Alzheimer's disease is the most frequent neurocognitive disorder associated with dementia, with a constantly increasing prevalence associated with an aging population. Amyloid deposition is considered as the first molecular event on the onset of Alzheimer's disease. It has already been demonstrated that low-dose radiotherapy is capable of reducing Alzheimer's disease-associated amyloid-β plaques and improving cognitive function in an animal model. In human, low-dose radiotherapy has demonstrated effectiveness in reducing bronchial amyloidosis.

The present study aims to conduct research by including 10 patients with a diagnosis of mild or moderately severe Alzheimer's disease and with evidence of amyloid pathology. Furthermore, the aim is to demonstrate the effectiveness of low-dose radiotherapy in reducing amyloid deposits in the human brain using molecular imaging (Flutemetamol(18F) PET) along with treatment of the specific target.

The investigators decided to use fractionated whole brain radiation doses of 1.8 Gy x 5 and 1.8 Gy x 3. Subjects will be followed with neurocognitive testing at 6 months post radiotherapy.

subjects 1-5 - 9Gy in 5 daily fractions

subjects 6-10 - 5.4Gy in 3 daily fractions

Inclusion Criteria:

• Clinical diagnosis of mild or moderate Alzheimer's disease.
• Amyloid PET scan positivity.
• Korean Mini-Mental State Examination score ≥10 and ≤24.
• Clinical dementia rating scale 0.5, 1 or 2.
• Ability to undergo neurocognitive assessment at baseline visit, alone or accomparined by a caregiver.
• Ability to understand the clinical trial and give an informed consent

Exclusion Criteria:

• previous therapeutic whole brain irradiation
• Evidence of seizure activity
• Evidence of active dermatological skin disease of the scalp.
• History of malignant tumors.
• Pregnant or breastfeeding.
• If the researcher determines that participation in this study is inadequate because of other findings that are considered clinically important.