A. Ismail (Alexandria, Egypt)
Specialized Universal Network of Oncology (SUN)Author Of 1 Presentation
78P - A dosimetric study of the non-intended irradiation to the internal mammary lymph nodes during locoregional radiotherapy to the breast
Abstract
Background
Adjuvant radiotherapy (RT) in breast cancer is an essential part of the local treatment of the breast and regional lymph nodes. Whether the internal mammary lymph nodes (IMNs) should be included in the RT field is controversial due to limited data. The low incidence of IMNs recurrence may be due to the incidental dose received. The aim of this study is to estimate the incidental irradiation dose recieved by IMNs during 3DCRT and whether this dose correlates with IMNs recurrence.
Methods
This retrospective dosimetric study included 137 cases treated at our institution during the year 2016-2017. Inclusion criteria: patients who underwent either MRM or BCS and were candidate to receive adjuvant locoregional radiotherapy (without intended inclusion of IMLNS in the radiotherapy field). For this study, the IMNs was contoured through the topography of the internal thoracic vessels starting cranially at the superior border of the first rib, caudally at the cranial end of the fourth rib. IMNs mean dose (IMDmean), maximum dose (IMN max) and minimum dose (IMN min) were obtained. In addition, the ipsilateral lung volume that received ≥20 Gy (V20), heart mean dose (for patients with left side tumors only), parasternal soft tissue thickness and the distance between the medial tangent field border and the mid-line were measured (both measured at level of the third rib).
Results
In all cases, PTV IM was covered by less than 95% of the prescribed dose. The IMLs mean dose was 28.50% (SD 20.71%) of the prescribed dose. There was no significant difference between the right and left side regarding IMND mean, lung v20 or heart mean dose. Six patients (4.37%) had IMNs recurrences, the IMLs mean dose in all of them was less than 28% of the prescribed dose. IMLs mean dose less than 28% significantly predicted IMLs recurrences (P value=0.05). IMN mean dose significantly correlated with the mean distance between mid line and medial tangent field border (0.8 cm) with P value< 0.0001.
Conclusions
IMN receives considerable incidental dose of radiation. The required dose to prevent against IMN recurrence may be lower than the prescribed dose for other nodal areas. Prospective trials are needed to determine the optimum dose and indication to irradiate IMN.
Legal entity responsible for the study
Alexandria University, Egypt.
Funding
Has not received any funding.
Disclosure
All authors have declared no conflicts of interest.