Abstract
The objective of this study is to increase the accuracy of dose transmission in radiation therapy using two types of treatment tables, standard exact couch (Varian 21EX, Varian Medical Systems, Milpitas, CA) and 6D robotic couch (Novalis, BrainLAB A.G., Heimstetten, Germany)). We examined the dose attenuation based on the two types of treatment tables and studied the dose of attenuation using the phase (In/Out) for the standard exact couch. We measured the relative dose according to the incident angle of a penetrative photon beam under a treatment table. The incident angle of the photon beam was from $0^{\circ}$ to $360^{\circ}$ in the increments of $5^{\circ}$. The reference angle was set to $0^{\circ}$. Furthermore, the relative dose of the 6D robotic couch was measured using 6 MV and 15 MV, and that of the standard exact couch was measured at the sliding rail position (In-Out) using 6 MV and 10 MV. In the case of the standard exact couch, the measured relative dose was 16.53% (rails at the "In position," $175^{\circ}$, 6 MV), 12.42% (rails at the "In position," $175^{\circ}$, 10 MV), 13.13% (rails at the "Out position," $175^{\circ}$, 6 MV), and 9.96% (rails at the "Out position," $175^{\circ}$, 10 MV). In the case of the 6D robotic couch, the measured relative dose was 6.82% ($130^{\circ}$, 6 MV) and 4.92% ($130^{\circ}$, 15 MV). The photon energies were surveyed at the same incident angle. The dose attenuation for an energy of 10 MV was 4~5% lower than that for 6 MV. This indicated that the higher photon energy, lesser is the attenuation. The results of this study indicated that the attenuation rate for the 6D robotic couch was confirmed to be 1% larger than that for the standard exact couch at 6 MV and $180^{\circ}$. In the case of the standard exact couch, the dose attenuation was found to change rapidly in accordance with the phase ("In position" and "Out position") of the sliding rail.
본 연구는 방사선치료에서 방사선 선량전달의 정확도를 높이기 위해 두 종류의 치료테이블 6D robotic couch (BrainLab, Feldkirchen, Germany)와 Standard exact couch (Varian Exact couch$^{TM}$, Varian Medical Systems, Milpitas, CA, USA)를 이용하여 Rail의 위상(In-Out)에 따른 상대선량을 측정하여, 선량감쇠율을 계산하였다. 치료테이블을 투과하는 조사에너지의 조사각 $0^{\circ}$에서 $360^{\circ}$까지의 상대 선량을 각각 측정하였으며, 조사각이 $0^{\circ}$일 때 측정된 선량을 기준으로 하여 $5^{\circ}$ 간격으로 선량의 변화를 측정하고 선량 감쇠율을 계산하였다. Standard exact couch의 광자선 에너지는 6 MV와 10 MV를 사용하였으며 치료테이블의 Rail 위상(In position, Out position)에 따른 상대 선량을 측정하였다. 6D robotic couch는 6 MV와 15 MV의 광자선 에너지를 사용하였다. Standard exact couch의 광자선의 최대 선량차이는 Rail In position에서 6 MV ($175^{\circ}$), 10 MV ($175^{\circ}$)일 때, 선량차이는 각각 16.53%, 12.42%, Out position에서 6 MV ($225^{\circ}$), 10 MV ($225^{\circ}$)일 때, 선량차이는 각각 15.15%, 9.96%였다. 6D robotic couch에서는 6 MV ($130^{\circ}$)와 15 MV ($130^{\circ}$)일 때, 선량차이는 각각 6.82%, 4.92%였다. 본 연구를 통해, 치료테이블의 종류에 따른 선량 감쇠율은 6D robotic couch가 Standard exact couch보다 6 MV에서 조사각 $180^{\circ}$ 기준 약 1% 더 발생함을 확인하였고, Stnadard exact couch인 경우, Sliding rail의 위상(In position, Out position)에 따라 선량 감쇠가 급격히 변화하는 것을 확인하였다.
