A density assignment method for dose monitoring in head-and-neck radiotherapy

Abstract : Background and purpose - During head-and-neck (H&N) radiotherapy, the parotid glands (PGs) may be overdosed; thus, a tool is required to monitor the delivered dose. This study aimed to assess the dose accuracy of a patient-specific density assignment method (DAM) for dose calculation to monitor the dose to PGs during treatment. Patients and methods - Forty patients with H&N cancer received an intensity modulated radiation therapy (IMRT), among whom 15 had weekly CTs. Dose distributions were calculated either on the CTs (CT), on one-class CTs (1C-CT, water), or on three-class CTs (3C-CT, water-air-bone). The inter- and intra-patient DAM uncertainties were evaluated by the difference between doses calculated on CT and 1C-CTs or 3C-CTs. PG mean dose (D) and spinal cord maximum dose (D) were considered. The cumulated dose to the PGs was estimated by the mean D of the weekly CTs. Results - The mean (maximum) inter-patient DAM dose uncertainties for the PGs (in cGy) were 23 (75) using 1C-CTs and 12 (50) using 3C-CTs (p ≤ 0.001). For the spinal cord, these uncertainties were 118 (245) and 15 (67; p ≤ 0.001). The mean (maximum) DAM dose uncertainty between cumulated doses calculated on CTs and 3C-CTs was 7 cGy (45 cGy) for the PGs. Considering the difference between the planned and cumulated doses, 53% of the ipsilateral and 80% of the contralateral PGs were overdosed by +3.6 Gy (up to 8.2 Gy) and +1.9 Gy (up to 5.2 Gy), respectively. Conclusion - The uncertainty of the three-class DAM appears to be clinically non-significant (<0.5 Gy) compared with the PG overdose (up to 8.2 Gy). This DAM could therefore be used to monitor PG doses and trigger replanning.
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Journal articles
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Submitted on : Tuesday, October 23, 2018 - 4:21:33 PM
Last modification on : Friday, June 21, 2019 - 10:44:52 AM

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A Barateau, N Perichon, J Castelli, U Schick, O Henry, et al.. A density assignment method for dose monitoring in head-and-neck radiotherapy. Strahlentherapie und Onkologie, Springer Verlag (Germany), 2018, 195 (2), pp.175-185. ⟨10.1007/s00066-018-1379-y⟩. ⟨hal-01902640⟩

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