Nastaran Momeni - Department of Medical Physics, School of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
Mohammad Ali Broomand - Department of Clinical Oncology, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
Zahra Roozmand - Department of Medical Physics, School of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran
Nima Hamzian - Department of Medical Physics, School of Medicine, Shahid Sadoughi University of Medical Sciences, Yazd, Iran

Background: Radiotherapy is considered a compromise between the amount of killed tumor cells and the damage caused to the healthy tissue. Regarding this, radiobiological modeling is performed to individualize and optimize treatment strategies.Objective: This study aimed to determine the normal tissue complication probability (NTCP) of acute ocular pain following radiotherapy.Material and Methods: In this prospective observational study, the clinical data were collected from ۴۵ patients with head and neck cancers and skull-base tumors, and dosimetric data were recorded after contouring the eye globe. Acute ocular pain was prospectively assessed with a three-month follow-up. The Lyman-Kutcher-Berman (LKB) parameters were estimated using the Area Under Curve (AUC) of Receiver Operating Characteristic (ROC) maximization and Maximum Likelihood (MLH) methods, and the NTCP of acute ocular pain was then determined using generalized LKB radiobiological model. The model performance was evaluated with AUC, Brier score, and Hosmer-Lemeshow tests.Results: Six out of ۴۵ (۱۳.۳۳%) patients developed acute ocular pain (grade ۱ or more). LKB model showed a weak dose-volume effect (n=۰.۰۹), tolerance dose for a ۵۰% complication (TD۵۰) of ۲۷.۵۴ Gy, and slope parameter (m) of ۰.۳۸. The LKB model showed high prediction performance. The LKB model predicted that NTCP would be less than ۲۵% if the generalized equivalent uniform dose (gEUD) was kept below ۲۰ Gy. Conclusion: The LKB model showed a high performance in determining the NTCP of ocular pain so that the probability of ocular pain will be less than ۲۵% if the eye globe mean dose is kept below ۱۲ Gy.

Normal Tissue Complication Probability, Dose-Response, Radiotherapy, Lyman-Kutcher-Burman, Ocular Pain