Individual 3D-printed fixation masks for radiotherapy: first clinical experiences

Comprehensive clinical implementation, workflow, and FMEA of bespoke silicone bolus cast from 3D printed molds using open-source resources

BACKGROUND

Bolus materials have been used for decades in radiotherapy. Most frequently, these materials are utilized to bring dose closer to the skin surface to cover superficial targets optimally. While cavity filling, such as nasal cavities, is desirable, traditional commercial bolus is lacking, requiring other solutions. Recently, investigators have worked on utilizing 3D printing technology, including commercially available solutions, which can overcome some challenges with traditional bolus.

PURPOSE

To utilize failure modes and effects analysis (FMEA) to successfully implement a comprehensive 3D printed bolus solution to replace commercial bolus in our clinic using a series of open-source (or free) software products.

METHODS

3D printed molds for bespoke bolus were created by exporting the DICOM structures of the bolus designed in the treatment planning system and manipulated to create a multipart mold for 3D printing. A silicone (Ecoflex 00-30) mixture is poured into the mold and cured to form the bolus. Molds for sheet bolus of five thicknesses were also created. A comprehensive FMEA was performed to guide workflow adjustments and QA steps.

RESULTS

The process map identified 39 and 30 distinct steps for the bespoke and flat sheet bolus workflows, respectively. The corresponding FMEA highlighted 119 and 86 failure modes, with 69 shared between the processes. Misunderstanding of plan intent was a potential cause for most of the highest-scoring failure modes, indicating that physics and dosimetry involvement early in the process is paramount.

CONCLUSION

FMEA informed the design and implementation of QA steps to guarantee a safe and high-quality comprehensive implementation of silicone bolus from 3D printed molds. This approach allows for greater adaptability not afforded by traditional bolus, as well as potential dissemination to other clinics due to the open-source nature of the workflow.

A retrospective study on improving the accuracy of radiotherapy for patients with breast cancer with lymph node metastasis using Styrofoam

BACKGROUND

To retrospectively analyze the accuracy of radiotherapy using cone beam computed tomography (CBCT), Styrofoam fixation, and breast bracket fixation in the chest wall target area and supraclavicular lymphatic drainage area (supraclavicular target area) of patients with breast cancer.and compare the setting efficiency and comfort satisfaction.

PATIENTS AND METHODS

A total of 65 patients with postoperative lymphatic metastasis of breast cancer, including 36 cases of Styrofoam fixation and 29 cases of breast bracket fixation, were recruited from March 2021 to August 2022 and retrospectively analyzed. All the patients underwent CBCT scans weekly, and the setup errors of the chest wall and supraclavicular target volume were compared and recorded. The planning target volume (PTV) margins of the two groups were calculated using the correlation MPTV = 2.5Σ + 0.7σ. The setup time and comfort satisfaction scores of the two groups were recorded and analyzed. The correlations among errors in each direction were analyzed using the Pearson correlation analysis.

RESULTS

There was a significant difference in the left-right direction (X) axis of the chest wall target area between the Styrofoam and breast bracket groups (1.59 ± 1.47 mm vs. 2.05 ± 1.64 mm, P = 0.012). There were statistical differences in the ventrodorsal direction (Z) and bed angle of the supraclavicular target area, the data were (1.36 ± 1.27 mm vs. 1.75 ± 1.55 mm, P = 0.046; 0.47 ± 0.47° vs. 0.66 ± 0.59°, P = 0.006, respectively). In the X, Y, and Z directions, the respective PTV margins of the two groups in the chest wall target area were 5.01 mm, 5.99 mm, and 5.47 mm in the Styrofoam group, while those in the breast bracket group were 6.10 mm, 6.34 mm, and 6.10 mm, respectively. Moreover, the PTV margins of the supraclavicular target in the three directions were 3.69 mm, 3.86 mm, and 4.28 mm in the Styrofoam group, while those in the breast bracket group were 3.99 mm, 3.72 mm, and 5.45 mm, respectively. The setup time of the two groups was 3.4 ± 1.1 min and 5.5 ± 3.1 min (P = 0.007). The subjective comfort satisfaction scores of the two groups were 27.50 ± 1.24 and 25.44 ± 1.23 (P < 0.001).

