Three-dimensional printer-aided casting of soft, custom silicone boluses (SCSBs) for head and neck radiation therapy

Technical note: Commissioning of a low-cost system for directly 3D printed flexible bolus

PURPOSE

To present the commissioning process of a low-cost solution for directly 3D printed flexible patient specific bolus.

METHODS

The 3D printing solution used in this study consisted of a resin stereolithography 3D printer and a flexible curing resin. To test the dimensional accuracy of the 3D printer, rectangular cuboids with varying dimensions were 3D printed and their measured dimensions were compared to the designed dimensions. Percent Depth Dose (PDD) profiles were measured by irradiating film embedded in a 3D printed phantom made of the flexible material. A CT of the phantom was acquired and used to replicate the irradiation setup in the treatment planning system. PDDs were calculated for both the native HU of the phantom, and with the phantom HU overridden to 300 HU to match its physical density. Dosimetric agreement was characterized by comparing calculated to measured depths of R90, R80, and R50. Upon completion of the commissioning process, a bolus was 3D printed for a clinical case study for treatment of the nose.

RESULTS

Dimensional accuracy of the printer and material combination was found to be good, with all measured dimensions of test cuboids within 0.5 mm of designed. PDD measurements demonstrated the best dosimetric agreement when the material was overridden to 300 HU, corresponding to the measured physical density of the material of 1.18 g/cc. Calculated and measured depths of R90, R80, and R50 all agreed within 1 mm. The bolus printed for the clinical case was free from defects, highly conformal, and led to a clinically acceptable plan.

CONCLUSION

The results of the commissioning measurements performed indicate that the 3D printer and material solution are suitable for clinical use. The 3D printer and material combination can provide a low-cost solution a clinic can implement in-house to directly 3D print flexible bolus.

A quick guide on implementing and quality assuring 3D printing in radiation oncology

As three-dimensional (3D) printing becomes increasingly common in radiation oncology, proper implementation, usage, and ongoing quality assurance (QA) are essential. While there have been many reports on various clinical investigations and several review articles, there is a lack of literature on the general considerations of implementing 3D printing in radiation oncology departments, including comprehensive process establishment and proper ongoing QA. This review aims to guide radiation oncology departments in effectively using 3D printing technology for routine clinical applications and future developments. We attempt to provide recommendations on 3D printing equipment, software, workflow, and QA, based on existing literature and our experience. Specifically, we focus on three main applications: patient-specific bolus, high-dose-rate (HDR) surface brachytherapy applicators, and phantoms. Additionally, cost considerations are briefly discussed. This review focuses on point-of-care (POC) printing in house, and briefly touches on outsourcing printing via mail-order services.

Organ sparing treatment for penile cancer using a 3D-printed high-dose-rate brachytherapy applicator

PURPOSE

We present a case study of the treatment of localized squamous cell carcinoma on the glans penis with a custom-fabricated high-dose-rate (HDR) brachytherapy applicator.

METHODS AND MATERIALS

A cylindrically shaped applicator was fabricated with eight embedded channels suitable for standard plastic brachytherapy catheters. An additional custom silicone bolus/sleeve was designed to be used with the 3D-printed applicator to provide an additional offset from the source to skin to reduce the surface dose and for patient comfort.

RESULTS

The patient (recurrent cT1a penile cancer) underwent CT simulation, and the brachytherapy plan was created with a nominal prescription dose of 40 Gy in 10 fractions given bidaily to the surface, and 35 Gy at 5 mm depth. Dose coverage to the clinical target volume was 94% (D90). Most fractions were treated with only 5-10 min of setup time. Follow up visits up to 1 year showed no evidence of disease with no significant changes in urinary and sexual function and limited cosmetic detriment to the patient.

CONCLUSIONS

Patient-specific organ-sparing HDR plesiotherapy using 3D printing technology can provide reliable and reproducible patient setup and may be effective in achieving disease control for superficial penile cancer, although preserving patient quality of life.

3D-printed bolus ensures the precise postmastectomy chest wall radiation therapy for breast cancer

Purpose

To investigate the values of a 3D-printed bolus ensuring the precise postmastectomy chest wall radiation therapy for breast cancer.

Methods and materials

In the preclinical study on the anthropomorphic phantom, the 3D-printed bolus was used for dosimetry and fitness evaluation. The dosimetric parameters of planning target volume (PTV) were assessed, including D_min, D_max, D_mean, D_95%, homogeneity index (HI), conformity index (CI), and organs at risk (OARs). The absolute percentage differences (|%diff|) between the theory and fact skin dose were also estimated, and the follow-up was conducted for potential skin side effects.

