Automated review of patient position in DIBH breast hybrid IMRT with EPID images.

Deep Inspiration Breath Hold (DIBH) is a respiratory-gating technique adopted in radiation therapy to lower cardiac irradiation. When performing DIBH treatments, it is important to have a monitoring system to ensure the patient's breath hold level is stable and reproducible at each fraction. In this retrospective study, we developed a system capable of monitoring DIBH breast treatments by utilizing cine EPID images taken during treatment. Setup error and intrafraction motion were measured for all fractions of 20 left-sided breast patients. All patients were treated with a hybrid static-IMRT technique, with EPID images from the static fields analyzed. Ten patients had open static fields and the other ten patients had static fields partially blocked with the multileaf collimator (MLC). Three image-processing algorithms were evaluated on their ability to accurately measure the chest wall position (CWP) in EPID images. CWP measurements were recorded along a 61-pixel region of interest centered along the midline of the image. The median and standard deviation of the CWP were recorded for each image. The algorithm showing the highest agreement with manual measurements was then used to calculate intrafraction motion and setup error. To measure intrafraction motion, the median CWP of the first EPID frame was compared with that of the subsequent EPID images of the treatment. The maximum difference was recorded as the intrafraction motion. The setup error was calculated as the difference in median CWP between the MV DRR and the first EPID image of the lateral tangential field. The results showed that the most accurate image-processing algorithm can identify the chest wall within 1.2 mm on both EPID and MV DRR images, and measures intrafraction motion and setup errors within 1.4 mm.

Endobronchially Implanted Real-Time Electromagnetic Transponder Beacon-Guided, Respiratory-Gated SABR for Moving Lung Tumors: A Prospective Phase 1/2 Cohort Study.

Purpose: Endobronchial electromagnetic transponder beacons (EMT) provide real-time, precise positional data of moving lung tumors. We report results of a phase 1/2, prospective, single-arm cohort study evaluating the treatment planning effects of EMT-guided SABR for moving lung tumors. Methods and Materials: Eligible patients were adults, Eastern Cooperative Oncology Group 0 to 2, with T1-T2N0 non-small cell lung cancer or pulmonary metastasis ≤4 cm with motion amplitude ≥5 mm. Three EMTs were endobronchially implanted using navigational bronchoscopy. Four-dimensional free-breathing computed tomography simulation scans were obtained, and end-exhalation phases were used to define the gating window internal target volume. A 3-mm expansion of gating window internal target volume defined the planning target volume (PTV). EMT-guided, respiratory-gated (RG) SABR was delivered (54 Gy/3 fractions or 48 Gy/4 fractions) using volumetric modulated arc therapy. For each RG-SABR plan, a 10-phase image-guided SABR plan was generated for dosimetric comparison. PTV/organ-at-risk (OAR) metrics were tabulated and analyzed using the Wilcoxon signed-rank pair test. Treatment outcomes were evaluated using RECIST (Response Evaluation Criteria in Solid Tumours; version 1.1). Results: Of 41 patients screened, 17 were enrolled and 2 withdrew from the study. Median age was 73 years, with 7 women. Sixty percent had T1/T2 non-small cell lung cancer and 40% had M1 disease. Median tumor diameter was 1.9 cm with 73% of targets located peripherally. Mean respiratory tumor motion was 1.25 cm (range, 0.53-4.04 cm). Thirteen tumors were treated with EMT-guided SABR and 47% of patients received 48 Gy in 4 fractions while 53% received 54 Gy in 3 fractions. RG-SABR yielded an average PTV reduction of 46.9% (P < .005). Lung V5, V10, V20, and mean lung dose had mean relative reductions of 11.3%, 20.3%, 31.1%, and 20.3%, respectively (P < .005). Dose to OARs was significantly reduced (P < .05) except for spinal cord. At 6 months, mean radiographic tumor volume reduction was 53.5% (P < .005). Conclusions: EMT-guided RG-SABR significantly reduced PTVs of moving lung tumors compared with image-guided SABR. EMT-guided RG-SABR should be considered for tumors with large respiratory motion amplitudes or those located in close proximity to OARs.

