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Determination of the Radiobiological Parameters That Describe the Dose-Response Relations of Xerostomia and Disgeusia From Head and Neck Radiotherapy

P Mavroidis

P Mavroidis¹*, C Peixoto Xavier² , B Costa Ferreira³ , L Khouri⁴ , M do Carmo Lopes⁵ , S Stathakis¹ , N Papanikolaou¹ , (1) University of Texas Health Science Center, UTHSCSA, San Antonio, TX, (2) University of Coimbra, Coimbra, Coimbra, (3) University of Aveiro, Coimbra, Coimbra, (4) IPOCFG, EPE, Coimbra, Coimbra, (5) IPOCFG, EPE, Coimbra, Coimbra

Presentations

SU-E-T-399 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To estimate the radiobiological parameters that describe the dose-response relations of xerostomia and disgeusia from head and neck cancer radiotherapy. To identify the organs that are best correlated with the manifestation of those clinical endpoints. Finally, to evaluate the goodness-of-fit by comparing the model predictions against the actual clinical results.

Methods: In this study, 349 head and neck cancer patients were included. For each patient the dose volume histograms (DVH) of parotids (separate and combined), mandible, submandibular glands (separate and combined) and salivary glands were calculated. The follow-up of those patients was recorded at different times after the completion of the treatment (7 weeks, 3, 7, 12, 18 and 24 months). Acute and late xerostomia and acute disgeusia were the clinical endpoints examined. A maximum likelihood fitting was performed to calculate the best estimates of the parameters used by the relative seriality model. The statistical methods of the error distribution, the receiver operating characteristic (ROC) curve, the Pearson’s test and the Akaike's information criterion were utilized to assess the goodness-of-fit and the agreement between the pattern of the radiobiological predictions with that of the clinical records.

Results: The estimated values of the radiobiological parameters of salivary glands are D50 = 25.2 Gy, γ = 0.52, s = 0.001. The statistical analysis confirmed the clinical validity of those parameters (area under the ROC curve = 0.65 and AIC = 38.3).

Conclusion: The analysis proved that the treatment outcome pattern of the patient material can be reproduced by the relative seriality model and the estimated radiobiological parameters. Salivary glands were found to have strong volume dependence (low relative seriality). Diminishing the biologically effective uniform dose to salivary glands below 30 Gy may significantly reduce the risk of complications to the patients irradiated for prostate cancer.


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