Abstract
We analyzed a large patient and volunteer study of external respiratory motion in order to develop a population database of respiratory information. We analyzed 120 lung, liver, and abdominal patients and 25 volunteers without lung disease to determine the extent of motion using the Varian Real‐Time Position Management system. The volunteer respiratory motion was measured for both abdominal and thoracic placement of the RPM box. Evaluation of a subset of 55 patients demonstrates inter‐ and intrafraction variation over treatment. We also calculated baseline drift and duty cycle for patients and volunteers. The mean peak‐to‐peak amplitude (SD) for the patients was 1.0 (0.5) cm, and for the volunteers it was abdomen 0.8 (0.3) cm and thoracic 0.2 (0.2) cm. The mean period (SD) was 3.6 (1.0) s, 4.2 (1.1) s, and 4.1 (0.8) s, and the mean end exhale position (SD) was 60% (6), 58% (7), and 56% (7) for patient, volunteer abdomen, and volunteer thoracic, respectively. Baseline drift was greater than 0.5 cm for 40% of patients. We found statistically significant differences between the patient and volunteer groups. Peak‐to‐peak amplitude was significantly larger for patients than the volunteer abdominal measurement and the volunteer abdominal measurement is significantly larger than the volunteer thoracic measurement. The patient group also exhibited significantly larger baseline drift than the volunteer group. We also found that peak‐to‐peak amplitude was the most variable parameter for both intra‐ and interfraction motion. This database compilation can be used as a resource for expected motion when using external surrogates in radiotherapy applications.PACS number: 87.19.Wx, 87.55.Km
Highlights
Patient respiratory data is and readily accessible through external surrogates, which are frequently used to monitor respiratory motion
Population statistics The population mean and standard deviation of the peak-to-peak amplitude, period, and end exhale phase are shown in Table 2, and the histograms comparing these measurements for patients, volunteer abdominal, and volunteer thoracic are shown in Figs. 2(a), 2(b), and 2(c)
Our study examines the external motion of the chest wall and not internal tumor motion
Summary
Patient respiratory data is and readily accessible through external surrogates, which are frequently used to monitor respiratory motion. External chest wall and abdominal surrogate motion are used clinically for 4D CT,(1,2) to gate images for patient setup, respiratory gated treatments, and for motion tracking.[3,4,5,6]. The changing tension in the belt is measured to produce the respiratory signal. Both these surrogates are commercially available and currently used clinically. Internal tumor motion can be tracked with real time X-ray imaging, but this is at the cost of increased radiation dose to patients. External surrogates can complement X-ray-based imaging techniques as a means to reduce the required frequency of imaging interventions
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