Radiotherapy Immobilization Mask Molding Through the Use of 3D-Printed Head Models

Abstract

Purpose:To evaluate the feasibility of a workflow free of a simulation appointment using three-dimensional-printed heads and custom immobilization devices.Materials and Methods:Simulation computed tomography scans of 11 patients who received radiotherapy for brain tumors were used to create three-dimensional printable models of the patients’ heads and neck rests. The models were three-dimensional-printed using fused deposition modeling and reassembled. Then, thermoplastic immobilization masks were molded onto them. These setups were then computed tomography-scanned and compared against the volumes from the original patient computed tomography-scans. Following translational +/− rotational coregistrations of the volumes from three-dimensional-printed models and the patients, the similarities and accuracies of the setups were evaluated using Dice similarity coefficients, Hausdorff distances, differences in centroid positions, and angular deviations. Potential dosimetric differences secondary to inaccuracies in the rotational positioning of patients were calculated.Results:Mean angular deviation of the 3D-printout from the original volume for the Pitch, Yaw, and Roll were 1.1° (standard deviation = 0.77°), 0.59° (standard deviation = 0.41°), and 0.79° (standard deviation = 0.86°), respectively. Following translational + rotational shifts, the mean Dice similarity coefficients of the three-dimensional-printed and original volumes was 0.985 (standard deviation = 0.002) while the mean Hausdorff distance was 0.9 mm (standard error of the mean: 0.1 mm). The mean centroid vector displacement was 0.5 mm (standard deviation: 0.3 mm). Compared to plans that were coregistered using translational + rotational shifts, the D95 of the brain from three-dimensional-printed heads adjusted for TR shifts only differed by −0.1% (standard deviation = 0.2%).Conclusions:Patient head volumes and positions at simulation computed tomography scans can be accurately reproduced using three-dimensional-printed models, which can be used to mold radiotherapy immobilization masks onto. This strategy, if applied on diagnostic computed tomography scans, may allow symptomatic and frail patients to avoid a computed tomography-simulation and mask molding session in preparation for palliative whole brain radiotherapy.

A review of 3D printed patient specific immobilisation devices in radiotherapy

“…Data captured from the literature also reveals that 78% (n = 14) of studies used 3D printing to fabricate the end-use immobiliser or headrest, while 11% (n = 2) used 3D printing to produce a replica of a head over which a traditional thermoformed mask immobiliser was created [32,38], and one study used 3D printing to produce several immobilisers as well as a head for thermoforming a traditional mask over [10]. Six of the studies examined the accuracy of the 3D printed immobilisers, with four studies finding a good level of accuracy in face masks on human volunteers [29][30][31]34], and one study finding a high degree of accuracy compared to the initial CAD model [11].…”

“…Summarising the literature on 3D printed immobilisation devices, the identified advantages of the technology included: improved patient comfort [9,29,34,37], reduced patient visits to a clinic [32,35,41], elimination of the stressful thermoforming process for face masks [29,31,34,40], high accuracy and tolerance to the patient [11,[29][30][31]34], repeatable positional accuracy [29,33,34,36,39,42], less damage to surrounding healthy tissue [40,42], similar beam attenuation properties to traditional polymer masks [10,11,33,39] and the opportunity to consider additional features to improve fit or patient engagement [37,38]. Disadvantages that were identified in the literature included: the potential for the 3D printing process to negatively influence the material behaviour of a device [30], inaccuracies due to conversion of scan data (e.g.…”

“…Disadvantages that were identified in the literature included: the potential for the 3D printing process to negatively influence the material behaviour of a device [30], inaccuracies due to conversion of scan data (e.g. CT) to 3D model [35], the slow process of 3D printing which is unsuitable for rapid deployment or modification [11,32], lower accuracy compared to surgical immobilisation [38] and costs that may be the same or higher than traditional immobilisers [38].…”

“…Production time also remains unclear, with the 2002 study claiming five days to 3D print a mask [11], while a more recent 2018 study recorded a 36 h print time for a human head in order to thermoform a mask over [32]. These times are significantly longer than more immediate traditional methods of thermoforming or surgically attaching immobilisers, however, a lack of information reported in literature does not provide enough evidence to provide a clear understanding of the time to 3D print immobilisation devices.…”

3D‐printed headrest for frameless Gamma Knife radiosurgery: Design and validation

“…Pham et al used 3D-printed head models from patients' CT scans to fabricate thermoplastic masks before a patient's simulation. 5 Haefer et al and Sato et al demonstrated the feasibility of using 3D-printed masks for immobilization in linac-based radiotherapy of head and neck cancers. 6,7 The purpose of this study was to design and validate a 3Dprinted headrest for patient immobilization for frameless Gamma Knife SRS treatments.…”