Program Information
Decision Rule for Adaptive Plan Modification for Radiotherapy of Head-And-Neck Cancer Patients Based On Accumulated Dose
S van Kranen*, O Hamming-Vrieze , R Graaf , J Sonke , Netherlands Cancer Institute, Amsterdam, The Netherlands
Presentations
SU-K-605-17 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 605
Purpose: The delivered dose may deviate from the planned dose due to systematic and progressive anatomical changes. The purpose of this work was to develop a decision rule for adaptive radiotherapy that selects patients with the largest dosimetric discrepancies.
Methods: For 89 patients treated with a simultaneously-integrated-boost to 70 Gy in 35 fractions, dose was recalculated on the daily cone-beam CT and accumulated on the planning CT. Relevant DVH-parameters were extracted for various organs-at-risk (OARs), and the CTV1 (70 Gy) and CTV2 (54.25 Gy) +2mm (to account for delineation uncertainty). Given the first f fractions, regression analysis was applied to estimate the final accumulated ΔDVH-parameters (accumulated – planned) and the corresponding prediction-interval at uncertainty level a. Patients for which the prediction-interval was below\above (for CTV or OAR respectively) the c% highest\lowest final ΔDVH-parameter distribution were marked as candidates for adaptive intervention. Receiver-Operator-Curves were constructed by varying the uncertainty level a, simultaneously evaluating all OARs and CTVs for fractions 5-20.
Results: The accumulated mean dose for the parotid glands (PGs), constrictor muscle and oral cavity differed from planned with respectively: 0.6±1.2 Gy, 0.2±0.6 Gy, 0.2±1.1 Gy, the D99% for the CTV1 and CTV2, with -0.5±0.8 Gy and -0.4±0.5 Gy. With c =95%/85%/75% for each OAR\CTV, 16/32/50 patients were regarded as candidates for adaptive intervention. DVH-parameter prediction was capable of modeling the progressive changes to PGs and other VOIs. Patients could be identified with an area under the curve ranging from 0.55 (fraction 5), 0.80 (fraction 12) to 0.95 (fraction 20), more or less independent of c.
Conclusion: A decision rule based on daily dose accumulation was successfully developed to predict predefined deviations in DVH-parameters early in treatment with high accuracy. The clinical workload can be balanced with tolerance to dose discrepancies.
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