Whole brain radiotherapy with hippocampal avoidance and simultaneous integrated boost for brain metastases: a dosimetric volumetric-modulated arc therapy study

Abstract BACKGROUND Recently Hippocampal Avoidance (HA-) WBRT has become a recommended treatment option in patients with multiple (≥ 5) brain metastases and good prognosis. We wanted to investigate the dosimetric feasibility of dose painting technique combining HA-WBRT with a simultaneous integrated boost (SIB) to tumours. METHOD 5 patients who had a CT simulation fused with brain MRI with fine cuts, were selected for this study. Volumes were contoured on T1w contrast images. Whole brain prescription dose was 30Gy in 12 fractions. A PTV margin of 2mm was applied to lesions, except when these were ≤5mm from organs at risks (OARs). A simultaneous integrated boost (SIB) of 48Gy and 40.2Gy was prescribed to these volumes respectively. Hippocampal constraints followed RTOG 0933 protocol. For lesions ≤5mm from OARs, the acceptable D0.03cc≤42Gy was allowed. All plans were planned on EclipseTM v.13.6 TPS using 6MV photons, VMAT technique with 3 coplanar and 1 non-coplanar arcs for Varian TrueBeam machine. RESULTS Plans had between 6–24 lesions with GTV and PTV of 3.02–11.32cc and 7.05–31.74cc respectively. 3 of the plans had lesions within/adjacent to brainstem or hippocampus. The achieved PTV_40.2Gy D95% 37.42–39.05Gy with Conformity Index (CI)(95%) 0.63–1.06, PTV_48Gy D95% 44.64–47.04Gy with CI(95%) 0.75–0.97 and GTV_48Gy D95% 47.44–50.16Gy. Whole brain Dmean 31.87–33.15Gy with a Homogeneity Index (D2%-D98%/Dmean) 0.18–0.58. Hippocampal D100% 8.69–10.1Gy, D0.03cc 16.5–40.43Gy and Dmean 12.66–24.68Gy. SUMMARY: There was a steep learning curve when adopting this technique and multiple plan iterations were made to achieve target constraints. To meet acceptable OAR constraints, SIB coverage was compromised. Lesions ≤5mm from hippocampus resulted in higher Hippocampal average Dmean 22.8Gy vs. 12.8Gy. The significance of this value should be tested in clinical trials. Overall, HA-SIB-WBRT seems feasible even with ≥ 5 brain metastases and could result in better brain metastases control then HA-WBRT alone.

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A new option in brain-metastases: Hippocampal-sparing whole-brain radiotherapy with simultaneous integrated boost VMAT-IGRT.

Journal of Clinical Oncology ◽

10.1200/jco.2019.37.15_suppl.e13589 ◽

2019 ◽

Vol 37 (15_suppl) ◽

pp. e13589-e13589

Author(s):

Alicia Marin ◽

Margarita Martin ◽

Emma Gonzalez ◽

Lisselott Torres ◽

David Hernandez ◽

...

Keyword(s):

Brain Metastases ◽

Whole Brain Radiotherapy ◽

Progression Free Survival ◽

Simultaneous Integrated Boost ◽

Rank Test ◽

Whole Brain ◽

Free Survival ◽

Brain Radiotherapy ◽

Integrated Boost ◽

Hippocampal Sparing

e13589 Background: We report our experience with volumetric modulated arc therapy (VMAT-IGRT) use to plan and deliver whole brain radiotherapy whit a simultaneous integrated boost in patients with brain metastases, using hippocampal sparing. Methods: In this retrospective study 57 patients with brain metastases were treated with radiotherapy VMAT-IGRT were administered in 12 daily fractions of 2.7Gy for a total of 32.4Gy (EBD 40Gy) to whole-brain and simultaneous integrated boost to brain metastases, multiple targets, in 12 fractions to 3.4Gy for a total dose of 40.8Gy (EBD 60Gy). The primary endpoint was intracranial progression-free survival (PFS) and secondary endpoints were preserves neurocognitive function and overall survival (OS). Survival rates were determined by Kaplan-Meier method. Differences between survival curves were analyzed by the log-rank test. Results: From January 2015 to December 2018, 57 patients were enrolled. The median follow-up time was 7 months. PFS6, PFS12 and PFS18 were 91.3%, 70.8% and 70.8% respectively. mOS, OS6, OS12 and OS18 were 10 months (95% IC 4.2-15.7 months), 67.2%, 48.6% and 35.3% respectively. Response rates were as follows: 29RC (50.9%), 21RP (36.8%), 7SD (12.3%) and 0PD (0%). Long progression-free survival patients: PFS > 12, 15 and 18 months for initial diagnosis 70%, 70% and 70% respectively. Conclusions: Whole-brain radiotherapy with simultaneous integrated boost to brain-metastases: VMAT-IGRT is safe and promising and possibly produces survival and tolerance benefits. Sparing the hippocampus during cranial irradiation poses important technical challenges with respect to contouring and treatment planning.

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