Postoperative stereotactic radiosurgery for resected brain metastasis

Hypofractionated stereotactic radiotherapy (HFSRT) versus single fraction stereotactic radiosurgery (SRS) to the resection cavity of brain metastases after surgical resection (SATURNUS): study protocol for a randomized phase III trial

BACKGROUND

The brain is a common site for cancer metastases. In case of large and/or symptomatic brain metastases, neurosurgical resection is performed. Adjuvant radiotherapy is a standard procedure to minimize the risk of local recurrence and is increasingly performed as local stereotactic radiotherapy to the resection cavity. Both hypofractionated stereotactic radiotherapy (HFSRT) and single fraction stereotactic radiosurgery (SRS) can be applied in this case. Although adjuvant stereotactic radiotherapy to the resection cavity is widely used in clinical routine and recommended in international guidelines, the optimal fractionation scheme still remains unclear. The SATURNUS trial prospectively compares adjuvant HFSRT with SRS and seeks to detect the superiority of HFSRT over SRS in terms of local tumor control.

METHODS

In this single center two-armed randomized phase III trial, adjuvant radiotherapy to the resection cavity of brain metastases with HFSRT (6 - 7 × 5 Gy prescribed to the surrounding isodose) is compared to SRS (1 × 12-20 Gy prescribed to the surrounding isodose). Patients are randomized 1:1 into the two different treatment arms. The primary endpoint of the trial is local control at the resected site at 12 months. The trial is based on the hypothesis that HFSRT is superior to SRS in terms of local tumor control.

DISCUSSION

Although adjuvant stereotactic radiotherapy after resection of brain metastases is considered standard of care treatment, there is a need for further prospective research to determine the optimal fractionation scheme. To the best of our knowledge, the SATURNUS study is the only randomized phase III study comparing different regimes of postoperative stereotactic radiotherapy to the resection cavity adequately powered to detect the superiority of HFSRT regarding local control.

TRIAL REGISTRATION

The study was retrospectively registered with ClinicalTrials.gov, number NCT05160818, on December 16, 2021. The trial registry record is available on  https://clinicaltrials.gov/study/NCT05160818 . The presented protocol refers to version V1.3 from March 21, 2021.

Dosimetric feasibility of direct post-operative MR-Linac-based stereotactic radiosurgery for resection cavities of brain metastases

BACKGROUND

Post-operative radiosurgery (SRS) of brain metastases patients is typically planned on a post-recovery MRI, 2-4 weeks after resection. However, the intracranial metastasis may (re-)grow in this period. Planning SRS directly on the post-operative MRI enables shortening this time interval, anticipating the start of adjuvant systemic therapy, and so decreasing the chance of extracranial progression. The MRI-Linac (MRL) allows the simultaneous execution of the post-operative MRI and SRS treatment. The aim of this work was investigating the dosimetric feasibility of MRL-based post-operative SRS.

METHODS

MRL treatments based on the direct post-operative MRI were simulated, including thirteen patients with resectable single brain metastases. The gross tumor volume (GTV) was contoured on the direct post-operative scans and compared to the post-recovery MRI GTV. Three plans for each patient were created: a non-coplanar VMAT CT-Linac plan (ncVMAT) and a coplanar IMRT MRL plan (cIMRT) on the direct post-operative MRI, and a ncVMAT plan on the post-recovery MRI as the current clinical standard.

RESULTS

Between the direct post-operative and post-recovery MRI, 15.5 % of the cavities shrunk by > 2 cc, and 46 % expanded by ≥ 2 cc. Although the direct post-operative cIMRT plans had a higher median gradient index (3.6 vs 2.7) and median V3Gy of the skin (18.4 vs 1.1 cc) compared to ncVMAT plans, they were clinically acceptable.

CONCLUSION

Direct post-operative MRL-based SRS for resection cavities of brain metastases is dosimetrically acceptable, with the advantages of increased patient comfort and logistics. Clinical benefit of this workflow should be investigated given the dosimetric plausibility.

Dosimetric Parameters in Hypofractionated Stereotactic Radiotherapy for Brain Metastases: Do Flattening Filter-Free Beams Bring Benefits? A Preliminary Study

PURPOSE

This study aimed to compare the dosimetric results of flattening filter-free (FFF) vs. flattened (FF) treatment plans for fractionated stereotactic radiotherapy (fSRT), with the goal to highlight potential advantages of FFF beams.

METHODS

A group of 18 patients with brain metastases treated with fSRT (30 Gy delivered in 5 fractions) were included. The dosimetric parameters evaluated were: (1) physical dosimetric parameters (number of monitor units (MUs), conformity index (CI), dose gradient index (DGI), beam on time (BOT)); (2) clinical dosimetric parameters pertaining to target volume (PTV) and organs at risk (OARs). Two treatment plans were performed for all patients: one used 6 MV FFF beams and the other used 6 MV flattened beams.

RESULTS

A slight increase in MUs was observed for the FFF mode (+23.3 MUs). The CI showed a difference of -2.7% for the FF plans (p = 0.28), correlated with a poorer coverage of the PTV. DGI values reported in terms of PTV are in line with international recommendations and showed a +1.9% difference for FFF plans. An average BOT of 90.3 s was reported for FFF plans, which was 2.3 times shorter than that required for FF plans delivery (p ≤ 0.001). A slight decrease of PTV coverage (-1.26%, p = 0.036) for FF plans can be considered relevant, but no other significant differences were observed between the two optimizations. No statistically significant benefit of using FFF beams to reduce V₂₀ for normal brain could be demonstrated.

