Definitive radiotherapy is one of the important methods for inoperable locally advanced lung cancer. The recommended dose for definitive radiotherapy is 60-70Gy, and the optimal dose is still uncertain. Residual lesion after radiotherapy is a risk factor for recurrence. High doses to targeted tumor areas can effectively improve the local control rate, while minimizing toxic side effects. The regression pattern of primary lesions in lung caner after radiotherapy has not been clarified. This study intends to retrospectively collect clinical data of lung cancer patients with definitive radiotherapy, and explore the pattern of tumor regression after radiotherapy. It will help optimize the radiotherapy plan for lung cancer, so as to improve the efficacy and prognosis.

This study intends to retrospectively screen and include participants according to inclusion and exclusion criteria, and collect the clinical data of participants by previous medical records. Imaging tools will be used to quantify changes in the spatial location, diameter and volume of target lesions to evaluate tumor regression rate and radiotherapy efficacy, and to explore tumor regression pattern and establish model. In addition, the relationship between tumor regression rate, incidence of adverse radiation events, prognosis and related factors will be analysed.

Inclusion Criteria:

1. Age ≥18 years old;
2. Stage II-III lung cancer with a clear pathological diagnosis report or medical record, not undergoing surgery before radiotherapy;
3. The primary lung lesion received definitive radiotherapy (defined as conventional fractionation radiotherapy with dose ≥50Gy, stereotactic radiotherapy with biologically effective dose ≥100Gy);
4. The target lesion of the lung receiving radiotherapy can be measured;
5. Imaging data can be obtained before and after radiotherapy;
6. Complete radiotherapy as planned, or the actual received dose has reached the defined definitive dose.

Exclusion Criteria：

1. Before radiotherapy, the primary lesion of the lung had received local treatment such as surgery or ablative treatment;
2. The radiotherapy plan was not completed, and the actual dose received did not reach the definitive dose (defined as conventional fractionation radiotherapy with dose <50Gy, stereotactic radiotherapy with biologically effective dose <100Gy)；
3. Required imaging data cannot be obtained;
4. Other conditions considered by the investigator to be inappropriate for enrollment.

Stage II-III lung cancer patients who have received definitive radiotherapy.

Research data including study protocol and statistical analysis plan will be shared after the study is completed and the research results are published.

The data will become available starting 1 year and ending 4 years following article publication.

The data will be made available upon request for researchers who provide a methodologically sound proposal. The data will be accessible for non-commercial research purposes only and will be used to explore additional hypotheses related to the study's objectives.