TH‐AB‐BRB‐10: How Many Lesions Can Be Treated with Radiosurgery? Whole Brain Dose From Radiosurgery of Multiple Targets

• Published in: Medical physics (Lancaster) 2015-06, Vol.42 (6Part41), p.3706-3706
• Main Authors: Becker, S, Jozsef, G, Presser, J, Kondziolka, D
• Format: Article
• Language: English
• Subjects: Brain; Cancer; Dosimetry; Radiation treatment; Radiosurgery
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4926141

Purpose: Multiple brain metastases are a frequent indication for stereotactic radiosurgery (SRS). There is concern that as radiation doses to normal brain increase, neurocognitive toxicity increases too. In this report, we estimate how many lesions and what total volume of tumor(s) can be irradiated before a whole brain dose of 8 Gy is reached. Methods: Multiple tumor SRS was simulated in Matlab (Mathworks, Inc) using pre‐calculated dose distributions (kernels) created from single isocenter shots for 4mm, 8mm and 16mm targets, and composite shots for 24mm and 36mm targets in GammaPlan (Elekta, Inc Sweden). Tumors of varying size from 1–36mm were randomly placed throughout the brain and covered with dose until the mean normal brain dose reached 8Gy. Selection of tumor size, dose coverage, selectivity, normalization, and maximum dose were based off NYU Gamma Knife clinical metastases database. Scenarios were run both for mixed tumor sizes and a select few fixed tumors sizes. Results: The mean number of tumors treated, V12, and total tumor volume treated using mixed tumor size distribution were 40.1±8.6, 180.2±28.8cc, and 41.1±12.7cc. For the simulation runs utilizing tumor size fixed ranges of 0–4mm, 4–8mm, 8–16mm, 16–24mm, 24–36mm, the average contribution per tumor to a whole brain dose was 0.045Gy, 0.097Gy, 0.359Gy, 0.635Gy, and 1.203Gy, respectively. Conclusion: GK SRS would require an average of 6.7 24–36mm tumors, 177.3 0–4mm tumors, or 40.1 tumors of mixed sizes to be treated to reach 8 Gy whole normal brain dose for a single session. Therefore, this study alleviates the concern that radiosurgery for a large number of tumors or treating additional newly formed metastases after previous SRS can lead to high whole brain doses. The ability to safely retreat enables the physician to consider new SRS instead of whole brain radiotherapy when additional metastases appear.