With strict immobilisation, image-guidance and 6-DOF correction, our current practice of applying 3-mm planning margins for target volumes and critical structures appears safe. Lower image-guidance action thresholds plus verification with end-to-end testing would be recommended before further reducing margins.

Introduction Various techniques for whole breast radiation therapy (WBRT) have been reported to increase dose to contralateral tissues. Heart dose is of critical importance as there is no apparent dose threshold below which there is no risk. The aim of this study was to compare planning techniques for WBRT that achieves the best target dosimetry and lowest organ at risk (OAR) dose. Methods Thirty early‐stage whole breast patient datasets, 15 each left‐ and right‐sided cases, were retrospectively selected. Five techniques were generated for each data set: three‐dimensional conformal radiation therapy (3DCRT), hybrid intensity modulated radiation therapy (HYI), hybrid volumetric modulated arc therapy (VMAT) – (HYV), reduced arc VMAT – bowtie (BT), and BT flattening filter free (FFF) – (BTFFF). Plan goals and OARs were evaluated and compared between techniques. Results BT had the highest median conformity index (CI) values (0.82, IQR: 0.80–0.85 left and 0.83, IQR 0.80–0.86 right). BT recorded lower mean heart doses (median value 1.19Gy, IQR: 0.90–1.55), and BTFFF recorded lower heart V2.5 Gy , V5 Gy ; median 3.96% (IQR: 2.90–6.80) and 0.90% (IQR: 0.50–1.50) respectively for left‐sided patients. There was a statistically significant difference in all ipsilateral lung measures, (p < 0.001) with BTFFF producing significantly lower doses across all measures: mean, V5 Gy , V10 Gy and V20 Gy . Conclusion Overall BT and BTFFF techniques produced lower OAR doses and equivalent PTV coverage for WBRT. BT and BTFFF techniques increased contralateral lung and breast doses; however, these were within prescribed tolerances and comparable to results published in the literature.