Image-Guided Intensity-Modulated Radiotherapy for Single Vocal Cord Irradiation in Early Glottic Cancers

The larynx anatomy is graphically presented in figure 1.1 . The vocal cords in the center of the larynx are muscular bands covered by thin mucosa layers. Together, the right and left vocal cords have a V-shape, when viewed from cranial. The vocal cords play key roles in the control of the airflow during breathing, the protection of airway, and in the production of sound for speech. Cancer of the larynx is one of the most common cancers in Europe, with about 52,000 new cases annually, 90% occurring in men. 95% of all cancers of the larynx are squamous cell carcinomas [65]. Cancer of the larynx is mainly caused by consumption of tobacco and alcohol. Nevertheless, tobacco dominates the risk for cancer of the vocal cords. Over 90% of the present incidences of laryngeal cancers could be prevented by avoiding smoking and alcohol consumption. The most common symptoms observed in early glottic cancers are; the presence of hoarseness, sore throat, shortness of breath, and the feeling of a lump in the throat. Hoarseness, which is a an early symptom for glottic lesions, is the main symptom which causes patients to seek medical consultation [65]. A complete ear, nose, and throat check (with mirrors and laryngscopes) and histology examination are common steps in the examination of suspected laryngeal cancer patients. Vocal cord mobility and exact tumor extension are carefully assessed to aid specifying the exact stage (TNM staging) of the tumor [65]. The stage of the tumor is important for establishing the treatment policy. This thesis discusses treatment of early stage glottic cancers (Carcinoma in situ (Tis), and tumors limited to one vocal cord (T1a), with no regional/distant lymph node metastasis (N0M0))

IMRT for image-guided single vocal cord irradiation

Purpose: We have been developing an image-guided single vocal cord irradiation technique to treat patients with stage T1a glottic carcinoma. In the present study, we compared the dose coverage to the affected vocal cord and the dose delivered to the organs at risk using conventional, intensity-modulated radiotherapy (IMRT) coplanar, and IMRT non-coplanar techniques. Methods and Materials: For 10 patients, conventional treatment plans using two laterally opposed wedged 6-MV photon beams were calculated in XiO (Elekta-CMS treatment planning system). An in-house IMRT/beam angle optimization algorithm was used to obtain the coplanar and non-coplanar optimized beam angles. Using these angles, the IMRT plans were generated in Monaco (IMRT treatment planning system, Elekta-CMS) with the implemented Monte Carlo dose calculation algorithm. The organs at risk included the contralateral vocal cord, arytenoids, swallowing muscles, carotid arteries, and spinal cord. The prescription dose was 66 Gy in 33 fractions. Results: For the conventional plans and coplanar and non-coplanar IMRT plans, the population-averaged mean dose ± standard deviation to the planning target volume was 67 ± 1 Gy. The contralateral vocal cord dose was reduced from 66 ± 1 Gy in the conventional plans to 39 ± 8 Gy and 36 ± 6 Gy in the coplanar and non-coplanar IMRT plans, respectively. IMRT consistently reduced the doses to the other organs at risk. Conclusions: Single vocal cord irradiation with IMRT resulted in good target coverage and provided significant sparing of the critical structures. This has the potential to improve the quality-of-life outcomes after RT and maintain the same local control rates