(Sunday, 7/14/2019)
Room: ePoster Forums
Purpose: The objective of this work was to correlate various dosimetric indices of the lacrimal glands with the patient reported dry eye syndrome 1 month after whole brain radiotherapy. Additionally, to determine its dose-response relation using two normal tissue complication probability (NTCP) models.
Methods: 54 patients received whole brain radiotherapy (WBRT) (25-40 Gy in 10-20 fractions) and had complete treatment and follow-up data. The lacrimal glands were retrospectively delineated with the aid of fused MRI’s. Patients completed the Subjective Evaluation of Symptom of Dryness (SESoD) at baseline and one month (1M) post-RT. The dry eye severity endpoints analyzed were ≥1 (grade 1) and ≥2 (grade 2) point increase in SESoD score at 1M. The clinical data were fitted by the Lyman-Kutcher-Burman (LKB) and Relative Seriality (RS) NTCP models.
Results: At 1M, 17 patients (32%) and 13 (24%) had grade 1 and grade 2 toxicity. The dose-volume indices in the rage V6Gy-V14Gy were found to correlate best with the follow-up data with their AUC values ranging between 0.66 and 0.68 for the two severity endpoints. The values for the D50, m and n parameters of the LKB model were 47.1Gy, 0.94 and 1.0, for grade 1 and 53.5Gy, 0.74 and 1.0 for grade 2. Similarly, the values for the D50, γ and s parameters of the RS model were 47.1Gy, 0.28 and 0.0001, for grade 1 and 54.0Gy, 0.37 and 0.0001 for grade 2. Patients with parotid V10Gy ≥95% had 4.4 (95% CI: 1.3-15.4) times higher rate vs. <95% for both grades.
Conclusion: Patient-reported SESoD was found to be related with the dose metrics V6Gy-V14Gy. A threshold of V10Gy ≤ 95% was found to significantly reduce the risk for SESoD. The dose-response curve of SESoD could be determined by fitting the clinical data with the LKB and RS NTCP models.
Keywords
NTCP, Dose Response, Bioeffect Dose
Taxonomy
TH- Radiobiology(RBio)/Biology(Bio): RBio- LQ/TCP/NTCP/outcome modeling
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