Alzheimer's Disease (AD) is the most frequent neurodegenerative disease associated with dementia, with a constantly increasing prevalence associated with an aging population. Amyloid deposition is considered the first molecular event occurring in AD: as already showed in an animal model, a low-dose radiotherapy (RT) course is capable of reducing AD-associated amyloid-β plaques and improve cognitive function. This pilot study wishes to investigate in 10 patients with a diagnosis of prodromal or early probable AD and with evidence of amyloid pathology the effectiveness of a short course low dose RT radiotherapy to reduce amyloid deposits in the human brain using molecular imaging (18F-Florbetapir) to show the effectiveness of the treatment on the specific target.

Inclusion Criteria:

• Ability to understand the clinical trial and give an informed consent
• Clinical diagnosis of prodromal AD, or mild or moderate AD
• Ability to undergo neurocognitive assessment at baseline visit, alone or accompanied by a caregiver
• Amyloid PET scan positivity
• Ability to follow the 5-days RT regiment, alone or accompanied by a caregiver

Exclusion Criteria:

• Inclusion in another disease modifying clinical trial
• Previous therapeutic brain irradiation
• Evidence of vascular cognitive impairment on Magnetic Resonance Imaging (MRI) (Fazekas score >1 and Wahlund score >=10/30)
• Oncologic disease (excluding skin cancer) active or in remission from less than 5 years
• Evidence of substance abuse (alcohol and/or other drugs) with a dependence during the previous 12 months (DSM-IV criteria)
• Presence of subdural hygroma's, subdural hematomas or hydrocephalus
• Significant psychiatric comorbidity as assessed during the clinical evaluation by the neurologist/geriatrician in charge
• Active or recent (within 3 months) cerebral infection/haemorrhage
• Immunocompromised status
• Prior history of seizure
• Dermatological skin disease of the scalp
• Women who are pregnant or breast feeding or who intend to become pregnant during the course of the study;
• Lack of safe contraception, defined as: female participants of childbearing potential, not using and not willing to continue using a medically reliable method of contraception for the entire study duration, such as oral, injectable, or implantable contraceptives, or intrauterine contraceptive devices, or who are not using any other method considered sufficiently reliable by the investigator in individual cases;