Browsing by Subject "Adaptive radiation therapy"

Abstract

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.

Purpose: The goal of this study is to investigate the necessity of adaptive radiation therapy (ART) for lung cancer patients treated with intensity modulated radiation therapy (IMRT) by quantifying the change in the tumor volume and its associate impacts on the target, lungs and esophagus.

Materials and Methods: Fifteen patients enrolled on an IRB-approved lung dose escalation phase I study were treated with IMRT (58-72 Gy, 2Gy/fraction), along with concurrent cisplatin and etoposide. Contrasted CT scans were acquired prior to RT and in the 2nd and 5th weeks of treatment. Tumor, lung and esophagus volumes were segmented on all CT datasets. The clinical target volumes were enlarged by 3 - 5 mm for planning target volume (PTV) expansions. The original plan (generated on pre-RT CT set) was recomputed on the subsequent CT sets and doses were accumulated by deformable registration to approximate the actual delivery. Five patients with the largest tumor shrinkage were selected and their original plans were re-optimized on the 2nd and 5th week CT sets. The plans on the 3 CT sets were summed to simulate ART. Comparisons were made between the original plan, approximated actual treatment and ART plan. Comparison metrics included QUANTEC dose parameters (lungs: V5, V20, and mean dose; esophagus: V35, V50, V70), equivalent uniform dose (EUD), maximum dose to the highest 1% of volume, and target volume covered by the prescription dose. Dosimetric and volumetric changes were tested for significance (Wilcoxon signed-rank test).

Results: Compared to the original plan, the approximated actual delivery had significantly increased lung dose and volume metrics: V5 = 8.10%, V20 = 4.08% (p < 0.05), and EUD (5.42%, p < 0.05). Tumor shrinkage-induced esophageal and lung volume motion outside the originally segmented volume was significant, ranging from 67.2%- 185%, and 16%-49.7% of the original volume (p < 0.05), respectively. The correlation between the original GTV volume and esophageal EUD increase was significant (ρ = 0.83, p < 0.005). Elevated esophagus EUD and spinal cord maximum dose were observed in most patients, with averages of 7.19% and 4.39% (p > 0.05), respectively. PTV/GTV volumes receiving 100% of prescription dose decreased (week 2/5 PTV = -10.0%/-6.88%, week 2/5 GTV = -6.7%/-4.1%), along with slightly increased dose to the highest 1% of volume. Compared to the approximated actual delivery, ART plans overall were superior in lowering dose to the lungs (V5=-4.42% (p=0.3125), V20=-7.52% (p=0.625)), esophagus (V35=-25.98% (p=0.3125), EUD =-13.18% (p=0.1094)), and spinal cord (Dmax=-15.82% (p=0.0625)).

Conclusions: RT-induced esophageal volume displacement and increased lung dose-volume metrics during treatment are significant. Adaptive plan re-optimization may be warranted in cases with larger tumors, where sizeable changes are expected during radiotherapy.