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

Abstract

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 (D₉₉ ) used as the point of comparison.

Results: Both modalities met ICRU50 target heterogeneity objectives (TD D₉₉ = 48.0 Gy vs. IMRT = 48.1 Gy, P = 0.26; TD D₁ = 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 D₅₀ = 51.1 Gy vs. IMRT = 50.9 Gy, P = 0.03). No significant difference was found in prescription dose coverage (TD V₅₀ = 85.5% vs. IMRT = 82.0%, P = 0.09). TD plans produced a statistically significant reduction in V₅ ipsilateral lung doses (TD V₅ = 23.2% vs. IMRT = 27.2%, P = 0.04), while other queried OARs remained comparable (TD ipsilateral lung V₂₀ = 13.2% vs. IMRT = 14.6%, P = 0.30; TD heart V₅ = 2.7% vs. IMRT = 2.8%, P = 0.47; TD heart V₁₀ = 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.

Keywords: Breast cancer; TomoDirect; dosimetry; radiation therapy; tomotherapy.