초록
목 적 : 토모테라피를 이용한 방사선치료 시 종양의 위치 변화에 따른 피부선량을 알아보기 위해 Gafchromic EBT3 film을 이용하여 피부선량을 측정하고, 치료계획 선량과 비교하여 그 차이를 알아보고자 한다. 대상 및 방법 : 피부선량 측정을 위한 팬톰은 I'm RT Phantom(IBA Dosimetry, Germany)을 사용하였으며, 2.5 mm CT영상을 획득한 후 Pinnacle(ver9.2, Philips Medical System, USA)을 이용하여 종양의 위치와 피부 선량 측정 점을 설정하였다. 종양(40.75 cm3)의 위치는 팬톰의 중앙과 표면으로부터 5 mm, 10 mm 거리로, 토모테이블 감약을 고려하여 팬톰의 천장과 바닥방향으로 대칭하게 각각 설정하였으며, 피부 선량의 측정점은 표면으로부터 3 mm, 5 mm 두께로 3회 반복 측정하였다. TomoHD(TomoHD treatment system, Tomotherapy Inc., Madison, Wisconsin, USA)를 이용하여 토모테라피 치료 계획을 수립하고, Gafchromic EBT3 필름을 팬톰 내 삽입하여 3회 반복 측정한 뒤 측정된 피부 선량과 치료계획 선량을 비교하였다. 결 과 : 팬톰의 상부 측 피부선량은 종양이 중앙에 위치한 경우 5 mm, 3 mm에서 7.53 cGy, 7.25 cGy였으며, 천장 측 피부로부터 5 mm 떨어져 위치한 경우 각각 18.06 cGy, 16.89 cGy, 10mm 떨어진 경우 각각 20.37 cGy, 18.27 cGy의 값을 나타내었다. 팸톰 하부 측 피부선량은 종양이 중앙에 위치한 경우 5 mm, 3 mm에서 각각 8.82 cGy, 8.29 cGy였으며, 하부 측 피부로부터 5mm 떨어져 위치한 경우 각각 21.69 cGy, 19.78 cGy, 10mm 떨어진 경우 각각 20.48 cGy, 19.57 cGy로 나타났다. 종양이 중앙에 위치한 경우의 피부 선량은 치료계획 시보다 3.2~17.1%이상 증가한 반면, 종양이 천장 측 5 mm에 위치한 경우 2.8~9.0%로 감소하였고, 토모테이블 방향으로 피부선량은 치료계획 선량에 비해 평균 11%이상 증가함을 보였다. 결 론 : 이번 연구 결과 토모테라피를 위한 치료 계획 시 피부선량은 실제 피부선량과 오차가 발생하였으며, 특히 토모 테이블 방향으로의 피부 선량은 치료계획상의 피부선량보다 증가하는 것을 알 수 있었다. 따라서 토모 테이블과 근접하여 위치한 종양의 치료 시 정확한 선량 계산 시스템과 피부선량의 검증 노력이 필요할 것으로 사료된다.
Purpose : To verify the skin dose in Tomotherapy-based radiation treatment according to the change in tumor locations, skin dose was measured by using Gafchromic EBT3 film and compared with the planned doses to find out the gap between them. Materials and Methods : In this study, to measure the skin dose, I'm RT Phantom(IBA Dosimetry, Germany) was utilized. After obtaining the 2.5mm CT images, tumor locations and skin dose measuring points were set by using Pinnacle(ver 9.2, Philips Medical System, USA). The tumor location was decided to be 5mm and 10mm away from surface of the phantom and center. Considering the attenuation of a Tomo-couch, we ensured a symmetric placement between the ceiling and floor directions of the phantom. The measuring point of skin doses was set to have 3mm and 5mm thickness from the surface. Measurement was done 3 times. By employing TomoHD(TomoHD treatment system, Tomotherapy Inc., Madison, Wisconsin, USA), we devised Tomotherapy plans, measured 3 times by inserting Gafchromic EBT3 film into the phantom and compared the measurement with the skin dose treatment plans. Results : The skin doses in the upper part of the phantom, when the tumor was located in the center, were found to be 7.53 cGy and 7.25 cGy in 5mm and 3mm respectively. If placed 5mm away from the skin in the ceiling direction, doses were 18.06 cGy and 16.89 cGy; if 10mm away, 20.37 cGy and 18.27 cGy, respectively. The skin doses in the lower part of the phantom, when the tumor was located in the center, recorded 8.82 cGy and 8.29 cGy in 5mm and 3mm, each; if located 5mm away from the lower part skin, 21.69 cGy and 19.78 cGy were respectively recorded; and if 10mm away, 20.48 cGy and 19.57 cGy were recorded. If the tumor was placed in the center, skin doses were found to increase by 3.2~17.1% whereas if the tumor is 5mm away from the ceiling part, the figure decreased to 2.8~9.0%. To the Tomo-couch direction, skin doses showed an average increase of 11% or over, compared to the planned treatment. Conclusion : This study found gaps between planned skin doses and actual doses in the Tomotherapy treatment planning. Especially to the Tomo-cocuh direction, skin doses were found to be larger than the planned doses. Thus, during the treatment of tumors near the Tomo-couch, doses will need to be more accurately calculated and more efforts to verify skin doses will be required as well.
