Tungsten Filled 3-Dimensional Printed Lung Blocks for Total Body Irradiation

PURPOSE

Lung blocks for total-body irradiation are commonly used to reduce lung dose and prevent radiation pneumonitis. Currently, molten Cerrobend containing toxic materials, specifically lead and cadmium, is poured into molds to construct blocks. We propose a streamlined method to create 3-dimensional (3D)-printed lung block shells and fill them with tungsten ball bearings to remove lead and improve overall accuracy in the block manufacturing workflow.

METHODS AND MATERIALS

3D-printed lung block shells were automatically generated using an inhouse software, printed, and filled with 2 to 3 mm diameter tungsten ball bearings. Clinical Cerrobend blocks were compared with the physician drawn blocks as well as our proposed tungsten filled 3D-printed blocks. Physical and dosimetric comparisons were performed on a linac. Dose transmission through the Cerrobend and 3D-printed blocks were measured using point dosimetry (ion-chamber) and the on-board Electronic-Portal-Imaging-Device (EPID). Dose profiles from the EPID images were used to compute the full-width-half-maximum and to compare with the treatment-planning-system. Additionally, the coefficient-of-variation in the central 80% of full-width-half-maximum was computed and compared between Cerrobend and 3D-printed blocks.

RESULTS

The geometric difference between treatment-planning-system and 3D-printed blocks was significantly lower than Cerrobend blocks (3D: -0.88 ± 2.21 mm, Cerrobend: -2.28 ± 2.40 mm, P = .0002). Dosimetrically, transmission measurements through the 3D-printed and Cerrobend blocks for both ion-chamber and EPID dosimetry were between 42% to 48%, compared with the open field. Additionally, coefficient-of-variation was significantly higher in 3D-printed blocks versus Cerrobend blocks (3D: 4.2% ± 0.6%, Cerrobend: 2.6% ± 0.7%, P < .0001).

CONCLUSIONS

We designed and implemented a tungsten filled 3D-printed workflow for constructing total-body-irradiation lung blocks, which serves as an alternative to the traditional Cerrobend based workflow currently used in clinics. This workflow has the capacity of producing clinically useful lung blocks with minimal effort to facilitate the removal of toxic materials from the clinic.

Chest wall pain after single-fraction thoracic stereotactic ablative Radiotherapy: Dosimetric analysis from the iSABR trial

BACKGROUND AND PURPOSE

Concerns over chest wall toxicity has led to debates on treating tumors adjacent to the chest wall with single-fraction stereotactic ablative radiotherapy (SABR). We performed a secondary analysis of patients treated on the prospective iSABR trial to determine the incidence and grade of chest wall pain and modeled dose-response to guide radiation planning and estimate risk.

MATERIALS AND METHODS

This analysis included 99 tumors in 92 patients that were treated with 25 Gy in one fraction on the iSABR trial which individualized dose by tumor size and location. Toxicity events were prospectively collected and graded based on the CTCAE version 4. Dose-response modeling was performed using a logistic model with maximum likelihood method utilized for parameter fitting.

RESULTS

There were 22 grade 1 or higher chest wall pain events, including five grade 2 events and zero grade 3 or higher events. The volume receiving at least 11 Gy (V11Gy) and the minimum dose to the hottest 2 cc (D2cc) were most highly correlated with toxicity. When dichotomized by an estimated incidence of ≥ 20 % toxicity, the D2cc > 17 Gy (36.6 % vs. 3.7 %, p < 0.01) and V11Gy > 28 cc (40.0 % vs. 8.1 %, p < 0.01) constraints were predictive of chest wall pain, including among a subset of patients with tumors abutting or adjacent to the chest wall.

CONCLUSION

For small, peripheral tumors, single-fraction SABR is associated with modest rates of low-grade chest wall pain. Proximity to the chest wall may not contraindicate single fractionation when using highly conformal, image-guided techniques with sharp dose gradients.

A clinical solution for non-toxic 3D-printed photon blocks in external beam radiation therapy

PURPOSE

A well-known limitation of multi-leaf collimators is that they cannot easily form island blocks. This can be important in mantle region therapy. Cerrobend photon blocks, currently used for supplementary shielding, are labor-intensive and error-prone. To address this, an innovative, non-toxic, automatically manufactured photon block using 3D-printing technology is proposed, offering a patient-specific and accurate alternative.

