David J Thomson1, William J Beasley2, Kate Garcez3, Lip W Lee3, Andrew J Sykes3, Carl G Rowbottom2, Nicholas J Slevin4. 1. Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK; The University of Manchester, Manchester Academic Health Science Centre, Institute of Cancer Sciences, Manchester, UK. 2. The University of Manchester, Manchester Academic Health Science Centre, Institute of Cancer Sciences, Manchester, UK; Christie Medical Physics and Engineering, The Christie NHS Foundation Trust, Manchester, UK. 3. Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK. 4. Department of Clinical Oncology, The Christie NHS Foundation Trust, Manchester, UK; The University of Manchester, Manchester Academic Health Science Centre, Institute of Cancer Sciences, Manchester, UK. Electronic address: nick.slevin@christie.nhs.uk.
Abstract
INTRODUCTION: Interfractional anatomical alterations may have a differential effect on the dose delivered by step-and-shoot intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). The increased degrees of freedom afforded by rotational delivery may increase plan robustness (measured by change in target volume coverage and doses to organs at risk [OARs]). However, this has not been evaluated for head and neck cancer. MATERIALS AND METHODS: A total of 10 patients who required repeat computed tomography (CT) simulation and replanning during head and neck IMRT were included. Step-and-shoot IMRT and VMAT plans were generated from the original planning scan. The initial and second CT simulation scans were fused and targets/OAR contours transferred, reviewed, and modified. The plans were applied to the second CT scan and doses recalculated without repeat optimization. Differences between step-and-shoot IMRT and VMAT for change in target volume coverage and doses to OARs between first and second CT scans were compared by Wilcoxon signed rank test. RESULTS: There were clinically relevant dosimetric changes between the first and the second CT scans for both the techniques (reduction in mean D95% for PTV2 and PTV3, Dmin for CTV2 and CTV3, and increased mean doses to the parotid glands). However, there were no significant differences between step-and-shoot IMRT and VMAT for change in any target coverage parameter (including D95% for PTV2 and PTV3 and Dmin for CTV2 and CTV3) or dose to any OARs (including parotid glands) between the first and the second CT scans. CONCLUSIONS: For patients with head and neck cancer who required replanning mainly due to weight loss, there were no significant differences in plan robustness between step-and-shoot IMRT and VMAT. This information is useful with increased clinical adoption of VMAT.
INTRODUCTION: Interfractional anatomical alterations may have a differential effect on the dose delivered by step-and-shoot intensity-modulated radiotherapy (IMRT) and volumetric-modulated arc therapy (VMAT). The increased degrees of freedom afforded by rotational delivery may increase plan robustness (measured by change in target volume coverage and doses to organs at risk [OARs]). However, this has not been evaluated for head and neck cancer. MATERIALS AND METHODS: A total of 10 patients who required repeat computed tomography (CT) simulation and replanning during head and neck IMRT were included. Step-and-shoot IMRT and VMAT plans were generated from the original planning scan. The initial and second CT simulation scans were fused and targets/OAR contours transferred, reviewed, and modified. The plans were applied to the second CT scan and doses recalculated without repeat optimization. Differences between step-and-shoot IMRT and VMAT for change in target volume coverage and doses to OARs between first and second CT scans were compared by Wilcoxon signed rank test. RESULTS: There were clinically relevant dosimetric changes between the first and the second CT scans for both the techniques (reduction in mean D95% for PTV2 and PTV3, Dmin for CTV2 and CTV3, and increased mean doses to the parotid glands). However, there were no significant differences between step-and-shoot IMRT and VMAT for change in any target coverage parameter (including D95% for PTV2 and PTV3 and Dmin for CTV2 and CTV3) or dose to any OARs (including parotid glands) between the first and the second CT scans. CONCLUSIONS: For patients with head and neck cancer who required replanning mainly due to weight loss, there were no significant differences in plan robustness between step-and-shoot IMRT and VMAT. This information is useful with increased clinical adoption of VMAT.