Manufacture and evaluation of 3-dimensional printed sizing tools for use during intraoperative breast brachytherapy

Preclinical Dosimetry for Small Animal Radiation Research in Proton Therapy: A Feasibility Study

Purpose

To evaluate the feasibility of the three-dimensional (3D) printed small animal phantoms in dosimetric verification of proton therapy for small animal radiation research.

Materials and Methods

Two different phantoms were modeled using the computed-tomography dataset of real rat and tumor-bearing mouse, retrospectively. Rat phantoms were designed to accommodate both EBT3 film and ionization chamber. A subcutaneous tumor-bearing mouse phantom was only modified to accommodate film dosimetry. All phantoms were printed using polylactic-acid (PLA) filament. Optimal printing parameters were set to create tissue-equivalent material. Then, proton therapy plans for different anatomical targets, including whole brain and total lung irradiation in the rat phantom and the subcutaneous tumor model in the mouse phantom, were created using the pencil-beam scanning technique. Point dose and film dosimetry measurements were performed using 3D-printed phantoms. In addition, all phantoms were analyzed in terms of printing accuracy and uniformity.

Results

Three-dimensionally printed phantoms had excellent uniformity over the external body, and printing accuracy was within 0.5 mm. According to our findings, two-dimensional dosimetry with EBT3 showed acceptable levels of γ passing rate for all measurements except for whole brain irradiation (γ passing rate, 89.8%). In terms of point dose analysis, a good agreement (<0.1%) was found between the measured and calculated point doses for all anatomical targets.

Conclusion

Three-dimensionally printed small animal phantoms show great potential for dosimetric verifications of clinical proton therapy for small animal radiation research.

Emerging technologies in brachytherapy

Brachytherapy is a mature treatment modality. The literature is abundant in terms of review articles and comprehensive books on the latest established as well as evolving clinical practices. The intent of this article is to part ways and look beyond the current state-of-the-art and review emerging technologies that are noteworthy and perhaps may drive the future innovations in the field. There are plenty of candidate topics that deserve a deeper look, of course, but with practical limits in this communicative platform, we explore four topics that perhaps is worthwhile to review in detail at this time. First, intensity modulated brachytherapy (IMBT) is reviewed. The IMBT takes advantage ofanisotropicradiation profile generated through intelligent high-density shielding designs incorporated onto sources and applicators such to achieve high quality plans. Second, emerging applications of 3D printing (i.e. additive manufacturing) in brachytherapy are reviewed. With the advent of 3D printing, interest in this technology in brachytherapy has been immense and translation swift due to their potential to tailor applicators and treatments customizable to each individual patient. This is followed by, in third, innovations in treatment planning concerning catheter placement and dwell times where new modelling approaches, solution algorithms, and technological advances are reviewed. And, fourth and lastly, applications of a new machine learning technique, called deep learning, which has the potential to improve and automate all aspects of brachytherapy workflow, are reviewed. We do not expect that all ideas and innovations reviewed in this article will ultimately reach clinic but, nonetheless, this review provides a decent glimpse of what is to come. It would be exciting to monitor as IMBT, 3D printing, novel optimization algorithms, and deep learning technologies evolve over time and translate into pilot testing and sensibly phased clinical trials, and ultimately make a difference for cancer patients. Today's fancy is tomorrow's reality. The future is bright for brachytherapy.

Validation of 3D printing materials for high dose-rate brachytherapy using ionisation chamber and custom phantom

Methods.Measurements were taken with the Exradin A20 (Standard Imaging) ionisation chamber, and the 'homemade' MARM phantom was made with the 3D Ultimaker 2+ printer using PLA material. The material used for validation was ABS Medical from Smart Materials 3D. The irradiation was undertaken with a¹⁹²Ir source by means of Varian's GammaMed Plus iX HDR equipment. EBT3 films were used to run additional tests. We compared different measurements for PLA, ABS Medical, and water. Additional validation methods, described in the bibliography, were also compared.Results.The measurements with the ionisation chamber that we obtained using the MARM phantom with PLA and ABS within the clinically relevant range (0.5-1.5 cm) differ with respect to the measures in the water reference, by 2.3% and 0.94%, respectively.Discussion.The literature describes highly heterogeneous validation methods, complicating the performance of systematic reviews and comparisons between materials. Thus, creating a phantom represents a single effort that will quickly pay off. This system enables comparisons, ensuring that geometric conditions remain stable-something that is not always possible with radiochromic films. The use of a calibrated ionisation chamber in the corresponding energy range, combined with the 'homemade' MARM phantom applied according to the proposed methodology, allows a differentiation between the attenuation of the material itself and the drop in the dose due to distance.Conclusion.The validation method for 3D printing materials, using an ionisation chamber and the MARM PLA phantom, represents an accessible, standardisable solution for manufacturing brachytherapy applicators.