Results

In preclinical studies, a 3D-printed bolus can better ensure the radiation coverage of PTV (HI 0.05, CI 99.91%), the dose accuracy (|%diff| 0.99%), and skin fitness (mean air gap 1.01 mm). Of the 27 eligible patients, we evaluated the radiation dose parameter (median(min–max): D_min 4967(4789–5099) cGy, D_max 5447(5369–5589) cGy, D_mean 5236(5171–5323) cGy, D_95% 5053(4936–5156) cGy, HI 0.07 (0.06–0.17), and CI 99.94% (97.41%–100%)) and assessed the dose of OARs (ipsilateral lung: D_mean 1341(1208–1385) cGy, V₅ 48.06%(39.75%–48.97%), V₂₀ 24.55%(21.58%–26.93%), V₃₀ 18.40%(15.96%–19.16%); heart: D_mean 339(138–640) cGy, V₃₀ 1.10%(0%–6.14%), V₄₀ 0.38%(0%–4.39%); spinal cord PRV: D_max 639(389–898) cGy). The skin doses in vivo were D_theory 208.85(203.16–212.53) cGy, D_fact 209.53(204.14–214.42) cGy, and |%diff| 1.77% (0.89–2.94%). Of the 360 patients enrolled in the skin side effect follow-up study (including the above 27 patients), grade 1 was the most common toxicity (321, 89.2%), some of which progressing to grade 2 or grade 3 (32, 8.9% or 7, 1.9%); the radiotherapy interruption rate was 1.1%.

Conclusion

A 3D-printed bolus can guarantee the precise radiation dose on skin surface, good fitness to skin, and controllable acute skin toxicity, which possesses a great clinical application value in postmastectomy chest call radiation therapy for breast cancer.

Dosimetric considerations for moldable silicone composites used in radiotherapy applications

Due to their many favorable characteristics, moldable silicone (MS) composites have gained popularity in medicine and recently, in radiotherapy applications. We investigate the dosimetric properties of silicones in radiotherapy beams and determine their suitability as water substitutes for constructing boluses and phantoms. Two types of silicones were assessed (ρ= 1.04 g/cm³ and ρ= 1.07 g/cm³). Various dosimetric properties were characterized, including the relative electron density, the relative mean mass energy‐absorption coefficient, and the relative mean mass restricted stopping power. Silicone slabs with thickness of 1.5 cm and 5.0 cm were molded to mimic a bolus setup and a phantom setup, respectively. Measurements were conducted for Co‐60 and 6 MV photon beams, and 6 MeV electron beams. The doses at 1.5 cm and 5.0 cm depths in MS were measured with solid water (SW) backscatter material (D_MS–SW), and with a full MS setup (D_MS–MS), then compared with doses at the same depths in a full SW setup (D_SW–SW). Relative doses were reported as D_MS–SW/D_MS–SW and D_MS–MS/D_SW–SW. Experimental results were verified using Monaco treatment planning system dose calculations and Monte Carlo EGSnrc simulations. Film measurements showed varying dose ratios according to MS and beam types. For photon beams, the bolus setup D_MS–SW/D_SW–SW exhibited a 5% relative dose reduction. The dose for 6 MV beams was reduced by nearly 2% in a full MS setup. Up to 2% dose increase in both scenarios was observed for electron beams. Compared with dose in SW, an interface of MS–SW can cause relatively high differences. We conclude that it is important to characterize a particular silicone's properties in a given beam quality prior to clinical use. Because silicone compositions vary between manufacturers and differ from water/SW, accurate dosimetry using these materials requires consideration of the reported differences.

Technical note: Evaluation of a silicone-based custom bolus for radiation therapy of a superficial pelvic tumor

Purpose

Use of standard‐of‐care radiation therapy boluses may result in air‐gaps between the target surface and bolus, as they may not adequately conform to each patient's unique topography. Such air‐gaps can be particularly problematic in cases of superficial pelvic tumor radiation, as the density variation may result in the radiation delivered to the target site being inconsistent with the prescribed dose. To increase bolus fit and thereby dose predictability and homogeneity, we designed and produced a custom silicone bolus for evaluation against the clinical standard.

