Abscopal Effect from the Low-dose Radiotherapy in Polymetastatic Cancer Patients Receiving Stereotactic Radiotherapy

Inclusion Criteria:

• Patients who can provide their written informed consent

• Age ≥19 years

• Patients with histologically confirmed primary solid (irrespective of the status ofthe primary tumor)

• Patients with ECOG performance status 0-2

• Patients planning stereotactic body radiotherapy (three fractions) for extracranialmetastases

• Based on RECIST v1.1, patients with at least one extracranial measurable lesionother than SBRT lesions

• Patients with one or more measurable lesions, which are not suitable for SBRT orpalliative radiotherapy and can be considered for LDRT (bone metastasis is notindicated for LDRT)

• Patients with hematologic function suitable for radiotherapy (absolute neutrophilcount ≥1,500/mm^3, hemoglobin ≥9 g/dL, platelet count ≥100,000/mm^3)

• Patients with a life expectancy of 6 months or more according to the researcher'sjudgment

Exclusion Criteria:

• Patients participating in other clinical studies that may affect the efficacy/safetyof this clinical study

• Patients with brain metastasis

• Patients planning SBRT for all measurable lesions due to oligometastasis

• Patients with a history of radiotherapy for extracranial metastases within 3 monthsof the enrollment

• Patients unable to cooperate with stereotactic body radiotherapy

• Patients who are pregnant or planning to

• Patients with advanced or multiple malignancies requiring aggressive treatment (excluding skin cancers other than melanoma or intraepithelial cancer)

• Patients who have received systemic steroid therapy or immunosuppressive therapywithin 2 weeks of enrollment - Patients with an (e.g. allergic disease, radiationpneumonitis, etc.) (The use of steroids for preventive purposes is allowed (e.g., toprevent vomiting during chemotherapy)) active autoimmune disease requiring systemictreatment within the past 2 years, evidence of clinically severe autoimmune disease,or syndrome requiring systemic steroid or immunosuppressive therapy (Patients whoneed intermittent use of bronchodilators, inhaled steroids, or topical steroidinjections, hypothyroid patients on stable hormone replacement therapy, type 1diabetes patients, or patients recovering from childhood asthma/atopic dermatitisare permitted)

• Patients with active infection requiring systemic treatment