Background: For newly-diagnosed patients with brain metastasis, conventional whole-brain radiation therapy (WBRT) might still remain a common palliative management even for those with brain oligometastases. However, WBRT-related late consequences, particularly a decline in neurocognitive functions (NCFs), are a major concern. Actually, WBRT-related neurocognitive dysfunction is usually characterized as deterioration involving learning and memory, in which the extremely radiosensitive hippocampus indeed plays a critical role. In order to postpone or mitigate the effect of conventional WBRT-induced neurocognitive impairments, there have been some strategies and options in clinical practice. Among them, the technique of highly precise and accurate stereotactic radiosurgery or stereotactic radiotherapy (i.e., hypofractionated stereotactic radiotherapy, HS-SRT) might have been widely administered in irradiating purely focal metastatic foci in cancer patients with a limited number of brain metastases.

Methods: Newly-diagnosed cancer patients harboring 1-3 brain metastatic lesions are eligible if they are still in a fair/good performance status. All recruited patients should receive baseline brain MRI examination and pre-radiotherapy neurocognitive assessment. Sticking to the principles of stereotactic radiosurgery/radiotherapy (SRS/SRT), treatment planning will be designed via the technique of volumetric-modulated arc therapy (VMAT) to achieve both satisfactory in-field local control (but assuring of hippocampal avoidance) and a tolerably low incidence of radiation necrosis, a course of hypofractionated stereotactic radiotherapy (HF-SRT) is delivered within 2 weeks with a cumulative dose of 3000 - 3500 cGy in 5 fractions. Accordingly, a battery of neuropsychological measures, which includes 7 standardized neuropsychological tests (e.g., executive functions, verbal and non-verbal memory, working memory, and psychomotor speed), is used to evaluate neurocognitive functions for our registered patients. The primary outcome measure is cognitive-deterioration-free survival, which is defined mainly as the time from enrollment to a NCF decline of exceeding than 1 SD away from the baseline involving at least one of the assessed NCF tests. Additionally, patients who expire before 6 months or are alive but fail to undergo all the neurocognitive testing administered would also be defined as suffering from cognitive deterioration. There are quite a few secondary endpoints of interest, including the patterns of (CNS) failure, actual local control rates, time to (CNS) progression, and cumulative incidence of radiation necrosis. Expected results: This prospective neurocognitive study aims to examine thoroughly the impact of the technique of highly focal brain irradiation administered with a course of hypofractionated SRT delivered to brain metastatic lesions merely (but sparing hippocampal structures), on neurocognitive performance, time to (CNS) progression, and patterns of (CNS) failure, in patients with brain oligometastases and a fair/good performance status. It is anticipated that (in-field) local control would be durable and that neurocognitive outcomes would also be maintained favorably. Moreover, we also expect that the patterns of (CNS) failure and the individual time to progression will be clearly demonstrated in this prospective longitudinal neurocognitive study.