Aims: To determine (1) if the lower border of a standard anterior radiotherapy field to the supraclavicular fossa matches the upper limit of level II/III axillary dissection; and (2) whether standard lung blocks in patients prescribed axillary radiotherapy shield target axillary tissue in women with breast cancer.
Materials and methods: Between 1999 and 2001, 30 women with breast cancer undergoing level II/III axillary dissection had titanium clips placed to define the upper and medial limits of surgery. At radiotherapy planning, a supraclavicular fossa field similar to that described in the UK START trial protocol was simulated, with head twist applied to position the inferior field border (50% isodose) 1 cm below and parallel to the lower border of the clavicle. The field position was recorded on X-ray film. The location of the most superior axillary clip was measured in relation to this inferior field border on the X-ray film. The location of the most medial clip was measured in relation to the lung/chest wall interface.
Results: The median distance between the most superior clip and the inferior border of the supraclavicular field was 3.6 cm (0.8-6.9 cm), representing significant underlap in all cases. In addition, five out of 30 (17%) patients had surgical clips over 2.0 cm medial to the lung/chest wall interface, suggesting that medial lymph nodes in an undissected axilla would be shielded by standard lung blocks in patients prescribed axillary radiotherapy.
Conclusion: Current standard radiation fields to the supraclavicular fossa, as applied in this study, leave apical axillary lymph nodes untreated in a high proportion of patients. Standard lung shielding, as applied in this study to patients simulated for axillary radiotherapy, protect medial axillary lymph nodes in a few patients. A change in practice is recommended.