Dosimetric differences between local failure and local controlled non-small cell lung cancer patients treated with stereotactic body radiotherapy: A matched-pair study

Introduction: Concerns were raised about the accuracy of pencil beam (PB) calculation and potential underdosing of medically inoperable non-small cell lung cancer (NSCLC) treated with stereotactic body radiation therapy (SBRT). From our institutional series, we designed a matched-pair study where each local failure and controlled patient was matched based upon several clinical factors, to investigate the dose difference between the matched-pair. Methods: Eighteen pairs of NSCLC patients, treated with 50 Gy in five fractions, were selected. These patients were matched based on treatment intent, tumour size, histology and clinical follow-up. All PB calculated clinical plans were retrospectively recalculated with a MC algorithm. The D₉₉ and D_{M ean} of the gross tumour volume (GTV) and D₉₅ and D_{M ean} of the planning tumour volume (PTV) from PB and Monte Carlo (MC) calculation were compared between local failures and controls using the Mann–Whitney test. Results: The mean PB calculated D95 of PTV was 50.4 Gy for both failures and controls (P = 0.85), indicating no planning differences between the groups. From MC calculations, the mean (±SD) of GTV D₉₉, GTV D_{M ean}, PTV D₉₅, PTV D_{M ean} were 47.6 ± 2.6/46.3 ± 2.4, 50.4 ± 2.1/49.8 ± 1.6, 44.4 ± 2.7/43.6 ± 3.1, 48.7 ± 2.4/48.2 ± 2.4 Gy for failure/controlled groups, respectively, and there was no significant difference between two groups (all P > 0.1). The dose differences between MC and PB calculations were in agreement with other literatures and there was no significant difference between two groups. Conclusions: While PB algorithms may overestimate tumour doses relative to MC algorithms, our matched-pair study did not find dose differences between local failure and local controlled cases.