Advantages of simulating thoracic cancer patients in an upright position

Abstract

Purpose: To compare lung volume and respiratory motion in supine and upright positions to assess the potential advantages of treating thoracic cancer patients in an upright position.

Methods and materials: A multi-position MRI scanner (FONAR, Melville, NY) was used to take MRI images of 5 healthy volunteers in both supine and upright setup positions. In each case, a series of sagittal cine MR scans were acquired during normal respiration, followed by a volumetric scan taken during breath-hold at end of normal expiration. The trajectory of points inside the lung was automatically detected and tracked in the cine images and then analyzed using a deformable image registration technique together with a principal component analysis model. The exhale volume images were imported into a treatment planning system and lung volumes were delineated and compared for different setup positions.

Results: The amplitude of motion for a set of landmark points in the lung volume ranged from 2 mm (distant from the diaphragm) to 29 mm (close to the diaphragm) in the superior-inferior direction. A linear regression to the amplitude of respiratory motion versus distance from the diaphragm for each volunteer showed that the motion was 3 mm less on average in the upright position than in the supine position, although there was variability among individuals. The average exhale lung volume was 27% (751 cm(3)) larger (range: 9%-53%, 250-1390 cm(3)) when volunteers were in the upright position compared with the supine position.

Conclusions: The magnitude of motion inside the lung was smaller and the absolute lung volumes were much larger in the upright position than in the supine position, which suggests that treating thoracic patients in the upright position may allow for a reduction in the mean lung dose.