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.

Four dimensional digital tomosynthesis using on-board imager for the verification of respiratory motion.

PURPOSE: To evaluate respiratory motion of a patient by generating four-dimensional digital tomosynthesis (4D DTS), extracting respiratory signal from patients' on-board projection data, and ensuring the feasibility of 4D DTS as a localization tool for the targets which have respiratory movement. METHODS AND MATERIALS: Four patients with lung and liver cancer were included to verify the feasibility of 4D-DTS with an on-board imager. CBCT acquisition (650-670 projections) was used to reconstruct 4D DTS images and the breath signal of the patients was generated by extracting the motion of diaphragm during data acquisition. Based on the extracted signal, the projection data was divided into four phases: peak-exhale phase, mid-inhale phase, peak-inhale phase, and mid-exhale phase. The binned projection data was then used to generate 4D DTS, where the total scan angle was assigned as ±22.5° from rotation center, centered on 0° and 180° for coronal "half-fan" 4D DTS, and 90° and 270° for sagittal "half-fan" 4D DTS. The result was then compared with 4D CBCT which we have also generated with the same phase distribution. RESULTS: The motion of the diaphragm was evident from the 4D DTS results for peak-exhale, mid-inhale, peak-inhale and mid-exhale phase assignment which was absent in 3D DTS. Compared to the result of 4D CBCT, the view aliasing effect due to arbitrary angle reconstruction was less severe. In addition, the severity of metal artifacts, the image distortion due to presence of metal, was less than that of the 4D CBCT results. CONCLUSION: We have implemented on-board 4D DTS on patients data to visualize the movement of anatomy due to respiratory motion. The results indicate that 4D-DTS could be a promising alternative to 4D CBCT for acquiring the respiratory motion of internal organs just prior to radiotherapy treatment.

Direction-modulated brachytherapy for high-dose-rate treatment of cervical cancer. I: theoretical design.

PURPOSE: To demonstrate that utilization of the direction-modulated brachytherapy (DMBT) concept can significantly improve treatment plan quality in the setting of high-dose-rate (HDR) brachytherapy for cervical cancer. METHODS AND MATERIALS: The new, MRI-compatible, tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten-alloy rod (ρ = 18.0 g/cm(3)), enclosed in Delrin tubing (polyoxymethylene, ρ = 1.41 g/cm(3)), with a total thickness of 6.4 mm. The Monte Carlo N-Particle code was used to calculate the anisotropic (192)Ir dose distributions. An in-house-developed inverse planning platform, geared with simulated annealing and constrained-gradient optimization algorithms, was used to replan 15 patient cases (total 75 plans) treated with a conventional tandem and ovoids (T&O) applicator. Prescription dose was 6 Gy. For replanning, we replaced the conventional tandem with that of the new DMBT tandem for optimization but left the ovoids in place and kept the dwell positions as originally planned. All DMBT plans were normalized to match the high-risk clinical target volume V100 coverage of the T&O plans. RESULTS: In general there were marked improvements in plan quality for the DMBT plans. On average, D2cc for the bladder, rectum, and sigmoid were reduced by 0.59 ± 0.87 Gy (8.5% ± 28.7%), 0.48 ± 0.55 Gy (21.1% ± 27.2%), and 0.10 ± 0.38 Gy (40.6% ± 214.9%) among the 75 plans, with best single-plan reductions of 3.20 Gy (40.8%), 2.38 Gy (40.07%), and 1.26 Gy (27.5%), respectively. The high-risk clinical target volume D90 was similar, with 6.55 ± 0.96 Gy and 6.59 ± 1.06 Gy for T&O and DMBT, respectively. CONCLUSIONS: Application of the DMBT concept to cervical cancer allowed for improved organ at risk sparing while achieving similar target coverage on a sizeable patient population, as intended, by maximally utilizing the anatomic information contained in 3-dimensional imaging. A series of mechanical and clinical validations are to be followed.

HDR brachytherapy of rectal cancer using a novel grooved-shielding applicator design.

