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Dosimetry, breast cancer, posterior boost, axillary lymph nodes, supraclavicular lymph nodes
Background: The axillary and supraclavicular nodal volume treatment results in improvement of local control and survival after breast conserving surgery (BCS) or modified radical mastectomy (MRM). Studies on the depth of these nodes have questioned the consistent use of standard fields for all patients. This study was done to assess the dose delivery to these lymph nodes with conventional treatment techniques according to body mass index (BMI).
Methods: Twenty six patients with breast cancer undergoing breast surgery were included and computed tomography (CT) simulation was done. Their axillary and supraclavicular nodal volumes were contoured for planning target volume (PTV). Supraclavicular and posterior axillary fields were generated for each patient with digital reconstruction radiography (DRR) technique. Then the dose distribution of the two conventional methods - anterior-posterior field (AP), and anterior field with posterior boost (AP+PA boost) - for total dose of 5000 cGy, was examined with radiotherapy dose plan program. An AP planned field suitable for PTV, was designed and compared to AP+PA boost. The diameter of axilla was measured at the center of AP field in CT scan. Data were analyzed in relationship to BMI.
Results: PTV coverage and excessively irradiating normal tissues (hot points), proved to have significant differences in each method (p < 0.001 to 0.01). Axillary and supraclavicular LNs were in 1.6 to 10 and 0.5 to 6.3 cm depth, respectively. Depth of the prescribed dose, which was gained from planned field, had a significant statistical association with BMI (p < 0.05).
Conclusions: Current standard fields are not appropriate for all patients, because of poor coverage of PTV. To sum up, 3D CT planning is strongly recommended for patients with high BMI.
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