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Aim: The aim of this study was to evaluate the performance of various radiobiological models in predicting the occurrence of acute esophagitis (AE) during radiation therapy (RT) of head, neck, and thoracic tumors with concurrent and sequential chemotherapy. According to recent studies, the probability of AE following RT by normal tissue complication probability models is predictable.Materials and Methods: A total of 100 patients with nasopharynx, larynx, Hodgkin's lymphoma, spinal metastases, and oral cavity and lung tumors were included in the study. Half of these patients were treated by concurrent chemo-radiotherapy (Con. CRT) and the other half were treated by radiotherapy alone or sequential chemo-radiotherapy (RT + seq. CRT). Radiobiological models of several types were used as follows,: Lyman-generalized equivalent uniform dose (gEUD), Lyman-MED, log-logistic, logit, and logistic. Parameters were estimated using maximum likelihood estimation, and models were compared using Akaike information criteria.Results: Based on follow-up data, the behavior of dose-response curves differed markedly between the Con. CRT and RT + seq. CRT groups. The best fit with clinical results was offered by the Lyman-MED model for the Con. CRT group and the Lyman-gEUD model for the RT + seq. CRT group. Depending on the model used, the parameter of D50 was considerably lower (up to three times) in the Con. CRT group compared to the RT + seq. CRT group.Conclusions: The incidence of AE significantly differed between the two treatment groups in all the models. New parameter estimates could be used for predicting the probability of acute esophagitis after chemo-RT. [ABSTRACT FROM AUTHOR]

Introduction: The pituitary gland is frequently irradiated during radiation therapy of head and neck tumors which can influence the quality of life of the patients after radiation therapy. This study aimed to estimate the normal tissue complication probability (NTCP) for the pituitary gland in head and neck cancers using two radiobiological models. Material and Methods: 53 patients including 20 cases with nasopharyngeal cancer and 33 cases with brain tumor were studied. The dosimetric properties of each plan including minimum, mean and maximum doses were extracted from the dose-volume histogram curve. For estimation of pituitary gland response for each patient, the BIOPLAN software was used to calculate NTCP by LKB model and Matlab software was applied to calculate NTCP by equivalent uniform dose (EUD) model. Models' parameters including TD50, 𝛾50, and 'a' were extracted from a previous study of radiobiological modeling of pituitary gland response to radiation therapy. For statistical analysis, the T-test was used to compare two models. Results: The average mean doses of 30.42 and 51.29 (Gy) of the pituitary gland were obtained for nasopharyngeal and brain tumor patients, respectively. The average NTCPs of the pituitary gland for nasopharyngeal patients estimated by LKB and Log-logistic models were 3.84 and 3.91%, respectively. In brain tumors, the average NTCP was 16.33% for LKB and 16.41% for Log-logistic models. The results showed that the log-logistic and LKB models provided comparable results and no statistically significant difference (P-value< 0.05) was found between two models. Conclusion: The NTCP results indicated that the average NTCP of the pituitary gland for nasopharyngeal patients was approximately four times lower than that of brain tumors. Finally, implementation of follow up studies and modeling investigations are recommended for accurate estimation of pituitary gland complications following radiation therapy. [ABSTRACT FROM AUTHOR]

Introduction: The current study aimed to compare the performance of radiobiological models in predicting acute esophagitis (AE) complications after three-dimensional conformal radiation therapy (3D-CRT). Material and Methods: Out of a total of 100 patients, 50 patients with concurrent chemotherapy and 50 patients without such therapy were treated with different total doses and a daily dose range of 1.8-2.4 Gy on the basis of 5 days a week for 3 months. Predictions of AE were based on Lyman--Kutcher--Burman (LKB) and equivalent uniform dose (EUD)-based radiobiological models. Consequently, 3 months of follow-up were performed to monitor the complication incidence among the studied patients. Receiver operating characteristic (ROC) and univariable logistic regression analyses were carried out to determine the effect of mean dose, volume percentage, and weight loss percentage on the probability of AE grade ≥ 2. Results: The EUD-based model showed a better concordance with the clinical data for all patients (area under the curve [AUC]=0.919) and the concurrent chemoradiotherapy (CCRT) group (AUC=0.986). For the radiation therapy group, the LKB model had a better performance than the EUD-based model (AUC=0.921). Grade ≥ 2 esophagitis occurred 37.94±4.0 and 68.39±7.1 days after the initiation of radiation therapy in the chemoradiation and radiation therapy groups, respectively. Conclusion: The EUD-based model showed a higher agreement with the follow-up data. The incidence time of grade ≥ 2 AE in the CCRT was approximately two times shorter than that in the non-CCRT group. [ABSTRACT FROM AUTHOR]