Poster — Thur Eve — 13: Monitoring the Breathing Patterns of Lung Patients throughout the Course of Treatment — Preliminary Experience with the RADPOS System

The RADPOS system is a new in vivo dosimetry tool that combines a MOSFET dosimeter with an electromagnetic positioning sensor to allow for simultaneous measurement in real‐time of dose and spatial coordinates at a specific location. A study is currently underway using the RADPOS system during the 4DCT and external beam treatments of lung cancer patients. Each day, RADPOS detectors are positioned at marked points on the patient's chest and abdomen while a fourth detector is placed on the CT or treatment couch for reference. Position coordinates of the sensors are read in real‐time at a rate of 20–25 Hz and total dose is read at the end of each treatment fraction. Measurements have been completed on 11 patients during the 4DCT and 7–16 treatment fractions. The standard deviation of the average dose measured at each point ranged from 3.0 to 13.7 cGy (7.7 to 14.0%) at CT zero and from 2.5 to 11.1 cGy (2.8 to 9.2%) at the site of the tumour. Variations in amplitude of breathing motion have been found to be patient‐specific. Some patients had very consistent breathing patterns, with interfraction variations in average amplitude and period as low as 11.4% and 4.2% respectively, while others had variations as high as 38.9% and 50.0% . Daily set‐up of the RADPOS system was completed quickly, requiring minimal additional time for each scheduled treatment fraction. Acknowledgements: This project is supported by grants from HTX and ORCC Foundation. Financial and technical support from Best Medical Canada is also acknowledged.