본 연구에서는 방사선사를 포함한 레이저, 갠트리 및 온-보드 영상장치의 총체적 셋업의 정확성을 평가하고자 하였다. 경험이 많은 방사선사에게 매일 아침 마커블록을 카우치의 Lock bar 시스템에 고정하고 마커블록을 레이저 중심에 맞추도록 하였다. 71일간 마커블록을 2D/2D 정합으로 위치를 보정하기 위하여 $0^{\circ}$ and $270^{\circ}$ 각도에서 한 쌍의 kV 영상을 획득하였다. 정합이 되었을 때 원격으로 카우치를 조정하여 셋업에러를 보정하고 보정 값은 저장하였다. 상하방향(vertical)과 앞뒤방향(longitudinal) 평균오차를 분석한 결과 상하방향은 0.65, 앞뒤방향은 0.66으로 나타났으며 반면에 좌우방향(lateral)은 0.01으로 나타났다. 상하방향과 앞뒤방향의 p 값은 모두 0.00으로 통계적으로 유의하게 나타났으며, 좌우방향에서는 p 값이 0.829로 나타나 계통오차를 발견하기 어려웠다. 총체적 셋업평가방법은 일간으로 시행하기에 유용하고 편리하였다. 그러나 계통오차를 줄이기 위해서 여전히 레이저와 OBI의 일간 점검은 필요하다.
본 연구에서는 방사선사를 포함한 레이저, 갠트리 및 온-보드 영상장치의 총체적 셋업의 정확성을 평가하고자 하였다. 경험이 많은 방사선사에게 매일 아침 마커블록을 카우치의 Lock bar 시스템에 고정하고 마커블록을 레이저 중심에 맞추도록 하였다. 71일간 마커블록을 2D/2D 정합으로 위치를 보정하기 위하여 $0^{\circ}$ and $270^{\circ}$ 각도에서 한 쌍의 kV 영상을 획득하였다. 정합이 되었을 때 원격으로 카우치를 조정하여 셋업에러를 보정하고 보정 값은 저장하였다. 상하방향(vertical)과 앞뒤방향(longitudinal) 평균오차를 분석한 결과 상하방향은 0.65, 앞뒤방향은 0.66으로 나타났으며 반면에 좌우방향(lateral)은 0.01으로 나타났다. 상하방향과 앞뒤방향의 p 값은 모두 0.00으로 통계적으로 유의하게 나타났으며, 좌우방향에서는 p 값이 0.829로 나타나 계통오차를 발견하기 어려웠다. 총체적 셋업평가방법은 일간으로 시행하기에 유용하고 편리하였다. 그러나 계통오차를 줄이기 위해서 여전히 레이저와 OBI의 일간 점검은 필요하다.
We evaluated the overall setup accuracy for the On-Board Imager (OBI, Varian Medical Systems Inc., Palo Alto, CA, USA), with attention to the laser, the gantry, and operator performance. We let experienced technicians place the marker block on the couch using a lock bar system, with alignment to the...
We evaluated the overall setup accuracy for the On-Board Imager (OBI, Varian Medical Systems Inc., Palo Alto, CA, USA), with attention to the laser, the gantry, and operator performance. We let experienced technicians place the marker block on the couch using a lock bar system, with alignment to the isocenter of the laser, every morning. A pair of radiographic images of the marker block was acquired at $0^{\circ}$ and $270^{\circ}$ angles to the kV arm to correct the position using a 2D/2D matching technique. Once the desired match was achieved, the couch was moved remotely to correct the setup error and the parameters were saved. The average for the vertical and the longitudinal displacements were 0.65 mm and 0.66 mm, and 0.01 mm for the lateral displacement. The average for the vertical and longitudinal displacements were statistically significant at the 0.05 level (p value=0.000 for both), while the p value for the lateral direction was 0.829. These results show that the tendencies to displacement in vertical and longitudinal directions occur through systematic error, while systematic error was not found in the lateral displacement. This daily overall evaluation is practical and easy to find the systematic and random errors in the setup system; however, a daily QA for laser and OBI alignment is still needed to minimize the systematic error in aligning patients.
We evaluated the overall setup accuracy for the On-Board Imager (OBI, Varian Medical Systems Inc., Palo Alto, CA, USA), with attention to the laser, the gantry, and operator performance. We let experienced technicians place the marker block on the couch using a lock bar system, with alignment to the isocenter of the laser, every morning. A pair of radiographic images of the marker block was acquired at $0^{\circ}$ and $270^{\circ}$ angles to the kV arm to correct the position using a 2D/2D matching technique. Once the desired match was achieved, the couch was moved remotely to correct the setup error and the parameters were saved. The average for the vertical and the longitudinal displacements were 0.65 mm and 0.66 mm, and 0.01 mm for the lateral displacement. The average for the vertical and longitudinal displacements were statistically significant at the 0.05 level (p value=0.000 for both), while the p value for the lateral direction was 0.829. These results show that the tendencies to displacement in vertical and longitudinal directions occur through systematic error, while systematic error was not found in the lateral displacement. This daily overall evaluation is practical and easy to find the systematic and random errors in the setup system; however, a daily QA for laser and OBI alignment is still needed to minimize the systematic error in aligning patients.
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문제 정의
This study showed the long term stability of the overall setup system, i.e., the combined output quality of the laser, gantry, OBI, and technical operation. This evaluation of overall setup is practical and easy to perform on a daily basis; however, a daily QA for laser and OBI alignment are also needed to minimize the systematic error.
제안 방법
1. Experimental setup of the marker block to verify geometric accuracy of the OBI by comparing DRR images.
In this study, we tried to find the systematic errors in the setup system such as the laser and OBI alignment, including the radiation technician's performance.
Setup fields were added in the treatment planning system (Eclipse 8.1, Varian Medical Systems, Inc., Palo Alto, CA, USA) using the CT images of the marker block. Both anterior and lateral DRR for each setup field were generated so that the patient repositioning process could be performed.
, AP and lateral images) has been acquired the patient position is analyzed by 2D/2D matching, a match environment where the kV images and DRRs are overlaid. The operator can apply both automated and manual matching tools to align the kV images with the corresponding DRR, with the couch shift parameters being updated as the match is adjusted. Once the desired match is achieved, the couch shift parameters are downloaded to the linear accelerator and the couch is moved remotely to correct the setup error.
This evaluation of overall setup is practical and easy to perform on a daily basis; however, a daily QA for laser and OBI alignment are also needed to minimize the systematic error. The results of this study will be applied to the daily patients’ setup data and evaluate the patients’ setup accuracy.
, Palo Alto, CA, USA) kV imaging system delivers image-guided radiation therapy with options to correct patient setup using kV images before and during treatment. We correct the setup for every patient treated with the IMRT and the 3D-CRT in our department using the OBI system. We use mostly the 2D/2D match technique in the clinic, rather than 3D/3D, to avoid excessive radiation dosing with the 3D cone beam in CT imaging.
대상 데이터
The marker block designed to view the OBI alignment consists of a radiopaque ball and four rods in a plastic block (Fig. 1). The radiopaque rods are placed so as not to be overlaid with rods in the AP and lateral portal images (Fig.
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Yoo S, Kim GY, Hammoud R, et al: A quality assurance program for the on-board $imager^{\circledR}$ . Med Phys 33:4431-4447 (2006)
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