Methods

A custom bolus was created for the pelvic regions of both an anthropomorphic phantom and a pelvic patient with squamous cell carcinoma of the penile shaft. Molds were designed using computed tomography (CT) scans, then 3D‐printed and cast with silicone rubber to yield the boluses. Air‐gap measurements were performed on custom and standard‐of‐care Superflab gel sheet boluses by analyzing total volume between the bolus and target surface, as measured from CT scans. Therapeutic doses of radiation were delivered to both boluses. Radiation dose was measured and compared to the expected dose using nine optically stimulated luminescent dosimeters (OSLDs) placed on the phantom.

Results

Mean air‐gap volume between the bolus and phantom was decreased from 314 ± 141 cm³ with the standard bolus to 4.56 ± 1.59 cm³ using the custom device. In the case of the on‐treatment patient, air‐gap volume was reduced from 169 cm³ with the standard bolus to 46.1 cm³ with the custom. Dosimetry testing revealed that the mean absolute difference between expected and received doses was 5.69%±4.56% (15.1% maximum) for the standard bolus and 1.91%±1.31% (3.51% maximum) for the custom device. Areas of greater dose difference corresponded to areas of larger air‐gap.

Conclusions

The custom bolus reduced air‐gap and increased predictability of radiation dose delivered compared to the standard bolus. The custom bolus could increase the certainty of prescribed dose‐delivery of radiation therapy for superficial tumors.

3D Printing Polymer-based Bolus Used for Radiotherapy

Bolus is a kind of auxiliary device used in radiotherapy for the treatment of superficial lesions such as skin cancer. It is commonly used to increase skin dose and overcome the skin-sparing effect. Despite the availability of various commercial boluses, there is currently no bolus that can form full contact with irregular surface of patients' skin, and incomplete contact would result in air gaps. The resulting air gaps can reduce the surface radiation dose, leading to a discrepancy between the delivered dose and planned dose. To avoid this limitation, the customized bolus processed by three-dimensional (3D) printing holds tremendous potential for making radiotherapy more efficient than ever before. This review mainly summarized the recent development of polymers used for processing bolus, 3D printing technologies suitable for polymers, and customization of 3D printing bolus. An ideal material for customizing bolus should not only have the feature of 3D printability for customization, but also possess radiotherapy adjuvant performance as well as other multiple compound properties, including tissue equivalence, biocompatibility, antibacterial activity, and antiphlogosis.

The Clinical Application of 3D-Printed Boluses in Superficial Tumor Radiotherapy

During the procedure of radiotherapy for superficial tumors, the key to treatment is to ensure that the skin surface receives an adequate radiation dose. However, due to the presence of the built-up effect of high-energy rays, equivalent tissue compensators (boluses) with appropriate thickness should be placed on the skin surface to increase the target radiation dose. Traditional boluses do not usually fit the skin perfectly. Wet gauze is variable in thickness day to day which results in air gaps between the skin and the bolus. These unwanted but avoidable air gaps lead to a decrease of the radiation dose in the target area and can have a poor effect on the outcome. Three-dimensional (3D) printing, a new rising technology named “additive manufacturing” (AM), could create physical models with specific shapes from digital information by using special materials. It has been favored in many fields because of its advantages, including less waste, low-cost, and individualized design. It is not an exception in the field of radiotherapy, personalized boluses made through 3D printing technology also make up for a number of shortcomings of the traditional commercial bolus. Therefore, an increasing number of researchers have tried to use 3D-printed boluses for clinical applications rather than commercial boluses. Here, we review the 3D-printed bolus’s material selection and production process, its clinical applications, and potential radioactive dermatitis. Finally, we discuss some of the challenges that still need to be addressed with the 3D-printed boluses.

Evaluating 3D-printed Bolus Compared to Conventional Bolus Types Used in External Beam Radiation Therapy

BACKGROUND

When treating superficial tumors with external beam radiation therapy, bolus is often used. Bolus increases surface dose, reduces dose to underlying tissue, and improves dose homogeneity.

INTRODUCTION

The conventional bolus types used clinically in practice have some disadvantages. The use of Three-Dimensional (3D) printing has the potential to create more effective boluses. CT data is used for dosimetric calculations for these treatments and often to manufacture the customized 3D-printed bolus.

PURPOSE

The aim of this review is to evaluate the published studies that have compared 3D-printed bolus against conventional bolus types.

METHODS AND RESULTS

A systematic search of several databases and a further appraisal for relevance and eligibility resulted in the 14 articles used in this review. The 14 articles were analyzed based on their comparison of 3D-printed bolus and at least one conventional bolus type.