CONCLUSIONS

The application of Styrofoam fixation in radiotherapy of breast cancer in the supraclavicular lymph node area has several advantages as compared to breast bracket fixation, including higher positioning accuracy, smaller external expansion boundary, improved work efficiency, and patients' comfort, which might provide a reference for clinical work.

A Novel Immobilization Method for the Treatment of Head and Neck Cancer Using 3D Printing

Proper immobilization is critical for the delivery of high-quality radiation therapy. In cases when traditional immobilization is not feasible, 3-dimensional (3D) printing may provide a better-tolerated custom immobilization that is comparably effective. We present the successful treatment of a patient with inoperable oropharyngeal squamous cell carcinoma who was unable to tolerate traditional immobilization. To avoid covering the face, we created a 3D-printed cradle for the back of his head and neck. This design enabled the patient to tolerate traditional simulation scans with and without intravenous contrast and was subsequently able to undergo volumetric modulated arc therapy treatment. He successfully underwent treatment without evidence of disease more than 2 years after completion. The effect of 3D printing within the context of radiation oncology, as well as in other specialties, will undoubtedly continue to increase the variety of treatment options available to patients.

A total inverse planning paradigm: Prospective clinical trial evaluating the performance of a novel MR-based 3D-printed head immobilization device

Background and purpose

Brain radiotherapy (cnsRT) requires reproducible positioning and immobilization, attained through redundant dedicated imaging studies and a bespoke moulding session to create a thermoplastic mask (T-mask). Innovative approaches may improve the value of care. We prospectively deployed and assessed the performance of a patient-specific 3D-printed mask (3Dp-mask), generated solely from MR imaging, to replicate a reproducible positioning and tolerable immobilization for patients undergoing cnsRT.

Material and methods

Patients undergoing LINAC-based cnsRT (primary tumors or resected metastases) were enrolled into two arms: control (T-mask) and investigational (3Dp-mask). For the latter, an in-house designed 3Dp-mask was generated from MR images to recreate the head positioning during MR acquisition and allow coupling with the LINAC tabletop. Differences in inter-fraction motion were compared between both arms. Tolerability was assessed using patient-reported questionnaires at various time points.

Results

Between January 2020 - July 2022, forty patients were enrolled (20 per arm). All participants completed the prescribed cnsRT and study evaluations. Average 3Dp-mask design and printing completion time was 36 h:50 min (range 12 h:56 min - 42 h:01 min). Inter-fraction motion analyses showed three-axis displacements comparable to the acceptable tolerance for the current standard-of-care. No differences in patient-reported tolerability were seen at baseline. During the last week of cnsRT, 3Dp-mask resulted in significantly lower facial and cervical discomfort and patients subjectively reported less pressure and confinement sensation when compared to the T-mask. No adverse events were observed.

Conclusion

The proposed total inverse planning paradigm using a 3D-printed immobilization device is feasible and renders comparable inter-fraction performance while offering a better patient experience, potentially improving cnsRT workflows and its cost-effectiveness.

Clinical value of styrofoam fixation in intracranial tumor radiotherapy

Objective

To analyze the application value of two postural fixation techniques.(styrofoam combined with head mask and fixed headrest combined with head mask) in intracranial tumor radiotherapy via cone beam computed tomography (CBCT).

Methods

This study included 104 patients with intracranial tumors undergoing radiotherapy. The patients were divided into two groups: Group A (54 cases with styrofoam fixation) and Group B (50 cases with fixed headrest fixation). The positional deviation in 3D space between the two groups was compared using CBCT. The set-up errors were expressed as median (25th percentile, 75th percentile)or M(p25, p75) since the set-up errors in all directions were not normally distributed,The Mann-Whitney U test was performed.

Results

The age and gender of patients in the two groups were not significantly different. The set-up errors of A in lateral (X), longitudinal (Y), vertical (Z), and yaw(Rtn) axes were 1.0 (0,1) mm, 1.0 (0,1) mm, 1.0 (0,2) mm, and 0.4 (0.1, 0.8) degrees, respectively while the set-up errors of B were 1.0 (0,1) mm, 1.0 (1,2) mm, 1.0 (0,2) mm, and 0.5 (0.15,0.9) degrees, respectively. Moreover, patients in the styrofoam group had significantly smaller set-up errors in the Y-axis than patients in the headrest group (p=0.001). However, set-up errors in the X, Z, and Rtn axes were not significantly different between the two groups. The expansion boundaries of the target area in the X, Y, and Z directions were 1.77 mm, 2.45 mm, and 2.47 mm, respectively. The outer expansion boundaries of the headrest group were 2.03 mm, 3.88 mm, and 2.57 mm in X, Y, and Z directions, respectively. The set-up times of groups A and B were (32.71 ± 5.21) seconds and (46.57 ± 6.68) seconds, respectively (p=0.014). Patients in group A had significantly better comfort satisfaction than patients in group B (p=0.001).