METHODS AND MATERIALS

The study investigates the development of patient-specific photon shielding blocks using 3D-printing for three different patient cases. A 3D-printed photon block shell filled with tungsten ball bearings (BBs) was designed to have similar dosimetric properties to Cerrobend standards. The generation of the blocks was automated using the Eclipse Scripting API and Python. Quality assurance was performed by comparing the expected and actual weight of the tungsten BBs used for shielding. Dosimetric and field geometry comparisons were conducted between 3D-printed and Cerrobend blocks, utilizing ionization chambers, imaging, and field geometry analysis.

RESULTS

The quality assurance assessment revealed a -1.3% average difference in the mass of tungsten ball bearings for different patients. Relative dose output measurements for three patient-specific blocks in the blocked region agreed within 2% of each other. Against the Treatment Planning System (TPS), both 3D-printed and Cerrobend blocks agreed within 2%. For each patient, 6 MV image profiles taken through the 3D-printed and Cerrobend blocks agreed within 1% outside high gradient regions. Jaccard distance analysis of the MV images against the TPS planned images, found Cerrobend blocks to have 15.7% dissimilarity to the TPS, while that of the 3D-printed blocks was 6.7%.

CONCLUSIONS

This study validates a novel, efficient 3D-printing method for photon block creation in clinical settings. Despite potential limitations, the benefits include reduced manual labor, automated processes, and greater precision. It holds potential for widespread adoption in radiation therapy, furthering non-toxic radiation shielding.

An Affordable Platform for Virtual Reality-Based Patient Education in Radiation Therapy

PURPOSE

The goal of this study was to develop and assess the effectiveness of an affordable smartphone-based virtual reality (VR) patient education platform with 360-degree videos produced depicting a first-person patient perspective during the radiation therapy (RT) care path to reduce patient anxiety.

METHODS AND MATERIALS

Three disease site-specific (breast, pelvis, head and neck) VR videos were filmed using a 360-degree camera to portray the first-person perspective of a patient's standard RT appointments, including a computed tomography simulation and the first RT treatment session. Instruction is given for possible clinical implementation. Patient participation was divided into 2 groups: (1) Group A (n = 28) included patients participating before simulation and later after the first treatment, and (2) Group B (n = 33) included patients participating only while undergoing treatment. Patients viewed their disease site-specific video using an inexpensive cardboard VR viewer and their smartphone, emulating an expensive VR-headset. Surveys were administered assessing patient anxiety, comfort, satisfaction, and knowledge of RT on a 5-point Likert-type scale.

RESULTS

Patients in Group A and Group B while undergoing treatment both indicated that their anxiety "decreased a little" in the survey, after watching the VR video (Group A, median on a 5-point Likert-type scale, 4 [IQR, 4-5]; Group B, 4 [IQR, 4-4]). The VR aspect of the videos was especially liked by patients while undergoing treatment, with 96.4% in Group A and 90.9% in Group B reporting that the VR aspect of the videos was helpful. All Group A participants believed that the VR videos would be beneficial to new patients.

CONCLUSIONS

Our affordable VR patient education platform effectively immerses a patient in their care path from simulation through initial treatment delivery, reducing anxiety and increasing familiarity with the treatment process.

Closing the Loop: Toward Sustainable 3D Print Recycling in the Clinic

PURPOSE/OBJECTIVE(S)

THREE-DIMENSIONAL (: 3D) printing is becoming ubiquitous in Radiation Therapy resulting in large amounts of plastic waste generated. We report on the feasibility, workflows, material properties and cost effectiveness of 3D print recycling to increase sustainability of 3D printing in clinics.

MATERIALS/METHODS

Polylactic acid (PLA) prints were recycled using a consumer-grade recycling system consisting of i) plastic shredder to granulate used prints ii) heated extruder to melt material into filament iii) fan-cooled path for rapid cooling iv) spooling rig and v) pelletizer to cut filament into more regularized pellets as input material for step ii). The recovery percentage of material was characterized after each step by weighing inputs/outputs; timing and workloads were also recorded. Resulting recycled filaments were characterized in diameter and tensile strength and were compared between two different extruder nozzle configurations and with vs without pelletization to find an optimal recycling process. Recycled filament was finally used to create clinical items and evaluated. Lastly, a cost analysis over the past 1 year of recycling use was performed to determine the cost effectiveness of the recycling system.

