A compensating system of respiratory motion for tumor tracking: design and verification

Using the reverse motion of the treatment couch, this study offset the organ displacement generated by respiratory motion to solve the current clinical problem of increasing field sizes and safety margin expansions. This study used the self-designed simulated respiratory system (SRS) coupled with radiochromic EBT film to verify the self-developed respiratory compensation system. Pressure signals were generated from SRS to simulate abdomen movements during respiratory motion. The respiratory compensation system takes the phase of the pressure signals as the respiratory motion phase and adjusts the pressure signal gain to make the compensation signal amplitude close to the displacement of the target region. A linear accelerator is used to irradiate a 300 cGy dose on the EBT film. The experimental results suggested that the average dose percentage in the target region for the sine-wave amplitudes of 5, 10 and 15 mm with compensation improved by 6.9 ∼ 20.3% over the cases without compensation. The 80% isodose area with compensation improved by 22.8 ∼ 77.2% over the cases without compensation. The average dose percentage in the target region with compensation for respiratory motion distances of 5, 10 and 15 mm improved by 10.3 ∼ 18.7%. The 80% isodose area improved by 22.4 ∼ 55.1% after compensation. The average dose percentage of the compensated target region indicates that the proposed respiratory compensation system could improve the issue of the inability to constantly irradiate the target region caused by respiratory motion.