A respiratory compensating system: design and performance evaluation.

This study proposes a respiratory compensating system which is mounted on the top of the treatment couch for reverse motion, opposite from the direction of the targets (diaphragm and hemostatic clip), in order to offset organ displacement generated by respiratory motion. Traditionally, in the treatment of cancer patients, doctors must increase the field size for radiation therapy of tumors because organs move with respiratory motion, which causes radiation-induced inflammation on the normal tissues (organ at risk (OAR)) while killing cancer cells, and thereby reducing the patient's quality of life. This study uses a strain gauge as a respiratory signal capture device to obtain abdomen respiratory signals, a proposed respiratory simulation system (RSS) and respiratory compensating system to experiment how to offset the organ displacement caused by respiratory movement and compensation effect. This study verifies the effect of the respiratory compensating system in offsetting the target displacement using two methods. The first method uses linac (medical linear accelerator) to irradiate a 300 cGy dose on the EBT film (GAFCHROMIC EBT film). The second method uses a strain gauge to capture the patients' respiratory signals, while using fluoroscopy to observe in vivo targets, such as a diaphragm, to enable the respiratory compensating system to offset the displacements of targets in superior-inferior (SI) direction. Testing results show that the RSS position error is approximately 0.45 ~ 1.42 mm, while the respiratory compensating system position error is approximately 0.48 ~ 1.42 mm. From the EBT film profiles based on different input to the RSS, the results suggest that when the input respiratory signals of RSS are sine wave signals, the average dose (%) in the target area is improved by 1.4% ~ 24.4%, and improved in the 95% isodose area by 15.3% ~ 76.9% after compensation. If the respiratory signals input into the RSS respiratory signals are actual human respiratory signals, the average dose (%) in the target area is improved by 31.8% ~ 67.7%, and improved in the 95% isodose area by 15.3% ~ 86.4% (the above rates of improvements will increase with increasing respiratory motion displacement) after compensation. The experimental results from the second method suggested that about 67.3% ~ 82.5% displacement can be offset. In addition, gamma passing rate after compensation can be improved to 100% only when the displacement of the respiratory motion is within 10 ~ 30 mm. This study proves that the proposed system can contribute to the compensation of organ displacement caused by respiratory motion, enabling physicians to use lower doses and smaller field sizes in the treatment of tumors of cancer patients.

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.