RESULTS

PLA prints were recycled with an overall efficiency of 79.3 ± 12.2% (standard deviation) between color batch runs. The best recycled filament quality was produced using the pelletization process and wider 3.25mm extruder nozzle. Relative to new filament, tensile strength testing showed recycled filament strength was 79% vs 70% (pelletized vs unpelletized) and 86% vs 60% (3.25mm vs 2.85mm nozzle). Extrusion and spooling procedures proved difficult to optimize, requiring lots of operator supervision (∼45 minutes per spool, mean 475g) and achieved a best filament diameter of 2.85 ± 0.09mm. A cost analysis shows that without accounting for operator time, it would require over 25 years to recoup the cost of the recycling system.

CONCLUSION

Over the past 1-year, clinical 3D printing at our site consisted of 40 patient boluses and 25 electron cutouts, consuming about 6.5kg of PLA. Due to infection control concerns only 35% of this material was eligible for recycling, however 3.5 times that amount was collected from other printing activities. Recycling reduced new filament use by 56% ($470). Recycling workflows proved difficult to streamline and resulted in filament diameter that was marginally outside common industry standards and about 20% less strong but deemed adequate for clinical printing. Although the cost savings analysis indicates a poor return on investment, increasing the scale of the operation would be beneficial. To achieve this, we plan to recycle PLA boluses after disinfection and solicit other clinics in our hospital network and local 3D printing hobbyist community to recycle their prints.

Predicting Local Control with Dosimetric Parameters in Patients Receiving Individualized Stereotactic Ablative Radiotherapy for Lung Tumors

PURPOSE/OBJECTIVE(S)

Stereotactic ablative radiotherapy (SABR) is an effective treatment option for lung tumors. The individualized lung tumor SABR (iSABR) trial was a phase II single-arm study that personalized lung tumor SABR dose and fractionation based on tumor size, location, and histology with very low rates of local recurrence (LR). A secondary analysis of this trial was conducted to assess for potential dosimetric predictors of LR, in order to help guide future clinical treatment planning.

MATERIALS/METHODS

From 2011 to 2018, local, regional and distant recurrence data were prospectively collected from 204 patients (261 lung SABR treatments) enrolled in a prospective trial. Baseline characteristics and treatment details were evaluated. Dosimetric and treatment plan parameters were evaluated for their potential to predict LR, using logistic regression and chi-squared analyses.

RESULTS

The majority of treated tumors were peripheral (71%, vs 29% central), primary lesions (76%, versus 24% metastatic), and of adenocarcinoma histology (67%, versus 13% squamous cell carcinoma and 19% other). The median follow-up was 24 months (range 2-95). Twenty-seven (10.3%) LRs occurred, with a median time to LR of 15 months (range 6-81 months). There were no significant associations between the overall cohort and the dosimetric parameters. However, for the multi-fraction cohort, an increased proportion of the PTV receiving 110% and 115% of the prescription dose were associated with lower LR (p = 0.01 and p = 0.01 respectively). Specifically for the 50 Gy in 4 fraction cohort, an increased D1cc, D0.03cc, as well as the proportion of the PTV receiving 110%, 115%, and 120% of the prescription dose were associated with lower LR (p < 0.001, p = 0.001, p = 0.003, p < 0.001, p = 0.004, respectively). There was no association of LR with prescription dose expressed as biologically effective dose using an alpha/beta of 10 Gy (BED10), D99%, or single- versus multi-fraction regimens.

CONCLUSION

SABR for lung tumors using the individualized protocol on this trial showed excellent LR rates. We identified dosimetric parameters that were associated with LR, including V110% and V115% within the multi-fraction cohort, as well as the 50 Gy in 4 fraction cohort the D1cc, D0.03cc, and proportions of the PTV receiving 110%, 115%, and 120% of the prescription dose in the 50 Gy in 4 fraction cohort. Optimal thresholds for these parameters will be identified in further analyses. There did not appear to be an association with LR and BED10, D99%, or comparing single- vs multi-fraction regimens.

