Trans Tasman Radiation Oncology Group 20.01 CHEST-RT (Chemotherapy and Immunotherapy in Extensive Stage Small cell with Thoracic Radiotherapy) is a single-arm, open-label, prospective, multicentre phase II trial study that aims to establish the safety, feasibility and describe the efficacy of incorporating thoracic radiotherapy (TRT) (concurrent or sequential) to chemotherapy and immunotherapy in patients with extensive-stage small-cell lung cancer.

A single arm of up to 30 evaluable participants given TRT concurrent or sequentially with chemoimmunotherapy will be enrolled. Participants should commence radiotherapy with cycle 3 or cycle 4 of chemotherapy. Those not suitable for concurrent radiotherapy due to large tumour volumes may receive sequential radiotherapy. Accounting for a 15% non-evaluable rate, up to 35 participants will be enrolled. An independent data and safety monitoring committee will review the data and assess safety and feasibility. Progression to a phase III trial would be considered feasible if ≤20% of participants experienced ≥grade 3 oesophageal toxicity and ≤10% experienced ≥grade 3 pneumonitis. This approach would be considered feasible if there is ≤20% treatment discontinuation of systemic therapy secondary to radiation toxicities and ≥75% of participants have tumour volumes that can be safely treated to a dose of 30 Gy in 10 fractions. The primary outcome of the trial is safety and feasibility, and survival and responses will be assessed as secondary endpoints. A predefined subgroup analysis of toxicity will be performed on group 1 (concurrent TRT) versus group 2 participants (consolidation TRT).

This study was approved by the Peter MacCallum Human Research Ethics Committee (HREC/73189/PMCC-2021). The protocol, technical and clinical data will be disseminated by conference presentations and publications. Any modifications to the protocol will be formally documented by administrative letters and will be submitted to the approving HREC for review and approval.

Australian New Zealand Clinical Trials Registry (ACTRN12621000586819) and ClinicalTrials.gov identifier (NCT05796089).