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The Dosimetric Study of Hippocampal-Avoidance Whole Brain Radiotherapy with Intensity Modulated Proton Therapy

T Sun*, X Lin, Y Yin, Shandong cancer hospital and institute,Shandong first medical university and shandong academy of medical sciences, Jinan, ShandongCN,

Presentations

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

Room: AAPM ePoster Library

Purpose: whole brain radiotherapy (HA-WBRT) for multiple brain metastases may prevent treatment-related cognitive decline, compared to standard WBRT. The purpose of this study was to compare the dosimetic differences of volumetric-modulated arc therapy (VMAT) and intensity-modulated proton therapy (IMPT) for hippocampal sparing whole-brain radiotherapy with simultaneous integrated boost (SIB) in patients with multiple brain metastases.


Methods: total of 10 patients with multiple brain metastases previously treated with whole-brain radiotherapy with hippocampal sparing were reviewed. The hippocampus was contoured on diagnostic T1-weighted magnetic resonance imaging (MRI) which had been fused with the planning CT image set. Hippocampal avoidance regions were created using a 5mm volumetric expansion around the hippocampus. Prescription dose was 30 Gy (RBE) for whole brain (PTV-WB) and 45 Gy (RBE) for brain metastases (PTV-BM) in 10 fractions. Two plans were designed for each patient: VMAT with two 358 degrees arcs and IMPT with 2 fields. The goal of the plan is to minimize the dose to the organs at risk, especially the hippocampus, while ensuring the dose to the target.


Results: plans showed significant dosimetric improvements in multiple dosimetric parameters. The dose coverage of PTV-WB and PTV-BM was significantly increased in IMPT plans. The mean dose to the hippocampus was reduced to 799.5 cGy (RBE) in IMPT plans compared to VMAT 1189.2 Gy (RBE) (p<0.01); D100% to the hippocampus was reduced to 450.2 cGy(RBE)in IMPT compared to VMAT 940.3 cGy (RBE) (p<0.001). IMPT plans reduced the maximum dose of lens, braintem, spinalcord and optic-nerves and the mean dose of inner ears significantly compared to VMAT plans.


Conclusion: IMPT plans improve both the target coverage and the organs at risk sparing in whole-brain radiotherapy and simultaneous integrated boost for multiple brain metastases with hippocampal sparing.

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