Development of an MR and CT compatible non-invasive temperature based optical fiber respiration sensor for use in radiotherapy

We have developed a non-invasive temperature based respiration sensor to track the breathing cycle during respiratory gating that is not subject to the limitations of an external marker. The sensor tracks the breathing cycle by measuring temperature difference between inspiratory and expiratory air. Because it doesn’t require movement of the abdomen, it can be used with forced shallow breathing (FSB) or thermoplastic body mask immobilization. The sensor is compatible for use in computed tomography (CT), magnetic resonance (MR), and linear accelerator environments. The respiration signal was tested with five volunteers using FSB and compared to simultaneously recorded signal from an external marker. Temperature readings were also tested in a CT, MR, and linear accelerator environment. The sensor’s effect on image quality was evaluated for CT and MR. The temperature sensor successfully recorded the breathing cycle for all volunteers, while the external marker had one failure. Fluctuation in temperature sensor signal was similar to background in both a CT and MR environment. There was greater signal fluctuation when the sensor was placed in a high energy linear accelerator field and given a high dose. The fluctuation was acceptable when the sensor was outside the radiation field. It is recommended that the sensor be placed outside the treatment field during treatment. Image quality was not affected by the temperature sensor for CT or MR. We have shown that the temperature based respiration sensor can successfully track breathing cycles even when external markers fail. Performance is maintained in MR and ionizing radiation environments; however, it is recommended that it not be used in the direct path of a high energy beam. We have verified that respiratory signals can be obtained without deterioration of CT or MR images. It is anticipated that this device would be highly suitable for respiratory gating in radiation therapy.