The investigators aim to use xenon-enhanced ventilation computed tomography (CT) to design personalized functional lung avoidance radiotherapy for lung cancer patients who are scheduled to receive lung radiation therapy. The investigators' goal is to optimally protect the lung function of the patients and reduce the incidence of radiation pneumonitis.

There has been an increase in the application of radiation therapy in the treatment of lung tumors; however, the associated side effect, called radiation pneumonitis, can significantly reduce lung function and the quality of life of patients, eventually leading to fatal consequences. The investigators aim to use xenon-enhanced ventilation computed tomography (CT) to design personalized functional lung avoidance radiotherapy for lung cancer patients who are scheduled to receive lung radiation therapy. The investigators' goal is to optimally protect the lung function of the patients and reduce the incidence of radiation pneumonitis.

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.