Evaluation of set-up shift values detected in CBCT and kV-kV images taken on set-up day and interfraction treatment days in patients with laryngeal cancer who underwent image-guided radiotherapy

Abstract

Objectives: The aim of this study is to retrospectively analyze the first image values obtained with cone-beam computed tomography (CBCT)/kilovoltage (kV-kV) image on the set-up day, and the kV-kV image values taken on the following treatment days in the vertical (Vert), longitudinal (Long), and lateral (Lat) directions separately, and to evaluate the shift values in three axes within the framework of clinical applicability.

Patients and methods: Between March 2020 and November 2021, a total of 30 laryngeal cancer patients (18 males, 12 females; mean age: 58.2 years) planned for curative radiation therapy treatment with intensity-modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) technique were included in the study. In order to keep the patients stable on the treatment table during irradiation and to minimize set-up errors, immobilization was performed using thermoplastic masks that also included the head-shoulder area. Tomography images of cases were taken with computed tomography (CT) with a 2.5 mm slice thickness to be used in the treatment planning systems (TPS). Planning CT images were transferred to the Eclipse TPS, and target volumes and critical organs were defined on the system for each patient. Double-Arc VMAT and 7-field IMRT plans were designed with a total treatment dose of 66-70 Gray on TPS by the same medical physicist. All IMRT and VMAT treatments were performed on the Varian Trilogy device and pre-treatment and set-up images were taken using the Varian on-board imaging system. Images of each patient were collected by taking CBCT/kV-kV on the first set-up day and then kV-kV images every day or every other day until the end of the treatment. The shift value of the CBCT and kV-kV images obtained around 17/24 on average per patient was recorded and extracted the mean shift values for the Vert, Long, and Lat directions from the offline review system on TPS. Shift on the images approved by the same radiation oncologist with reference to the target volume and bone structures on CBCT/kV-kV images taken on set-up day and pre-treatment were retrospectively analyzed for each patient.

Results: The CBCT/kV-kV images taken on the set-up day and the kV-kV images taken every other day were analyzed in two different ways. The first analysis included CBCT/kV-kV images taken on the set-up day and the kV-kV images taken every other day during all treatment time. The analysis of the first group’s mean shift values was found as Vert: 0.24 mm, Long: 0.27 mm, and Lat: 0.32 mm, respectively. In the second analysis, the image taken on the day of the set-up was excluded, the kV-kV images taken on during the treatment days were examined within themselves, and the mean shift value was found as Vert: 0.13 mm, Long: 0.20 mm, and Lat: 0.27 mm, respectively. Analysis revealed that the mean shift values in the Vert, Long, and Lat directions were ≤1 mm both in the first and second analyzed groups. The shift values are among the limit values determined for the image-guided radiotherapy (IGRT) technique to be applied to head and neck cancer patients.

Conclusion: The evaluation of the images taken on the set-up day and subsequent fractions, and the follow-up of the shifts on the images are important in terms of the quality assurance of the applied IGRT to the patients. In addition to correct positioning with CBCT/kV-kV on the day of set-up, it is recommended to take kV-kV images every other day and follow up with weekly CBCT imaging to monitor the change in the patient's anatomical structure throughout the treatment.

Cite this article as: Çini N, Ceylaner Biçakçi B. Evaluation of set-up shift values detected in CBCT and kV-kV images taken on set-up day and interfraction treatment days in patients with laryngeal cancer who underwent image-guided radiotherapy. D J Med Sci 2023;9(1):12-18. doi: 10.5606/fng.btd.2023.126.

A written informed consent was obtained from each patient.

Data Sharing Statement:
The data that support the findings of this study are available from the corresponding author upon reasonable request.

All authors contributed equally to the article.

The authors declared no conflicts of interest with respect to the authorship and/or publication of this article.

The authors received no financial support for the research and/or authorship of this article.