Evaluation of Microscopic Tumour Extension in Localized Stage Non-Small-Cell Lung Cancer for Stereotactic Radiotherapy Planning

SIMPLE SUMMARY: Stereotactic radiotherapy for localised stage non-small-cell lung carcinoma is an alternative indication for patients who are inoperable or refuse surgery. A study showed that the microscopic tumour extension of non-small-cell lung carcinoma varied according to the histological type, which allowed us to deduce adapted margins for the clinical target volume. The objectives of our retrospective study are. The objective of our study is to measure the microscopic tumour extension of T1N0 or T2aN0 primary lung tumors who underwent surgery. The margin required to cover the microscopic tumour extension with a 95% probability is 4.4 mm and 2.9 mm for squamous cell carcinoma and adenocarcinoma, respectively. Multivariate analysis showed a statistically significant relationship between the maximum microextension distance and size with the shrinkage coefficient. ABSTRACT: Background: Stereotactic radiotherapy for localised stage non-small-cell lung carcinoma (NSCLC) is an alternative indication for patients who are inoperable or refuse surgery. A study showed that the microscopic tumour extension (ME) of NSCLC varied according to the histological type, which allowed us to deduce adapted margins for the clinical target volume (CTV). However, to date, no study has been able to define the most relevant margins for patients with stage 1 tumours. Methods: We performed a retrospective analysis including patients with adenocarcinoma (ADC) or squamous cell carcinoma (SCC) of localised stage T1N0 or T2aN0 who underwent surgery. The ME was measured from this boundary. The profile of the type of tumour spread was also evaluated. Results: The margin required to cover the ME of a localised NSCLC with a 95% probability is 4.4 mm and 2.9 mm for SCC and ADC, respectively. A significant difference in the maximum distance of the ME between the tumour-infiltrating lymphocytes (TILs), 0–10% and 50–90% (p < 0.05), was noted for SCC. There was a significant difference in the maximum ME distance based on whether the patient had chronic obstructive pulmonary disease (COPD) (p = 0.011) for ADC. Multivariate analysis showed a statistically significant relationship between the maximum microextension distance and size with the shrinkage coefficient. Conclusion: This study definitively demonstrated that the ME depends on the pathology subtype of NSCLC. According to International Commission on Radiation Units and Measurements (ICRU) reports, 50, 62 and 83 CTV margins, proposed by these results, should be added to the GTV (Gross tumour volume). When stereotactic body radiation therapy is used, this approach should be considered in conjunction with the dataset and other margins to be applied.