Post-Operative Stereotactic Radiotherapy for Resected Brain Metastases: Results of the Multicenter Analysis (AURORA) of the German Working Group "Stereotactic Radiotherapy"

PURPOSE/OBJECTIVE(S)

While the results of prospective studies support the use of postoperative stereotactic radiotherapy (RT) to the resection cavity (RC) as the standard of care after surgery, there are several issues that need to be investigated such as factors for improving local control, risk of leptomeningeal disease and radiation necrosis. Further, the optimal dose and fractionation is still under debate.

MATERIALS/METHODS

The working group "Stereotactic Radiotherapy" of the German Society of Radiation Oncology (DEGRO) analyzed its multi-institutional database with 661 patients who received postoperative stereotactic RT to the RC. Treatment was performed at 13 centers between 2008 and 2021. Patient characteristics, treatment details, and follow-up data including overall survival (OS), local control (LC) were evaluated. Cox Regression and Kaplan-Meier curves with Log-rank Tests were calculated for selected variables.

RESULTS

In this retrospective study, overall survival was 61.5% at 1 year, 47.6% at 2 years, and 35.5% at 3 years, and local control was 84.6% at 1 year, 74.8% at 2 years, and 72.8% at 3 years. 96% of patients were treated with hypofractionated stereotactic radiotherapy (HSRT), only 26 patients received single fraction radiosurgery (4%). Prognostic factors associated with overall survival were Karnofsky Performance Status, RPA and GPA class, controlled primary tumor and absence of extracranial metastases, whereas prognostic factor associated with local control was planning target volume (23 mL or less).

CONCLUSION

HSRT is the most common fractionation form in the treatment of RCs in this multicenter analysis. This approach results in excellent OS and LC outcomes. OS in patients with resected brain metastases is mainly influenced by performance status. In regard to local control, RT of large cavities remain a challenge with significantly worse outcome.

RADT-06. SPARING OF MOTOR STRUCTURES IN ADJUVANT RADIATION THERAPY AFTER RESECTION OF BRAIN METASTASES: APPLICATION OF NTMS-DERIVED DTI-BASED MOTOR FIBER TRACKING IN ADJUVANT STEREOTACTIC RT TREATMENT PLANNING

BACKGROUND

Resection of brain metastases (BM) close to the motor cortex and the corticospinal tract (CST) bears a significant risk for treatment-related morbidity. Navigated transcranial mapping (nTMS) combined with diffusion-tensor-imaging (DTI) based fiber tracking (DTI-FTTMS) is a valuable tool to guide the neurosurgeon along the CST to preserve motor function. This study aims to proof the practicability of DTI-FTTMS in local adjuvant stereotactic RT planning in the management of BM. Method: Pre-surgical generated DTI-FTTMS-based CST reconstructions of 24 patients with 25 resected BM were incorporated into the RT planning system and elastic fused with planning imaging. The CST was delineated as the planning risk volume (PRV-FTTMS). Fractionated stereotactic intensity-modulated RT (IMRT) plans (7 x 5 Gy) were retrospectively calculated and then optimized to preserve PRV-FTTMS. Areas covered by the planning target volume (PTV) were not spared (overlap).

RESULTS

In regular plans mean dose (Dmean) of complete PRV-FTTMS was 5.4 ± 2.5 Gy. Regarding PRV-FTTMS portions within the 8.75 Gy (25% of prescription dose) isodose level Dmean was 18.2 ± 4.3 Gy and after plan optimization 13.1 ± 3.8Gy (-28.0%, p < 0.001). Within the 17.5 Gy (50%) isodose line PRV-FTTMS Dmean was reduced by 31.7% from 24.3 ± 3 Gy to 16.6 ± 4.8 Gy (p< 0.001). There was no decline of the effective treatment dose, PTV Dmean in regular plans was 36.9 ± 0.7 Gy vs. 37.7 ± 1.4Gy (p=0.013) after adaption. PTV coverage (V35Gy(%)*100) did not change with plan optimization: 0.99 vs. 0.99 (p=0.43). Dose constraints of organs at risk were all met both in regular and optimized plans.

CONCLUSION

DTI-FTTMS based motor tracts could be implemented in the adjuvant stereotactic RT planning of cavities after resection of BM. A significant dose reduction of motor structures within critical dose levels seems possible without reducing PTV treatment dose. However, the functional benefit needs to be investigated prospectively within clinical trials.

[Determination and interpretation of in vitro solubility behavior of pharmaceutical agents. 2. The effect of surface tension of the dissolution medium on the liberation of drugs in commercial preparations (tablets, dragees)]

The influence of submicellar surfactants in the dissolution media on drug liberation from commercial products was investigated (paddle-method, flow through-method). The results depend on the product tested and the tester used. Addition of surfactants accelerates, retards or doesn't alter in vitro liberation with the paddle-method, accelerates or doesn't influence flow through-liberation. Equivalence of the release profiles of the individual products with both testers was proved. Addition of surfactants may alter in vitro drug release from commercial products but should be compulsory only when (improved) in vivo-in vitro correlation was demonstrated.

[The determination and interpretation of in-vitro dissolution behavior of pharmaceutical substances. 1. Powders, mixtures and granules]

Dissolution testing of hydrophobic powders with the flow-through method but without powder preparation doesn't guarantee accurate, reproducible and reasonable results in aqueous test media of high surface tension. Mixing drug powders with seasand or using fast desintegrating granules enables an exact determination and realistic valuation of the dissolution behaviour. Addition of surfactants generally accelerates the dissolution rate but problems as drug agglomeration and flotation remain.