Abstract
Development and comparison of spine-shaped phantoms generated by two different 3D-printing technologies, digital light processing (DLP) and Polyjet has been purposed to utilize in patient-specific quality assurance (QA) of stereotactic body radiation treatment. The developed 3D-printed spine QA phantom consisted of an acrylic body phantom and a 3D-printed spine shaped object. DLP and Polyjet 3D printers using a high-density acrylic polymer were employed to produce spine-shaped phantoms based on CT images. Image fusion was performed to evaluate the reproducibility of our phantom, and the Hounsfield units (HUs) were measured based on each CT image. Two different intensity-modulated radiotherapy plans based on both CT phantom image sets from the two printed spine-shaped phantoms with acrylic body phantoms were designed to deliver 16 Gy dose to the planning target volume (PTV) and were compared for target coverage and normal organ-sparing. Image fusion demonstrated good reproducibility of the developed phantom. The HU values of the DLP- and Polyjet-printed spine vertebrae differed by 54.3 on average. The PTV Dmax dose for the DLP-generated phantom was about 1.488 Gy higher than that for the Polyjet-generated phantom. The organs at risk received a lower dose for the 3D printed spine-shaped phantom image using the DLP technique than for the phantom image using the Polyjet technique. Despite using the same material for printing the spine-shaped phantom, these phantoms generated by different 3D printing techniques, DLP and Polyjet, showed different HU values and these differently appearing HU values according to the printing technique could be an extra consideration for developing the 3D printed spine-shaped phantom depending on the patient’s age and the density of the spinal bone. Therefore, the 3D printing technique and materials should be carefully chosen by taking into account the condition of the patient in order to accurately produce 3D printed patient-specific QA phantom.
Highlights
Nowadays, advanced radiotherapy such as stereotactic body radiation therapy (SBRT) delivered high radiation dose into a small size of the tumor region using highly elaborated radiation fluence, and patient-specific quality assurance (QA) plays an important role [1, 2]
The CT images of carrageenan surrounding the spine were homogeneous in all slices and showed Hounsfield units (HUs) values of 8–10, as already observed in our pre-study
[26] the related research had reported that the average HU value of spine depending on different age groups decreased as the patients’ age increased and the differences in HU values from L1 to 4th Lumbar were significant among different age groups. [27, 35, 36] our finding suggests that each 3D printing technique has its own special advantage in terms of the HU value that depends on the patient’s age and it demonstrated that careful selection of the 3D printing technique and printing materials is required since even when the same material, which is known to have a similar density to the human spine, was applied for 3D printing, the calculated HU values from two different 3D printed spine phantom sets were different
Summary
Nowadays, advanced radiotherapy such as stereotactic body radiation therapy (SBRT) delivered high radiation dose into a small size of the tumor region using highly elaborated radiation fluence, and patient-specific quality assurance (QA) plays an important role [1, 2]. The SBRT could be performed in patients with spinal tumors, and the target volume for radiation treatment such as spine SBRT unavoidably includes the spinal cord during the radiation treatment planning process [3,4,5]. Spine SBRT requires the inclusion of a steep dose gradient in delivered dose distribution, high prescription dose, small size of radiation fields, and extra image guidance [1, 6] to exclude the spinal cord from the delivered dose distribution. To verify and increase the accuracy of spine SBRT and most of the radiation treatment, the QA process using a specialized patient-specific phantom has become increasingly important since patient-specific QA using a highly customized patient-specific phantom could clearly determine the accuracy of radiation treatment planning [7, 8]. The characteristics of 3D printing, such as the versatility and variety of materials for 3D printing as well as the ability to customize products with the desired geometrical features are being promoted to utilize this latest technology in various fields and these merits of 3D printing have been recently integrated into the field of medical physics, especially in the development of bolus, compensators, and QA phantoms
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