Central Nervous System

PV QA 2 - Poster Viewing Q&A 2

MO_16_2875 - Feasibility of a Risk-Adapted Approach to Whole Brain Radiation Therapy

Monday, October 22
10:45 AM - 12:15 PM
Location: Innovation Hub, Exhibit Hall 3

Feasibility of a Risk-Adapted Approach to Whole Brain Radiation Therapy
T. Yanagihara1, I. Bundalevski2, J. Kouri2, K. Hsieh3, M. Hwang4, T. J. C. Wang5, and H. Ashamalla6; 1Weill Cornell Medical College - New York Presbyterian Brooklyn Methodist Hospital, New York, NY, 2New York Presbyterian Brooklyn Methodist Hospital, New York, NY, 3New York Presbyterian Columbia University Medical Center, New York, NY, 4Department of Radiation Oncology, Columbia University Medical Center, New York, NY, 5Department of Neurological Surgery, Columbia University Medical Center, New York, NY, 6New York - Presbyterian Brooklyn Methodist Hospital, Brooklyn, NY

Purpose/Objective(s): Prior work has demonstrated that brain metastases (BMs) are not randomly distributed across the brain. We hypothesize that a risk-based approach to whole brain radiotherapy (WBRT) will reduce neurocognitive toxicity without jeopardizing intracranial disease control. In this study, we sought to identify regions of the brain that may be spared based on a low risk of developing a BM and then determine the dosimetric feasibility of a risk-adapted approach to WBRT.

Materials/Methods: A retrospective review of 103 patients with a new diagnosis of BMs was performed and each BM was manually contoured on the patient’s T1-post gadolinium MRI scan then co-registered to a standard space. The center of gravity was computed for each lesion and the coordinates were mapped onto a standard atlas of 52 anatomical regions. The observed frequency of involvement for each region was compared with the expected value, which assumed that all voxels in the brain were at equal risk of having a BM. After Bonferroni correction for multiple comparisons, regions at significantly reduced risk of developing a BM were considered for avoidance as well as anatomically adjacent regions having < 1% risk of harboring a BM. Three patients treated on the NRG-CC001 protocol were re-planned with a goal of sparing this larger area of normal tissue. Plans were evaluated using protocol constraints and the homogeneity index (HI) was computed as [(D10%/D90%)/Dp]*100 with Dp being the prescription dose.

Results: A total of 3,042 BMs were contoured. The paired hippocampus, parahippocampal gyrus, amygdala and temporal poles as well as the thalamus and brainstem were all identified to have a cumulative risk of < 5% of harboring disease. Re-planning with these regions excluded from the PTV did not sacrifice target coverage (mean PTV D98% = 26.85 +/- 1.56 Gy) relative to plans that were generated for NRG-CC001 (mean PTV D98% = 26.45 +/- 1.96 Gy). Constraints to the hippocampus were also maintained (mean D100% = 9.26 +/- 0.12 Gy and Dmax = 14.94 +/- 0.62 Gy for the experimental avoidance region vs. D100% = 9.67 +/- 0.26 Gy and Dmax = 15.03 +/- 0.83 Gy for the standard hippocampal avoidance region). There were no major deviations from protocol guidelines. Interestingly, the HI of plans using the experimental avoidance region were over 25% more homogeneous with a mean HI = 7.27 +/- 1.89% compared to HA-WBRT patients mean HI = 9.84 +/- 3.61%.

Conclusion: BMs are not evenly distributed across the brain and several regions of interest, including the hippocampus, a large portion of the adjacent temporal lobes, thalamus and entire brainstem may be spared with a limited effect on intracranial control. Dosimetric studies demonstrate that radiation planning is feasible and a prospective study of risk-adapted WBRT could utilize planning parameters of NRG-CC001.

Author Disclosure: T. Yanagihara: Research Grant; Optune. I. Bundalevski: None. J. Kouri: None. T.J. Wang: Honoraria; Elekta, Wolthers Kluwer. Consultant; Abbvie, Merck, Doximity, Elekta. Advisory Board; American Cancer Society North Jersey, AstraZeneca. Travel Expenses; Abbvie, AstraZeneca, Elekta. Stock Options; Doximity. H. Ashamalla: None.

Ted Yanagihara, MD, PhD

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