CC01 (IBA Dosimetry, Schwarzenbruck, Germany) ion chamber, edge (Sun Nuclear Inc., Melbourne, FL) diode detector, Thermoluminescent dosimeter (TLD; Harshaw/ Bicon, Solon, Ohio, USA), and Gafchromic EBT2 (International Specialty Products, Wayne, NJ) films for output factors in a small field.
The output factors were measured using CC13 thimble ion chambers (IBA Dosimetry, Germany), CC01 thimble ion chambers (IBA Dosimetry, Germany) and an EDGE detector (Sun Nuclear, USA) with varied field sizes (0.5×0.5∼10×10 cm2 ).
The output factors were measured using the CC13, CC01, EDGE, TLD, and Gafchromic EBT2 films for photon beam from a 6 MV accelerator with a Novalis Tx linear accelerator. The detectors for the CC13, CC01 and EDGE measured the water phantom, and the output factors for the TLD and Gafchromic EBT2 film were used for the solid phantom (PMMAPolymethylmethacrylate).
The scanned images were calibrated in the range from 0 to 1000 cGy (0, 10, 20, 30, 50, 70, 100, 120, 150, 200, 250, 300, 350, 400, 450, 500, 700, and 1000 cGy) in the red, green and blue channels to analyze the scanned-images using the OmniPro I’mRT Version 1.7 (IBA Dosimetry, Schwarzenbruck, Germany).

대상 데이터

The Novalis Tx which is the state-of-the-art medical linear accelerator, was used in these experiments. Fig.
The radiation fields of the medical linear accelerators (Novalis Tx; Varian Medical Systems, CA, USA and BrainLAB, Feldkirchen, Germany) are measured using an IBA Blue phantom (IBA Dosimetry GmbH, Schwarzenbruck, Germany). The accelerator is comprised of a 3 dimensional servo (the Blue Phantom tank with mechanics), a control unit with integrated two channel electrometer (CU500E) and two single detectors (ionization chambers). For this system, it can be attached to the Blue phantom including single semiconductor detectors, cylindrical and parallel ionization chambers.
The output factors were measured using the CC13, CC01, EDGE, TLD, and Gafchromic EBT2 films for photon beam from a 6 MV accelerator with a Novalis Tx linear accelerator. The detectors for the CC13, CC01 and EDGE measured the water phantom, and the output factors for the TLD and Gafchromic EBT2 film were used for the solid phantom (PMMAPolymethylmethacrylate). All the measured output factors were normalized to a 10×10 cm² field size.

성능/효과

The difference in the output factor between 2×2 cm2 to 10×10 cm2 field size was less than 2%, but compared to the EDGE detector there were differences of −55.11, −22.23, −42.32, and −7.91% for the CC13, CC01, TLD, and Gafchromic EBT2 films in the 0.5 cm field size.

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