G. Perry

A prospective comparison of three systems of patient immobilization for prostate radiotherapy

PURPOSE The study compared the setup reliability of 3 patient immobilization systems, a rubber leg cushion, the alpha cradle, and the thermoplastic Hipfix device, in 77 patients with cT1-T3, N0, M0 prostate cancer receiving conformal radiotherapy. METHODS AND MATERIALS Port films were analyzed and compared to simulation films to estimate the setup errors in the three coordinate axes (anterior-posterior, cranial-caudal, medial-lateral). A total vector error was calculated from these shifts. RESULTS The Hipfix was found significantly superior to the other two devices in reducing mean setup errors in all axes (p < 0.005). The average field-positioning error with the Hipfix ranged from 1.9 mm to 2.6 mm for all axes, whereas the deviation for the other two systems ranged from 2.7 to 3. 4 mm. Errors greater than 10 mm were virtually eliminated with the Hipfix system. There was a reduction in the mean total vector error in the alpha cradle and Hipfix patient cohorts over time, reflecting improved efficacy as a result of experience. CONCLUSION There was a significant difference in the performance of each immobilization device. The Hipfix was consistently more reliable in reducing setup errors than the other devices.

Long-term side-effects of intermittent androgen suppression therapy in prostate cancer : results of a phase II study

To assess the feasibility and tolerability of intermittent androgen suppression therapy (IAS) in prostate cancer.

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 vivodosimetry 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 lungcancer patients. Each day, RADPOS detectors are positioned at marked points on the patients 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.

SU-GG-T-341: Initial Results of Real-Time External Surface Motion and Dose Monitoring Study for Lung Patients

Purpose: To describe results from an ongoing clinical trial that aims to evaluate the potential of the RADPOS system, which combines a MOSFET dosimeter and electromagnetic positioning sensor, for applications in external beam treatments for lungcancer patients. Method and Materials: Measurements were done at the time of each patients 4DCT and throughout the course of treatment. Each day, three RADPOS sensors were positioned at marked points on the patients chest and abdomen while a fourth detector was placed on the CT or treatment couch for reference. Position coordinates of the sensors and dose information can be read in real‐time, but for these trials the total dose was read after each treatment fraction. Results: Measurements have been completed on ten patients during 7–14 fractions each. The standard deviation of the average dose measured at each point ranged from 3.0–13.7 cGy at CT zero and 2.5–11.1 cGy at the site of the tumour. Large differences were sometimes seen between data collected during the 4DCT and treatment fractions. Most patients settled into a more consistent breathing pattern as treatment progressed, with maximum interfraction variations in average amplitude and period between 0.9–3.5 mm and 0.2–1.8 s during treatment. A cross‐correlation analysis comparing the displacements measured simultaneously at the three locations found that correlation varied between patients, as no two detectors were consistently the most correlated. The magnitude of the correlation coefficients also varied greatly, ranging from ρ=0.13–0.24 for Patient G and from ρ=0.74–0.81 for Patient E. Conclusion: RADPOS system can provide real‐time feedback regarding motion due to breathing, coughing or other patient movement. Variations in breathing patterns are patient‐specific and should be monitored to ensure accurate positioning and treatment delivery. Acknowledgements: This project is supported by grants from HTX and ORCC Foundation. Financial and technical support from Best Medical Canada is also acknowledged.