3D printing as a transformative tool for microneedle systems: Recent advances, manufacturing considerations and market potential

The present review aims at identifying the key progress points that have been made on the use of 3D printing to manufacture microneedles in the past 3 years. The advances in the field of photopolymerization and extrusion-based 3D printing are outlined. The study revealed that the printing resolution and the material properties are the two critical parameters that have the most influential effect on the outcome of every microneedle printing endeavour. Finally, the authors attempt to estimate the impact of 3D printing on the transdermal drug delivery market.

Characterization of 3D-printed bolus produced at different printing parameters

We aimed to analyze the effects of printing parameters on characterization of three-dimensional (3D) printed bolus used in external beam radiotherapy. Two sets of measurements were performed to investigate the dosimetric and physical characterization of 3D-printed bolus at different printing parameters. In the first step, boluses were produced at different infill-percentages, infill-patterns and printing directions. Two-dimensional (2D) dose measurements were performed in Elekta Versa HD linear accelerator using 6 MV photon energy. Measured 2D dose maps for both printed and reference bolus materials were compared using the 2D gamma analysis method. Additionally, patient-specific bolus was produced with defined optimum printing parameters for anthropomorphic head and neck phantom. Then, point dose measurements were performed to evaluate the feasibility of printed bolus in clinical use. In the second step, physical measurements were carried out to evaluate the printing accuracy, the mean hounsfield unit (HU) value and the weight of 3D-printed boluses. According to our measurement, infill-percentage, infill-pattern and printing direction significantly changed the dosimetric and physical properties of the 3D-printed bolus independently. Maximum gamma passing rate at 1.5 and 5 cm depths were found as 93.8% and 98.8%, respectively, for 60% infill-percentage, sunglass fill infill-pattern and horizontal printing direction. The printing accuracy of the products was within 0.4 mm. Dosimetric and physical properties of the printed bolus material changed significantly with the selected printing parameters. Therefore, it is important to note that each combination of these printing parameters that will be used in the production of patient-specific bolus should be investigated separately.

Three-dimensional printing in radiation oncology: A systematic review of the literature

Purpose/objectives

Three‐dimensional (3D) printing is recognized as an effective clinical and educational tool in procedurally intensive specialties. However, it has a nascent role in radiation oncology. The goal of this investigation is to clarify the extent to which 3D printing applications are currently being used in radiation oncology through a systematic review of the literature.

Materials/methods

A search protocol was defined according to preferred reporting items for systematic reviews and meta‐analyses (PRISMA) guidelines. Included articles were evaluated using parameters of interest including: year and country of publication, experimental design, sample size for clinical studies, radiation oncology topic, reported outcomes, and implementation barriers or safety concerns.

Results

One hundred and three publications from 2012 to 2019 met inclusion criteria. The most commonly described 3D printing applications included quality assurance phantoms (26%), brachytherapy applicators (20%), bolus (17%), preclinical animal irradiation (10%), compensators (7%), and immobilization devices (5%). Most studies were preclinical feasibility studies (63%), with few clinical investigations such as case reports or series (13%) or cohort studies (11%). The most common applications evaluated within clinical settings included brachytherapy applicators (44%) and bolus (28%). Sample sizes for clinical investigations were small (median 10, range 1–42). A minority of articles described basic or translational research (11%) and workflow or cost evaluation studies (3%). The number of articles increased over time (P < 0.0001). While outcomes were heterogeneous, most studies reported successful implementation of accurate and cost‐effective 3D printing methods.

