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Finding the Optimal Treatment Modality for Hippocampal Avoidance Whole Brain Radiation Therapy (HA-WBRT)

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S Zieminski

S Zieminski*, M Khandekar , Y Wang , Department of Radiation Oncology, Massachusetts General Hospital, Harvard Medical School, Boston, MA


SU-I-GPD-T-317 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: To compare the quality of (1) VMAT plans with standard (STD) and (2) multi-criteria optimization (MCO) to (3) IMRT with MCO for hippocampal avoidance whole brain radiation therapy (HA-WBRT) in RayStation treatment planning system (TPS). To assess the improvement provided by MCO for VMAT treatments incorporating simultaneous integrated boost (SIB) to multiple targets of variable sizes at differential proximity to the hippocampus.

Methods: Ten patients previously treated with step-and-shoot MCO-IMRT (RayStation v4.0) on an Elekta Infinity accelerator with Agility multileaf collimators (5-mm leaves) were re-planned with STD- and MCO-VMAT (RayStation v4.7). All patients received 30 Gy in 15 fractions to PTV30 (2-mm PTV expansion from the whole brain excluding hippocampus with margin), with eight getting 37.5 Gy in SIB to PTV37.5 (up to 12 metastatic lesions with a 2-mm PTV expansion). The IMRT plans used eight to ten non-coplanar fields, whereas the VMAT plans used two coplanar full arcs and a vertex half arc. The averaged target coverage, organ dose and delivery time provided by the three modalities were compared, and a paired t-test was performed.

Results: Cumulative averages of Dmean and V10 for hippocampus were both lower for MCO-VMAT compared to STD-VMAT or MCO-IMRT, as was the Dmax for lens and cochlea. Dmax to hippocampus was similar in all three plans. V30 and V25 for PTV30, as well as D95 for PTV37.5, were higher for MCO-VMAT. In particular, the improvement was statistically significant when compared to STD-VMAT. Improved plan quality parameters such as a decrease in overall plan Dmax and total monitor units (MU) were also observed for MCO-VMAT, as compared to STD-VMAT and MCO-IMRT.

Conclusion: MCO-VMAT is the optimal modality for HA-WBRT on Elekta Agility with RayStation TPS, in terms of PTV coverage, OAR avoidance and delivery efficiency, compared to STD-VMAT and MCO-IMRT.

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