Optical scan and 3D printing guided radiation therapy - an application and provincial experience in cutaneous nasal carcinoma.

BACKGROUND: Single field Orthovoltage radiation is an acceptable modality used for the treatment of nasal cutaneous cancer. However, this technique has dosimetric pitfalls and unnecessary excessive exposure of radiation to organs at risk (OAR). We present the clinical outcome of a case series of cutaneous nasal tumours using a novel technique incorporating an optical scanner and a 3-dimensional (3D) printer to deliver treatments using parallel opposed (POP) fields. MATERIALS AND METHODS: The POP delivery method was validated using ion chamber and phantom measurements before implementation. A retrospective chart review of 26 patients treated with this technique between 2015 and 2019 was conducted. Patients' demographics and treatment outcomes were gathered and tabulated. These patients first underwent an optical scan of their faces to collect topographical data. The data were then transcribed into 3D printing algorithms, and positive impressions of the faces were printed. Custom nose block bolus was made with wax encased in an acrylic shell; 4 cm thick using the printed face models. Custom lead shielding was also generated. Treatments were delivered using 250 KeV photons POP arrangement with 4 cm diameter circle applicator cone and prescribed to the midplane. Dose and fractionation were as per physician discretion. RESULTS: Phantom measurements at mid-plane were found to match the prescribed dose within ±0.5%. For the 26 cases in this review, the median age was 78.5 years, with 15 females and 11 males. 85% of cases had Basal cell carcinoma (BCC); 1 had squamous cell carcinoma (SCC), one had synchronous BCC + SCC, and 1 had Merkel cell carcinoma. Twenty-one cases had T1N0 disease, 4 had T2N0, and 1 had T3N0. Dose and fractionation delivered were 40Gy in 10 fractions for the majority of cases. The complete response rate at a median follow-up of 6 months was 88%; 1 patient had a refractory tumour, and one patient had a recurrence. Toxicities were minor with 81% with no reported side effects. Three patients experienced grade 3 skin toxicity. CONCLUSIONS: Utilization of optic scanner and 3D printing technology, with the innovative approach of using POP orthovoltage beams, allows an effective and efficient way of treatment carcinomas of the nose with a high control rate and low toxicity profiles.

An anthropomorphic maxillofacial phantom using 3-dimensional printing, polyurethane rubber and epoxy resin for dental imaging and dosimetry.

OBJECTIVE: The aim of this study was to construct an anthropomorphic maxillofacial phantom for dental imaging and dosimetry purposes using three-dimensional (3D) printing technology and materials that simulate the radiographic properties of tissues. METHODS: Stereolithography photoreactive resins, polyurethane rubber and epoxy resin were modified by adding calcium carbonate and strontium carbonate powders or glass bubbles. These additives were used to change the materials' CT numbers to mimic various body tissues. A maxillofacial phantom was designed using CT images of a head. RESULTS: Commercial 3D printing resins were found to have CT numbers near 120 HU and were used to print intervertebral discs and an external skin for the maxillofacial phantom. By adding various amounts of calcium carbonate and strontium carbonate powders the CT number of the resin was raised to 1000 & 1500 HU and used to print bone mimics. Epoxy resin modified by adding glass bubbles was used in assembly and as a cartilaginous mimic. Glass bubbles were added to polyurethane rubber to reduce the CT number to simulate soft tissue and filled spaces between the printed anatomy and external skin of the phantom. CONCLUSION: The maxillofacial phantom designed for dental imaging and dosimetry constructed using 3D printing, polyurethane rubbers and epoxy resins represented a patient anatomically and radiographically. The results of the designed phantom, materials and assembly process can be applied to generate different phantoms that better represent diverse patient types and accommodate different ion chambers.

4D in vivo dose verification for real-time tumor tracking treatments using EPID dosimetry.

