Pifenidone Prophylactic Therapy for Radiation Lung Injury in Patients Who Have Previously Received Immune Checkpoint Inhibitors

This study is testing whether pirfenidone — a drug typically used for lung scarring — can prevent or reduce radiation-related lung damage in lung cancer patients who have previously received immunotherapy (checkpoint inhibitor drugs). **You may be eligible if:** - You are 18 or older with lung cancer - You have received at least 2 cycles of immunotherapy (PD-1 or PD-L1 inhibitor drugs) within the past 6 months - You are in good general health (ECOG score 0 or 1) - You are expected to live at least 3 months - Your organ function tests are within acceptable ranges **You may NOT be eligible if:** - You have an active autoimmune disease requiring treatment (such as rheumatoid arthritis or type 1 diabetes) - You have active hepatitis B, hepatitis C, tuberculosis, or HIV - You have had a solid organ or bone marrow transplant - You are allergic to pirfenidone - You are participating in another drug trial - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.