A dosimetric study to improve the quality of nodal radiotherapy in breast cancer

OBJECTIVES: Field-based planning for regional nodal breast radiotherapy (RT) used to be standard practice. This study evaluated a field-based posterior axillary boost (PAB) and two forward-planned intensity-modulated RT (IMRT) techniques, aiming to replace the first. METHODS: Supraclavicular and axillary nodes, humeral head, brachial plexus, thyroid, and oesophagus were retrospectively delineated on 12 CT scans. Three plans, prescribed to 40.05 Gy, were produced for each patient. Breast plans consisted of field-in-field IMRT tangential fields in all three techniques. Nodal plans consisted of a field-based PAB (anterior and posterior boost beam), and 2 forward-planned techniques: simple IMRT 1 (anterior and posterior beam with limited segments), and a more advanced IMRT 2 technique (anterior and fully modulated posterior beam). RESULTS: The nodal V(90%) was similar between IMRT 1: mean 99.5% (SD 1.0) and IMRT 2: 99.4% (SD 0.5). Both demonstrated significantly improved results (p = 0.0001 and 0.005, respectively) compared to the field-based PAB technique. IMRT 2 lung V(12Gy) and humeral head V(10Gy) were significantly lower (p = 0.002, 0.0001, respectively) than the field-based PAB technique. IMRT 1 exhibited significantly lower brachial plexus D(max) and humeral head V(5), (10), and (15Gy) doses (p = 0.007, 0.013, 0.007 and 0.007, respectively) compared to the field-based PAB technique. The oesophagus and thyroid dose difference between methods was insignificant. CONCLUSIONS: Both IMRT techniques achieved the dose coverage requirements and reduced normal tissue exposure, decreasing the risk of radiation side effects. Despite the increased cost of IMRT, compared to non-IMRT techniques (1), both IMRT techniques are suitable for supraclavicular and axillary nodal RT. ADVANCES IN KNOWLEDGE: Forward-planned IMRT already resulted in significant dose reduction to organs at risk and improved planning target volume coverage.(1) This new, simplified forward-planned IMRT one technique has not been published in this context and is easy to implement in routine clinical practice.