Shaping success: clinical implementation of a 3D-printed electron cutout program in external beam radiation therapy

Purpose

The integration of 3D-printing technology into radiation therapy (RT) has allowed for a novel method to develop personalized electron field-shaping blocks with improved accuracy. By obviating the need for handling highly toxic Cerrobend molds, the clinical workflow is significantly streamlined. This study aims to expound upon the clinical workflow of 3D-printed electron cutouts in RT and furnish one year of in-vivo dosimetry data.

Methods and materials

3D-printed electron cutouts for 6x6 cm, 10x10 cm, and 15x15 cm electron applicators were designed and implemented into the clinical workflow after dosimetric commissioning to ensure congruence with the Cerrobend cutouts. The clinical workflow consisted of four parts: i) the cutout aperture was extracted from the treatment planning system (TPS). A 3D printable cutout was then generated automatically through custom scripts; ii) the cutout was 3D-printed with PLA filament, filled with tungsten ball bearings, and underwent quality assurance (QA) to verify density and dosimetry; iii) in-vivo dosimetry was performed with optically stimulated luminescence dosimeters (OSLDs) for a patient's first treatment and compared to the calculated dose in the TPS; iv) after treatment completion, the 3D-printed cutout was recycled.

Results

QA and in-vivo OSLD measurements were conducted (n=40). The electron cutouts produced were 6x6 cm (n=3), 10x10 cm (n=30), and 15x15 cm (n=7). The expected weight of the cutouts differed from the measured weight by 0.4 + 1.1%. The skin dose measured with the OSLDs was compared to the skin dose in the TPS on the central axis. The difference between the measured and TPS doses was 4.0 + 5.2%.

Conclusion

The successful clinical implementation of 3D-printed cutouts reduced labor, costs, and removed the use of toxic materials in the workplace while meeting clinical dosimetric standards.

Learning image representations for content-based image retrieval of radiotherapy treatment plans

Objective.In this work, we propose a content-based image retrieval (CBIR) method for retrieving dose distributions of previously planned patients based on anatomical similarity. Retrieved dose distributions from this method can be incorporated into automated treatment planning workflows in order to streamline the iterative planning process. As CBIR has not yet been applied to treatment planning, our work seeks to understand which current machine learning models are most viable in this context.Approach.Our proposed CBIR method trains a representation model that produces latent space embeddings of a patient's anatomical information. The latent space embeddings of new patients are then compared against those of previous patients in a database for image retrieval of dose distributions. All source code for this project is available on github.Main results.The retrieval performance of various CBIR methods is evaluated on a dataset consisting of both publicly available image sets and clinical image sets from our institution. This study compares various encoding methods, ranging from simple autoencoders to more recent Siamese networks like SimSiam, and the best performance was observed for the multitask Siamese network.Significance.Our current results demonstrate that excellent image retrieval performance can be obtained through slight changes to previously developed Siamese networks. We hope to integrate CBIR into automated planning workflow in future works.

Abstract 109: A Longitudinal Telehealth Curriculum for Radiation Oncology Centers in Low and Middle-Income Countries Transitioning from 2D to 3D External Beam Radiation Therapy

Purpose: The transition from 2-dimensional (2D) to 3-dimensional (3D) external beam radiation therapy (EBRT) can dramatically improve the quality of radiotherapy in low and middle-income countries (LMICs); however, many cancer centers in LMICs lack training support to effectively make this transition. Remote training is a low-cost, accessible option to bridge this gap, and we sought to evaluate the efficacy of such a program.

Methods: The nonprofit Rayos Contra Cancer identified 9 LMIC operational cancer centers in the Middle East and Northern Africa that had recently acquired technology to transition from 2D to 3D EBRT. Baseline information for each center was collected electronically, then a team of EBRT content experts developed a 12-week, 25-session continuing medical education curriculum. Each session invited live participation using Zoom video communications and lasted 1 - 2 hours. Participants were administered a Likert scale (1-5) confidence evaluation on 13 foundational topics in 3D EBRT and a 49-point knowledge-based multiple-choice examination pre- and post- curriculum. Anonymous feedback with 1-5 satisfaction scores for each session was solicited midway and at the conclusion of the curriculum. Training was provided for free.

