The Need for Adaptive Intensity Modulated Radiotherapy Replanning in Head-and-Neck Patients with Anatomical Changes During Treatment
Purpose: The aim of this study is to quantify the effectiveness of adaptive radiation therapy (ART) when anatomical changes to the tumor and/or the organs are observed for head and neck patients during the course of intensity modulated radiation therapy (IMRT).
Methods and Materials: In this study, ART was retrospectively studied in 10 head and neck cancer treated patients after examining the 2nd CT, obtained after the first several fractions of radiotherapy, to see if anatomical changes had taken place. The adaptive treatment plan (ATP) was generated on the 2nd CT to mimic the relative dose-volume histograms of the spinal cord, brainstem, parotid glands, larynx, and oral cavity from the original treatment plan. The total ATP was generated as the sum of the original treatment plan delivered to the initial CT for the first several fractions and the ATP delivered to the 2nd CT for the remaining fractions. The delivered treatment plan (DTP) was generated as the sum of the original treatment plan delivered to the initial CT for the first several fractions and the original treatment plan delivered to the 2nd CT for the remaining fractions. For quantification of the effectiveness of ART, planning target volume (PTV) coverage and homogeneity, maximum dose to the brainstem and spinal cord, and median, mean doses, and D1% (highest dose to 1% volume) for the parotid glands, the oral cavity, and the larynx were compared between the adaptive treatment plan (ATP) and delivered treatment plan (DTP) using the Wilcoxon signed-rank test, a non-parametric comparison test. For a total of 15 comparisons, significance was set at p = 0.0033 accounting for Bonferroni correction.
Results: For ATP compared to DTP, PTV44/70 homogeneity was improved by 10.38% (p = 0.0234) and 7.96% (p = 0.04922) respectively. PTV44/70 coverage (%volume covered by prescription dose) were improved by 7.27% (p = 0.0078) and 12.00% (p = 0.0020) respectively. Maximum dose to the spinal cord and brainstem were reduced by 6.47% (p = 0.0195) and 8.24% (p = 0.0098), respectively. Median and mean doses for the parotid glands were reduced by 6.01% (p = 0.0029) and 4.14% (p = 0.0043) respectively whereas D1% remained approximately the same with a reduction of 0.78% (p = 0.8789). Median dose to oral cavity was reduced by 0.20%, but mean dose and D1% increased by 0.43% and 2.12%, respectively; however all oral cavity changes were insignificant (p = 0.9102, p = 0.7344, and p = 0.2031 respectively). Similarly, larynx mean dose was reduced by 3.54%, median dose was reduced by 2.15%, and D1% was reduced by 7.11%, but all reductions were statistically insignificant (p = 0.5625, p = 0.6875, and p = 0.8789 respectively).
Conclusions: In cases where anatomical changes are observed during therapy, ART can be applied to significantly reduce median parotid glands dose and improve target coverage. However, these changes are small and may not be clinically significant, implying that adaptive radiotherapy may not provide benefit for head-and-neck cases, on average.
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