[Background] For newly-diagnosed patients with brain metastases (BMs), conventional whole-brain radiotherapy (WBRT) might still remain a common palliative management. 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.

To postpone the occurrence and mitigate neurocognitive impairments associated with conventional WBRT, there have been some strategies in the clinical practice of radiation oncology. Among them, the technology/technique of highly precise/accurate stereotactic radiosurgery or stereotactic radiotherapy (i.e., hypofractionated stereotactic radiotherapy, HS-SRT) might have been widely administered in irradiating exclusively the focal brain metastatic lesions, particularly in cancer patients with a limited number of brain metastases. By contrast, the planning strategy of hippocampus avoidance during the course of whole-brain irradiation has also been well-established in preserving NCFs.

[Methods] Newly-diagnosed cancer patients harboring 1 - 4 brain metastatic lesions are eligible if they still have fair/good performance status. Eligible and enrolled should receive baseline brain MRI examination and pre-WBRT neurocognitive assessment. Although non-randomized, this phase II trial comprises two prospective (radiotherapeutic) cohorts with individually different planning techniques and prescription schedules. Cohort I represents patients referred for arranging partial-brain irradiation; namely, a course of hypofractionated stereotactic radiotherapy (HF-SRT) is delivered within 2 weeks with a cumulative dose of 3000 - 3500 cGy in 5 fractions. By contrast, Cohort II stands for patients referred for arranging the course of hippocampus-sparing WBRT (HS-WBRT), delivered within 3 weeks with a cumulative dose of 3000 cGy in 12 fractions, during which the planning technique of simultaneous integrated boost (SIB) is employed to focally escalate the dose irradiating the brain metastatic foci. Besides, adhering to several international clinical practice guidelines, the synergic use of the neuroprotective agent (memantine) will be routinely applied in the treatment Cohort II (HS-WBRT). In both treatment cohorts, 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.

The primary outcome measure is the median time of CNS progression-free survival (CNS-PFS). Secondary outcome measures encompass both neuro-oncological endpoints and neurocognitive endpoints, among which there is cognitive-deterioration-free survival (CD-free survival). CD-free survival 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.

[Expected results] This prospective observational study aims to examine thoroughly and analyze the comparatively between the two radiotherapeutic cohorts (HF-SRT versus HS-WBRT), addressing both CNS tumor control and neurocognitive functional outcomes. It is expected that the patterns of (CNS) failure and individual time to progression will be clearly demonstrated in this prospective observational study encompassing two distinct radiotherapeutic cohorts.

Inclusion Criteria:

• Patients with pathologically-confirmed non-hematopoietic malignancy who are referred for postoperative adjuvant or therapeutic hypofractionated stereotactic radiotherapy (HF-SRT)
• A Fair/good performance status no worse than Eastern Cooperative Group (ECOG) of 2 or an acceptable performance status of Karnofsky Score (KPS) at least 70
• The number and extent of brain metastatic lesions should be no more than three metastatic foci with a greatest diameter no more than 4 cm shown on pre-radiotherapy MRI; namely, that is the clinical setting of oligometastatic brain disease or brain oligometastases

Exclusion Criteria:

• Patients with their primary cancer arising from hematological malignancies (i.e., malignant lymphomas, leukemia), germ cell tumors, or malignant meningiomas
• Patients with MRI-identified metastasis within 5 mm peri-hippocampally
• Patients with metastasis involving the brain stem
• Clinical suspicion of leptomeningeal spreading
• History of prior radiotherapy including stereotactic radiosurgery delivered to brain/head region for any reasons

Patients with newly-diagnosed brain oligometastases and an acceptable performance status would receive baseline neurocognitive assessment.