Conclusions

Three‐dimensional printing is rapidly growing in radiation oncology and has been implemented effectively in a diverse array of applications. Although the number of 3D printing publications has steadily risen, the majority of current reports are preclinical in nature and the few clinical studies that do exist report on small sample sizes. Further dissemination of ongoing investigations describing the clinical application of developed 3D printing technologies in larger cohorts is warranted.

3D printer-based novel intensity-modulated vaginal brachytherapy applicator: feasibility study

Purpose

To design a novel high-dose-rate intracavitary applicator which may lead to enhanced dose modulation in the brachytherapy of gynecological cancers.

Material and methods

A novel brachytherapy applicator, auxiliary equipment and quality control phantom were modeled in SketchUp Pro 2017 modeling software and printed out from a MakerBot Replicator Z18 three-dimensional printer. As a printing material polylactic acid (PLA) filament was used and compensator materials including aluminum, stainless-steel and Cerrobend alloy were selected according to their radiation attenuation properties. To evaluate the feasibility of the novel applicator, two sets of measurements were performed in a Varian GammaMed iX Plus high-dose rate iridium-192 (¹⁹²Ir) brachytherapy unit and all of the treatment plans were calculated in Varian BrachyVision treatment planning system v.8.9 with TG43-based formalism. In the first step, catheter and source-dwell positioning accuracy, reproducibility of catheter and source positions, linearity of relative dose with changing dwell times and compensator materials were tested to evaluate the mechanical stability of the designed applicator. In the second step, to validate the dosimetric accuracy of the novel applicator measured point dose and two-dimensional dose distributions in homogeneous medium were compared with calculated data in the treatment planning system using PTW VeriSoft v.5.1 software.

Results

In mechanical quality control tests source-dwell positioning accuracy and linearity of the designed applicator were measured as ≤ 0.5 mm and ≤ 1.5%, respectively. Reproducibility of the treatment planning was ≥ 97.7% for gamma evaluation criteria of 1 mm distance to agreement and 1% dose difference of local dose. In dosimetric quality control tests, maximum difference between measured and calculated point dose was found as 3.8% in homogeneous medium. In two-dimensional analysis, the number of passing points was greater than 90% for all measurements using gamma evaluation criteria of 3 mm distance to agreement and 3% dose difference of local dose.

Conclusions

The novel brachytherapy applicator met the necessary requirements in quality control tests.

Development and assessment of 3D-printed individual applicators in gynecological MRI-guided brachytherapy

Purpose

To evaluate the clinical use of 3D printing technology for the modelling of individual applicators for advanced gynecological tumors in magnetic resonance imaging (MRI)-based brachytherapy (BT).

Material and methods

We tested individually designed 3D-printed applicators in nine patients with advanced gynecological cancer. Before BT was performed, all patients were treated with external beam radiotherapy (EBRT). The most common indication for individualized BT was advanced gynecological tumors where the use of standard BT applicators was not feasible. Other indications were suboptimal dose-volume histogram (DVH) parameters for high-risk clinical target volume (CTV-T_HR) at the first BT (V₁₀₀ ≤ 90% of CTV-T_HR volume and D₉₈ ≤ 80%, D₉₀ ≤ 100%, and D₁₀₀ ≤ 60% of dose aim). The EQD₂ dose aim to the target volume D₉₀ CTV-T_HR per one BT fraction was 20 Gy for cervical or recurrent endometrial cancer and 16 Gy for vaginal cancer patient. The first BT with the standard applicator in situ was used as the virtual plan for designing a 3D-printed applicator. The next BT was performed with a 3D-printed applicator in situ. The primary endpoint was to improve CTV-T_HR DVH parameters without exceeding the dose to the organs at risk (OARs).

Results

All DVH parameters for CTV-T_HR were significantly higher with the use of an individually designed applicator. Mean D₉₀ CTV-T_HR improved from 14.1 ±5.4 Gy to 22.0 ±2.5 Gy and from 7.1 Gy to 16.2 Gy for cervical/recurrent endometrial and vaginal cancer, respectively (p < 0.001). The mean D_2cm³ bladder, rectum, sigmoid, and bowel dose was within institutional dose constraints, and increased from 13.0 ±1.5 Gy to 13.6 ±1.5 Gy (p = 0.045), 10.8 ±1.2 Gy to 11.7 ±1.3 Gy (p = 0.004), 8.9 ±3.2 Gy to 10.3 ±3.3 Gy (p = 0.008), and 8.7 ±3.8 Gy to 9.2 ±3.1 Gy (p = 0.2).