CONCLUSION

These dosimetric results encourage the implementation of fSRT with standard flattened beams in centers where FFF linacs are not available.

Survival Outcomes and Predictors for Recurrence of Surgically Treated Brain Metastasis From Non-Small Cell Lung Cancer

Background

There are numerous factors to consider in deciding whether to undergo surgical treatment for brain metastasis from lung cancer. Herein, we aimed to analyze the survival outcome and predictors of recurrence of surgically treated brain metastasis from non-small cell lung cancer (NSCLC).

Methods

A total of 197 patients with brain metastasis from NSCLC who underwent microsurgery were included in this study.

Results

A total of 114 (57.9%) male and 83 (42.1%) female patients with a median age of 59 years (range, 27–79) was included in this study. The median follow-up period was 22.7 (range, 1–126) months. The 1-year and 2-year overall survival (OS) rates of patients with brain metastasis secondary to NSCLC were 59% and 43%, respectively. The 6-month and 1-year progression-free survival (PFS) rates of local recurrence were 80% and 73%, respectively, whereas those of distant recurrence were 84% and 63%, respectively. En-bloc resection of tumor resulted in better PFS for local recurrence (1-year PFS: 79% vs. 62%, p=0.02). Ventricular opening and direct contact between the tumor and the subarachnoid space were not associated with distal recurrence and leptomeningeal seeding. The difference in PFS of local recurrence according to adjuvant resection bed irradiation was not significant. Moreover, postoperative whole-brain irradiation did not show a significant difference in PFS of distant recurrence. In multivariate analysis, only en-bloc resection was a favorable prognostic factor for local recurrence. Contrastingly, multiple metastasis was a poor prognostic factor for distant recurrence.

Conclusion

En-bloc resection may reduce local recurrence after surgical resection. Ventricular opening and contact between the tumor and subarachnoid space did not show a statistically significant result for distant recurrence and leptomeningeal seeding. Multiple metastasis was only meaningful factor for distant recurrence.

Post-operative radiation therapy to the surgical cavity with standard fractionation in patients with brain metastases

The paradigm for post-operative cavity radiation therapy has shifted to more targeted, less morbid approaches. Single-fraction or hypofractionated radiation therapy is a common approach to treating the postoperative cavity but is associated with a local failure rate 20–40%. We employed an alternative treatment strategy involving fractionated partial brain radiation therapy to the surgical cavity. Patients with brain metastases who underwent radiation treatment 30–42 Gy in 3 Gy/fraction regimens to surgical cavity were retrospectively identified. The 6-month and 12-month freedom from local failure rates were 97.0% and 88.2%. Three patients (7%) experienced local failure at 4, 6, and 22 months. Of these, the histologies were colorectal adenocarcinoma (N = 1) and breast adenocarcinoma (N = 2). The 6-month and 12-month freedom from distant brain metastases rates were 74.1% and 68.8%, respectively, and the 6-month and 12-month overall survival rates were 84.9% and 64.3% respectively. The median overall survival was 39 months, and there were no events of late radionecrosis. Fractionated partial brain irradiation to the surgical cavity of resected brain metastases results in low rates of local failure. This strategy represents an alternative to SRS and WBRT.

Post-operative stereotactic radiosurgery versus observation for completely resected brain metastases: a single-centre, randomised, controlled, phase 3 trial

Background

After brain metastasis resection, whole-brain radiation therapy (WBRT) decreases local recurrence but may cause cognitive decline. We performed this study to determine if stereotactic radiosurgery (SRS) to the surgical cavity improved local tumor tumor-free recurrence rates compared to surgical resection alone as an alternative to the need for immediate WBRT.

Methods

The main entry criteria for the study included patients >3 years of age, with a Karnofsky Performance Score ≥ 70, who were able to undergo an MRI scan and who had a complete resection of 1–3 brain metastases (the maximum diameter of the resection cavity had to be ≤4cm). Patients were assigned randomly to either SRS treatment of the resection cavity (within 30 days of surgery) or observation (OBS). Patients were stratified by histology, tumor size, and number of metastases. Patients were recruited at a single tertiary cancer center. The primary endpoint was time to local recurrence in the resection cavity assessed by blinded central review of brain MRI scans in the intention-to-treat population. The trial was registered at clinicaltrials.gov (Trial NCT00950001, status: closed to new participants).

Findings

Between 8/13/2009 and 2/16/2016, 132 patients were randomized to OBS (N=68) or SRS (N=64), with 128 patients available for analysis. We stratified by metastasis size (maximum diameter of ≥3 cm vs. <3 cm), histology (melanoma vs. other), and number of metastases (one vs. two or three). The 12-month local tumor recurrence-free rate was 43% (OBS) (95% CI 31%–59%) and 72% (SRS) (95% CI 60%–87%) (hazard ratio [HR] 0.46, 95% confidence interval [CI] 0.24–0.88, p=0.015).

Interpretation

This prospective randomized trial of patients undergoing surgical resection for 1–3 brain metastases indicates that SRS administered to the resection cavity significantly lowers local recurrence compared to observation alone. Thus, the use of SRS after brain metastasis resection is an alternative to WBRT.