Evaluating the Dose to the Lower Posterior Cervical Lymph Nodes and Risk of Supraclavicular Failure in Regional Nodal Irradiation for Breast Cancer Using 3D-Conformal Radiation Therapy and Intensity Modulated Radiation Therapy

Abstract

Regional nodal irradiation (RNI) reduces the risk of loco-regional and distant recurrences, as well as breast cancer mortality in axillary node-positive breast cancer. Recently, the use of more conformal techniques such as intensity modulated radiotherapy (IMRT) have increased in order to better spare normal tissues and organs-at-risk. More conformal radiation to nodal targets has resulted in questions regarding the RTOG consensus guideline definitions of the supraclavicular (SCL) region and in particular whether it should routinely include the lower posterior cervical nodes (level Vb). We aimed to quantify the dose delivered to the level Vb lymph nodes using 3DCRT and IMRT for RNI and whether an increase in failures in the level Vb lymph nodes occur with more conformal treatment. We implemented IMRT for RNI in April 2013, so studied eligible cases of RNI from 4/2013-12/2016 excluding those with SCL lymph nodes prior to radiation, metastatic disease, inoperable and bilateral disease. The following nodal targets were routinely contoured for RNI planning per RTOG consensus atlas: axilla CTV&PTV, SCL CTV&PTV, internal mammary CTV&PTV. IMRT was used when heart and lung dose constraints could not be met with 3DCRT. For this analysis, level Vb was retroactively contoured using RTOG consensus guidelines for Head and Neck nodal levels. Mean dose to level Vb was obtained using dose volume histograms and the t-test was used to compare differences in mean dose between the IMRT and 3DCRT patients, p<0.05 considered significant. Charts were reviewed for recurrence events. We identified 251 eligible patients, 169 (67.3%) treated with 3DCRT and 82 (32.7%) treated with IMRT. The mean dose to the level Vb lymph nodes was 45.8Gy (± 10.4Gy) for 3DCRT and 30.2Gy (± 11.0Gy) for IMRT, p <0.0001. With a median follow-up of 27.7 months (29.6 months 3DCRT; 21.3 months IMRT), 25 patients (10%) developed a recurrence (14 3DCRT; 11 IMRT) at a median time of 16.6 months (17.9 months 3DCRT; 15.6 months IMRT). Recurrences included 5 local (2%), 5 regional (2%) and 21 distant (8.4%). Of the 5 regional recurrences, 4 involved the SCL (2 3DCRT; 2 IMRT); 1 was isolated, 3 also had other loco-regional + distant failures. .The 4 SCL recurrences were triple negative in 2 (50%) and all initially had ≥5 axillary lymph nodes positive. The one isolated SCL recurrence was partially in Level Vb and treated with 3DCRT We found that IMRT results in a significantly lower dose to level Vb compared to 3DCRT but was not associated with an increase in SCL failures in the level Vb/SCL region. SCL recurrences occurred in those that had many nodes positive and were accompanied by failure at other/ distant sites. This study does not support routinely changing the border of the SCL volume to include level Vb.