Adaptative radiotherapy in head and neck cancers

Abstract

Introduction In head and neck cancers, intensity modulated radiation therapy enables to save significantly parotid glands. During the seven weeks treatment period, morphological changes are likely to degrade the initial dosimetric benefit. The objective of the study is to quantify the benefit of weekly dose replanning for the salivary glands. Materials and methods The study includes eleven patients treated in IMRT with simultaneous integrated boost (70 Gy–63 Gy–56 Gy) for locally advanced head and neck cancer. During treatment, weekly scans with manual segmentation were performed for each patient. Replanning dose distributions were calculated on each CT image. Two cumulatives doses distributions (with and without replanning) were then reported on the initial scanner planning by elastic registration (demons registration methods with trilinear interpolation of the dose). Three doses distributions (initially planned, cumulative with weekly replanning and without weekly replanning) were finally compared. The risk of oral hyposialia (reduction of the salivary flow) was estimated by the NTCP model (n = 1, m = 0.4 and TD50 = 39.9 Gy) for each of the three dose distributions. Results The mean decrease of salivary glands volume during treatment was 27% [7–42%]. At the time of the initial planning, the mean dose to the parotid glands was 30.9 Gy, it increased to 32.5 Gy after cumulative dose without replanning but could be reduced to 28.9 Gy because of the weekly replanning. The risk of oral hyposialia was: 28.8% on the initial planning, 32.6% after the cumulative dose without replanning and 24.3% after the cumulative dose with weekly replanning (given outcome for five patients in the immediate). Conclusions The parotid glands are overdosed during treatment compared to initial planning. Adaptive radiotherapy enables to keep the dosimetric benefit of IMRT planned in the parotid glands. A randomized study starts to validate the clinical benefit of this adaptive strategy (ARTIX Study).