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Clinical Analysis of the Approximate Multi-Phase Biological Effective Dose (BED) Calculation

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K Kauweloa

K Kauweloa1,2*, A Gutierrez1,2 , A Bergamo1,2 , S Stathakis1,2 , N Papanikolaou1,2 , P Mavroidis1,2 (1) University of Texas Health Science Center, San Antonio, TX, (2) Cancer Therapy and Research Center, San Antonio, TX,


SU-E-T-490 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: An approximate, multi-phase biological effective dose (BED) equation was introduced to simplify 3D-BED calculations by treatment planning systems. The purpose of this work is to analyze its clinical accuracy within patients receiving two phase treatments (e.g., primary and boost phases).

Methods: Twenty prostate and brain cancer patients were studied. MATLAB was used to calculate the true-BED (BEDT) and approximate-BED (BEDA), on a voxel-basis within both phases, using the physical dose matrices that were exported from Pinnacle3 (Philips Medical, Fitchburg, WI). The data was analyzed using the percent error equation of BEDA with respect to BEDT. The Bland-Altman Analysis and the Pearson’s Correlation Coefficient were also used in order to study the impact of the dose distributions on the accuracy of BEDA.

Results: It was shown that when the dose-per-fractions (DPF) between both phases were equal, the error was zero. Within brain cancer patients, 50 percent of the Optic Chiasms and Brainstems, 60-70 percent of the Left and Right Optic Nerves, and 80 percent of the Normal Brain and Spinal Cord had a BEDA with less than a 1 percent error. For prostate cancer patients, 60-70 percent of the Rectum and Bladder also had a BEDA with less than a 1 percent error. The BA-Analysis and PCC also revealed the significant impact of the dose distribution and the locations of the OAR and target on the accuracy of BEDA.

Conclusion: The results displayed accurate BEDA calculations in certain cases such as the Normal Brain, yet patients with large errors still existed. Due to the imprecision of BEDA on OARs, and the difficulty in predicting when it would be accurate, we recommend using BEDA only for targets due to a greater probability of seeing equivalent DPF values in both phases because of the homogeneous dose distributions delivered to the target volumes.

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