Is high-dose stereotactic body radiotherapy (SBRT) for stage I non-small cell lung cancer (NSCLC) overkill? A systematic review

Background and purpose: For stereotactic body radiotherapy (SBRT), typically a scheme of 60 Gy in 3-8 fractions is applied, producing local tumour control rates around 90%. The dose specification is in one point only and ignores possible underdosages at the edge of the planning target volume (PTV). We investigated the doses at the edge of the PTV and correlated this with local tumour control with the aim to shed light on the radiation dose needed to eradicate stage I NSCLC. Materials and methods: Published data on the freedom from local progression (FFLP) data from SBRT and accelerated high-dose conventional radiotherapy series for stage I NSCLC with a follow up of at least 30 months were included. The EQD(2,T) was calculated from the dose at the periphery of the PTV. Results; Fifteen studies for SBRT (1076 patients) showed a median FFLP of 88.0 +/- 10.4% with a median EQD(2,T) of 76.9 +/- 17.4 Gy. The median FFLP was 87.6 +/- 6.0% for the accelerated schedules with an EQD(2,T) of 86.9 +/- 39.1 Gy, respectively. No significant relation was found between FFLP and the EQD(2,T) (p = 0.23). Conclusions: Several fractionated and accelerated schedules with equal biological doses achieve the same tumour control rates as SBRT. Lower, but more uniform doses to the whole PTV may be sufficient to achieve similar control rates, with the possibility to deliver SBRT in adapted schedules, beneficial to centrally located tumours in the vicinity of critical structures like the oesophagus and great vessels.