Purpose: To demonstrate the superior quality of the dose distribution given by a novel axillary boost planning technique for nodal coverage during breast/chestwall radiotherapy
Methods: Six breast cancer patients previously planned with the traditional monoisocentric posterior axillary boost (PAB) technique were replanned with a volumetric axillary boost (VMAB) to complement the current 3D tangent and supraclavicular (SCLV) fields. The at-risk nodal volumes had been delineated during the planning process as well. The dose distributions were then compared for major differences with the key endpoints being the nodal region dose volume histograms (DVH), ipsilateral lung DVHs, and maximum dose hotspot within the plan. The original PAB plans were designed balancing the tradeoff off nodal dose coverage and overall hotspot while the VMAB plans optimized both. The ideal hotspot was considered < 110% of the whole breast/cw dose and the ideal nodal coverage was considered D95 = 95-100% of 45-50 Gy depending on the original patient prescription.
Results: Due to the limited sample size, no statistically significant differences were observed between the traditional 3D PAB technique and VMAB. Two statistically significant differences (p < 0.05) were observed for lymph node dose coverage for level 1 V95% and level 2 V100%, where the VMAB increased coverage by a mean value of 14.9% and 30.3%, respectively. Level 2 V95%, was not significant (p = 0.053) with a mean increase of 20.7%, but may become significant with a higher sample size. Differences in maximum dose, level 3 lymph node dose coverage, and lung doses were not found to be close to significance.
Conclusion: This novel planning technique, VMAB, results in significantly improved dose coverage of nodal regions while avoiding increase of undesirable hotspots and/or lung dose. Though implemented clinically, future work will confirm these findings with a larger sample size to discern true statistical certainty.