Results: Among centers, 260 participants enrolled in training, including 39 medical physicists, 36 radiation oncologists, 54 radiation therapists, 15 dosimetrists, and 116 in training or other roles. Pre- and post-curriculum average examination scores were 22.95/49 (53.4%, N = 171) and 30.76/49 (62.8%, N=87), respectively. Pre- and post-curriculum confidence evaluation showed an average of 1.4/5 (27.7%, N=260) and 3.86 (77.2%, N=74) confidence among 13 topics. Satisfaction surveys (halfway N=51, end N=48) showed high satisfaction with helpfulness (4.3/5) enjoyableness (4.2/5), and well-preparedness (4.4/5) of sessions.

Conclusion: Satisfaction, confidence, and knowledge domains were all measured with favorable results. This innovative low-cost telehealth model for EBRT training is a promising vehicle for advancing cancer care in LMICs by providing educational support.

Citation Format: Fei Yang, Raymond Carter, Soha Ahmed, Tia Plautz, Piotr Dubrowski, Shada Wadi-Ramahi, Sarah Ashmeg, Frank Ascoli, Daniel Wakefield, Justus Adamson, Benjamin Li. A Longitudinal Telehealth Curriculum for Radiation Oncology Centers in Low and Middle-Income Countries Transitioning from 2D to 3D External Beam Radiation Therapy [abstract]. In: Proceedings of the 9th Annual Symposium on Global Cancer Research; Global Cancer Research and Control: Looking Back and Charting a Path Forward; 2021 Mar 10-11. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2021;30(7 Suppl):Abstract nr 109.

CT-less electron radiotherapy simulation and planning with a consumer 3D camera

Purpose

Electron radiation therapy dose distributions are affected by irregular body surface contours. This study investigates the feasibility of three‐dimensional (3D) cameras to substitute for the treatment planning computerized tomography (CT) scan by capturing the body surfaces to be treated for accurate electron beam dosimetry.

Methods

Dosimetry was compared for six electron beam treatments to the nose, toe, eye, and scalp using full CT scan, CT scan with Hounsfield Unit (HU) overridden to water (mimic 3D camera cases), and flat‐phantom techniques. Radiation dose was prescribed to a depth on the central axis per physician’s order, and the monitor units (MUs) were calculated. The 3D camera spatial accuracy was evaluated by comparing the 3D surface of a head phantom captured by a 3D camera and that generated with the CT scan in the treatment planning system. A clinical case is presented, and MUs were calculated using the 3D camera body contour with HU overridden to water.

Results

Across six cases the average change in MUs between the full CT and the 3Dwater (CT scan with HU overridden to water) calculations was 1.3% with a standard deviation of 1.0%. The corresponding hotspots had a mean difference of 0.4% and a standard deviation of 1.9%. The 3D camera captured surface of a head phantom was found to have a 0.59 mm standard deviation from the surface derived from the CT scan. In‐vivo dose measurements (213 ± 8 cGy) agreed with the 3D‐camera planned dose of 209 ± 6 cGy, compared to 192 ± 6 cGy for the flat‐phantom calculation (same MUs).

Conclusions

Electron beam dosimetry is affected by irregular body surfaces. 3D cameras can capture irregular body contours which allow accurate dosimetry of electron beam treatment as an alternative to costly CT scans with no extra exposure to radiation. Tools and workflow for clinical implementation are provided.

