간암의 방사선치료 시 호흡운동 감소장치(respiratory motion reduction device, RRD)의 유용성에 관한 연구

Abstract

Purpose: Planning target volume (PTV) for tumors in abdomen or thorax includes enough margin for breathing-related movement of tumor volumes during treatment. Depending on the location of the tumor, the magnitude of PTV margin extends from 10 ㎜ to 30 ㎜, which increases substantial volume of the irradiated normal tissue hence, resulting in increase of normal tissue complication probability (NTCP). We developed a simple and handy method which can reduce PTV margins in patients with liver tumors, respiratory motion reduction device (RRD). Materials and methods: For 10 liver cancer patients, the data of internal organ motion were obtained by examining the diaphragm motion under fluoroscope. It was tested for both supine and prone position. A RRD was made using MeV-Green and Styrofoam panels and then applied to the patients. By analyzing the diaphragm movement from patients with RRD, the magnitude of PTV margin was determined and dose volume histogram (DVH) was computed using AcQ-Plan, a treatment planning software. Dose to normal tissue between patients with RRD and without RRD was analyzed by comparing the fraction of the normal liver receiving to 50% of the isocenter dose. DVH and NTCP for normal liver and adjacent organs were also evaluated. Results: When patients breathed freely, average movement of diaphragm was 12±1.9 ㎜ in prone position in contrast to 16±1.9 ㎜ in supine position. In prone position, difference in diaphragm movement with and without RRD was 3±0.9 ㎜ and 12 ㎜, respectively, showing that PTV margins could be reduced to as much as 9 ㎜. With RRD, volume of the irradiated normal liver reduced up to 22.7% in DVH analysis. Conclusion: Internal organ motion due to breathing can be reduced using RRD, which is simple and easy to use in clinical setting. It can reduce the organ motion-related PTV margin, thereby decrease volume of the irradiated normal tissue.