Does size matter? Investigating the optimal planning target volume margin for postoperative stereotactic radiosurgery to resected brain metastases

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OBJECTIVE

The optimal margin size in postoperative stereotactic radiosurgery (SRS) for brain metastases is unknown. Herein, the authors investigated the effect of SRS planning target volume (PTV) margin on local recurrence and symptomatic radiation necrosis postoperatively.

METHODS

Records of patients who received postoperative LINAC-based SRS for brain metastases between 2006 and 2016 were reviewed and stratified based on PTV margin size (1.0 or > 1.0 mm). Patients were treated using frameless and framed SRS techniques, and both single-fraction and hypofractionated dosing were used based on lesion size. Kaplan-Meier and cumulative incidence models were used to estimate survival and intracranial outcomes, respectively. Multivariate analyses were also performed.

RESULTS

A total of 133 patients with 139 cavities were identified; 36 patients (27.1%) and 35 lesions (25.2%) were in the 1.0-mm group, and 97 patients (72.9%) and 104 lesions (74.8%) were in the > 1.0–mm group. Patient characteristics were balanced, except the 1.0-mm cohort had a better Eastern Cooperative Group Performance Status (grade 0: 36.1% vs 19.6%), higher mean number of brain metastases (1.75 vs 1.31), lower prescription isodose line (80% vs 95%), and lower median single fraction–equivalent dose (15.0 vs 17.5 Gy) (all p < 0.05). The median survival and follow-up for all patients were 15.6 months and 17.7 months, respectively. No significant difference in local recurrence was noted between the cohorts. An increased 1-year rate of symptomatic radionecrosis was seen in the larger margin group (20.9% vs 6.0%, p = 0.028). On multivariate analyses, margin size > 1.0 mm was associated with an increased risk for symptomatic radionecrosis (HR 3.07, 95% CI 1.13–8.34; p = 0.028), while multifraction SRS emerged as a protective factor for symptomatic radionecrosis (HR 0.13, 95% CI 0.02–0.76; p = 0.023).

CONCLUSIONS

Expanding the PTV margin beyond 1.0 mm is not associated with improved local recurrence but appears to increase the risk of symptomatic radionecrosis after postoperative SRS.

ABBREVIATIONS ECOG = Eastern Cooperative Group; GTR = gross-total resection; GTV = gross tumor volume; IDL = isodose line; LINAC = linear accelerator; MVA = multivariate analysis; OS = overall survival; PTV = planning target volume; SFED = single fraction–equivalent dose; SRS = stereotactic radiosurgery; STR = subtotal resection; WBRT = whole-brain radiation therapy.

Article Information

Correspondence Kirtesh R. Patel: Yale School of Medicine, New Haven, CT. kirtesh.patel@yale.edu.

INCLUDE WHEN CITING Published online April 20, 2018; DOI: 10.3171/2017.9.JNS171735.

J.J. and M.C. contributed equally to this work and share first authorship.

Disclosures The authors report no conflict of interest concerning the materials or methods used in this study or the findings specified in this paper.

© AANS, except where prohibited by US copyright law.

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    Cumulative incidence of local recurrence stratified by margin group. Figure is available in color online only.

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    Cumulative incidence of symptomatic radiation necrosis stratified by margin group. Figure is available in color online only.

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