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Impact On Skin Dose Due to Weight Loss for Head & Neck Cancer Treated Using Volumetric Arc Therapy (VMAT) : A Phantom Study

R Badkul*, J Edds , C Lominska , University of Kansas Medical Center, Kansas City, KS


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: During the course of radiation therapy for head/neck cancer majority of patients show symptoms of weight-loss.Weight loss may get skin more closer to the treating targets,causing skin dose to change.Aim of this study was to analyze change in skin dose due to weight-loss simulated using a phantom for head/neck VMAT plans.

Methods: In-house Head/neck phantom was designed to simulate head/neck anatomy and target volumes were drawn on CT-images.Weight loss was simulated using 0.5cm,1cm and1.5 cm bolus material on the phantom.VMAT plan was generated in Eclipse using 70Gy(35fractions) using Truebeam-Linac, 6MV-photon with 1.5cm bolus to simulate the initial anatomy. This plan was copied to no bolus scan,0.5cm bolus scan and 1.0cm bolus scan to simulated 1.5cm,1.0cm and 0.5cm weight-loss.Eight predefined skin locations,4 on each side of phantom were measured using MOSFET detectors.

Results: Average skin dose measured for single fraction treatment were 114.3cGy, 120.8cGy, 159.5cGy, 155.8cGy for right side of phantom and 112.3cGy, 145.8cGy, 145.3cGy, 161.8cGy for left side of the phantom; for no weight loss, 0.5cm weight loss, 1.0cm weight loss and 1.5cm weight loss respectively. Overall Weight loss increased the average measured skin dose by 17.8%, 34.5%, 40.2% for 0.5cm, 1.0cm and 1.5cm weight-loss respectively. Eclipse calculated skin doses were also increased as weight loss increased, up to the amount of 44% for maximum weight loss of 1.5cm which is close to measured difference. Due to inaccuracies in skin dose TPS calculations,it was difficult to compare with MOSFET measured values.

Conclusion: This phantom study shows that skin dose increases as patient loses weight during head and neck cancer treatment utilizing VMAT technique. Skin dose could go up to 44% higher depending on weight loss of the patient. Study suggest that re-planning should be considered if patient losses weight during head/neck treatment to spare skin and other OARs.


Not Applicable / None Entered.


TH- External beam- photons: Quality Assurance - VMAT

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