Central Nervous System
PV QA 2 - Poster Viewing Q&A 2
Purpose/Objective(s): Recent landmark randomized results from NCCTG-N107C established post-operative stereotactic radiosurgery (SRS) as the preferred standard of care over whole brain irradiation and observation. However, clinical target volume (CTV) design in these studies varied; and recently published contouring guidelines substantially increases the CTV volumes from these randomized studies. We thus sought to investigate the impact of deviation from these courting guidelines in post-operative SRS on patterns of recurrence. Our null hypothesis is the absence of impact of deviation from the contouring guidelines.
Materials/Methods: Following institutional review board approval, 76 patients with 78 resection cavities undergoing post-operative sterotactic radiosurgery SRS following surgical resection of brain metastases from 7/2011-10/2017 were retrospectively reviewed. Patients were excluded due to lack of follow-up imaging (n=18), whole brain radiotherapy (n=8), and delayed SRS after observation (n=9). The CTV for SRS included entire contrast enhancing surgical cavity with heterogeneity in inclusion of the surgical tract. Follow-up MR imaging was reviewed and fused with SRS plans to assess patterns of failure. Tumor control was calculated from the date of SRS to the date of failure, or last follow-up, using the Kaplan Meier Method with comparisons between groups made using log-rank t-tests.
Results: The median follow-up was 8.4 months [(interquartile range (IQR): 3.9-15.5)] for all patients and 8.7 months (IQR: 4.4-11.6) for surviving patients. Median age at SRS was 61 (IQR:53-66), median KPS was 80% (IQR: 70-90), and the most common primary was non-small cell lung cancer in 42%. The median SRS dose to resection cavity was 18Gy in 1 fraction to the 50% isodose (IQR: 16-20) with a median CTV volume of 6.9cc (IQR:3.1-10.0). The 1-year local failure rate at site of surgery and SRS was 21% (95% CI 4-37%). There was no difference in rates of local failure by age, primary type, KPS, control of extracranial disease, number of metastases, superficial versus deep location, SRS dose, or CTV volume. CTV contours included the entire surgical tract in 84%, and 0% included additional margin along the venous sinus or dural margin along the bone flap. Patterns of failure were infield or within 1-2mm of resection cavity in 60%, tract failure 20%, and marginal failure >5mm from resection cavity in 20%. No dural margin failures were noted along the bone flap irrespective of pre-operative dural contact. For deep lesions, 62% had the entire tract included in the CTV. The only tract recurrence noted was in a patient with a deep lesion without the tract covered with a 1-year rate of tract recurrence in this subset of 20% (95%CI 0-55%).
Conclusion: Deviation from contouring recommendation for including the dural tract along the bone flap does not appear to increase patterns of local recurrence; however, omission of the surgical tract in deep lesions may increase failure. Larger analyses are needed to better guide CTV design.
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