Brain and hippocampal doses in patients with repeated stereotactic radiosurgery for brain metastasis

Abstract

Purpose The study was designed to evaluate the cumulative dose exposure of brain and hippocampus following multiple stereotactic radiosurgery (SRS) procedures on a single patient. Materials and methods Ninety-four patients who received at least two SRS treatments were evaluated. Their SRS dose plans were summated to obtain dose volume parameters. Hippocampal structures were delineated, in addition to segmentation of the brain. Results A total of 267 treatments were delivered to 94 patients. The number of SRS procedures per patient varied from 2 to 7 (mean = 2.8), and the total number of lesions treated in a given patient over multiple treatments varied from 2 to 70 (mean = 11). The interval between the first and last SRS treatments varied from 1 to 79 months (mean = 16.2 months). The mean prescription dose was 16.7 Gy prescribed to isodose lines from 40 to 95%. The mean coverage, selectivity, Paddick conformity, and gradient index were 99.6%, 79%, 0.57, and 2.74, respectively. The mean summated dose delivered to the whole brain over the course of multiple treatments was 5.11 Gy. The hippocampal mean dose after summation was 2.95 Gy. Patients with plan PCIs averaging below the mean value of 0.57 had higher V8, V10, V12, and V15 values for a given total tumor volume when compared with more conformal plans (PCI > 0.57).Conclusions Repeat SRS delivered low cumulative doses to the brain and hippocampus with the lowest normal brain volumes irradiated in highly conformal plans.

Radiosurgery, reirradiation, and brachytherapy

“…Complication rates are low and consist mainly of transient radiation‐induced edema 1‐5 and reversible enlargement of tumor‐associated cysts 2 . Radiosurgery in the un‐resected population may be supported by the lower integral dose delivered to the brain using conventional intensity‐modulated radiation therapy (IMRT)‐based conformal therapy 6 …”