SU‐FF‐T‐216: Evaluation of Mid‐Treatment Tumor Motion for Hypo‐Fractionated Lung Radiosurgery Using Hi‐Art TomoTherapy System

Purpose: To investigate the variation of the daily mid‐treatment positioning setup of the helical TomoTherapy with MV‐CT for hypofractionated lung radiosurgery cases utilizing BodyFix rigid immobilization. Methods and Materials: 54 cases treated by a hypo‐fractionated Image Guided‐Intensity Modulated Radiosurgery technique and immobilized with the BodyFix double vacuum system were analyzed retrospectively to investigate the daily variation of mid‐treatment motion, as measured daily by MV‐CT scanning. Scans were performed prior to treatment as well as at mid‐treatment. In the treated cases, a margin of 7–9mm around the CTV was utilized as a PTV. The BodyFix double vacuum system with a lung compression belt was used to minimize breathing motion and intra‐fractional tumor motion. Patients were treated daily by two fractions (e.g., 12Gy/day=6Gy/fr×2fr immediately sequentially delivered after MV‐CT guidance). Results: For all cases, multiple MV‐CT scans were performed immediately before treatment to reach optimal treatment position. After image registration and subsequent adjustment, treatment was delivered. A mid‐treatment MV‐CT scan was obtained immediately after the first‐half treatment and then table adjustments were compared. Table adjustment for mid‐treatment was longitudinal: 1.3±0.7mm and vertical: 0.9±0.5mm. The lateral recorded adjustments of 0.1±0.3mm could not be accurately determined as movements of