The effect of radiotherapy technique on carotid artery dose in patients with early stage glottic laryngeal cancer

ABSTRACT Objective: The aim of this study is to compare two radiotherapy techniques in early stage glottic laryngeal cancer patients in terms of carotid artery doses. Method: In this study, we included 10 early-stage (T1/2) glottic larynx cancer patients. Both intensity-modulated radiotherapy (IMRT) and 3-dimension conformal radiotherapy (3DCRT) treatment plans were prepared for each patient. Treatment volumes (CTV, PTV) were created for all patients. The entire larynx was described as CTV to include both false and true vocal cords, anterior-posterior commissures, arytenoids, aryepiglottic folds, subglottic region. For planning target volüme (PTV), while 5-mm was added to CTV in all directions, 3-mm margin was given to protect the carotid artery and spinal cord in posterolaterally. Because of the low rate of nodal metastases for T1/2 glottic cancer, elective nodal irradiation was not planned. Spinal cord and carotid artery were contoured as the organ at risk (OAR). The doses of the target volumes, the OAR volumes, the homogeneity index (HI) were compared. In addition, V30 <%20, V10 < %50 were evaluated for carotid artery and the maximum dose was limited to 45Gy for spinal cord. Conformity index was calculated. Mann Whitney test was used for statistical analysis and p <0.05 was considered significant. Results: PTV parameters (Dmin, Dmean, Dmax, D90, D95) was compared in the 2 different technique. IMRT in comparison to 3DCRT significantly reduced the high-dose volumes (V30, V35, V50) of carotid artery (p < 0.001), but not to the low dose volume (V10). CI was similar (0.9 vs. 0.9, p = 0.3) compared to 3DCRT. However, HI was significantly improved with IMRT (0.1 vs. 0.08, p < 0.001). The maximum dose of spinal cord was lower in 3DCRT compared to IMRT (18 Gy vs. 44Gy). Conclusion: IMRT is a superior radiotherapy (RT) technique in patients with T1/T2 glottic cancer in terms of protecting carotid artery. Key words: Radiotherapy, glottic cancer, carotid artery, 3DCRT, IMRT