PRIME_LUNG: Primary Radiotherapy In MEtastatic Lung Cancer - A Pilot Study

35Gy/5# Central 40Gy/5# Large Tumours \>5cm (non-central) 36Gy/12# or 40Gy/15# Ultracentral lesions 50Gy/5# Peripheral Tumours ≤5cm

Permitted SoC chemoimmunotherapy for squamous patients will include single agent immunotherapy with Pembrolizumab or in combination with Carboplatin or Paclitaxel. Carbo/Paclitaxel/Pembro intravenous infusions are given every 3 weeks for cycle 1-4, followed by ongoing maintainence with Pembrolizumab from Cycle 5. For non-squamous patients, SoC chemoimmunotherapy will include single agent immunotherapy with Pembrolizumab or in combination with Carboplatin or Permetrexed. Carboplatin/Pemetrexed/Pembrolizumab infusions are given every 3 weeks for four cycles followed by maintenance with Pemetrexed/Pembrolizumab from Cycle 5.