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Incidental Radiation Exposure to the Internal Mammary Lymph Nodes in Breast Cancer Patients Undergoing
Vishwadeep Mishra1, Shashank Shekhar1, Sudeep Bisht2
1Department of Radiation Oncology, All India Institute Of Medical Sciences, Gorakhpur, Uttar Pradesh, India.
Background:
Breast cancer (BC) remains the most common malignancy among Indian women, with Stage III being the most frequent at diagnosis. While radiation therapy (RT) plays a pivotal role in the adjuvant treatment of breast cancer, the inclusion of internal mammary lymph nodes (IMLNs) in the radiation field remains controversial due to potential cardiopulmonary toxicity. However, the extent of incidental radiation to the IMLNs, especially with forward planning intensity-modulated radiation therapy (IMRT), remains under-explored.
Objective:
This study aimed to evaluate the incidental radiation dose received by the IMLNs in patients with leftsided breast cancer treated with forward planning IMRT.
Materials And Methods:
A total of 36 left-sided breast cancer patients, aged 35-60 years, who underwent modified radical mastectomy followed by adjuvant RT using IMRT, were retrospectively analyzed. CT-based planning and contouring were performed according to RTOG guidelines, with IMLNs contoured retrospectively using Jetwa et al.'s method. Dosimetric parameters for the planning target volume (PTV) and IMLNs were extracted and analyzed using dose-volume histograms. Statistical comparisons were made using the dependent Student's t-test.
Results:
The PTV received effective radiation coverage with a mean D95 of 38.47 Gy and a mean Dmean of 40.10 Gy. The IMLNs, although not directly targeted, received significant incidental radiation, with a mean D95 of 8.49 Gy, D50 of 21.59 Gy, and Dmean of 21.40 Gy. The maximum dose to the IMLNs (Dmax) reached 38.14 Gy. Comparative analysis revealed statistically significant differences in both Dmax and Dmean between PTV and IMLNs (p = 0.004 and p < 0.001, respectively).
Conclusion:
Forward planning IMRT provides substantial incidental radiation exposure to the IMLNs, which may have therapeutic implications in reducing recurrence risk. However, this exposure also necessitates careful consideration of potential long-term toxicities to adjacent organs. Further prospective studies are warranted to evaluate the clinical outcomes associated with incidental IMLN irradiation.
