Coverage of regional lymphatic drainage in helical IMRT for breast cancer
Results of the ACOSOG Z0011 trial suggest that in patients with breast cancer, non-palpable lymphadenopathy and 1 – 2 metastatic sentinel lymph nodes, sentinel lymph node biopsy yields comparable results to axillary lymph node dissection if followed by tangential adjuvant radiotherapy of the breast. Tangential radiotherapy has thus been incorporated as a prerequisite for the abandonment of axillary lymph node dissection in these patients. The degree to which the axillary and other lymphatic drainage is covered by intensity-modulated radiotherapy has not been reported.
We selected 5 consecutive patients from the IMRT-MC2-study, a randomised trial comparing 3D-conformal radiotherapy with a sequential boost to intensity-modulated radiotherapy with a simultaneous integrated boost. Axillary lymph node levels I-III, internal mammarian and periclavicular lymphatic drainage were retrospectively contoured and dosimetric parameters were analyzed. All patients were treated with helical tomotherapy up to a dose of 50,4 Gy for the whole breast and 64,4 Gy for the boost in 28 fractions using 6 MV-photons.
Mean doses to axillary lymph node levels I-III, internal mammarian and periclavicular lymphatic drainage were 33,2 Gy, 21,1 Gy, 8,6 Gy, 28,1 Gy and 7,1 Gy. This corresponds to a relative coverage of 66,9%, 41,8%, 17,1%, 55,7% and 14,1%.
In this exploratory analysis, axillary lymph node levels and internal mammarian lymphatic drainage received radiation doses using helical intensity-modulated radiotherapy that are comparable to those published for tangential radiotherapy for breast cancer.