Exclusive Hypofractionated Stereotactic Radiotherapy in Non-resectable Single Brain Metastasis

Cancer, Metastasis

radiotherapy, radiation oncology, brain metastasis, metastases, radiosurgery, neurosurgery, hypofractionation, stereotaxy

Patients with single brain metastasis without other metastatic site have a better prognosis, and they need a better brain metastasis control. For non-resectable and non-radiosurgical brain metastasis, the gold standard treatment is whole-brain irradiation with 30 Gy in 10 fractions, but the local control is not achieved in most of the cases. This study investigate the possibility to increase radiation dose in this metastasis with exclusive hypofractionated stereotactic radiotherapy.

For the planning, patients will undergo magnetic resonance imaging (MRI) 1.5 to 3 Tesla, with contrast and volumetric reconstruction of 1 mm and can be used MRI from the diagnosis of metastasis, if it is compatible with the planning system. Then, there will be individualized mask Mask Set for One Patient 41100 (BrainLAB AG, Heimstetten, Germany) for each patient. Patients will undergo computed tomography (CT) without contrast with 1-mm slices with tracking and stereotactic fixation. The images of MRI and CT are fused in the planning system IPLAN version 4.1 (BrainLAB AG, Heimstetten, Germany), where the plan will be implemented. The clinical target volume (CTV) is the macroscopic disease (GTV) displayed on the sign of T1 contrast. The planning target volume (PTV) is the CTV with 3-mm margin in all directions. Can be used multiple dynamic arcs, static conformal multiple fields, multiple static fields modulated and multiple static arcs. The dose-fractionation scheme will be 4 fractions of 7 Gy at the periphery of the PTV, a once daily on 4 consecutive working days. The dose to the PTV encompassing areas of the brainstem or optic tract will be reduced by 20%. The plans will be standardized at the isocenter. The isodose prescription will be the largest isodose that meets the following criteria: isodose covering at least 95% of the PTV with the prescription dose (V100 ≥ 95%) and 95% of prescription dose covering at least 99% of the PTV (V95 ≥ 99%). The maximum dose should be less than 35 Gy. The dose constraint reported by Ernst-Stecken et al will be respected at the expense of prescription isodose, where the normal brain volume (total brain volume less volume PTV) of 20 cc will not receive a dose of 4 Gy per fraction or larger, there is no maximum size limit of metastasis to be included in the study. Use as an index of compliance reported by the Paddick et al and Radiation Therapy Oncology Group (RTOG). Tests will be done for collision safety tests and quality control to ensure the alignment of isocenters radiation, mechanical and coincidence of lasers (Winston-Lutz test). After all, the patients are treated with 6-MeV photons in the linear accelerator Varian Clinac 600 CD (Varian Medical Systems, Palo Alto, CA, USA) with a system of micromultileaf m3 (BrainLAB AG, Heimstetten, Germany).

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