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Dosimetric Comparison of CT Compatible Plastic Cones to Traditional Metal Cones for IntraOp Radiation Therapy

S Jain1*, A Steinmann1, J Woollard1, N Gupta1, A Ayan1, (1) The Ohio State University Wexner Medical Center, Columbus, OH

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose:
Current workflow for Intra Operative Radiation Therapy (IORT) with Mobetron (IntraOp Medical) relies on hand calculations based on the prescription dose and depth, cone size and bevel. Radiance (a Monte Carlo treatment planning system) allows for treatment planning based on CT images of the patient with the cone attached. In this study, we compare CT-compatible plastic cones to metal cones that are currently used clinically, to characterize the clinical impact of transitioning to the new plastic cones.

Methods:
Percent Depth Dose, inline and crossline profiles for metal and plastic cones with 6MeV, 9MeV and 12MeV beams were taken in a PTW MP3 Water Phantom System using a Markus Electron chamber. Profiles were measured at depths ranging from 10mm to 30mm for 4cm, 6cm, 8cm and 10cm flat cones. The outputs at d(max) for 10cm flat cones were also measured. The following metrics were compared: depths at various doses in the PDDs (R30, R50, R80, R90 and R100), dosimetric field size (Full Width at Half Max), flatness and penumbra extent (d80 – d20 mm).

Results:
The average difference in depth values from the PDDs were 0.81±0.65mm (6MeV), 0.86±0.15 mm (9MeV) and 1.37±1.46 mm (12MeV). The differences in field sizes were less than 0.1mm; flatness differences were within 2% for all cones except 4cm cones, where they were within 2-3%. The average differences in penumbra of the plastic cone profiles as compared to commissioning data were -0.77±0.65 mm (6MeV), -0.79±0.43 mm (9MeV) and -0.72±0.28 mm (12MeV). Output measurements were 4.6%, 4.8% and 3.5% higher for the metal cones at 6, 9 and 12MeV respectively.

Conclusion:
This work established dosimetric equivalency of metal and plastic cones, demonstrating their potential use in CT-based IORT, and a transition for clinics to the new cones without any re-commissioning impact.

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Funding Support, Disclosures, and Conflict of Interest: This study was partially funded by IntraOp Medical Inc.

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