Isotoxic High Dose (iHD) Fractionated Stereotactic Radiation Therapy (fSRT) for Intact Brain Metastases : a Feasibility Study

Brain metastasis is the most challenging disease in the field of tumor treatment, with a median overall survival of only 1-2 months for untreated patients. Stereotactic radiotherapy (SRT) has the advantages of precise positioning, relatively concentrated dosage, shorter course, and lower toxicity. Several studies could effectively protect cognitive function and achieve better tumor control rate. Currently, it has gradually replaced WBRT as standard local treatment choice for brain metastases. SRT includes Stereotactic Radiosurgery (SRS) and Fractional Stereotactic Radiotherapy (fSRT). With the continuous updating of domestic radiation therapy equipment, the use of high-resolution multi leaf gratings enables the accuracy of fSRT based on linear accelerators to reach 0.5mm or even lower levels, and has gradually become one of the main choices for local treatment of a limited number of patients with brain metastases.

However, there is currently no prospective randomized controlled study data analyzing the clinical benefits of different segmentation and dosages of SRT. In retrospective data comparing different segmentation schemes, researchers found that higher BED was associated with better local control. However, the ASTRO guidelines recommend relatively conservative doses for SRT of brain metastases, especially as the lesion volume increases, and the recommended dose of BED10 for SRT was only 48 Gy (30 Gy/5 Fx). This is based on the consideration that higher radiation exposure will bring a higher risk of radiation-induced brain necrosis. However, with the continuous updates of SRT treatment equipment and technology, existing technologies can achieve higher dose coverage for more brain metastases while meeting the normal tissue limit. Therefore, this study conducted a prospective intervention study to explore the feasibility and safety of optimizing SRT dosage based on normal tissue tolerance for the treatment of brain metastases, in order to further improve the therapeutic effect of intracranial lesions with brain metastases.

This study is designed as a single arm open prospective study, assuming that under this treatment regimen, the proportion of patients with lesion prescription dose BED10>50 Gy is 90%, and the incidence of radiation-induced brain necrosis within 1 year is 8.5%. The planned enrollment period is 2 years and follow-up period is 1 year. A total of 35 people need to be enrolled.