CONCLUSION

The findings of this review indicated that 3D-printed bolus has a number of advantages. Compared to conventional bolus types, 3D-printed bolus was found to have equivalent or improved dosimetric measures, positional accuracy, fit, and uniformity. 3D-printed bolus was also found to benefit workflow efficiency through both time and cost effectiveness. However, factors such as patient comfort and staff perspectives need to be further explored to support the use of 3Dprinted bolus in routine practice.

Dose calculation of 3D printing lead shield covered by biocompatible silicone for electron beam therapy

This study aims to calculate the dose delivered to the upstream surface of a biocompatible flexible absorber covering lead for electron beam treatment of skin and subcutaneous tumour lesions for head and neck. Silicone (Ecoflex™ 00-30, Smooth-On, Easton, PA, USA) was used to cover the lead to absorb backscattered electrons from lead. A 3D printer (Zortrax M300, Zortrax, Olsztyn, Poland) was used to fabricate the lead shield. Analytic calculation, simplified Monte Carlo (MC) simulation, and detailed MC simulation which includes a modeling of metal-oxide-semiconductor field-effect transistor (MOSFET) detector were performed to determine the electron backscatter factor (EBF) for 6 MeV and 9 MeV electron beams of a Varian iX Silhouette. MCNP6.2 was used to calculate the EBF and corresponding measurements were carried out by using MOSFET detectors. The EBF was experimentally measured by the ratio of dose at the upstream surface of the silicone to the same point without the presence of the lead shield. The results derived by all four methods agreed within 2.8% for 6 MeV and 3.4% for 9 MeV beams. In detailed MC simulations, for 6 MeV, dose to the surface of 7-mm-thick absorber was 103.7 [Formula: see text] 1.9% compared to dose maximum (D_max) without lead. For 9 MeV, the dose to the surface of the 10-mm-thick absorber was 104.1 [Formula: see text] 2.1% compared to D_max without lead. The simplified MC simulation was recommended for practical treatment planning due to its acceptable calculation accuracy and efficiency. The simplified MC simulation was completed within 20 min using parallel processing with 80 CPUs, while the detailed MC simulation required 40 h to be done. In this study, we outline the procedures to use the lead shield covered by silicone in clinical practice from fabrication to dose calculation.

Customized 3D Bolus Applied to the Oral Cavity and Supraclavicular Area for Head and Neck Cancer

BACKGROUND/AIM

In this study, a new method to create a customized three-dimensional (3D) bolus by accurately considering the anatomy of an individual patient is demonstrated.

PATIENTS AND METHODS

A 3D bolus structure was created from an extended planning target volume (PTV) to reduce an inevitable skin reaction. In addition, during computed tomography simulation in patients with oral cavity cancers, a balloon was inserted into the mouth of a patient to secure space, and then the area surrounding the balloon was designed into a 3D bolus structure.

RESULTS

For patients with head and neck cancers, a customized 3D bolus can reduce the unnecessary skin dose by 14.4% compared to a commercial bolus. For patients with oral cavity cancer, the PTV and tongue doses were 93.8% and 8% of the prescribed dose, respectively.

CONCLUSION

The customized 3D bolus enables effective skin sparing and full coverage of the target area.

Development of a transparent and flexible patient-specific bolus for total scalp irradiation

A commercially available flat bolus (commercial bolus) would not fully fit the irregular surfaces of the scalp. We developed a transparent and flexible material with good fitting properties, analyzed its physical characteristics, and evaluated the clinical feasibility of the bolus fabricated using a three-dimensional (3D) printer (3D bolus). To evaluate the physical characteristics of the new material, treatment plans with virtual, 3D, and commercial boluses were created for water-equivalent phantoms using a radiation treatment planning system (RTPS). Using a head phantom and the dose volume histogram calculated with RTPS, dose distributions for total scalp irradiation were compared between the three treatment plans. To evaluate the clinical feasibility, the fitness and reproducibility of the 3D bolus were compared with the head phantom and clinical cases using dice similarity coefficient (DSC) measurements. A good agreement was observed between the percentage depth dose (PDD) curves for the virtual, 3D, and commercial boluses. The homogeneity indexes of the planning target volume (PTV) for the 3D and commercial boluses were 0.083 and 0.153, respectively, proving that the former achieved a better dose uniformity of PTV than the latter. Good fitness and reproducibility with the 3D bolus were observed in both the head phantom and two clinical cases, with mean DSC values of 0.854, 0.829, and 0.843, respectively. These results successfully demonstrated and verified the utility of the 3D bolus for total scalp irradiation.

