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Analysis of Commercial 4DCT Flaws and the Potential Benefits of a New Technique for Irregular Breathing Patients

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T Dou

T Dou*, D Thomas , J Lamb , D Low , Department of Radiation Oncology, University of California, Los Angeles, Los Angeles, CA


SU-E-J-25 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

To determine the distribution of inhalation to exhalation breathing amplitudes as measured using a commercial 4DCT and a proposed 4DCT protocol for irregular breathing patients.

External breathing surrogate signals correlating with lung tidal volume were collected using an abdominal bellows for a set of 50 patients. Breathing traces over 5-minute durations were evaluated and the peak inhalation and exhalation peaks identified. An arbitrary time point was identified and the nearest exhalation peak located within a ±180° gantry rotation period. The times at which the follow-up inhalation scans occurred were correlated with the couch velocity to determine whether the tumor would be within 180° of that specific peak inhalation given the CT scanner coverage, pitch, rotation period, tumor size, and tumor motion amplitude (defined in units of centimeters per bellows signal). The imaged tumor motion amplitude was based on which inhalation peak would be imaged and the couch location at that time relative to the exhalation peak. This analysis provided a series of measured breathing motion amplitudes, which were compared against the 85th percentile motion, consistent with the proposed 4DCT protocol. Because the 4DCT scans would yield a single amplitude determination for each patient, errors in the amplitude measurement were considered systematic. Therefore, the largest 5% and smallest 5% of the measured amplitudes were selected to identify over-and under-determined motion amplitudes.

30% of the patients exhibited breathing amplitude overestimations of at least 27%, while 30% showed underestimations of at least 34%.

For the majority of patients, the current system provided a high probability of correct breathing motion amplitude measurements. 30% had a significant chance of a systematic over- or under-estimation of tumor motion. The proposed protocol will be immune to such irregularities because the entire breathing trace is used for breathing motion amplitude assessments.

Funding Support, Disclosures, and Conflict of Interest: NIH R01CA096679

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