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Hippocampal-Sparing in Whole-Brain Radiation Therapy: A New VMAT Treatment Planning and Optimization Technique

D Soultan*, M Smith, J Edds, H Saleh, H Saleh, Kansas University Medical Center, Department of Radiation Oncology, Kansas City, KS

Presentations

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

Room: AAPM ePoster Library

Purpose: optimize hippocampus sparing in whole brain radiotherapy planning by utilizing available features in commercial treatment planning systems.

Methods: patients previously treated with 30Gy in 10 fractions of whole-brain radiotherapy with hippocampal-avoidance under NRG-CC001 clinical trial protocol were reviewed. Previous plans were designed with two to three VMAT arcs at couch 0º. New plans were generated in Eclipse v13.7 using two full arcs (181º-179º) at couch 0º, collimator (30º and 330º), and two half arcs (0º-179 º) at couch 90º, collimator (0º and 90º). A 40º avoidance sector (340º-20º) for each full arc was assigned, while a 30º avoidance sector (80º-110º) was assigned for each half arc. Jaw tracking was enabled in each plan. Upper, lower, and mean optimization objectives for PTV coverage and OARs (eyes, lens, optic nerves and chiasm) sparing were set to meet NRG-CC001 dose constraints and compliance criteria. In addition, generalized uniform equivalent dose gEUD feature was utilized; target and upper gEUD objectives for PTV and OARs were assigned, the corresponding alpha value of each structure's gEUD was entered based on AAPM TG-166. Paired t-tests were used to identify significant dosimetric differences between previously treated plans and new generated plans.

Results: seven new treatment plans meet NRG-CC001 doses requirements. Maximum dose to hippocampus was 10.6% lower on average (p<0.05), plans dosimetric quality parameters were not compromised; conformity index CI (p>0.05); homogeneity index HI (p>0.05); hotspots (p>0.05), doses to OARs complied with dose constrains, and number of total monitor units per plan was not significantly different (p>0.05) despite using more arcs compared to previously treated plans.

Conclusion: new treatment planning approach achieves a superior hippocampus avoidance up to 15% without compromising PTV coverage, OARs sparing, or plan quality. The reduction of hippocampus Dmax increases tolerance for potential dose escalation intended to individual metastases to further improve outcomes.

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Keywords

Brain, Optimization, Inverse Planning

Taxonomy

TH- External Beam- Photons: treatment planning/virtual clinical studies

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