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Prospective Treatment Plan Modeling To Guide Patient-Specific Treatment Setups for Hypofractionated Intracranial and Spinal Radiosurgery

L Ma

L Ma1*, B Wang2, S Hossain3, A Sahgal4,(1) UCSF Comprehensive Cancer Center, San Francisco, CA, (2) University Utah, Salt Lake City, UT, (3) University of Oklahoma Health Sciences Center, Oklahoma City, OK, (4) University of Toronto, Toronto, Canada

SU-E-T-162 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: Residual patient setup shifts such as 1 mm or 1 degree are commonly observed during online treatment setups of hypofractionated radiosurgery (HRS) of spine and intracranial lesions. To effectively guide patient-specific setups, a prospective treatment planning approach was developed for such treatments.

Methods: For a cohort of intracranial and spinal HRS treatments, individualized setup guidelines were prospectively determined via the following approach: (1) systematically shift and rotate 3D patient image data in incremental small steps. (2) For each step such as 0.1 mm or 0.1 degree, dose distributions from original treatment plan were recalculated. (3) Each resulting dose distributions were then iteratively checked against a set of preset dosimetric criteria for compliance. (4) From step 3, maximum tolerable shift levels along the major axes were then determined. Finally, we tested such an approached on a cohort of treatment cases performed at our institutions.

Results: For studied treatment sessions (n=63), the mean maximum tolerable shift levels including rotations projected unto the major axes were determined to be 2.0±0.7mm, 2.1±0.9 mm and 1.9±0.8 mm along the lateral, longitudinal, and vertical axis, respectively. Such tolerance levels were significantly (p=0.02) larger than the machine preset tolerance level of 1.0 mm that commonly enforced for all treatment sessions. However, more than 50% of the treatment sessions exhibited sub-millimeter tolerance level along certain directions to meet critical structure constraints. For example, a 0.6-mm anterior maximum shift could incur 36% increase in the maximum dose to the brainstem for one patient case.

Conclusion: Patient specific online setup guidelines for HRS has been demonstrated to prevent potential deleterious effects from residual shifts while facilitating online setups by providing more room of larger acceptable shifts for a majority of treatment cases.

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