Evaluation of Time Delay and Fluoroscopic Dose in a New Real-Time Tumor-Tracking Radiotherapy System

Abstract

A combined system comprising the LINIAC TrueBeam (Varian Medical Systems, Palo Alt, CA) and a new real-time tumor-tracking radiotherapy system, SyncTraX FX4® (Shimadzu Co., Kyoto, Japan), was installed in our institution. It consists of four pairs of an X-ray tube and a flat panel detector. The system was assessed on beam-on time delay between TrueBeam and SyncTraX FX4 and fluoroscopic dose during a real-time tracking. Delay time was measured by using a tumor-tracking radiotherapy phantom (CALIB PHANTOM ASSY, Shimadzu Co., Kyoto, Japan), in the cases of flattening filtered (FF) 6 MV photon beam, flattening filter-free (FFF) 6 MV photon beam, FF-10 MV photon beam, and FFF-10 MV photon beam with the LINAC TrueBeam. Half-value layer (HVL) in mm Al, effective kVp, and air-kerma rate during fluoroscopy were measured using a solid-state detector for the tube voltage (70–110 kV) and the current (50–100 mA). The LINAC delayed from the real-time tumor tracking system on beam-on by 140.9 ± 8.5, 119.8 ± 3.8, 126.1 ± 3.2 and 116.8 ± 9.7 ms for FF-6 MV, FFF-6 MV, FF-10 MV and FFF-10 MV, respectively. The HVL, effective kVp and air-kerma rates from X-ray tube #1 (X-ray tube #1 and #2 were embedded in the patient’s head side floor) were 4.98 ± 0.00 mm, 111.2 ± 0.1 kV and 9.14 ± 0.04 mGy/min for 110 kV X-ray at 100 mA. The HVL, effective kVp and air-kerma rates from X-ray tube #3 (X-ray tube #3 and #4 were embedded in the patient’s feet side floor), were 5.20 ± 0.00 mm, 110.0 ± 0.1 kV and 11.87 ± 0.06 mGy/min for 110 kV X-ray at 100 mA. These tube voltage and current are the maximum conditions of this study. The time delay of the real-time system is longer than the old system that used image intensifiers. The air-kerma rate from X-ray tube #3 was higher than that from X-ray tube #1.