Improving 3D-printing of megavoltage X-rays radiotherapy bolus with surface-scanner

Abstract

BackgroundComputed tomography (CT) data used for patient radiotherapy planning can nowadays be used to create 3D-printed boluses. Nevertheless, this methodology requires a second CT scan and planning process when immobilization masks are used in order to fit the bolus under it for treatment.This study investigates the use of a high-grade surface-scanner to produce, prior to the planning CT scan, a 3D-printed bolus in order to increase the workflow efficiency, improve treatment quality and avoid extra radiation dose to the patient.MethodsThe scanner capabilities were tested on a phantom and on volunteers. A phantom was used to produce boluses in the orbital region either from CT data (resolution ≈1 mm), or from surface-scanner images (resolution 0.05 mm). Several 3D-printing techniques and materials were tested. To quantify which boluses fit best, they were placed on the phantom and scanned by CT. Hounsfield Unit (HU) profiles were traced perpendicular to the phantom’s surface. The minimum HU in the profiles was compared to the HU values for calibrated air-gaps. Boluses were then created from surface images of volunteers to verify the feasibility of surface-scanner use in-vivo.ResultsPhantom based tests showed a better fit of boluses modeled from surface-scanner than from CT data. Maximum bolus-to-skin air gaps were 1-2 mm using CT models and always < 0.6 mm using surface-scanner models. Tests on volunteers showed good and comfortable fit of boluses produced from surface-scanner images acquired in 0.6 to 7 min. Even in complex surface regions of the body such as ears and fingers, the high-resolution surface-scanner was able to acquire good models. A breast bolus model generated from images acquired in deep inspiration breath hold was also successful. None of the 3D-printed bolus using surface-scanner models required enlarging or shrinking of the initial model acquired in-vivo.ConclusionsRegardless of the material or printing technique, 3D-printed boluses created from high-resolution surface-scanner images proved to be superior in fitting compared to boluses created from CT data. Tests on volunteers were promising, indicating the possibility to improve overall radiotherapy treatments, primarily for megavoltage X-rays, using bolus modeled from a high-resolution surface-scanner even in regions of complex surface anatomy.

Comparison of 3D printed nose bolus to traditional wax bolus for cost‐effectiveness, volumetric accuracy and dosimetric effect

“…In the case where a diagnostic CT is available for the patient prior to simulation, a 3D print could be generated from this CT and fit of the bolus confirmed with the planning CT rather than on the first day of treatment with kV or CBCT imaging. Optical surface scanning also provides an option for avoiding plaster bust acquisition for patients with significant claustrophobia; however, its use would not negate the need for a planning CT of the patient in a mask …”

“…Optical surface scanning also provides an option for avoiding plaster bust acquisition for patients with significant claustrophobia; however, its use would not negate the need for a planning CT of the patient in a mask. 17,18 The choice to 3D print the bolus as a shell with fill rather than as a whole piece was to reduce the time of printing and the exposure of staff to released particles in the air from the process of fused deposition modelling. There are no long-term health effect studies associated with 3D printer use in confined space.…”

Physical and dosimetric characterization of thermoset shape memory bolus developed for radiotherapy

“…[3][4][5][6] Improvement of dose distribution and dose index using 3D boluses compared with conventional boluses has been reported. [7][8][9][10][11] Three-dimensional bolus is made for several hours to several days using body surface data obtained from computed tomography (CT) images or surface scanner images of patients. There are two methods of applying the 3D bolus to radiotherapy planning.…”

“…In the first method, we use the 3D bolus created in advance for CT simulation (CTs). 8,9,11 This method requires the 3D bolus before CTs; hence, additional examination is needed to obtain body surface data. In addition, making 3D bolus sometimes requires several days; therefore, the local control rate of the tumor may reduce owing to delayed treatment initiation.…”

Low-Cost iPhone-Assisted Processing to Obtain Radiotherapy Bolus Using Optical Surface Reconstruction and 3D-Printing

“…The patient would therefore receive an extra X-ray irradiation. Some other designs based on optical scanning of the patient have also been proposed 7,8 . The currently used methods are expensive or require complicated processing.…”