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

Floris C J Reinders; Tristan C F van Heijst; Joel Mases; Chris H J Terhaard; Patricia A H Doornaert; Marielle E P Philippens; Cornelis P J Raaijmakers

doi:10.1016/j.phro.2021.10.006

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

Phys Imaging Radiat Oncol. 2021 Nov 10:20:76-81. doi: 10.1016/j.phro.2021.10.006. eCollection 2021 Oct.

Authors

Floris C J Reinders¹, Tristan C F van Heijst¹, Joel Mases¹, Chris H J Terhaard¹, Patricia A H Doornaert¹, Marielle E P Philippens¹, Cornelis P J Raaijmakers¹

Affiliation

¹ Department of Radiotherapy, University Medical Centre Utrecht, the Netherlands.

Abstract

Background and purpose: Conventional elective neck irradiation (ENI) in head and neck cancer consists of radiotherapy (RT) to the regional lymph node (LN) levels contoured on computed tomography. Hybrid Magnetic Resonance (MR) - RT modalities, such as combined magnetic resonance imaging - linear accelerators (MRLs), might enable new ENI strategies in which individual non-suspect lymph nodes (i-LNs) are targeted. In this treatment planning study, new MR-based strategies targeting i-LNs (i-ENI) were compared to conventional treatment.

Materials and methods: All i-LNs were delineated on MR images of ten retrospectively selected patients with T2-4aN0M0 laryngeal cancer. Three strategies were considered. Strategy A: Conventional ENI delivered with a conventional linear accelerator (35x 1.55 Gy). Strategy B: MRL-based i-ENI (35x 1.55 Gy) to the individual lymph nodes including a background dose to the conventional elective neck volumes (35x 1.03 Gy). Strategy C: Same as Strategy B, but without background dose. In all plans the dose prescription to the primary tumor was 35x 2 Gy. Mean dose (D _mean) reductions in the organs at risk (OAR) were compared using the Wilcoxon signed rank test.

Results: Compared to conventional ENI (strategy A), significant D _mean reductions of 6.0 Gy and 8.0 Gy were observed in the submandibular glands, of 9.4 Gy and 13 Gy in the carotid arteries and of 9.9 Gy and 19.4 Gy in the thyroid for strategy B and C, respectively. Large inter-patient variations of D _mean reductions were observed in all OARs.

Conclusion: MRL-based i-ENI is a new promising concept that could reduce the mean dose to OARs in the neck significantly for patients with laryngeal cancer.

Keywords: CA, carotid arteries; Dmean, mean dose; ENI, elective neck irradiation; Head and neck neoplasms; LNs, lymph nodes; Lymph nodes; MRL, magnetic resonance imaging linear accelerator; Magnetic resonance imaging; OAR, organ at risk; OC, oral cavity (OC); PCM, pharynx constrictor muscle; PG, parotid gland; Radiotherapy; SMG, submandibular gland; Squamous cell carcinoma of head and neck; i-ENI, individual non-suspect lymph node elective neck irradiation; i-LNs, individual lymph nodes.