A novel approach to embed eye shields in customized bolus on nasal dorsum treatment for electron radiotherapy

We aim to demonstrate the unique use of embedded lead eye shields in an electron wax bolus when treating the nasal dorsum. A patient presented to the clinic with squamous cell carcinoma of the nasal dorsum requiring treatment with en face electrons. A 3D customized wax bolus was designed and imported into the treatment planning system (TPS) to calculate the dose distribution. Due to high lens dose, the bolus was customized further to create 2 milled open slots in the wax, over the lens of eye, to allow lead sheets totaling 4 mm to be slid into the wax. The patient was brought back to the clinic to be scanned with the wax bolus fitting snugly over the nose, eyes, and cheek regions. The 3D milled insert holes were contoured on the CT in the TPS, assigned HU of 2758, to mimic the lead insertion. The lens dose with lead inserts was compared to the plan without lead insert. To further confirm the lens dose, EBT3 films were placed on the right and left eye under the bolus, and nose dorsum on the first day of treatment. The maximum dose of right lens, as calculated in the TPS with the simulated lead shields in place, decreased from 989.5cGy to 457cGy. The maximum dose of left lens decreased from 1085.4cGy to 501cGy. The dose readings from EBT3 films were in good agreement with the TPS, with deviation of 3.32%, 0.26%, and 3.44% for right lens, left lens, and nose, respectively. Daily positioning deviations compared to the plan were 0.65 ± 0.16cm and 0.63 ± 0.29cm for right eye and left eye, respectively. This novel device demonstrated the feasibility, in terms of dose calculation accuracy in the TPS and fabrication, of using customized bolus with lead inserts to conveniently shield the lens of the eyes in an electron treatment for the nose, enabling a streamlined daily setup.

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

Purpose

Frameless Gamma Knife stereotactic radiosurgery (SRS) uses a moldable headrest with a thermoplastic mask for patient immobilization. An efficacious headrest is time consuming and difficult to fabricate due to the expertise required to mold the headrest within machine geometrical limitations. The purpose of this study was to design and validate a three‐dimensional (3D)‐printed headrest for frameless Gamma Knife SRS that can overcome these difficulties.

Materials and methods

A headrest 3D model designed to fit within the frameless adapter was 3D printed. Dosimetric properties of the 3D‐printed headrest and a standard‐of‐care moldable headrest were compared by delivering a Gamma Knife treatment to an anthropomorphic head phantom fitted with an ionization chamber and radiochromic film. Ionization measurements were compared to assess headrest attenuation and a gamma index was calculated to compare the film dose distributions. A volunteer study was conducted to assess the immobilization efficacy of the 3D‐printed headrest compared to the moldable headrest. Five volunteers had their head motion tracked by a surface tracking system while immobilized in each headrest for 20 min. The recorded motion data were used to calculate the average volunteer movement and a paired t‐test was performed.

Results

The ionization chamber readings were within 0.55% for the 3D‐printed and moldable headrests, and the calculated gamma index showed 98.6% of points within dose difference of 2% and 2 mm distance to agreement for the film measurement. These results demonstrate that the headrests were dosimetrically equivalent within the experimental uncertainties. Average motion (±standard deviation) of the volunteers while immobilized was 1.41 ± 0.43 mm and 1.36 ± 0.51 mm for the 3D‐printed and moldable headrests, respectively. The average observed volunteer motion between headrests was not statistically different, based on a P‐value of 0.466.

Conclusions

We designed and validated a 3D‐printed headrest for immobilizing patients undergoing frameless Gamma Knife SRS.

Novel application of vinylpolysiloxane hearing aid impression mold as patient-specific bolus for head and neck cancer radiotherapy

Hearing aid impression material composed of vinylpolysiloxane is an ideal bolus material which may be used to aid in delivery of adjuvant radiation to complex surgical defects of the head and neck. It is affordable, easily accessed, and efficient.

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.

Dosimetric characterization of a rigid, surface-contour-specific thermoplastic bolus material

A dosimetric analysis of a commercially available thermoplastic sheet bolus, Klarity EZ Bolus^TM, was completed. Attenuation characteristics were evaluated using different configurations of a rectilinear water-mimicking plastic phantom irradiated by a high-energy linear accelerator using three photon energies, five electron energies. These results were compared with data obtained during the linear accelerator commissioning process to determine depths of water that attenuated beams similarly. CT scans of the flat, unmolded sheet bolus, as well as of the bolus molded to a cylindrical phantom, were analyzed. The product was found to form a durable and rigid, contour-specific bolus with a water-equivalent thickness of approximately 6 mm for a single sheet, and 11 mm for two sheets in tandem.

