2948 - Regional Lymph Node Doses from Radiotherapy Regimens for Early Breast Cancer in Randomized Trials Starting 1989-2008
Presenter(s)
F. Holt1, G. Ntentas1,2, S. Darby1, G. Mannu1, P. Poortmans3, T. J. Whelan4, D. Dodwell1, C. W. Taylor1, and F. K. Duane5,6; 1Nuffield Department of Population Health, University of Oxford, Oxford, United Kingdom, 2Guy's and St Thomas' NHS Foundation Trust, London, United Kingdom, 3Iridium Kankernetwerk, Department of Radiation Oncology, Antwerp, Belgium, 4McMaster University, Hamilton, ON, Canada, 5Trinity College, Dublin, Ireland, 6St.Luke's Radiation Oncology Network, Dublin, Ireland
Purpose/Objective(s): The association between regional lymph node dosimetry and survival from early breast cancer is unknown. Recent Early Breast Cancer Trialists' Collaborative Group meta-analysis demonstrated that regional lymph node radiotherapy (RT) for early breast cancer improved breast cancer survival in 7 randomized trials and one study allocating RT according to tumor laterality all starting 1989-2008. Various RT regimens were used in these trials, but few estimates of doses to lymph node clinical target volumes (CTVs) were made because these trials were mostly conducted prior to the routine use of standardized lymph node contouring guidelines, CT-based RT planning, and trial quality assurance. We estimated radiation doses to modern definitions of lymph node CTVs from all regional lymph node RT regimens within these trials. The aim was to place the clinical evidence from the meta-analysis into the context of current regional lymph node RT protocols.
Materials/Methods: First, published regional lymph node RT regimens were systematically described, categorized by the beam types and arrangements of RT fields targeting the axillary, supraclavicular and internal mammary lymph nodes, and reconstructed on a CT planning scan selected to represent average sternal anatomy. Second, average doses to lymph node CTVs as defined by ESTRO, RADCOMP and RTOG guidelines were estimated for each category of RT regimens. Doses from each RT regimen were weighted by the number of patients estimated to have received it.
Results: Thirty-seven RT regimens were identified. Thirty-five internal mammary lymph node (IMN) regimens were applied to an estimated 4979 patients within six trials. Eight different categories of beam type and arrangement targeting the IMNs were used. Overall average ESTRO IMN CTV V80% was 76.8%. This ranged from 41.4 to 93.2% for the different beam types and arrangements. RADCOMP IMN CTV V80% was 77.2% (range 43.6 to 93.5%) and RTOG IMN CTV V80% was 74.5% (range 39.9 to 87%). From 29 supraclavicular lymph node regimens (3986 patients, 4 trials, 3 categories of beam type and arrangement), average ESTRO supraclavicular CTV V80% was 94.4% (range 92.6 to 99.1%). For RADCOMP and RTOG results were 76.4% (range 68.0 to 78.7%). From 9 regimens targeting axillary level 3 lymph nodes (2629 patients, 3 trials, 2 categories of beam type and arrangement), average ESTRO axillary level 3 lymph node CTV V80% was 95.1% (range 80.3 to 99.2%). For RADCOMP and RTOG averages were 95.7% (range 82.1 to 99.4%) and 97.1% (range 87.0 to 99.9%) respectively. Regimens targeting axillary lymph nodes levels 1 and 2 could not be categorized as these lymph nodes were at least partly covered by breast/chest wall fields.
Conclusion: Our estimated doses to modern lymph node volumes from RT regimens used in these studies are likely lower than those achieved today. Current regional lymph node RT regimens likely provide greater relative survival benefits than those previously reported.