Radiation Treatment of T1-T2N0 Squamous Cell Carcinoma of the Glottic Larynx in the Modern Era

Abstract

adjustments, the trends could be largely compensated with eNAL (SI margin 3.5 mm). Correlation between movements of the primary and nodal CTVs in SI direction was poor (r Z 0.15). For this reason, even with perfect on-line set-up corrections of the primary CTV (no residual errors), the required SI margin for the nodal CTV would be as large as 7 mm. In Left-Right (LR) and Anterior-Posterior (AP) directions, movements of the primary and nodal CTVs were largely correlated (r Z 071/0.64). Even with the two off-line protocols, required PTV margins in LR and AP directions were limited to 2-3 mm for both CTVs. SI motion correlation between the cervical vertebrae and the primary CTV was poor ((r Z 0.19). When using the vertebrae as reference structure in image guidance, the required SI margin around the primary CTV would be 7 mm, even with daily on-line repositioning. Conclusions: Without set-up corrections, laryngeal cancer patients showed large SI interfraction time trends in set-up of the primary tumor that could partially or almost fully be compensated with eNAL and daily on-line, respectively. Due to poor SI motion correlation of the primary tumor and the nodes, even perfect daily repositioning of the primary CTV required a 7 mm PTV margin around the nodes. Small nodal PTV margins would require an adaptive approach to correct for the non-rigid motion. Even with daily online corrections, the required SI PTVmargin around the primary CTVwould be as large as 7mm, when using the vertebrae as reference structure in image guidance. Generally applied 5 mm PTV margins in head and neck cancer were often inadequate for the studied laryngeal cancer patients. Author Disclosure: B. Heijmen: None. A. Gangsaas: None. E. Astreinidou: None. S. Quint: None. P. Levendag: None.