Abstract
Early-stage squamous cell cancer (SCC) of the glottis has a good prognosis. Therefore, patients have long survival outcomes and may potentially suffer from late toxicities of radiotherapy. Radiotherapy with a conventional parallel-opposed-pair or anterior-oblique beam arrangements for stage 1 and 2 glottic SCC have field borders that traditionally cover the entire larynx, exposing organs-at-risk (e.g. carotid arteries, contralateral vocal cord, contralateral arytenoid and inferior pharyngeal constrictor muscles) to high radiation doses. The potential long-term risk of cerebrovascular events has attracted much attention to the dose that carotid arteries receive. Swallow and respiratory motion of laryngeal structures has been an important factor that previously limited reduction of the radiation treatment volume. Motion has been evaluated using multiple imaging modalities and this information has been used to calculate PTV margins for generation of more limited target volumes. This review discusses the current literature surrounding dose-effect relationships for various organs-at-risk and the late toxicities that are associated with them. This article also reviews the currently available data and effects of laryngeal motions on dosimetry to the primary target. We also review the current limitations and benefits of a more targeted approach of radiotherapy for early-stage glottic SCCs and the evolution of CT-based IGRT and MR-guided radiotherapy techniques that may facilitate a shift away from a conventional 3D-conformal radiotherapy approach.
Highlights
Squamous cell cancer (SCC) represents the most common invasive neoplasm of the larynx [1]
Spread beyond the vocal cord frequently occurs through invasion of the anterior commissure, as the attachment of Broyles’ ligament onto the thyroid cartilage serves as a weak point, where tumour may invade through the cricothyroid membrane into the laryngeal cartilage and supraglottic or subglottic spaces [10]
Fung et al compared the differences in the impact of 3D-conformal radiotherapy (3D-CRT) on voice in a small number of patients (n=17) who received radiotherapy to non-laryngeal SCC (60-74 Gy in 30-37 fractions, average laryngeal dose 50 Gy) and stage T1a glottis SCC (61 Gy in 25 fractions) [42]
Summary
Squamous cell cancer (SCC) represents the most common invasive neoplasm of the larynx [1]. Supraglottic and subglottic cancers are less common, accounting for up to 35% and 4% of all laryngeal cancers respectively [3]. Early-stage supraglottic and subglottic cancers may be more locally infiltrative and have a higher risk of lymph node metastases than glottic SCCs [4]. Management of early-stage (T1-T2/ N0) glottic and subglottic SCCs remains similar [5, 6]. The treatment paradigm for early-stage glottic SCC (ESGC) has remained unaltered for many decades. In ESGC, a “conventional” radiotherapy beam arrangement is still used to cover the tumour and a large volume of surrounding non-target tissue as laryngeal motion remains a concern. As the precision of radiotherapy delivery techniques continue to improve, there is a push for laryngeal radiotherapy to evolve in parallel. This paper reviews the historical context and potential shortcomings of conventional radiotherapy techniques and introduces the future concepts of adaptive radiotherapy, in the context of ESGCs
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