Stereotactic ablative body radiotherapy for the palliation of previously untreated head and neck cancer—a biological modelling study

Abstract Introduction: This is a radiobiological modelling study aimed at comparing stereotactic ablative body radiotherapy (SABR) with conventional palliative radiotherapy (CPRT) and curative-dose volumetric-modulated arc therapy (CD-VMAT) in the palliation of patients with previously untreated head and neck cancer. Methods: Three radiotherapy plans were generated for 8 patients with head and neck cancer: SABR, prescribed to 45 Gy in 5 fractions; CPRT, prescribed to 30 Gy in 5 fractions and CD-VMAT, prescribed to 70 Gy in 35 fractions. The tumour control probability (TCP) and normal tissue complication probability for salivary and swallowing function (NTCP saliva and NTCP swallow , respectively) were determined. From those values, the therapeutic ratio, as measured by the uncomplicated tumour control probability (UTCP), was determined. Results: Dosimetric objectives were achieved in all treatment plans. SABR had a higher mean TCP compared to CPRT and CD-VMAT (100% vs 81% vs 93%, p = 0·003). There were no statistically significant differences in the mean NTCPs for salivary or swallowing function (mean NTCP saliva 27% vs 41% vs 36%, p = 0·093 and mean NTCP swallow 9% vs 12% vs 23%, p = 0·093). This resulted in the mean UTCP being statistically significantly higher for SABR plans compared to CPRT and CD-VMAT (66% vs 42% vs 49%, p = 0·004). Conclusion: It is feasible to create SABR plans that satisfy the dosimetric objectives in this study. Based on radiobiological modelling, SABR has superior TCP and similar NTCP, leading to a better therapeutic ratio than CPRT and CD-VMAT.