A robotically assisted 3D printed quality assurance lung phantom for Calypso

Purpose. Radiation dose delivered to targets located near the upper-abdomen or in the thorax are significantly affected by respiratory-motion. Relatively large-margins are commonly added to compensate for this motion, limiting radiation-dose-escalation. Internal-surrogates of target motion, such as a radiofrequency (RF) tracking system, i.e. Calypso^®System, are used to overcome this challenge and improve normal-tissue sparing. RF tracking systems consist of implanting transponders in the vicinity of the tumor to be tracked using radiofrequency-waves. Unfortunately, although the manufacture provides a universal quality-assurance (QA) phantom, QA-phantoms specifically for lung-applications are limited, warranting the development of alternative solutions to fulfil the tests mandated by AAPM's TG142. Accordingly, our objective was to design and develop a motion-phantom to evaluate Calypso for lung-applications that allows the Calypso^®Beacons to move in different directions to better simulate truelung-motion.Methods and Materials.A Calypso lung QA-phantom was designed, and 3D-printed. The design consists of three independent arms where the transponders were attached. A pinpoint-chamber with a buildup-cap was also incorporated. A 4-axis robotic arm was programmed to drive the motion-phantom to mimic breathing. After acquiring a four-dimensional-computed-tomography (4DCT) scan of the motion-phantom, treatment-plans were generated and delivered on a Varian TrueBeam^®with Calypso capabilities. Stationary and gated-treatment plans were generated and delivered to determine the dosimetric difference between gated and non-gated treatments. Portal cine-images were acquired to determine the temporal-accuracy of delivery by calculating the difference between the observed versus expected transponders locations with the known speed of the transponders' motion.Results.Dosimetric accuracy is better than the TG142 tolerance of 2%. Temporal accuracy is greater than, TG142 tolerance of 100 ms for beam-on, but less than 100 ms for beam-hold.Conclusions.The robotic QA-phantom designed and developed in this study provides an independent phantom for performing Calypso lung-QA for commissioning and acceptance testing of Calypso for lung treatments.

A novel-integrated quality assurance phantom for radiographic and nonradiographic radiotherapy localization and positioning systems

PURPOSE

Various localization and positioning systems utilizing radiographic or nonradiographic methods have been developed to improve the accuracy of radiation treatment. Each quality assurance (QA) procedure requires its own phantom and is independent from each other, so the deviation between each system is unavailable. The purpose of this work is to develop and evaluate a single-integrated QA phantom for different localization and positioning systems.

METHODS

The integrated phantom was designed in three-dimensional (3D) CAD software and 3D printed. The phantom was designed with laser alignment marks, a raised letter "S" on the anterior surface for optical surface monitoring system registration, a core for radiofrequency (RF) tracking system alignment, eight internal fiducials for image alignment, and an isocentric bearing for Winston-Lutz test. Tilt legs and rotational stage were designed for rotational verification of optical surface mapping system and RF tracking system, respectively. The phantom was scanned using a CT scanner and a QA plan was created. This prototype phantom was evaluated against established QA techniques.

RESULTS

The QA result between the proposed procedure and established QA technique are 1.12 ± 0.31 and 1.14 ± 0.31 mm, respectively, for RF tracking system and 0.18 ± 0.06 and 0.18 ± 0.05 mm for Winston-Lutz test. There is no significant difference for the QA results between the established QA and proposed procedure (P > 0.05, t test). The accuracy of rotational verification for surface mapping system and RF tracking system are less than 0.5 and 1° compared the predefined value. The isocenter deviation of each location system is around l mm.

CONCLUSION

We have designed and evaluated a novel-integrated phantom for radiographic and nonradiographic localization and positioning systems for radiotherapy. With this phantom, we will reduce the variation in measurements and simplify the QA procedures.

Poster - Thur Eve - 71: Improved dose accuracy for plan checking IMRT breast plans

Dose verification as part of plan checking is a critical component of high quality patient care. IMSure QA is a software platform used at the BC Cancer Agency that facilitates dose verification for both conformal and IMRT plans. We have recently initiated treating breast tangents using IMRT at the Fraser Valley Centre and noted increased dose discrepancies (mean difference of -3%) between Eclipse and IMSure's QA module. We identified two potential sources of error: air flash and tissue heterogeneity. We extend our generated fluences 3cm past the breast contour and into air to account for breathing, set-up uncertainties and swelling. IMSure does not account for the fluence in air or air flash. We present an air-flash-correction factor based on the ratios of TMRs and Phantom Scatter Factors which use the field sizes of fields with and without the air flash. In addition, we present a method to improve the heterogeneity correction used by IMSure to better match that used by AAA. Effectively we remove the IMSure's inherent heterogeneity correction and manually apply a AAA-based heterogeneity-correction factor. We evaluated our correction factors on a sample of 8 patients (32 fields) using ANOVA methods to determine which dose corrections most accurately reproduce Eclipse's values. We found the air-flash correction coupled with IMSure's inherent-heterogeneity correction has the best dose accuracy (mean difference improved from -3% to 0.3%). The AAA-heterogeneity correction alone also improved the accuracy (mean difference improved from -3% to - 1.5%), which is acceptable for plan checking purposes.