Stage I non-small cell lung cancer (NSCLC) is curable and surgery is considered the standard of care for fit, good performance status patients. However, a high proportion of patients with stage 1 NSCLC are elderly and/or have medical co-morbidities and are therefore at higher risk of surgical complications. The optimal treatment for these patients is unknown. SABR may be an equally appropriate treatment but this need to be formally assessed. Funded by the NIHR Research for Patient Benefit, SABRtooth is a UK multi-centre, two-group individually randomised controlled feasibility study of patients with peripheral stage I non-small cell lung cancer considered at higher risk from surgery. In total, 54 patients are planned to be recruited from 4 treatment sites and 2 referral sites. This study aims to determine the feasibility and acceptability of performing a largescale definitive randomised phase III trial comparing surgery with stereotactic ablative radiotherapy (SABR). The qualitative substudy is an exploration of the reasons for nonparticipation in the SABRTooth trial. As the two treatments are very different, patients may have a strong preference for either surgery or SABR, or may feel uncomfortable to have a decision between such distinct options taken out of their hands. Understanding why patients choose not to participate or do not take up their treatment allocation will be crucial in demonstrating that recruiting to a larger scale phase III trial is feasible. We will explore what patients, who have declined particpation in the study or who intiailly consented but subsequently fail to take up their randomimsed treatment arm, understand, perceive and feel about, how the SABRTooth trial was presented to them and their expectations of study burden.

Inclusion Criteria:

1. Primary tumour characteristics.

2. Peripherally located tumour as defined in the RTOG 0236 study and UK SABR Consortium guidelines. This states that the tumour must be more than 2cm in axial diameter from a major airway.

   • This includes the trachea, carina, right and left main bronchus and extends to the bifurcation of the right upper, right middle, right lower, left upper and left lower lobe bronchioles

3. No evidence of hilar or mediastinal lymph nodes involvement.

   • Any hilar or mediastinal lymph nodes that are either
   • PET positive or >1cm in axial dimension must be sampled by mediastinoscopy, endobronchial ultrasound or oesophageal endoscopic ultrasound and demonstrate negative cytology and/or pathology

4. Local lung cancer MDT consensus opinion that patient is considered suitable for either surgical resection or SABR treatment AND also to be at higher risk complications from surgical resection

5. Age ≥ 18

6. Female patients must satisfy the investigator that they are not pregnant (negative pregnancy test within 72hrs of surgery of day 1 surgery/SABR), or are not of childbearing potential

7. Able and willing to provide written informed consent

Exclusion Criteria:

1. Previous radiotherapy within the planned treatment volume.
2. History of clinically significant diffuse interstitial lung disease
3. Any history of concurrent or previous invasive malignancy that in the opinion of the investigator could impact on trial outcomes
4. Clinical or radiological evidence of metastatic spread
5. History of psychiatric or addictive disorder or other medical condition that, in the opinion of the investigator, would preclude the patient from meeting the trial requirements
6. Previous systemic therapies, including targeted and experimental treatments, for their current lung cancer diagnosis