Abstract
Objective: To investigate the effect of anatomic and technical parameters on the incidental internal mammary lymph node (IMN) irradiation (IIMNI) dose among postmastectomy patients.Methods: We retrospectively delineated the IMN on planning CT images from 138 patients who had undergone postmastectomy radiotherapy (PMRT). We analyzed the IIMNI dose coverage and its relationship with anatomic and technical parameters.Results: The IIMNI mean dose was 32.85 ± 9.49 Gy, and 10 of 138 patients (7.25%) treated with PMRT received ≥45 Gy. In univariate analysis, the body weight, body mass index, body surface area, thoracic transverse diameter (DT), ratio of DT to the thoracic anteroposterior diameter (DAP)(RT/AP), planning target volume of IMN (PTVIMN) included in PTV (IMNin) and the ratio of IMNin to PTVIMN (RIMNin) and PTV posterior border were the parameters affecting IIMNI dose. In multivariate analysis, body weight, RT/AP, and RIMNin were correlative factors that affected IIMNI dose.Conclusions: For patients who underwent PMRT without IMN irradiation (IMNI), there was a wide variety in IIMNI doses. A minority of patients had adequate IIMNI dose coverage, and the higher IIMNI doses were associated with the less body weights and more RIMNin.
Highlights
Irradiation of the chest wall and regional lymph nodes is considered the standard treatment strategy for breast cancer patients with positive axillary lymph nodes (ALNs) after mastectomy or modified radical mastectomy (MRM) due to its recognized success in improving local tumor control and overall survival (OS) [1,2,3,4]
BMI, body mass index; BSA, body surface area; CTV, clinical target volume; PTV, planning target volume; DT, thoracic transverse diameter; DAP, thoracic anteroposterior diameter; SCF, supraclavicular fossa; PTVIMN, planning target volume of Internal mammary lymph nodes (IMNs); IMNin, PTVIMN included in PTV
Our study found significant variability in individual incidental IMNI (IIMNI) dose for patients who accepted postmastectomy radiation therapy (PMRT), and only 7.25% of the patients received a meaningful IIMNI dose when the IMNs were not included in the PTV
Summary
Irradiation of the chest wall and regional lymph nodes is considered the standard treatment strategy for breast cancer patients with positive axillary lymph nodes (ALNs) after mastectomy or modified radical mastectomy (MRM) due to its recognized success in improving local tumor control and overall survival (OS) [1,2,3,4]. Internal mammary lymph nodes (IMNs) irradiation (IMNI) can improve disease-free survival (DFS) and OS in patients with breast cancer, and the mortality risk from ischemic heart disease with IMNI is equal to patients without IMNI [5, 6]. Danish Breast Cancer Cooperative Group (DBCG)-IMN studies, patients with right-sided disease were allocated to the IMNI group, whereas left-sided patients were allocated to the no IMNI group [5]. For the left-sided disease subset, one study that reviewed patients treated at a single institution from 1984 to 2007 showed no significantly increased hazard with IMN radiotherapy in planned three-dimensional conformal radiotherapy (3D-CRT) [7]. Long-term radiotherapy toxicity, especially heart toxicity, should be considered for patients with left-sided breast cancer in whom long-term survival is expected [9]. In the contemporary irradiation techniques era, radiation-induced heart lesions are further lessened, and therapeutic drugs for heart and coronary artery disease are more diversified, so continued follow-up of cardiovascular disease induced by radiotherapy is still needed
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