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Deformable Image Registration Based Delivered Dose Estimation for Head and Neck Radiotherapy

A Kumarasiri

A Kumarasiri*, C Liu , M Chetvertkov , J Gordon , F Siddiqui , I Chetty , J Kim , Henry Ford Health System, Detroit, MI


SU-E-J-154 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose: To estimate the accumulated dose to targets and organs at risk (OAR) for head and neck (H&N) radiotherapy using 3 deformable image registration (DIR) algorithms.

Methods: Five H&N patients, who had daily CBCTs taken during the course of treatment, were retrospectively studied. All plans had 5 mm CTV-to-PTV expansions. To overcome the small field of view (FOV) limitations and HU uncertainties of CBCTs, CT images were deformably registered using a parameter-optimized B-spline DIR algorithm (Elastix, elastix.isi.uu.nl) and resampled onto each CBCT with a 4 cm uniform FOV expansion. The dose of the day was calculated on these resampled CT images. Calculated daily dose matrices were warped and accumulated to the planning CT using 3 DIR algorithms; SmartAdapt (Eclipse/Varian), Velocity (Velocity Medical Solutions), and Elastix. Dosimetric indices for targets and OARs were determined from the DVHs and compared with corresponding planned quantities.

Results: The cumulative dose deviation was less than 2%, on average, for PTVs from the corresponding plan dose, for all algorithms/patients. However, the parotids show as much as a 37% deviation from the intended dose, possibly due to significant patient weight loss during the first 3 weeks of treatment (15.3 lbs in this case). The mean(±SD) cumulative dose deviations of the 5 patients estimated using the 3 algorithms (SmartAdapt, Velocity, and Elastix) were (0.8±0.9%, 0.5±0.9%, 0.6±1.3%) for PTVs, (1.6±1.9%, 1.4±2.0%, 1.7±1.9%) for GTVs, (10.4±12.1%, 10.7±10.6%, 6.5±10.1%) for parotid glands, and (4.5±4.6%, 3.4±5.7%, 3.9±5.7%) for mucosa, respectively. The differences among the three DIR algorithms in the estimated cumulative mean doses (1SD (in Gy)) were: 0.1 for PTVs, 0.1 for GTVs, 1.9 for parotid glands, and 0.4 for mucosa.

Conclusion: Results of this study are suggestive that more frequent plan adaptation for organs, such as the parotid glands, might be beneficial during the course of H&N RT.

Funding Support, Disclosures, and Conflict of Interest: This study was supported in part by a research grant from Varian Medical Systems, Palo Alto, CA

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