Evaluation of treatment plan and dose distribution in volumetric modulated arc therapy for lung cancer by using cone-beam computed tomography

• Main Authors: Yu-Shan Chen, 陳雨姍
• Other Authors: 蔡佳容
• Format: Others
• Language: zh-TW
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/2x66e8

碩士 === 中山醫學大學 === 醫學影像暨放射科學系碩士班 === 106 === Research purposes: First, adaptive radiation therapy (ART) based on cone-beam computed tomography (CBCT) has emerged as a domain of dedicated cancer radiotherapy system. This study aims to evaluate the dose calculation using CBCT in ART treatment, as comparing to that using planning CT by polymer gel dosimeters. X-ray cone-beam computed tomography (CBCT) is most commonly used as a method of guidance of inter-fractional corrections before treatment in radiotherapy. Multi-detector CT (MDCT) combined with adaptive mean filtering has successfully contributed dose information from irradiated polymer gel dosimeters; however, CBCT has not yet been investigated. Therefore, this study aims to evaluate whether CBCT with different noise reduction filters is potential to achieve adequate dose resolutions in polymer gel dosimeters. Material and Methods: Each vial was filled with normoxic polymer gel and irradiated with uniform doses of 0-16Gy to generate dose response curves. After irradiation, CBCT was used to perform the dose measurement. In addition, image postprocessing using noise reduction filtering techniques have been examined. Moreover, a CIRS thorax phantom was used for the measurement of simulated treatment plans using both planning CT and CBCT. This phantom also was simulated a left-side lung cancer and heart, spine cord, and right-side lung, respectively, as organ-at-risk (OAR). Dose difference criterion /dose-to-agreement criteria of 3%/3 mm and 5%/5 mm were used for comparing the dose volumes calculated using the planning CT with those calculated using the CBCT. Results: Results indicated that dose response of slope was 1.33 Gy/ΔHU and 0.34 Gy/ΔGray scale for MDCT and CBCT in irradiated dose of 6-16Gy, respectively. Moreover, normalized least-mean fourth (NLMF) filter was performed the best dose resolution with 95% confidence of about 1 Gy, demonstrating a highly effective tool for noise reduction in CBCT gel dosimetry. Normoxic polymer gel dosimetry combined with CBCT and NLMF filtering provides a useful method for dose measurement in radiotherapy, especially in case of stereotactic body radiation therapy. In treatment plan system , the pass rate of the gamma evaluations with 3%/3mm is 80% for the treatment , which simulated by MDCT and CBCT at SAD =99.5 ,100 ,100.5 cm ,and the pass rate of the gamma evaluations with 5%/5mm even up to 90% , and it is clinically accepted.. Then, we analysis of actual irradiation to get the result. the results have to normalize to get the pass rate of MDCT and CBCT treatmeant. After the results are normalized, the pass rate of the gamma evaluations with f 3%/3mm and 5%/5mm both are over 90%, and the performance of the them has a certain degree of agreement. 4. Discussion and conclusion Gel dosimeters cannot serve as a conventional dose-verification method because of the low availability of the required instruments in radiation oncology departments, and because of variables that affect the readout process, which are as follows. (1) Interval between radiation exposure and readout (2) Response dose and time after radiation exposure(3) Gravity (4) Beam dose rate during radiation exposure. However, in this study, it was found that the gel dosimeter has ability in three-dimensional dose verification, and its radiation sensitive range happens in SBRT. if can find an effective filter of reducing noise (eg NLMF filter). The gel dosimeter will become more useful in dose verification for these complex treatments in the future. It is also verified that both MDCT and CBCT can be used for treatment planning simulation by gel dosimeter. However, CBCT often miss image information, and it is easy to misjudge electron density when simulating dose, which increases the difficulty and time required for planning. Under the same dose, the performance of CBCT in the low-dose area will also be significantly different from the MDCT program. Even though CBCT can obtain an image to complete the adaptive plan for treatment, its low image quality and the time required for the planning is still the biggest problem in CBCT. If we can improve its image quality to reduce material misjudgment and advance the artificial intelligence (AI) to shorten the planning time. CBCT is a nice tool to popularize the adaptive radiotherapy.(ART)