Conclusion

Styrofoam plus head thermoplastic mask body fixation technique has a higher positional accuracy in intracranial tumor radiotherapy than headrest plus head thermoplastic mask fixation. Besides, styrofoam plus head thermoplastic mask body fixation technique is associated with improved positioning efficiency, and better comfort than headrest plus head thermoplastic mask fixation, and thus can be effectively applied for intracranial tumor radiotherapy positioning.

Study on the application of 3D printing head film fixation technology in cranial radiotherapy

Objective: To investigate the use of 3D printing technology to customize individualized precise radiotherapy head masks for cranial radiotherapy patients. Through the comparison with thermoplastic head film, evaluate the effect of this material on deep dose attenuation and body surface dose, and evaluate its positioning accuracy and repeatability for clinical application. Methods: Thirty patients with head and neck radiotherapy were divided into the control group and the experimental group. The control group used the traditional thermoplastic head film fixation technique for body position fixation, and the experimental group used the 3D printing head film fixation technique. The patient setup was verified by kV-CBCT scanning to obtain the translational setup error and rotational setup error in the X, Y, and Z directions. Results: At a depth of 5 cm, both materials have a radiation attenuation rate of <1%. At the surface location, the body surface dose of control group increased by approximately 27%. With a 3D printing head film, the body surface dose increased by approximately 18%. The positioning of two groups of patients was verified by the kV-CBCT, and a total of 232 data sets were obtained. The average translation positioning errors in the X, Y, and Z direction of control group and experimental group were 1.29 mm, 1.42 mm, 1.38 mm and 1.16 mm, 1.24 mm, 1.16 mm, respectively. The average rotation positioning error in the X, Y, and Z direction of control group and experimental group were 1.29°, 1.02°, 1.01° and 1.08°, 0.96°, 1.00°, respectively. The translational setup errors in the Y and Z directions and rotational setup errors in the X direction significantly differed between the control and experimental groups (all p<0.05), but no statistical significance was found in the other directions (all p>0. 05). Conclusion: Compared to the traditional thermoplastic head membranes, 3D printing head membranes has shown a reliable and reproducible interactional positioning accuracy. Of course, further investigations are needed before the new technology can be used on a regular basis.

Development of a new poly-ε-caprolactone with low melting point for creating a thermoset mask used in radiation therapy

This study aimed to develop a poly-ε-caprolactone (PCL) material that has a low melting point while maintaining the deformation ability. The new PCL (abbreviated as 4b45/2b20) was fabricated by mixing two types of PCL with different molecular weights, numbers of branches, and physical properties. To investigate the melting point, crystallization temperature, elastic modulus, and elongation at break for 4b45/2b20 and three commercially available masks, differential scanning calorimetry and tensile tests were performed. The melting point of 4b45/2b20 was 46.0 °C, and that of the commercially available masks was approximately 56.0 °C (55.7 °C–56.5 °C). The elastic modulus at 60 °C of 4b45/2b20 was significantly lower than the commercially available masks (1.1 ± 0.3 MPa and 46.3 ± 5.4 MPa, p = 0.0357). In addition, the elongation at break of 4b45/2b20 were significantly larger than the commercially available masks (275.2 ± 25.0% and 216.0 ± 15.2%, p = 0.0347). The crystallization temperature of 4b45/2b20 (22.1 °C) was clinically acceptable and no significant difference was found in the elastic modulus at 23 °C (253.7 ± 24.3 MPa and 282.0 ± 44.3 MPa, p = 0.4). As a shape memory-based thermoset material, 4b45/2b20 has a low melting point and large deformation ability. In addition, the crystallization temperature and strength are within the clinically acceptable standards. Because masks made using the new PCL material are formed with less pressure on the face than commercially available masks, it is a promising material for making a radiotherapy mask that can reduce the burden on patients.