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Effect of the Small Field of View and Imaging Parameters to Image Quality and Dose Calculation in Adaptive Radiotherapy

Ubaidillah Allam, Fauzia Annisa Rahma, Purnomo Adi Teguh, Nasution Nuruddin, Wibowo Wahyu Edy, Pawiro Supriyanto Ardjo

Polish Journal of Medical Physics and Engineering

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2023

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Vol. 29, Iss. 2

130--142

EN

The use of cone beam computed tomography (CBCT) for dose calculation in adaptive radiotherapy has been investigated in many studies. Proper acquisition and reconstruction of preset parameters could improve the accuracy of dose calculation based on CBCT images. This study evaluated the impact of the modified image acquisition and preset reconstruction parameter available in X-Ray Volumetric Imaging (XVI) to improve CBCT image quality and dose calculation accuracy. Calibration curves were generated by scanning the CIRS phantom using CBCT XVI Elekta 5.0.4 and Computed Tomography (CT) Simulator Somatom, which served as CT image reference. Rando and Catphan 503 phantoms were scanned with various acquisition and reconstruction parameters for dose accuracy and image quality tests. The image quality test is uniformity, low contrast visibility, spatial resolution, and geometrical scale test for each image by following the XVI image quality test module. Acquisition and reconstruction parameters have an impact on the Hounsfield Unit (HU) value that is used as the HU-Relative Electron Density (RED) calibration curve. The dose difference for all the calibration curves was within 1% and passed the gamma passing rate. Images acquired using 120 kVp, F1 (with Bowtie Filter), and 50 mA (F1-120-50-10) scored the highest Gamma Index (GI) of 98.5%. For the image quality test, it scored 1.20% on the uniformity test, 2.14% on the low contrast visibility test, and 11 lp/cm on the spatial resolution test. However, F1-120-50-10 reconstructed with different reconstructions scored 3.83% and 4 lp/cm in contrast and spatial resolution test, respectively. CBCT reconstruction parameters work as a scatter correction. It could improve the dose accuracy and image quality. Nevertheless, without adequate CBCT acquisition protocols, it would produce an image with high uncertainty and cannot be fixed with reconstruction protocols. The F1-120-50-10 protocols generate the highest dose accuracy and image quality.

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Evaluation and risk factors of volume and dose differences of selected structures in patients with head and neck cancer treated on Helical TomoTherapy by using Deformable Image Registration tool

Bąk Bartosz, Skrobała Agnieszka, Adamska Anna, Józefacka Natalia, Styś Sara, Malicki Julian

Polish Journal of Medical Physics and Engineering

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2022

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Vol. 28, Iss. 2

60--68

EN

Introduction: The aim of this study was the evaluation of volume and dose differences in selected structures in patients with head and neck cancer during treatment on Helical TomoTherapy (HT) using a commercially available deformable image registration (DIR) tool. We attempted to identify anatomical and clinical predictive factors for significant volume changes probability. Material and methods: According to our institutional protocol, we retrospectively evaluated the group of 20 H&N cancer patients treated with HT who received Adaptive Radiotherapy (ART) due to soft tissue alterations spotted on daily MVCT. We compared volumes on initial computed tomography (iCT) and replanning computed tomography (rCT) for clinical target volumes (CTV) – CTV1 (the primary tumor) and CTV2 (metastatic lymph nodes), parotid glands (PG) and body contour (B-body). To estimate the planned and delivered dose discrepancy, the dose from the original plan was registered and deformed to create a simulation of dose distribution on rCT (DIR-rCT). Results: The decision to replan was made at the 4th week of RT (N = 6; 30%). The average volume reduction in parotid right PG[R] and left PG[L] was 4.37 cc (18.9%) (p < 0.001) and 3.77 cc (16.8%) (p = 0.004), respectively. In N = 13/20 cases, the delivered dose was greater than the planned dose for PG[R] of mean 3 Gy (p < 0.001), and in N = 6/20 patients for PG[L] the mean of 3.6 Gy (p = 0.031). Multivariate regression analysis showed a very strong predictor explaining 88% (R2 = 0.88) and 83% (R2 = 0.83) of the variance based on the mean dose of iPG[R] and iPG[L] (p < 0.001), respectively. No statistically significant correlation between volume changes and risk factors was found. Conclusions: Dosimetric changes to the target demonstrated the validity of replanning. A DIR tool can be successfully used for dose deformation and ART qualification, significantly reducing the workload of radiotherapy centers. In addition, the mean dose for PG was a significant predictor that may indicate the need for a replan.

