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Treatment Planning System Beam Modeling Parameters Exhibit High Variation Among Radiotherapy Institutions

M Glenn*, D Followill , R Howell , J Pollard-Larkin , S Zhou , S Kry , MD Anderson Cancer Center., Houston, TX


(Wednesday, 8/1/2018) 4:30 PM - 6:00 PM

Room: Karl Dean Ballroom A1

Purpose: This study aims to elucidate potential causes of failure in IROC Houston’s phantom credentialing program by evaluating the variation of treatment planning system (TPS) beam modeling parameters, which may directly impact the validity of dose calculations. Simultaneously, this study provides consensus values for TPS parameters that will provide clinical physicists with a reference to aid in TPS commissioning.

Methods: Beginning August 2017, TPS beam modeling parameter surveys were distributed with IROC Houston phantoms and through online facility questionnaires. The surveys, designed for Eclipse, Pinnacle³, and RayStation users, instructed physicists to report values used to model the radiation source and multileaf collimator (MLC) for each treatment machine and beam energy used clinically for IMRT. To facilitate survey participation, instructions were provided on how to identify requested beam modeling parameters within each TPS. Survey results were then isolated according to TPS, beam energy, and machine class and examined for trends.

Results: 539 beam models from 210 radiotherapy institutions were collected and aggregated between the phantom irradiation forms (83% response rate) and online questionnaires. While some parameters, such as Eclipse’s effective target spot size, exhibited good uniformity (>75% reported the same value), other variables presented broad distributions of values, especially for factors related to the characterization of the MLC. The parameters that showed these trends tended to be the same across different energies and classes.

Conclusion: This study demonstrates that high variation exists in TPS beam modeling parameters which are important for accurate beam model creation. These results can be employed by the radiotherapy community to compare parameter values obtained during commissioning. Future work will focus on assessing the sensitivity of TPS dose calculations to variations in beam modeling parameter values of the magnitude seen in clinical practice.

Funding Support, Disclosures, and Conflict of Interest: This work was supported by Public Health Service Grants CA180803 and CA214526, awarded by the National Cancer Institute, United States Department of Health and Human Services. Mallory Glenn is a recipient of the Rosalie B. Hite Graduate Fellowship awarded by MD Anderson Cancer Center UTHealth Graduate School of Biomedical Sciences.


Commissioning, Treatment Planning, Radiation Therapy


TH- External beam- photons: General (most aspects)

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