The use of sophisticated techniques such as gating and tracking treatments requires additional quality assurance to mitigate increased patient risks. To address this need, we have developed and validated an in vivo method of dose delivery verification for real-time aperture tracking techniques, using an electronic portal imaging device (EPID)-based, on-treatment patient dose reconstruction and a dynamic anthropomorphic phantom. Using 4DCT scan of the phantom, ten individual treatment plans were created, 1 for each of the 10 separate phases of the respiratory cycle. The 10 MLC apertures were combined into a single dynamic intensity-modulated radiation therapy (IMRT) plan that tracked the tumor motion. The tumor motion and linac delivery were synchronized using an RPM system (Varian Medical Systems) in gating mode with a custom breathing trace. On-treatment EPID frames were captured using a data-acquisition computer with a dedicated frame-grabber. Our in-house EPID-based in vivo dose reconstruction model was modified to reconstruct the 4D accumulated dose distribution for a dynamic MLC (DMLC) tracking plan using the 10-phase 4DCT dataset. Dose estimation accuracy was assessed for the DMLC tracking plan and a single-phase (50% phase) static tumor plan, represented a static field test to verify baseline accuracy. The 3%/3 mm chi-comparison between the EPID-based dose reconstruction for the static tumor delivery and the TPS dose calculation for the static plan resulted in 100% pass rate for planning target volume (PTV) voxels while the mean percentage dose difference was 0.6%. Comparing the EPID-based dose reconstruction for the DMLC tracking to the TPS calculation for the static plan gave a 3%/3 mm chi pass rate of 99.3% for PTV voxels and a mean percentage dose difference of 1.1%. While further work is required to assess the accuracy of this approach in more clinically relevant situations, we have established clinical feasibility and baseline accuracy of using the transmission EPID-based, in vivo patient dose verification for MLC-tracking treatments.

A modern mold room: Meshing 3D surface scanning, digital design, and 3D printing with bolus fabrication.

PURPOSE: This case series represents an initial experience with implementing 3-dimensional (3D) surface scanning, digital design, and 3D printing for bolus fabrication for patients with complex surface anatomy where traditional approaches are challenging. METHODS AND MATERIALS: For 10 patients requiring bolus in regions with complex contours, bolus was designed digitally from 3D surface scanning data or computed tomography (CT) images using either a treatment planning system or mesh editing software. Boluses were printed using a fused deposition modeling printer with polylactic acid. Quality assurance tests were performed for each printed bolus to verify density and shape. RESULTS: For 9 of 10 patients, digitally designed boluses were used for treatment with no issues. In 1 case, the bolus was not used because dosimetric requirements were met without the bolus. QA tests revealed that the bulk density was within 3% of the reference value for 9 of 12 prints, and with more judicious selection of print settings this could be increased. For these 9 prints, density uniformity was as good as or better than our traditional sheet bolus material. The average shape error of the pieces was less than 0.5 mm, and no issues with fit or comfort were encountered during use. CONCLUSIONS: This study demonstrates that new technologies such as 3D surface scanning, digital design and 3D printing can be safely and effectively used to modernize bolus fabrication.

Evaluating a potential technique with local optical flow vectors for automatic organ-at-risk (OAR) intrusion detection and avoidance during radiotherapy.

Various techniques of deep inspiration breath hold (DIBH) have been used to mitigate the likelihood and risk of exposing the heart, an organ-at-risk (OAR) for unintended radiation during left breast radiotherapy. However, issues of reproducibility of these techniques warrant further investigation into the feasibility of detecting the intrusion of an OAR into the treatment field during intra-fractional treatment delivery. The increase of high-dose, low-fraction radiotherapy treatments makes it important to immediately adapt treatment once an OAR is detected in the treatment field. This proof-of-concept implementation includes an algorithm that detects and tracks the motion at the edges of a treatment field and a control algorithm that adapts the treatment aperture according to the motion detected. In accordance to the AAPM Task-Group (TG-132) report, image registration techniques should be verified with virtual and physical phantoms prior to clinical application. Since most OARs move as a result of respiration-induced motion, we have used a lung phantom to generate images of a generic OAR intruding into a treatment field with known velocity. The phantom was programmed to move with sinusoidal and lung patient tumor motion patterns and the accuracy of intrusion tracking and MLC adaptation were benchmarked with the ground truth-programmed motion of the OAR. The motions were recorded with an electronic portal imaging device (EPID). An optimal cluster size of 9 × 9 motion vectors was found to provide the smallest average absolute position error of 0.3 mm. A strong linear correlation between the adapted MLC leaves and the actual OAR position was observed. The algorithm had a mean position tracking error of -0.4 ± 0.3 mm and a precision of 1.1 mm. It is possible to adapt MLC leaves based on the motion detected at the edges of the irradiated field, and it would be feasible to shield an unplanned intrusion of an OAR into the treatment field.

