Evaluation of Target Volume Location and Its Impact on Delivered Dose Using Cone-Beam Computed Tomography Scans for Patients with Head and Neck Cancer.

ABSTRACT

INTRODUCTION: Within radiation oncology, treatment of head and neck cancer is known for its unique challenges with patient weight loss and body contour changes. This study sought to quantify these changes through measuring the volume and position of specific target structures over the course of radiation treatment and determining if changes in these factors affected what dose was ultimately delivered. METHODS: This study utilized weekly cone-beam computed tomography (CBCT) images taken immediately before radiation treatments to measure the difference between the expected location and the actual location of clinical target volumes. Minimum and mean doses to planned target volumes (PTVs) were then calculated on the CBCT scans and compared with the expected planned dose. RESULTS: In the twenty patients included in this single-institutional study, a significant average difference of 2.47% (P < .0001) and 5.06% (P < .0001) was found in the locations of the high-risk and low-risk clinical target volumes, respectively. Software limitations reduced the sample size that could be used to compare delivered and planned dose to nine patients, but of that number, a significant decrease of 10% was found in the minimum dose delivered to both the high-risk (P = .0401) and low-risk (P = .0123) PTVs. Mean doses to the PTVs did not differ significantly and no correlation was found between any volumetric and dosimetric deviations. CONCLUSION: The results of this study support the presence of volume matching inaccuracies for patients with head and neck cancer with simultaneous altered minimum doses to PTVs. Based on these findings, it is suggested that institutions may benefit from a standardized treatment imaging protocol that would include a minimum of weekly full-trajectory CBCT scans to assess target volume location, particularly those of the inferior nodal volumes.