Development and validation of a 3D-printed bolus cap for total scalp irradiation

PURPOSE

The goal of total scalp irradiation (TSI) is to deliver a uniform dose to the scalp, which requires the use of a bolus cap. Most current methods for fabricating bolus caps are laborious, yet still result in nonconformity and low reproducibility, which can lead to nonuniform irradiation of the scalp. We developed and validated patient-specific bolus caps for TSI using three-dimensional (3D) printing.

METHODS AND MATERIALS

3D-printing materials were radiologically analyzed to identify a material with properties suitable for use as a bolus cap. A Python script was developed within a commercial treatment planning system to automate the creation of a ready-to-print, patient-specific 3D bolus cap model. A bolus cap was printed for an anthropomorphic head phantom using a commercial vendor and a computed tomography simulation of the anthropomorphic head phantom and bolus cap was used to create a volumetric-modulated arc therapy TSI treatment plan. The planned treatment was delivered to the head phantom and dosimetric validation was performed using thermoluminescent dosimeters (TLD). The developed procedure was used to create a bolus cap for a clinical TSI patient, and in vivo TLD measurements were acquired for several fractions.

RESULTS

Agilus-60 was validated as a new 3D-printing material suitable for use as bolus. A 3D-printed Agilus-60 bolus cap had excellent conformality to the phantom scalp, with a maximum air gap of 4 mm. TLD measurements showed that the bolus cap generated a uniform dose to the scalp within a 2.7% standard deviation, and the delivered doses agreed with calculated doses to within 2.4% on average. The patient bolus was conformal and the average difference between TLD measured and planned doses was 5.3%.

CONCLUSIONS

We have developed a workflow to 3D-print highly conformal bolus caps for TSI and demonstrated these caps can reproducibly generate a uniform dose to the scalp.

Workload implications for clinic workflow with implementation of three-dimensional printed customized bolus for radiation therapy: A pilot study

Bolus is commonly used in radiation therapy to improve radiation dose distribution to the target volume, but commercially available products do not always conform well to the patient surface. Tumor control may be compromised, particularly for superficial tumors, if bolus does not conform well and air gaps exist between the patient surface and the bolus. Three-dimensional (3D) printing technology allows the creation of highly detailed, variable shaped objects, making it an attractive and affordable option for customized, patient-specific bolus creation. The use of 3D printing in the clinical setting remains limited. Therefore, the objective of this study was to assess the implications on time and clinical fit using a workflow for 3D printing of customized bolus in companion animals with spontaneous tumors treated with radiation therapy. The primary aim of this study was to evaluate the time required to create a clinical 3D printed bolus. The secondary aims were to evaluate the clinical fit of the bolus and to verify the skin surface dose. Time to segmentation and 3D printing were documented, while the clinical fit of the bolus was assessed in comparison to the bolus created in the treatment planner. The mean and median time from segmentation to generation of 3D printed boluses was 6.15 h and 5.25 h, respectively. The 3D printed bolus was significantly less deviated from the planned bolus compared to the conventional bolus (p = 0.0078) with measured dose under the bolus within 5% agreement of expected dose in 88% of the measurements. Clinically acceptable 3D printed customized bolus was successfully created for treatment within one working day. The most significant impact on time is the 3D printing itself, which therefore has minimal implications on personnel and staffing. Quality assurance steps are recommended when implementing a 3D printing workflow to the radiotherapy clinic.

[Introduction and Applications of 3D Printing in Radiological Technology]

A 3D printing emerges as a common procedure in clinical radiology practice after installation of a module that converts the digital imaging and communications in medicine (DICOM) dataset into stereolithography (STL) data on medical workstations. However, they did not conventionally provide the appropriate filtering, sculpting, hollowing out, and Boolean (subtraction) operations on STL data. These functions are indispensable to handle the STL data to fabricate the smooth, low-cost, and sophisticated models. Here are some tips for handling the 3D data with three software packages through making a sample lumbar spine model. Because they are all free- and open-source software with the exception of Boolean operations, they could make it easy for anyone to fabricate their 3D model imaged by CT or MRI. We tested the loop subdivision surface algorithms for the smoothing, the sculpting function for removing a sharp prick, and the hollowing function to save the cost. Computer-aided design (CAD) is also used to fabricate the devices in medical research. We designed and developed a cap attached to a glass dosimeter to show the effectiveness of CAD in radiological research. Lastly, we discuss the important matters for 3D printing and examples of the clinical applications.