Reducing the tracking drift of an uncontoured tumor for a portal-image-based dynamically adapted conformal radiotherapy treatment.

Accurate tracking of organ motion during treatment is needed to improve the efficacy of radiation therapy. This work investigates the feasibility of tracking an uncontoured target using the motion detected within a moving treatment aperture. Tracking was achieved with a weighted optical flow algorithm, and three different techniques for updating the reference image were evaluated. The accuracy and susceptibility of each approach to the accumulation of position errors were verified using a 3D-printed tumor (mounted on an actuator) and a virtual treatment aperture. Tumor motion up to 15.8 mm (peak-to-peak) taken from the breathing patterns of seven lung cancer patients was acquired using an amorphous silicon portal imager at ~ 7.5 frames/s. The first approach (INI) used the initial image detected, as a fixed reference, to determine the target motion for each new incoming image, and performed the best with the smallest errors. This method was also the most robust against the accumulation of position errors. Mean absolute errors of 0.16, 0.32, and 0.38 mm were obtained for the three methods, respectively. Although the errors are comparable to other tracking methods, the proposed method does not require prior knowledge of the tumor shape and does not need a tumor template or contour for tracking. Graphical abstract.

Low-cost optical scanner and 3-dimensional printing technology to create lead shielding for radiation therapy of facial skin cancer: First clinical case series.

PURPOSE: Three-dimensional printing has been implemented at our institution to create customized treatment accessories, including lead shields used during radiation therapy for facial skin cancer. To effectively use 3-dimensional printing, the topography of the patient must first be acquired. We evaluated a low-cost, structured-light, 3-dimensional, optical scanner to assess the clinical viability of this technology. METHODS AND MATERIALS: For ease of use, the scanner was mounted to a simple gantry that guided its motion and maintained an optimum distance between the scanner and the object. To characterize the spatial accuracy of the scanner, we used a geometric phantom and an anthropomorphic head phantom. The geometric phantom was machined from plastic and included hemispherical and tetrahedral protrusions that were roughly the dimensions of an average forehead and nose, respectively. Polygon meshes acquired by the optical scanner were compared with meshes generated from high-resolution computed tomography images. Most optical scans contained minor artifacts. Using an algorithm that calculated the distances between the 2 meshes, we found that most of the optical scanner measurements agreed with those from the computed tomography scanner within approximately 1 mm for the geometric phantom and approximately 2 mm for the head phantom. We used this optical scanner along with 3-dimensional printer technology to create custom lead shields for 10 patients receiving orthovoltage treatments of nonmelanoma skin cancers of the face. Patient, tumor, and treatment data were documented. RESULTS: Lead shields created using this approach were accurate, fitting the contours of each patient's face. This process added to patient convenience and addressed potential claustrophobia and medical inability to lie supine. CONCLUSIONS: The scanner was found to be clinically acceptable, and we suggest that the use of an optical scanner and 3-dimensional printer technology become the new standard of care to generate lead shielding for orthovoltage radiation therapy of nonmelanoma facial skin cancer.

Creation of knowledge-based planning models intended for large scale distribution: Minimizing the effect of outlier plans.

