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Toward Electronic Compensation for TBI Using Dose Dynamic Arc Delivery

N Koch

N Koch*, C Mart , J Dise , M Ashenafi , D McDonald , J Peng , K Vanek , Medical University of South Carolina, Charleston, SC


TH-CD-708-12 (Thursday, August 3, 2017) 10:00 AM - 12:00 PM Room: 708

Purpose: Total body irradiation (TBI) is often performed at an extended distance. However, many facilities lack a large vault for their primary or back-up machine. Yet, techniques for small rooms need either complex treatment plans or more physical compensation to achieve uniform full-body dose. The purpose of this work was to develop a library of pre-defined dose dynamic arc fields that deliver an acceptably uniform dose to a range of patient body habitus with minimal use of physical compensators in a small room.

Methods: Measurements of 70 TBI patients’ body habitus in the supine and prone positions were retrospectively collected, i.e. 1,400 measurement points. Patients were separated into four groups for which optimal control point weightings were determined. These control points were written into each of four 120-degree arc fields and saved as a DICOM plan file for import into a TPS. Dose uniformity within the patients was then calculated using this new library of dynamic arc plans and compared to the dose uniformity obtained with a uniform TBI field.

Results: The average optimal relative beam intensity at the ankle for each patient group was 88.5±2.1%, 91.5±0.86%, 94.6±0.87%, and 97.5±1.1%, which reflected the varying degree of compensation needed. Compared to a uniform TBI field, the calculated dose uniformity along the patient’s midsagittal profile greatly improved from an average of 107.4±3.8% to 100.9±1.8% at the ankle, without additional compensation, while maintaining an average dose of 100.8% at the level of the umbilicus.

Conclusion: We have shown that a library of four plans each consisting of pre-defined dose dynamic arcs can produce an acceptably uniform total body dose across a range of body habitus. This simple approach avoids the complexities of translating couches or patient-specific MLC patterns of other small-room techniques, and can be delivered on any VMAT capable machine.

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