PURPOSE: The aim of this work was to design a novel high-dose rate (HDR) ((192)Ir) brachytherapy applicator for treatment of rectal carcinomas that uses tungsten shielding for possibly improved dosimetric results over commercial brachytherapy applicator(s). METHODS: A set of 15 single-depth applicators and one dual-depth applicator were designed and simulated using Monte Carlo (MCNPX). All applicators simulated were high-density tungsten alloy cylinders, 16-mm in diameter, and 60-mm long, with longitudinal grooves within which an (192)Ir source can be placed. The single-depth designs varied regarding the number and depth of these grooves, ranging from 8 to 16 and 1-mm to 3-mm, respectively. The dual-depth design had ten channels, each of which had two depths at which the source could be placed. Optimized treatment plans were generated for each design on data from 13 treated patients (36 fractions) with asymmetrical clinical target volumes (CTVs). All results were compared against the clinically treated plans which used intracavitary mold applicator (ICMA), as well as a recently designed, highly automated, and collimated intensity modulation device named dynamic modulated brachytherapy (DMBT) device. RESULTS: All applicator designs outperformed the ICMA in every calculated dosimetric criteria, except the total dwell times (∼30% increase). There were clear, but relative, tradeoffs regarding both the number of channels and the depth of each channel. Overall, the 12-channel, 1-mm depth, and 14-channel 2-mm depth designs had the best results of the simpler designs, sparing the healthy rectal tissues the most while achieving comparable CTV coverage with the dose heterogeneity index and lateral spill doses improving by over 10% and the contralateral healthy rectum dose dropping over 30% compared to ICMA. The ten-channel dual-depth design outperformed each single-depth design, yielding the best coverage and sparing. CONCLUSIONS: New grooved tungsten HDR-brachytherapy devices have been designed and simulated. The results of this work attest to the capability of these new, highly anisotropic, intelligently shielded applicators to limit dose to healthy tissues while maintaining a conformal prescription dose to the CTV.

Dynamic modulated brachytherapy (DMBT) for rectal cancer.

PURPOSE: All forms of past and current high-dose-rate brachytherapy utilize immobile applicators during treatment delivery. The only moving part is the source itself. This paradigm misses an important degree of freedom that, if explored, can in some instances produce previously unachievable dose conformality; that is, the dynamic motion of the applicator itself during treatment delivery. Monte Carlo and treatment planning simulations were used to illustrate the potential benefits of moving applicators for rectal cancer applications in particular. This concept is termed dynamic modulated brachytherapy (DMBT). METHODS: The DMBT system uses a high-density, 18.0 g∕cm(3), 45 mm long tungsten alloy shield, cylindrical in shape, with a small window on one side to encapsulate a (192)Ir source, to create collimation that results in a highly directional beam profile. This shield can be dynamically translated and rotated, using an attached robotic arm, during treatment to create a volumetric modulated arc therapy-type delivery, but from inside the rectal cavity. Monte Carlo simulations and planning optimization algorithms were developed inhouse to evaluate the effectiveness of this new approach using 36 clinical treatment plans comprised of 13 patients each treated using the intracavitary mold applicator (ICMA, Nucletron, The Netherlands) to quantify the potential clinical benefit. The prescription dose was 10 Gy∕fx and the group had an average clinical target volume of 9.0 ± 3.5 cm(3). Ideal phantom geometries were used to evaluate the impact of various shield dimensions and designs on the resulting plan quality. RESULTS: Simulations of ideal phantom geometries found that shields as small as 10 mm in diameter can produce high quality plans. For the clinical patient cases, compared to the ICMA, for equal prescription tumor coverage, the DMBT plans provided >30% decrease in D(5) (high dose volume) resulting in a ∼40% decrease in dose heterogeneity index. In addition, mean dose and D(98) showed a reduction (typically 40%-60%) on all critical structures evaluated. However, for a 10 Gy prescribed dose there was an increase in total treatment time on average from 7.6 to 20.8 min for a source with an air-kerma strength of 40.25 kU (10 Ci). CONCLUSIONS: Dosimetric properties of a novel DMBT system have been described and evaluated. Comparison with the ICMA commercial applicator has shown it to be a prospective step forward in high-dose-rate brachytherapy (192)Ir technology. Dynamic motion of an applicator during treatment, for any applicator and site in general, can provide additional degrees of freedom that, if properly considered, can potentially increase the plan quality significantly.

Liver motion during cone beam computed tomography guided stereotactic body radiation therapy.