Knowledge-based planning (KBP) can be used to estimate dose-volume histograms (DVHs) of organs at risk (OAR) using models. The task of model creation, however, can result in estimates with differing accuracy; particularly when outlier plans are not properly addressed. This work used RapidPlan™ to create models for the prostate and head and neck intended for large-scale distribution. Potential outlier plans were identified by means of regression analysis scatter plots, Cook's distance, coefficient of determination, and the chi-squared test. Outlier plans were identified as falling into three categories: geometric, dosimetric, and over-fitting outliers. The models were validated by comparing DVHs estimated by the model with those from a separate and independent set of clinical plans. The estimated DVHs were also used as optimization objectives during inverse planning. The analysis tools lead us to identify as many as 7 geometric, 8 dosimetric, and 20 over-fitting outliers in the raw models. Geometric and over-fitting outliers were removed while the dosimetric outliers were replaced after re-planning. Model validation was done by comparing the DVHs at 50%, 85%, and 99% of the maximum dose for each OAR (denoted as V50, V85, and V99) and agreed within -2% to 4% for the three metrics for the final prostate model. In terms of the head and neck model, the estimated DVHs agreed from -2.0% to 5.1% at V50, 0.1% to 7.1% at V85, and 0.1% to 7.6% at V99. The process used to create these models improved the accuracy for the pharyngeal constrictor DVH estimation where one plan was originally over-estimated by more than twice. In conclusion, our results demonstrate that KBP models should be carefully created since their accuracy could be negatively affected by outlier plans. Outlier plans can be addressed by removing them from the model and re-planning.

COMP report: CPQR technical quality control guidelines for radiation treatment centers.

The Canadian Organization of Medical Physicists (COMP), in close partnership with the Canadian Partnership for Quality Radiotherapy (CPQR) has developed a series of Technical Quality Control (TQC) guidelines for radiation treatment equipment. These guidelines outline the performance objectives that equipment should meet in order to ensure an acceptable level of radiation treatment quality. The TQC guidelines have been rigorously reviewed and field tested in a variety of Canadian radiation treatment facilities. The development process enables rapid review and update to keep the guidelines current with changes in technology. This announcement provides an introduction to the guidelines, describing their scope and how they should be interpreted. Details of recommended tests can be found in separate, equipment specific TQC guidelines published in the JACMP (COMP Reports), or the website of the Canadian Partnership for Quality Radiotherapy (www.cpqr.ca).

A quality assurance tool for high-dose-rate brachytherapy.

PURPOSE: The purpose of this work was to develop a quality assurance (QA) tool for high-dose-rate (HDR) brachytherapy that would quickly and easily verify both source positioning (dwell positions) and durations (dwell times). METHODS: The authors constructed a QA tool that combined radiochromic film to verify position with four photodiode detectors to verify dwell times. To characterize the temporal accuracy of the tool, a function generator powered four red light-emitting diodes that were optically coupled to the four photodiode detectors. The QA tool was used to verify the dwell positions and times of a commercial brachytherapy afterloader. Measurements of dwell time were independently verified by a one-dimensional optical camera that acquired 1000 lines/s. RESULTS: The temporal accuracy of the QA tool was found to be about 1 ms. For visual assessment, the source position could be located within about 0.5 mm. Evaluating the accuracy and precision of an HDR brachytherapy afterloader, the authors found that the bias in dwell time can exceed 60 ms and the dwell time associated with the first dwell position had an unexpectedly large standard deviation of 30 ms. They found that the source locations were much easier to locate on the film if a plastic catheter was used instead of a metal treatment tube. Scanning the films enabled the dwell positions to be determined within about 0.2 mm. CONCLUSIONS: For pretreatment QA, the authors found that this tool allowed verification of dwell positions and dwell times in about 6 min.

The dosimetric quality of brachytherapy implants in patients with small prostate volume depends on the experience of the brachytherapy team.

