Stereotactic ablative magnetic resonance image-guided radiotherapy and dosimetry application possibilities for early-stage laryngeal cancer

Abstract

Purpose/Objective: Laryngeal cancer is the one of the most common upper respiratory tract cancer with 40 025 new cases and 19 728 deaths in Europe in 2020 [1]. The overall survival rate for patients undergoing surgery is around 80% and 90% for RT [2]. Laryngeal preservation has been evaluated only in few clinical trials [3]. The aim of this study is to develop an innovative stereotactic ablative magnetic resonance image-guided radiotherapy (SMART) treatment method, clinical parameters and results of individualized phantom dosimetry measurements and apply it for early stage laryngeal cancer treatment in MRI-LINAC modality. Main objectives are to evaluate clinical and dosimetric parameters of early-stage laryngeal cancer patients, to introduce phantom-based dose verification method, including development and fabrication of individualized 3D printed phantom which enables dose mapping functions due to application of specially developed [4] radiationsensitive gels and to evaluate the feasibility of SMART method for the clinical laryngeal cancer treatment. Material/Methods: Diagnostic images of patients were acquired using CT (LightSpeed RT16), MRI (Siemens Magnetom Avanto 1.5T), and PET/CT facility. Six patients were treated using the adaptive radiotherapy modality Electa Unity, 1.5T MRI and patient treatment plans were prepared and analyzed using TPS Monaco. Gafchromic films and volumetric gel dosimetry were used for dose plans verification. Data of patients treated in Trilogy and Truebeam linacs and dose plans prepared by TPS Eclipse 15.5™ (Varian Medical Systems) were analyzed. For 3D printout was used ZORTRAX M300 printer. Special 3D printing materials were used. Dosimetric gels were prepared, irradiated and dosimetric characteristics investigated. Results: All TP were generated with 42.5Gy (8.5Gy/fr) in five fractions. MRI-CT individualized phantom was created based on patient DICOM images [1fig] and filled with dose gels. 3D printed components, dosimetric gel and in target center positioned radiochromic films were irradiated with one fraction dose and compared with planned in TPS. It was estimated phantom components and dose gel densities similarity to patient's tissues in Hounsfield units (HU). All structures met requirements: phantom (plastic/bone) 187HU, target 152HU, gelatin 10-15HU. Gamma passing rate was 95.7% to radiochromic films, 96.8% to dosimetric gels. During TP comparison (Eclipse/Monaco) was found that using SMART treatment method is possible to reduce treatment volume at least 15%. Conclusion: SMART treatment integration into clinical practice could improve access to services for cancer patients, shorten the duration of treatment, preserve laryngeal function, and protect organs at risk.