Earticle

왼쪽 폐암 방사선치료 시 IMRT와 VMAT 방사선치료기법 별 전산화치료계획을 수립하고, PTV와 주변 정상장기 별 선량을 선량체적히스트그램을 통해 각각 비교 분석하였다. IMRT와 VMAT 방사선치료 별 PTV 평균선량은 각각 67.2, 67.7 Gy, 최대선량은 68.7, 70.1 Gy였다. 심장 평균선량은 10.8, 17.7 Gy, 최대선량은 11.5, 43.0 Gy 였다. 왼쪽허파 평균선량은 19.5, 17.7 Gy, 최대선량은 68.5, 69.9 Gy, V5는 45.0, 42.7%, V20은 34.8, 33.6%였다. 식도 평균선량은 12.6, 11.5 Gy, 최대선량은 45.1, 43.0 Gy, V35는 2.5, 0.6%, V40은 0.1, 0.0%였다. 척수 최대선량은 31.2, 28.2 Gy였다. IMRT와 VMAT 방사선치료계획 비교 시 PTV 선량은 차이가 없었지만 정상자기 선량은 VMAT에 서 더 낮은 선량을 나타냈다. 이에 따라 왼쪽 폐암 방사선치료 시 VMAT을 적용하는 것이 방사선치료로 인한 부작용을 감소할 수 있을 것으로 사료된다.

For left lung cancer radiation treatment, a treatment plannig was established for each IMRT and VMAT radiation treatment technique, and the doses for PTV and organ at risk were compared and analyzed through dose volume histogram. The PTV mean dose for IMRT and VMAT radiation therapy were 67.2 and 67.7 Gy, and the maximum doses were 68.7 and 70.1 Gy, respectively. The heart mean dose were 10.8 and 17.7 Gy, and the maximum doses were 11.5 and 43.0 Gy. The mean dose to the left lung was 19.5 and 17.7 Gy, the maximum dose was 68.5 and 69.9 Gy, V5 was 45.0 and 42.7%, and V20 was 34.8 and 33.6%. Esophageal mean doses were 12.6 and 11.5 Gy, maximum doses were 45.1 and 43.0 Gy, V35 was 2.5 and 0.6%, and V40 was 0.1 and 0.0%. The maximum dose to the spinal cord was 31.2 and 28.2 Gy. When comparing IMRT and VMAT radiation therapy plans, there was no difference in PTV dose, but organ at risk dose showed a lower dose in VMAT. Accordingly, it is considered that the application of VMAT in radiation therapy for left lung cancer can reduce side effects caused by radiation therapy.

To quantitatively evaluate how setup errors in conjunction with dose gradients contribute to the error in IMRT dose quality assurance (DQA) measurements. The control group consisted of 5 DQA plans of which all individual field dose differences were less than ±5%. On the contrary, the examination group was composed of 16 DQA plans where any individual field dose difference was larger than ±10% even though their total dose differences were less than ±5%. The difference in 3D dose gradients between the two groups was estimated in a cube of 6 × 6 × 6 mm3 centered at the verification point. Under the assumption that setup errors existed during the DQA measurements of the examination group, a three dimensional offset point inside the cube was sought out, where the individual field dose difference was minimized. The average dose gradients of the control group along the x, y, and z axes were 0.21, 0.20, and 0.15 cGy․mm-1, respectively, while those of the examination group were 0.64, 0.48, and 0.28 cGy․mm-1, respectively. All 16 plans of the examination group had their own 3D offset points in the cube. The individual field dose differences recalculated at the offset points were mostly diminished and thus the average values of total and individual field dose differences were reduced from 3.1% to 2.2% and 15.4% to 2.2%, respectively. The offset distribution turned out to be random in the 3D coordinate. This study provided the quantitative data that support the large individual field dose difference mainly stems from possible geometric errors (e.g., random setup errors) under the influence of steep dose gradients of IMRT field.

세기조절방사선치료(Intensity Modulated Radiotherapy, IMRT)의 정도관리를 위해서 독립적인 방법으로 선량검증을 하는 것은 중요하다. 독립적 선량검증을 위해 팬톰과 이온전리함을 이용한 측정 방법이 보편적으로 이루어지지만 많은 시간과 노력이 요구된다. 본 연구에서는 세기조절방사선치료 시 시간에 따른 다엽콜리메이터의 움직임을 기록한 dynalog 파일을 이용하여 치료계획에서 도출된 총 실제 플루언스와 실제 치료 시의 모니터유닛(monitor unit, MU) 공간분포를 비교함으로써 간편한 세기조절방사선치료 정도관리 기술을 개발하였다. DICOM RT plan 파일로부터 총 실제 플루언스를 추출하고 MATLAB 코드를 이용하여 실제 치료 시 MU 공간분포를 dynalog 파일로부터 계산하였다. 개발된 방법의 효용성을 검증하기 위해 단계별조사기법과 동적조사기법으로 치료 받은 각 5명의 환자 데이터를 후향적으로 분석하였다. 분석 방법은 상용프로그램(Verisoft 3.1, PTW, German)에서 제공하는 감마인덱스를 사용하였다. 분석 결과 실제 치료 시의 MU 공간분포와 치료계획 상의 MU 공간분포 일치도가 평균 97.8±1.33%로 높은 일치도를 나타냈다. MU 공간분포 재구성의 정확도는 동적조사기법보다 단계별조사기법이 평균 1.4% 높았다. 본 연구에서 개발된 기술을 통해 세기조절방사선치료의 선량검증을 효과적으로 수행할 수 있다. 또한 분할치료 시 선량보정에 적용함으로써 맞춤형치료(adaptive radiotherapy)를 위한 기초자료로 사용될 수 있을 것이다.

The measurement-based verification for intensity modulated radiation therapy (IMRT) is a time-and labor-consuming procedure. Instead, this study aims to develop a MU fluence reconstruction method for IMRT QA. Total actual fluences from treatment planning system (TPS, Eclipse 8.6, Varian) were selected as a reference. Delivered leaf positions according to MU were extracted by the dynalog file generated after IMRT delivery. An in-house software was develop to reconstruct MU fluence from the acquired delivered leaf position data using MATLAB. We investigated five patient's plans delivered by both step-and-shoot IMRT and sliding window technologies. The total actual fluence was compared with the MU fluence reconstructed by using commercial software (Verisoft 3.1, PTW) and gamma analysis method (criteria: 3%/3 ㎜ and 2%/1 ㎜). Gamma pass rates were 91.8±1.33% and the reconstructed fluence was shown good agreement with RTP-based actual fluence. The fluence from step and shoot IMRT was shown slightly higher agreement with the actual fluence than that from sliding window IMRT. If moving from IMRT QA measurements toward independent computer calculations, the developed method can be used for IMRT QA. A point dose calculation method from reconstructed fluences is under development for the routine IMRT QA purpose.