Conclusions

With the use of individual 3D-printed applicators, all DVH parameters for CTV-T_HR significantly improved without compromising the dose constraints for the OARs.

Novel intraoperative radiotherapy utilizing prefabricated custom three-dimensionally printed high-dose-rate applicators

BACKGROUND

Intraoperative radiotherapy (IORT) is an effective strategy for the delivery of high doses of radiotherapy to a residual tumor or resection cavity with relative sparing of nearby healthy tissues. This strategy is an important component of the multimodality management of pediatric soft tissue sarcomas, particularly in cases where patients have received prior courses of external beam radiotherapy.

PURPOSE

Tumor beds with significant topographic irregularity remain a therapeutic challenge because existing IORT technologies are typically most reliable with flat surfaces. To address this limitation, we have developed a novel strategy to create custom, prefabricated high-dose-rate (HDR)-IORT applicators designed to match the shape of an anticipated surgical cavity.

METHODS AND MATERIALS

Silastic applicators are constructed using three-dimensional (3D) printing and are derived from volumetric segmentation of preoperative imaging.

RESULTS

HDR preplanning with the applicators improves dosimetric accuracy and minimizes incremental operative time. In this report, we describe the fabrication process for the 3D-printed applicators and detail our experience utilizing this strategy in two pediatric patients who underwent HDR-IORT as part of complex base of skull sarcoma resections.

CONCLUSIONS

Early experience suggests that usage of the custom applicators is feasible, versatile for a variety of clinical situations, and enables the uniform delivery of high superficial doses of radiotherapy to irregularly shaped surgical cavities.

3D printed drug delivery and testing systems - a passing fad or the future?

The US Food and Drug Administration approval of the first 3D printed tablet in 2015 has ignited growing interest in 3D printing, or additive manufacturing (AM), for drug delivery and testing systems. Beyond just a novel method for rapid prototyping, AM provides key advantages over traditional manufacturing of drug delivery and testing systems. These includes the ability to fabricate complex geometries to achieve variable drug release kinetics; ease of personalising pharmacotherapy for patient and lowering the cost for fabricating personalised dosages. Furthermore, AM allows fabrication of complex and micron-sized tissue scaffolds and models for drug testing systems that closely resemble in vivo conditions. However, there are several limitations such as regulatory concerns that may impede the progression to market. Here, we provide an overview of the advantages of AM drug delivery and testing, as compared to traditional manufacturing techniques. Also, we discuss the key challenges and future directions for AM enabled pharmaceutical applications.

3D-printed applicators for high dose rate brachytherapy: Dosimetric assessment at different infill percentage

PURPOSE

Dosimetric assessment of high dose rate (HDR) brachytherapy applicators, printed in 3D with acrylonitrile butadiene styrene (ABS) at different infill percentage.

MATERIALS AND METHODS

A low-cost, desktop, 3D printer (Hamlet 3DX100, Hamlet, Dublin, IE) was used for manufacturing simple HDR applicators, reproducing typical geometries in brachytherapy: cylindrical (common in vaginal treatment) and flat configurations (generally used to treat superficial lesions). Printer accuracy was investigated through physical measurements. The dosimetric consequences of varying the applicator's density by tuning the printing infill percentage were analysed experimentally by measuring depth dose profiles and superficial dose distribution with Gafchromic EBT3 films (International Specialty Products, Wayne, NJ). Dose distributions were compared to those obtained with a commercial superficial applicator.

RESULTS

Measured printing accuracy was within 0.5mm. Dose attenuation was not sensitive to the density of the material. Surface dose distribution comparison of the 3D printed flat applicators with respect to the commercial superficial applicator showed an overall passing rate greater than 94% for gamma analysis with 3% dose difference criteria, 3mm distance-to-agreement criteria and 10% dose threshold.

CONCLUSION

Low-cost 3D printers are a promising solution for the customization of the HDR brachytherapy applicators. However, further assessment of 3D printing techniques and regulatory materials approval are required for clinical application.