A single center, single arm, open-label, non-controlled, non-randomized imaging trial

All patients will undergo 3 [18F]F-AraG PET scanning procedures according to the institutional protocols

To assess the relative change in uptake of [18F]F-AraG in tumor lesions upon radiotherapy.

o Histologically confirmed NSCLC, melanoma, esophageal, or breast cancer
o Ongoing immunotherapy using an anti-PD-(L)1 agent
o Planned to be treated with high dose (24Gy) radiotherapy per clinical indication
o Be willing and able to provide written informed consent for the trial.
o Have a performance status of 0-2 on the ECOG Performance Scale
o Be above 18 years of age on day of signing informed consent.

o Subjects with a condition requiring systemic treatment with either corticosteroids (> 10 mg daily prednisone equivalent) or other immunosuppressive medications within 14 days of day 0. Inhaled or topical steroids, and adrenal replacement steroid >10 mg daily prednisone equivalent, are permitted in the absence of active autoimmune disease.
o Psychiatric or substance abuse disorders that would interfere with cooperation with the requirements of the trial.
o Patient is pregnant or breastfeeding or expecting to conceive within the projected duration of the trial, starting with the screening visit through 12 weeks after the last administration of [18F]F-AraG