Session Item

Stereotactic ablative body radiotherapy (SABR) is a well-tolerated and effective treatment for patients with early-stage, non-small cell lung cancer (NSCLC) and standard treatment option for inoperable, non-ultra central tumours. There is increasing evidence supporting the use of SABR in operable patients too. We aimed to analyse clinical outcomes of patients treated with SABR and evaluate clinical, pathological and dosimetric factors that may influence outcomes.

Patients with early stage NSCLC treated with SABR between September 2012 and December 2016 were included in this study and followed up until January 2021. Patient demographics, tumour characteristics, radiotherapy planning dosimetric parameters, tumour recurrence and survival data were collected from electronic patient record systems. Descriptive statistics were performed and SPSS software was used for analysing clinical outcomes.

n = 89. Median age 74 years (50 - 90), 49.5% of whom were male and 50.5% were female. Figure 1 summarises demographics of patients and tumour characteristics. 98.8% of patients had T1-2 tumours and 89.9% underwent SABR with 55Gy/5# fractionation.

Dosimetric data analysis showed that the mean planning target volume (PTV) (cc) was 26.6 and the median was 21.5. In subgroup analysis, patients treated with 55Gy/5# and 60Gy/8#, the median PTV was 48.1cc and 23.08cc respectively. The PTV was larger in range and larger on average in those treated with 5 fractions (mean PTV 26.6cc) as opposed to those treated with 8 (mean PTV 25.3cc). The median values for R100, R50, and D2cm were 1.1 (0.21 - 1.63), 6 (4.1 - 13.9) and 31.4 Gy (range 21.1 - 45.18). The median mean lung dose and V20 were 3.3 Gy (1.68 Gy -  6.3 Gy) and 4.15 % (1.29 % - 8.7 %) respectively. The median PTV maximum and minimum doses (Gy) were 74.85 (19.19 - 83.8) and 47.8 (29.66 - 71.9) respectively. The PTV V90% and PTV V100% doses were 99.9 (30.27 - 100) and 95.015 (20.8 - 99.66).

Patients had an overall median survival of 52.2 months (Kaplan-Meier survival analysis). Patients surviving to <1 year, 1 year, 2 years, 3 years, 4 years and 5 years and 6 years or more being 94.4%, 79.8%, 68.5%, 60.7%, 24.72% and 11.23% respectively.

9% of patients had local, 5.6% had regional and 14.6% had distant recurrent disease, 67% of patients had no recurrence. Of the variables examined, only the PTV volume and PTV minimum dose had an impact on overall survival on both uni- and multi-variate cox proportional analysis (Figure 2).

Figure 1. Patient demographics and tumour characteristics

Figure 2. Uni- and multi-variate cox proportional hazard analysis correlating clinical, pathological and dosimetric variables with outcomes

Our long term results show SABR is an effective treatment for early stage NSCLC with excellent overall survival and recurrence rates comparable to other series. Our study found dosimetric variables influencing survival which may need further exploration and may have clinical relevance.