Program Information
Pilot Study On the Location-Based Lung Motion Assessment
TK Lee1*, A Ewald2 , (1) Procure Proton Therapy Center, Oklahoma City, OK, (2) McLaren Cancer Institute, Flint, MI
Presentations
SU-F-J-119 (Sunday, July 31, 2016) 3:00 PM - 6:00 PM Room: Exhibit Hall
Purpose: In most of lung treatment cases with various radiotherapy beam modalities, 4DCT images are obtained in order to define ITV. ITV is defined with the signal from motion monitoring system, e.g. RPM. However, the signal is not consistent with tumor motion because it varies with location, its size, age, gender, etc. In the present study, the location-based motion assessment is presented.
Methods: 4DCT images of 70 patients were reviewed: 28-left-lung and 42-right-lung patients; 36-female and 34-male patients; the age range of 51.2-89.9; tumor-size range of 0.75-9.50cm with 25% of these adherent to bony-anatomy. Philips Big-Bore Simulation CT and RPM systems were used. The study was performed as follows. First, RPM signal and tumor motion in superior-inferior direction was compared. Second, the tumor size and its motion amplitude in all directions were measured at multiple locations. Third, the average tumor motion was calculated to assess general motion amplitudes at various locations.
Results: RPM amplitude is not consistent with lung tumor motion amplitude. The tumors of similar sizes at similar location present various motion amplitude up to 1.1cm difference, but in average, the standard deviation was <0.5cm. Almost regardless of tumor sizes, the tumor motion was greatest at lower lobe location (>=1.0cm), and the smallest at upper lobe location and when adherent to bony-anatomy (<=0.5cm).
Conclusion: The tumor size affects the motion amplitude less than does the tumor location. However, as the study results indicate that tumor motion has noticeable variation and so further study with more patient cases is needed. Also, for the same patient, the RPM signal presents instability of breathing, and clinically the patient with the instability of RPM breathing of <=10% is selected for respiratory-gated radiotherapy and ~25% of patients under current study was treated. Patient-specific motion-uncertainty margins are considered to be added following further study.
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