การประเมินความคลาดเคลื่อนของตำแหน่งการฉายรังสีจากภาพถ่ายเอกซเรย์คอมพิวเตอร์แบบรูปกรวยเทียบกับภาพรังสีอ้างอิงสามมิติจากการจำลองการรักษา ในผู้ป่วยมะเร็งที่ได้รับการฉายรังสีบริเวณทรวงอกด้วยเทคนิคการฉายรังสีแบบปรับความเข้มหมุนรอบตัวผู้ป่วย

Panratchanee Ruangtong

Authors

Panratchanee Ruangtong Radiotherapy Department, Maha Vajiralongkorn Thanyaburi Hospital

Keywords:

CBCT images, Reference images, Random error, Systematic error, CTV to PTV margin

Abstract

Background: Radiotherapy is an effective method for cancer treatment by delivering high-energy radiation to the tumor site. Therefore Image-Guided Radiation Therapy (IGRT) is essential in the treatment process to verify the tumor location prior to irradiation. The interfraction set up variation may affect the precision of radiation delivery. Objective: To evaluate the set up errors in radiotherapy positioning by comparing Cone Beam Computed Tomography (CBCT) images with reference images (a planning image used to guide and verify patient positioning) for verification before treatment with the Volumetric Modulated Arc Therapy (VMAT) technique. Method: During 1st June 2023 to 31th May 2024 The CBCT data was collected from 281 patients undergoing radiotherapy in the thoracic region with VMAT from three LINACs: Accuray-Radixact, Elekta-Infinity, and Elekta-Harmony Pro at Maha Vajiralongkorn Thanyaburi Hospital. The CBCT images were registered to the reference images and set up error on lateral, longitudinal, and vertical direction were recorded and analyzed using Microsoft Excel. Result: From a total of 3,409 CBCT images, the systematic errors in lateral, longitudinal, and vertical directions were 1.497 mm, 2.845 mm and 2.444 mm, respectively, and the random errors in lateral, longitudinal, and vertical directions were 2.833 mm, 3.108 mm, and 3.204 mm, respectively. Calculated Clinical Target Volume (CTV) to Planning Target Volume (PTV) margin by using the Van Herk formular in lateral, longitudinal, and vertical directions were 5.726 mm, 9.288 mm, and 8.353 mm, respectively. Conclusion: The CTV to PTV margin for thoracic radiotherapy patients were less than 10 mm, which remains within the recommended range of the Radiation Therapy Oncology Group (RTOG) protocols. These deviations may result from patient setup and internal organ motion. Therefore, improvements in patient immobilization devices should be considered to enhance comfort and stability. Additionally, IGRT should be performed before every treatment, and the use of 4D-CBCT and respiratory motion management techniques should be evaluated to improve treatment accuracy and reduce potential side effects.

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