TH-EF-BRD-11: Clinical Skin Toxicity Comparison and Phantom Dose Measurements for Head and Neck Patients Treated with IMRT Vs. VMAT

Authors


Abstract

Purpose:

Observations in our clinic have suggested a trend towards increased skin-toxicity for head and neck (HN) patients treated with Volumetric Modulated Arc Therapy (VMAT) compared with Intensity Modulated Radiation Therapy (IMRT). Here, we report on these observations and quantify surface dose differences between VMAT and IMRT treatment plans for HN cancer patients.

Methods:

We retrospectively compared skin-toxicity scores gathered by the treating physician according to the Common Terminology Criteria for Adverse Events (CTCAE v4.0) for head and neck squamous cell carcinoma (HNSCC) patients treated with IMRT (102) and VMAT (88) . A Cochran-Armitage test evaluated the relationship between treatment modality, chemotherapy and toxicity. Six patients with grade 3 skin-toxicities were selected from this cohort and the target/organ at risk volumes were transferred onto an anthropomorphic phantom using a deformable image registration based atlas (SmartSegmentation, Varian Medical). Two-arc VMAT and 9-field IMRT plans were optimized and delivered to the anthropomorphic phantom to produce similar, clinically-acceptable, dose distributions. Surface dose was measured using optically-stimulated luminescent dosimeters placed at 2 positions on the phantom's neck which were identical between VMAT and IMRT deliveries. N-factor ANOVA was performed to identify statistically significant differences in surface dose.

Results:

Our retrospective study showed a marginally significant higher skin-toxicity (Grade≥ 2) for VMAT compared with IMRT (35%vs.20%, p=0.06) for patients treated with radiation alone. Phantom measurements showed a significant effect of treatment modality on surface dose (F=42.5,p<0.001) with VMAT delivering 8% higher surface doses on average. No interaction was found between use of a thermoplastic mask and treatment with VMAT (F=0.02,p=0.884).

Conclusion:

This work indicates that marginal increases in skin dose and subsequent toxicity may be expected from HN patients treated with VMAT compared with IMRT. Our results motivate the need for techniques to spare the skin during VMAT treatment planning and for the early assessment of skin-toxicity.

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