PURPOSE: To investigate the dosimetric outcome of brachytherapy in patients with small prostate volume (PV). METHODS AND MATERIALS: Forty-three patients with small PV (<25 cm(3)) as determined using transrectal ultrasound and 120 patients with non-small PV (>25 cm(3)) that had received (125)I seed implants were reviewed in a retrospective cohort study. Implantations were performed under transrectal ultrasound guidance, and the prescription dose was 145 Gy. A CT and MRI scan of the pelvis were performed 1 month after implantation for dosimetric study. RESULTS: Compared with non-small PV patients, patients with small PV experienced larger 1-month edema (p<0.001); lower dose to 90% (the isodose enclosing 90% of PV and representing a minimum dose to that volume of the prostate [D(90)]) of the prostate (p=0.03); higher intracapsular seed density (p<0.001); and were less likely to achieve D(90)>or=140 Gy (p=0.013) in a postimplant dosimetric study. The number of patients with D(90)<140 Gy decreased steadily in both subsets of patients as the implant program matured (odds ratio=0.56 per year, p<0.001), but the small prostate group exhibited more improvement compared with the non-small prostate patients over the same time period. Multivariate analysis revealed that brachytherapy team experience rather than the size of prostate was a more important predictive factor of implant quality (p<0.001). CONCLUSIONS: This single institution experience demonstrated a significant learning curve in the initial years of a prostate brachytherapy program, especially for patients with small prostates. A small prostate itself is not a contraindication of brachytherapy. The quality of implant for patients with small prostates depends more on the skill of the brachytherapy team.

Leptospirosis in Hawaii, 1974-1998: epidemiologic analysis of 353 laboratory-confirmed cases.

The epidemiologic characterization of leptospirosis in the United States has been limited by difficulties associated with both case detection and confirmation. In addition, leptospirosis was eliminated from the list of National Notifiable Diseases in 1995. From 1974 until the cessation of national surveillance, Hawaii consistently had the highest reported annual incidence rate in the United States. From 1974 through 1998, 752 leptospirosis cases were reported in the State of Hawaii. Of these, 353 had exposures within the state and were laboratory confirmed. The mean annual incidence rate was 1.29 per 100,000. Cases were predominately male. Rates were highest in rural areas. Occupational exposures diminished over time while recreational exposures increased. This series represents the first large U.S. leptospirosis surveillance report since 1979. With leptospirosis recently being identified as a re-emerging zoonosis, continued national surveillance and case reporting should be reconsidered.

Evaluation of eight rapid screening tests for acute leptospirosis in Hawaii.

Leptospirosis is a major public health problem throughout the world. Clinical recognition of leptospirosis is challenging, and the definitive serologic diagnostic assay, the microscopic agglutination test, is time-consuming and difficult to conduct. Various serologic screening tests have been developed, but their performance among ill persons in the United States has not been established. Eight screening tests were compared using 379 serum samples obtained in 1998 and 1999 from a series of 236 patients (33 with confirmed infection). The median number of days between illness onset and specimen collection was 9. The overall sensitivity, by specimen, for each test was as follows: indirect hemagglutination assay (MRL Diagnostics, Cypress, Calif.), 29%; INDX Leptospira Dip-S-Tick (PanBio InDx, Inc., Baltimore, Md.), 52%; Biognost IgM IFA test (Bios GmbH Labordiagnostik, Gräfelfing, Germany), 40%; Biolisa IgM ELISA (Bios GmbH, Labordiagnostik), 48%; Leptospira IgM ELISA (PanBio Pty Ltd., Brisbane, Australia), 36%; SERION ELISA classic Leptospira (Institut Virion*Serion GmbH, Würzburg, Germany), 48%; LEPTO Dipstick(Organon-Teknika, Ltd., Amsterdam, The Netherlands), 34%; Biosave latex agglutination test (LATEX; Bios GmbH Labordiagnostik), 86%. Test specificity ranged from 85 to 100% among all tests except LATEX, for which the specificity was significantly lower, at 10%. Test sensitivity was particularly low (<25%) for all tests (except LATEX) on specimens collected during the first week of illness. This is the most comprehensive field trial of leptospirosis screening tests reported to date. The data indicate that immunoglobulin M detection tests have limited utility for diagnosing leptospirosis during the initial evaluation of patients seen in Hawaii, a time when important therapeutic decisions are made. Improved leptospirosis screening tests are needed.