Abstract
The three‐dimensional dose (3D) distribution of intensity‐modulated radiation therapy (IMRT) was verified based on electronic portal imaging devices (EPIDs), and the results were analyzed. Thirty IMRT plans of different lesions were selected for 3D EPID‐based dose verification. The gamma passing rates of the 3D dose verification‐based EPID system (Edose, Version 3.01, Raydose, Guangdong, China) and Delta4 measurements were then compared with treatment planning system (TPS) calculations using global gamma criteria of 5%/3 mm, 3%/3 mm, and 2%/2 mm. Furthermore, the dose–volume histograms (DVHs) for planning target volumes (PTVs) as well as organs at risk (OARs) were analyzed using Edose. For dose verification of the 30 treatment plans, the average gamma passing rates of Edose reconstructions under the gamma criteria of 5%/3 mm, 3%/3 mm, and 2%/2 mm were (98.58 ± 0.93)%, (95.67 ± 1.97)%, and (83.13 ± 4.53)%, respectively, whereas the Delta4 measurement results were (99.14% ± 1.16)%, (95.81% ± 2.88)%, and (84.74% ± 7.00)%, respectively. The dose differences between Edose reconstructions and TPS calculations were within 3% for D95%, D98%, and Dmean in each PTV, with the exception that the D98% of the PTV‐clinical target volume (CTV) in esophageal carcinoma cases was (3.21 ± 2.33)%. However, the larger dose deviations in OARs (such as lens, parotid gland, optic nerve, and spinal cord) can be determined based on DVHs. The difference was particularly obvious for OARs with small volumes; for example, the maximum dose deviation for the lens reached (−6.12 ± 5.28)%. A comparison of the results obtained with Edose and Delta4 indicated that the Edose system could be applied for 3D pretreatment dose verification of IMRT. This system could also be utilized to evaluate the gamma passing rate of each treatment plan. Furthermore, the detailed dose distributions of PTVs and OARs could be indicated based on DVHs, providing additional reliable data for quality assurance in a clinic setting.
Highlights
Compared with three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) has steep dose gradients
The traditional approach for verifying an IMRT plan is mainly done with two-dimensional (2D) or three-dimensional (3D) detectors based on a uniform phantom, such as a film, graphic matrix, or electronic portal imaging system (EPID).[1,2,3,4,5,6]
The gamma passing rates obtained through the Edose reconstructions and Delta[4] measurements were compared with the treatment planning system (TPS) calculations
Summary
Compared with three-dimensional conformal radiotherapy (3DCRT), intensity-modulated radiotherapy (IMRT) has steep dose gradients. Many factors can affect the dose accuracy in IMRT delivery, and these include (a) the leaf position, speed, and sequencing algorithm of the multileaf collimator (MLC), (b) the flatness and symmetry of the accelerator beam profile, (c) the accuracy of the physical model of the treatment planning system (TPS), and (d) more segments and variations in time and space of the dose rate. The traditional approach for verifying an IMRT plan is mainly done with two-dimensional (2D) or three-dimensional (3D) detectors based on a uniform phantom, such as a film, graphic matrix, or electronic portal imaging system (EPID).[1,2,3,4,5,6] the dose variation cannot be obtained solely through model-based dose verification due to the lack of patient’s anatomic information. Researchers have studied the feasibility of 3D dose verification using the patient anatomy combined with a calculation model.[7,8,9,10] Studies have shown that 3D dose verification could provide more information than 2D dose verification, such as the gamma passing rate, DVH, and the dose distributions in axial, coronal, and sagittal views
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