Abstract
Background: Pre-operative radiosurgery (SRS) preceding the resection of brain metastases promises to circumvent limitations of post-operative cavity SRS. It minimizes uncertainties regarding delineation and safety margins and could reduce dose exposure of the healthy brain (HB). Methods: We performed a systematic treatment plan comparison on 24 patients who received post-operative radiosurgery of the resection cavity at our institution. Comparative treatment plans were calculated for hypofractionated stereotactic radiotherapy (7 × 5 Gray (Gy)) in a hypothetical pre-operative (pre-op) and two post-operative scenarios, either with (extended field, post-op-E) or without the surgical tract (involved field, post-op-I). Detailed volumetric comparison of the resulting target volumes was performed, as well as dosimetric comparison focusing on targets and the HB. Results: The resection cavity was significantly smaller and different in morphology from the pre-operative lesion, yielding a low Dice Similarity Coefficient (DSC) of 53% (p = 0.019). Post-op-I and post-op-E targets showed high similarity (DSC = 93%), and including the surgical tract moderately enlarged resulting median target size (18.58 ccm vs. 22.89 ccm, p < 0.001). Dosimetric analysis favored the pre-operative treatment setting since it significantly decreased relevant dose exposure of the HB (Median volume receiving 28 Gy: 6.79 vs. 10.79 for pre-op vs. post-op-E, p < 0.001). Dosimetrically, pre-operative SRS is a promising alternative to post-operative cavity irradiation that could furthermore offer practical benefits regarding delineation and treatment planning. Comparative trials are required to evaluate potential clinical advantages of this approach.
Highlights
Neurosurgical resection is recommended by current international guidelines for large, symptomatic brain metastases (BM), or for the procurement of a pathologic sample [1,2]
We identified 24 patients who presented for the post-operative irradiation of the resection cavity at our institution in 2016 and 2017
On the same series, we conducted a proof-of-concept volumetric and dosimetric experiment to simulate the effects of pre-operative stereotactic radiosurgery (SRS) and the effects of different contouring approaches
Summary
Neurosurgical resection is recommended by current international guidelines for large, symptomatic brain metastases (BM), or for the procurement of a pathologic sample [1,2]. The position of WBRT has been challenged by the increasing use of more precise modalities such as single-fraction stereotactic radiosurgery (SRS) or hypofractionated stereotactic radiotherapy (HFSRT) This was recently demonstrated by two phase 3 trials, concluding that SRS improves local control over observation, as reported by Mahajan et al, while significantly reducing neurocognitive toxicity when compared to WBRT, as reported by Brown et al [6,7]. Pre-operative radiosurgery (SRS) preceding the resection of brain metastases promises to circumvent limitations of post-operative cavity SRS. It minimizes uncertainties regarding delineation and safety margins and could reduce dose exposure of the healthy brain (HB). Dosimetric analysis favored the pre-operative treatment setting since it significantly decreased relevant dose exposure of the HB (Median volume receiving 28 Gy: 6.79 vs. 10.79 for pre-op vs. post-op-E, p < 0.001)
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