Incidental dose distribution to locoregional lymph nodes of breast cancer patients undergoing adjuvant radiotherapy with tomotherapy - is it time to adjust current contouring guidelines to the radiation technique?

Michael Mayinger,Stephanie Elisabeth Combs,Daniel Habermehl,Hendrik Dapper,Severin Kampfer,Kai Joachim Borm,Markus Oechsner,Constantin Dreher,Marciana-Nona Duma

doi:10.1186/s13014-019-1328-7

Abstract

Purpose/objective(s)Along with breast-conserving surgery (BCS), adjuvant radiotherapy (RT) of patients with early breast cancer plays a crucial role in the oncologic treatment concept. Conventionally, irradiation is carried out with the aid of tangentially arranged fields. However, more modern and more complex radiation techniques such as IMRT (intensity-modulated radio therapy) are used more frequently, as they improve dose conformity and homogeneity and, in some cases, achieve better protection of adjacent risk factors. The use of this technique has implications for the incidental- and thus unintended- irradiation of adjacent loco regional lymph drainage in axillary lymph node levels I-III and internal mammary lymph nodes (IMLNs). A comparison of a homogeneous “real-life” patient collective, treated with helical tomotherapy (TT), patients treated with 3D conformal RT conventional tangentially arranged fields (3DCRT) and deep inspiration breath hold (3DCRT-DIBH), was conducted.Materials/methodsThis study included 90 treatment plans after BCS, irradiated in our clinic from January 2012 to August 2016 with TT (n = 30) and 3D-CRT (n = 30), 3DCRT DIBH (n = 30). PTVs were contoured at different time points by different radiation oncologists (> 7). TT was performed with a total dose of 50.4 Gy and a single dose of 1.8 Gy with a simultaneous integrated boost (SIB) to the tumor cavity (TT group). Patients irradiated with 3DCRT/3DCRT DIBH received 50 Gy à 2 Gy and a sequential boost. Contouring of lymph drainage routes was performed retrospectively according to RTOG guidelines.ResultsAverage doses (DMean) in axillary lymph node Level I/Level II/Level III were 31.6 Gy/8.43 Gy/2.38 Gy for TT, 24.0 Gy/11.2 Gy/3.97 Gy for 3DCRT and 24.7 Gy/13.3 Gy/5.59 Gy for 3DCRT-DIBH patients. Internal mammary lymph nodes (IMLNs) Dmean were 27.8 Gy (TT), 13.5 Gy (3DCRT), and 18.7 Gy (3DCRT-DIBH). Comparing TT to 3DCRT-DIBH dose varied significantly in all axillary lymph node levels and the IMLNs. Comparing TT to 3DCRT significant dose difference in Level I and IMLNs was observed.ConclusionDose applied to locoregional lymph drainage pathways varies comparing tomotherapy plans to conventional tangentially arranged fields. Studies are warranted whether dose variations influence loco-regional spread and must have implications for target volume definition guidelines.

Highlights

Radiation therapy (RT), with or without a boost to the surgical bed, has a crucial role in the adjuvant treatment of early breast cancer by improving local control and is advocated in national and international treatment recommendations [1, 2]
Dose applied to locoregional lymph drainage pathways varies comparing tomotherapy plans to conventional tangentially arranged fields
The patients were treated with deep inspiration breath hold (DIBH) if the heart Mean Dose (Dmean) dose was higher than 3Gy in the FB radiotherapy treatment plan - according to institutional guidelines [19]

Summary

Introduction

Radiation therapy (RT), with or without a boost to the surgical bed, has a crucial role in the adjuvant treatment of early breast cancer by improving local control and is advocated in national and international treatment recommendations [1, 2]. Overall survival (OS) benefit of adjuvant RT for breast cancer patients is well established [3,4,5]. Radiation therapy in these studies was delivered to the breast and to all corresponding lymphatic drainage regions, including the axilla, supraclavicular fossa, and internal mammary lymph nodes (IMLNs). Recently, results of two randomized trials have shown reduced rate of breast-cancer recurrence, improved disease-free survival and distant disease-free survival after irradiation of the locoregional nodal drainage system in lymph-node positive patients and nodenegative patients with risk factors [7, 8]. Poortmans reported a small benefit on overall survival [8]

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