Abstract
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. 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 1.55Gy). Strategy B: MRL-based i-ENI (35x 1.55Gy) to the individual lymph nodes including a background dose to the conventional elective neck volumes (35x 1.03Gy). Strategy C: Same as Strategy B, but without background dose. In all plans the dose prescription to the primary tumor was 35x 2Gy. Mean dose (D mean) reductions in the organs at risk (OAR) were compared using the Wilcoxon signed rank test. Compared to conventional ENI (strategy A), significant D mean reductions of 6.0Gy and 8.0Gy were observed in the submandibular glands, of 9.4Gy and 13Gy in the carotid arteries and of 9.9Gy and 19.4Gy in the thyroid for strategy B and C, respectively. Large inter-patient variations of D mean reductions were observed in all OARs. 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.
Highlights
For the treatment of regional occult metastases in patients with laryngeal cancer, elective neck irradiation (ENI) to the regional lymph node (LN) levels is prescribed with a radiation dose of 46–55 Gy
With the advent of new magnetic resonance imaging (MRI) techniques it is possible to better visualize soft-tissue structures including individual non-suspect lymph nodes (i-LNs). This enables a new approach for ENI in which we propose to identify clinically non-suspect i-LNs with MRI and treat them which we refer to as individual lymph node treatment in elective neck irradiation (i-ENI)
Significant mean dose (Dmean) reductions were achieved with Magnetic Resonance (MR)-based iENI in the submandibular gland (SMG), parotid gland (PG), pharynx constrictor muscle (PCM), carotid arteries (CA) and thyroid, compared to conventional treatment
Summary
For the treatment of regional occult metastases in patients with laryngeal cancer, elective neck irradiation (ENI) to the regional lymph node (LN) levels is prescribed with a radiation dose of 46–55 Gy. 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. 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). Large inter-patient variations of Dmean 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
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