Magnetic resonance guided elective neck irradiation targeting individual lymph nodes: A new concept

Abstract

Highlights Individual elective lymph nodes can be identified using multiple Dixon T2-weighted turbo spin echo with fat suppression. Magnetic Resonance guided individual lymph node irradiation results in lower dose to the organs at risk. Especially the submandibular glands, carotid arteries and thyroid can be spared. The magnetic field on the magnetic resonance imaging - linear accelerator did not lead to increased skin dose depositions.

Target Definition in MR-Guided Adaptive Radiotherapy for Head and Neck Cancer

“…The next step in elective lymph node irradiation is a new concept of individual lymph node irradiation, which was introduced in 2021 [ 103 ]. The idea of this concept is to target all individual lymph nodes visible on T2-weighted MR images ( Figure 4 ).…”

“…The idea of this concept is to target all individual lymph nodes visible on T2-weighted MR images ( Figure 4 ). A planning study in laryngeal cancer patients showed that such a strategy results in a reduction in mean dose values to OARs up to 20 Gy [ 103 ]. A prerequisite for the implementation of this concept is having access to an MR-guided treatment modality, as small individual lymph nodes are not visible on cone beam CT, and day-to-day variation due to motion and shifts in individual lymph nodes needs to be corrected for.…”

“…The next step will be to validate the sentinel lymph node procedure for other HNSCC subsites, but it will also be to further develop the MR lymphography so that it is possible to not only identify the sentinel lymph node, but also predict whether this lymph node harbors metastases. With MR-guided systems, it is already possible to target individual lymph nodes [ 103 ], so the next step will be to only target draining lymph nodes on MR-guided systems and limit toxicity.…”

Detectability and intra-fraction motion of individual elective lymph nodes in head and neck cancer patients on the Magnetic Resonance Image guided linear accelerator

“…In a previous study we proved that large dose reductions (>5 Gy) could be achieved with elective lymph node irradiation for several Organs At Risk (OARs) such as the submandibular glands, carotid arteries and thyroid [14] . In another study, the MRI visibility and displacement of elective lymph nodes during radiotherapy in HNC patients was described [15] , in order to estimate safe inter-fraction radiotherapy margins for this new treatment concept.…”

“…All studies use conventional lymph node levels for ENI based on Computed-Tomography (CT) according to international guidelines [13] . However, with modern imaging modalities such as Magnetic Resonance Imaging (MRI) smaller soft tissue structures, such as individual lymph nodes, can be better visualized compared to CT [14] . As occult metastases are expected to harbor inside lymph nodes, it would be logical to restrict ENI to only individual lymph nodes instead of the larger lymph node levels they are located in.…”