Inclusion Criteria:  Patients aged 20-80 years, with lung cancer receiving thoracic radiotherapy in NTUH, from February 2020 to December 2024.  Exclusion Criteria:  The age is less than 20 years old or older than 80 years old. Unstable clinical condition, unable to maintain apnea for 15 second, and history of prior adverse reaction to xenon. Renal insufficiency patients. Claustrophobia Those who are pregnant.