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Synthetic CT in assessment of anatomical and dosimetric variations in radiotherapy - procedure validation

Grządziel Aleksandra, Gądek Adam, Bekman Barbara, Wendykier Jacek, Ślosarek Krzysztof

Polish Journal of Medical Physics and Engineering

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2020

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Vol. 26, Iss. 4

185--192

EN

Introduction: One of many procedures to control the quality of radiotherapy is daily imaging of the patient's anatomy. The CBCT (Cone Beam Computed Tomography) plays an important role in patient positioning, and dose delivery monitoring. Nowadays, CBCT is a baseline for the calculation of fraction and total dose. Thus, it provides the potential for more comprehensive monitoring of the delivered dose and adaptive radiotherapy. However, due to the poor quality and the presence of numerous artifacts, the replacement of the CBCT image with the corrected one is desired for dose calculation. The aim of the study was to validate a method for generating a synthetic CT image based on deformable image registration. Material and methods: A Head & Torso Freepoint phantom, model 002H9K (Computerized Imaging Reference Systems, Norfolk, USA) with inserts was imaged with CT (Computed Tomography). Then, contouring and treatment plan were created in Eclipse (Varian Medical Systems, Palo Alto, CA, USA) treatment planning system. The phantom was scanned again with the CBCT. The planning CT was registered and deformed to the CBCT, resulting in a synthetic CT in Velocity software (Varian Medical Systems, Palo Alto, CA, USA). The dose distribution was recalculated based on the created CT image. Results: Differences in structure volumes and dose statistics calculated both on CT and synthetic CT were evaluated. Discrepancies between the original and delivered plan from 0.0 to 2.5% were obtained. Dose comparison was performed on the DVH (Dose-Volume Histogram) for all delineated inserts. Conclusions: Our findings suggest the potential utility of deformable registration and synthetic CT for providing dose reconstruction. This study reports on the limitation of the procedure related to the limited length of the CBCT volume and deformable fusion inaccuracies.

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Adaptacyjna radioterapia u chorych z powodu raka pęcherza moczowego

Poncyljusz Maria, Bulski Wojciech

Inżynier i Fizyk Medyczny

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2020

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Vol. 9, nr 6

441--444

PL

Strategia adaptacyjnej radioterapii stosowana w grupie pacjentów chorych z powodu raka pęcherza moczowego polega na przygotowaniu biblioteki planów leczenia. Przed napromienianiem wykonywane jest badanie obrazowe tomografii komputerowej wiązką stożkową, a następnie wybierany jest odpowiedni plan. Metoda ta zapewnia podwyższenie precyzji w dostarczeniu przepisanej dawki do obszaru leczonego i poprawę ochrony organów krytycznych, w szczególności jelit. Przed wprowadzeniem adaptacyjnej radioterapii konieczne jest wybranie odpowiedniej techniki przygotowania biblioteki planów, która będzie możliwa do zrealizowania w ośrodku. Niezbędne jest również przeszkolenie personelu i przygotowanie procedur minimalizujących ryzyko wystąpienia błędu.

EN

The strategy of adaptive radiotherapy for bladder cancer patients consists in preparing treatment plan library. After performing the cone beam CT imaging preceding the irradiation, an appropriate plan is selected. This method results in an improvement in the clinical target volume coverage and a dose reduction to the organs at risk, particularly the small bowel. Before introducing adaptive radiotherapy it is necessary to select the appropriate technique for preparing treatment plan library that will be possible to implement in the clinic. It is also crucial to train personnel and prepare procedures for minimizing the risk of error.

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Effect of Changing Phantom Thickness on Helical Radiotherapy Plan: Dosimetric Analysis

Karaca Sibel

Polish Journal of Medical Physics and Engineering

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2019

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Vol. 25, Iss. 2

121--126

EN

Purpose: The aim of this study is to investigate the effect of changing phantom thickness on high dose region of interest (HD_ROI) and low dose ROI’s (LW_ROI’s) doses during helical radiotherapy (RT) by utilizing Adaptive RT (ART) technique. Materials and Methods: The cylindrical phantom (CP) is wrapped with different thickness boluses and scanned in the kilovoltage computed tomography (KVCT). HD_ROI and LW_ROI’s were created in contouring system and nine same plans (1.8 Gy/Fr) were made with images of different thicknesses CP. The point dose measurements were performed using ionization chamber in Helical Tomotherapy (HT) treatment machine. For detecting thickness reduction effect, CP was irradiated using bolus-designed plans and it was irradiated using without bolus plan. The opposite of this scenario was applied to determine the thickness increase. KVCT and megavoltage CT (MVCT) images were used for dose comparison. The HT Planned Adaptive Software was used to see the differences in the planning and verification doses at dose volume histograms (DVH). Results: Point dose measurements showed a 4.480% dose increase in 0.5 cm depth reduction for HD_ROI. These differences reached 8.508% in 2 cm depth and 15,279% in 5 cm depth. At the same time, a dose reduction of 0.665% was determined for a 0.5cm depth increase, a dose reduction of 1.771% was determined for a 2 cm depth increase, a dose reduction of 5.202% was determined for a 5 cm depth increase for the HD_ROI. The ART plan results show that the dose changes in the HD_ROI was greater than the LW_ROI’s. Conclusion: Phantom thicknesses change can lead to a serious dose increase or decrease in the HD_ROI and LW_ROI’s.