Clinical Implementation of Daily Dose Accumulation and Adaptive Radiotherapy

Abstract

Widespread clinical use of dose accumulation and adaptive radiotherapy has been hampered by limited tools to efficiently aggregate and evaluate clinical data. The purpose of this work is to assess the clinical feasibility of daily dose accumulation and advanced analytical tools to support adaptive radiotherapy of head and neck cancers in clinical practice. Dose accumulation (Dacc) accuracy and impact was evaluated on more than 350 CBCT and CT images of HN cancer patients enrolled on a prospective registry cohort evaluating sub-weekly target volume/OAR adaptive radiation therapy using a previously validated DIR algorithm. CBCT padding was achieved by performing DIR optimized with a quasi-Newton algorithm, regularized with minimization of the weighted Dirichlet energy, and driven by correlation coefficients between the CT and the CBCT images with iterative smoothing at the boundaries. Dose calculation accuracy on the CBCT padded with the weekly CT (wCT) was evaluated relative the CT acquired on the same day. The utility of adaptive planning was evaluated using the difference between adaptive planned and Dacc to critical normal tissues and the ability to maintain delivery of the adaptive planned target dose through assessment of the Dacc based on wCT and daily CBCT. Advanced analytical tools enabled efficient analysis of all datapoints. CBCT padded with wCT enabled dose calculation accuracy to within +/- 2% for 95% of structures. Adaptive tumor-based replanning enabled a median dosimetric reduction relative to the planned dose of 6.4% for critical normal tissues, with an inter-quartile range (IQR) of -16.6% to 1.3%. Twenty-three structures from 9 patients were planned to within 30% of their clinical goal. Adaptive replanning enabled all but 4 structures (1 parotid gland, adaptive plan at 72 cGy over clinical goal; 3 larynxes within 300 cGy over clinical goal) to meet their clinical goal in the presence of physiological response of tissues. The Dacc to these structures was within 750 cGy of the adaptive planned dose. Compared to the original planned dose, the Dacc deviated by a median of 1.3%, IQR: -1.9-3.6% for parallel structures and median -2.4%, IQR: -8.0-0.5% for serial structures. Compared to the adaptive planned dose, the Dacc deviated by median -1.1%, IQR: -3.2-1.7% for parallel structures and median 0.5%, IQR: 0.1-1.4% for serial structures. Dacc using on only wCT introduces uncertainty of up to +/-4.5% for normal tissues. For clinical targets (GTVs and CTVs), compared to the original planned dose, the Dacc deviated by median 0.2%, IQR: -0.9-1.0%. Compared to the adaptive planned dose, the Dacc deviated by 0.8%, IQR: 0.6-0.9% for targets. Dacc using on only wCT introduces uncertainty of up to +/- 1.7%. Adaptive radiotherapy can reduce the dose to normal tissues and enable a more accurate delivery of the planned dose. Dose accumulation using daily CBCT padded with the wCT is necessary to ensure the most accurate calculation of the delivered dose.