(Tuesday, 7/31/2018) 4:30 PM - 6:00 PM
Room: Karl Dean Ballroom C
Purpose: In a study comparing clinical outcomes, it was observed that meningioma patients treated with proton therapy presented more frequently with radiation-induced visual toxicity than those treated with photon therapy. This work aims to identify the factors that led to this observed outcome.
Methods: 82 patients were selected for analysis based on availability of dosimetric and clinical data. The cohort consisted of 42 proton-treated patients (10 with toxicity) and 40 photon-treated patients (3 with toxicity). All recorded visual toxicities were CTCAE grade 2 or 3. Multivariate logistic regression analysis with backward elimination (criteria of p < 0.05) was performed with radiotherapy (RT)-associated visual toxicity as the response parameter. Initial predictor variables included age at RT, gender, optic structure maximum dose, radiation modality, tumor site, and pre-RT surgical status. Optic structure maximum dose was compared across modalities. Utilizing Monte Carlo techniques, relative biological effectiveness (RBE)-weighted dose in optic structures was investigated for proton patients with visual toxicities.
Results: Multivariate analysis revealed that radiation modality (p = 0.02) and age at RT (p = 0.04) were the only significant predictors associated with RT-induced visual toxicity. The odds ratio for modality was 5.76 (95% CI: 1.49-29.6) while that of age at RT was 1.05 (95% CI: 1.00-1.10). For a constant proton RBE of 1.1, there was no significant association between radiation modality and optic structure maximum dose. Variable RBE-weighted dose resulted in a median increase in maximum optic structure dose of 8% (range: 4-20%) over constant RBE dose for patients with visual toxicity.
Conclusion: In this cohort of patients treated for meningioma with proton or photon therapy, radiation modality and age at RT were the only significant predictors for RT-associated visual toxicity. Further investigation of the influence of modality-specific factors is warranted.
Funding Support, Disclosures, and Conflict of Interest: Funding for this work was provided by National Institutes of Health grant 5U19CA021239 and Cancer Prevention and Research Institute of Texas grant RP160232.
Keywords
Statistical Analysis, Protons, Dose Response
Taxonomy
TH- Radiobiology(RBio)/Biology(Bio): RBio- LQ/TCP/NTCP/outcome modeling
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