Title

Including patient specific trade-off for single fraction radiosurgery treatment planning for spine.

Document Type

Conference Proceeding

Publication Date

2018

Publication Title

Med Phys

Abstract

Purpose: Treatment planning for single fraction spine stereotactic radiosurgery (SRS) requires maximizing dose coverage to planning target volume (PTV) while meeting dose constraints to nearby organs-at-risk, in particular, spinal cord. Due to close proximity between PTVand cord, arriving at a clinically acceptable plan is challenging and highly planner-dependent. In this work, we identified patient-specific attainable trade-off between PTV coverage and cord dose, which was then applied to 12 cases retrospectively to demonstrate that a clinically suitable plan can be achieved in a consistent and efficient manner. Methods: Twenty-five spine patients treated with 18 Gy in single fraction using VMAT with PTV's between T2 and T11 were retrospectively studied. From these patients, correlation functions were established between volume of the PTV region within 5 mm to cord [Vol(PTV5mmTo-Cord)], 16 or 17 Gy coverage to PTV5mmToCord [V16Gy(PTV5mmTo-Cord), V17Gy(PTV5mmToCord)], and dose to 10% of cord [D10%(cord)]: F1(Vol(PTV5mmToCord), V16Gy(PTV5mmToCord)), F2(Vol(PTV5mmTo-Cord), V17Gy(PTV5mmToCord)), F3(Vol(PTV5mmToCord), D10%(cord)). The three correlation functions, F1, F2 and F3, represent the attainable tradeoff between coverage of PTV that is in closest proximity to cord and sparing of cord. The correlations were applied to develop new plans for an independent group of 12 previous spine patients. The optimization objectives included patient specific goals of D10%(cord), V16Gy(PTV5mmToCord) and V17Gy(PTV5mmToCord), as determined by the value of Vol (PTV5mmToCord) for each case. PTV coverage, cord dose, plan homogeneity, conformity and gradient index were compared between treated and newly developed plans. Results: In comparison to treated plans for the 12 patents, after one iteration of plan optimization, V18Gy(PTV) in new plans increased by 1.1 ± 1.2% (P = 0.01) to 98.5 ± 0.7%, D10%(cord) decreased by 0.34 ± 0.44 Gy (P = 0.02) to 8.69 ± 0.38 Gy, while homogeneity, conformity and gradient index remained comparable. Conclusion: Utilizing patient-specific attainable trade-off to guide plan optimization can efficiently achieve high quality plans. Further improvement in efficiency is feasible with script-based automatic planning effort.

Volume

45

Issue

6

First Page

e590

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