Static beam tomotherapy as an optimisation method in whole‐breast radiation therapy (WBRT)

INTRODUCTION: TomoTherapy (Accuray, Sunnyvale, CA) has recently introduced a static form of tomotherapy: TomoDirect™ (TD). This study aimed to evaluate TD against a contemporary intensity modulated radiation therapy (IMRT) alternative through comparison of target and organ at risk (OAR) doses in breast cancer cases. A secondary objective was to evaluate planning efficiency by measuring optimisation times. METHODS: Treatment plans of 27 whole‐breast radiation therapy (WBRT) patients optimised with a tangential hybrid IMRT technique were replanned using TD. Parameters included a dynamic field width of 2.5 cm, a pitch of 0.251 and a modulation factor of 2.000; 50 Gy in 25 fractions was prescribed and planning time recorded. The planning metrics used in analysis were ICRU based, with the mean PTV minimum (D(99)) used as the point of comparison. RESULTS: Both modalities met ICRU50 target heterogeneity objectives (TD D(99) = 48.0 Gy vs. IMRT = 48.1 Gy, P = 0.26; TD D(1) = 53.5 Gy vs. IMRT = 53.0 Gy, P = 0.02; Homogeneity index TD = 0.11 vs. IMRT = 0.10, P = 0.03), with TD plans generating higher median doses (TD D(50) = 51.1 Gy vs. IMRT = 50.9 Gy, P = 0.03). No significant difference was found in prescription dose coverage (TD V(50) = 85.5% vs. IMRT = 82.0%, P = 0.09). TD plans produced a statistically significant reduction in V(5) ipsilateral lung doses (TD V(5) = 23.2% vs. IMRT = 27.2%, P = 0.04), while other queried OARs remained comparable (TD ipsilateral lung V(20) = 13.2% vs. IMRT = 14.6%, P = 0.30; TD heart V(5) = 2.7% vs. IMRT = 2.8%, P = 0.47; TD heart V(10) = 1.7% vs. IMRT = 1.8%, P = 0.44). TD reduced planning time considerably (TD = 9.8 m vs. IMRT = 27.6 m, P < 0.01), saving an average planning time of 17.8 min per patient. CONCLUSIONS: TD represents a suitable WBRT treatment approach both in terms of plan quality metrics and planning efficiency.