PURPOSE: Understanding motion characteristics of liver such as, interfractional and intrafractional motion variability, difference in motion within different locations in the organ, and their complex relationship with the breathing cycles are particularly important for image-guided liver SBRT. The purpose of this study was to investigate such motion characteristics based on fiducial markers tracked with the x-ray projections of the CBCT scans, taken immediately prior to the treatments. METHODS: Twenty liver SBRT patients were analyzed. Each patient had three fiducial markers (2 × 5-mm gold) percutaneously implanted around the gross tumor. The prescription ranged from 2 to 8 fractions per patient. The CBCT projections data for each fraction (∼650 projections∕scan), for each patient, were analyzed and the 2D positions of the markers were extracted using an in-house algorithm. In total, >55 000 x-ray projections were analyzed from 85 CBCT scans. From the 2D extracted positions, a 3D motion trajectory of the markers was constructed, from each CBCT scans, resulting in left-right (LR), anterior-posterior (AP), and cranio-caudal (CC) location information of the markers with >55 000 data points. The authors then analyzed the interfraction and intrafraction liver motion variability, within different locations in the organ, and as a function of the breathing cycle. The authors also compared the motion characteristics against the planning 4DCT and the RPM™ (Varian Medical Systems, Palo Alto, CA) breathing traces. Variations in the appropriate gating window (defined as the percent of the maximum range at which 50% of the marker positions are contained), between fractions were calculated as well. RESULTS: The range of motion for the 20 patients were 3.0 ± 2.0 mm, 5.1 ± 3.1 mm, and 17.9 ± 5.1 mm in the planning 4DCT, and 2.8 ± 1.6 mm, 5.3 ± 3.1 mm, and 16.5 ± 5.7 mm in the treatment CBCT, for LR, AP, and CC directions, respectively. The range of respiratory period was 3.9 ± 0.7 and 4.2 ± 0.8 s during the 4DCT simulation and the CBCT scans, respectively. The authors found that breathing-induced AP and CC motions are highly correlated. That is, all markers moved cranially also moved posteriorly and vice versa, irrespective of the location. The LR motion had a more variable relationship with the AP∕CC motions, and appeared random with respect to the location. That is, when the markers moved toward cranial-posterior direction, 58% of the markers moved to the patient-right, 22% of the markers moved to the patient-left, and 20% of the markers had minimal∕none motion. The absolute difference in the motion magnitude between the markers, in different locations within the liver, had a positive correlation with the absolute distance between the markers (R(2) = 0.69, linear-fit). The interfractional gating window varied significantly for some patients, with the largest having 29.4%-56.4% range between fractions. CONCLUSIONS: This study analyzed the liver motion characteristics of 20 patients undergoing SBRT. A large variation in motion was observed, interfractionally and intrafractionally, and that as the distance between the markers increased, the difference in the absolute range of motion also increased. This suggests that marker(s) in closest proximity to the target be used.

SU-E-T-317: Dynamic Modulated Brachytherapy (DMBT): Robotic Applicator Design.

PURPOSE: To investigate the hardware necessary for implementing our Dynamic Modulated Brachytherapy (DMBT) treatment concept for rectal cancer. METHODS: The DMBT robot has three major parts: 1) shield and shield delivery module, 2) controlling module, and 3) DMBT controlling and monitoring software. The shield is a tungsten alloy cylinder (r=0.95cm, l=4.5cm) with a 5.5mm rectangular-shaped opening. The shield is controlled by an aluminum pipe with gear set (1:3) and linear actuator (2mm/turn). An Ir-192 radiation source will be placed through the aluminum pipe. The power source is a Nema-17 stepping motor with EvoDrive ST-17 (EVA Robotics, Queensland, Australia) and USB-6009 DAQ (National Instrument, Austin, TX). With our in-house operating program through LabView (National Instrument, Austin, TX), we can make and load plans for treatment as well as testing. Checking the shield position is also possible through the operating program. For safety, a lexan sheath tube and emergency buttons are built-in. RESULTS: The DMBT robot has 2 degrees of freedom, which are linear translation and rotation. With our power delivery system, the spatial resolutions are 0.0125mm (linear stage) and 0.012Ës (rotation). In 0.5s, motors achieve the desired position with the maximum speeds 450 step/s (1Ës), 7,500 step/s (30Ës), and 12,000 step/s (5mm). Four registers are triggered with USB-6009 DAQ signals. The operating program includes gages for checking shield position, loading treatment plans, and safety buttons. CONCLUSIONS: In all, we have designed the hardware components of the DMBT system for rectal cancer. For treatment, the system needs more elements to support the DMBT robot; lexan sheath tube holder, DMBT robot security joint, and a system for reducing friction between the tube and shield. We will also refine our system to be more compact by using DC servomotors instead of the larger Nema-17 stepping motors.