Brachytherapy for Central Serous Chorioretinopathy.

Brachytherapy is widely used for the treatment of choroidal melanoma and has recently been explored for the treatment of wet age-related macular degeneration. We propose the use of low dose radiation via episcleral brachytherapy in refractory cases of central serous chorioretinopathy (CSCR). The pathogenesis of CSCR involves dilatation and hyperpermeability of large choroidal vessels. Low dose radiation can induce intimal proliferation in large choroidal vessels and decrease their hyperpermeability. Concerns about the use of brachytherapy in CSCR include damage to the choriocapillaris or the retinal vessels. This can be addressed with the use of a specialized device through which a very precise and appropriate dose can be delivered. The dose of the radiation delivered decreases exponentially at a depth of approximately 0.5-1.5 mm from the devise-sclera interface. Considering an increased choroidal thickness in cases of CSCR, delivery of a safe dose can be assured.

Two-year outcomes of episcleral brachytherapy adjunct to anti-VEGF therapy for treatment-resistant nAMD.

PURPOSE: This study was designed to demonstrate the safety and feasibility of episcleral brachytherapy (ESB) for the treatment of anti-vascular endothelial growth factor (anti-VEGF) resistant neovascular age-related macular degeneration (nAMD) in a 6-subject cohort adjunct to anti-VEGF therapy. METHODS: Six eyes of six subjects with anti-VEGF resistant nAMD (persistent fluid or hemorrhage despite frequent anti-VEGF treatment) were treated with ESB between May 2018 and July 2018 as part of a larger early feasibility trial. Baseline and follow-up exams with multi-modal imaging were conducted. RESULTS: In this analysis, six eyes were included. The mean age was 74.7 years; 33% were female; 67% had polypoidal choroidal vasculopathy. The mean number of lifetime anti-VEGF injections received prior to the study enrollment was 33.9 injections and 10 injections in the year prior to the study enrollment. In the first and second years following ESB, the mean number of injections was 8.5 and 8, respectively. No evidence of radiation-induced toxicity through 2 years following ESB was observed. The mean baseline VA was 55.3 letters. At 1 year, the mean VA increased by 3.2 letters and 1.7 letters at year 2. At 2 years, the mean change in vascular complex on ICGA was - 18%, - 43% on OCTA, and - 5% on FA. The subjects also experienced a mean decrease in CRT on OCT of 21% after 2 years. CONCLUSIONS: The results from this six-subject cohort with 2-year data support additional investigations of ESB for nAMD, specifically those with persistent disease activity and treatment resistant nAMD.

Pilot Study: Texture Analysis of PET Imaging Demonstrates Changes in 18F-FDG Uptake of the Brain After Prophylactic Cranial Irradiation.

Prophylactic cranial irradiation (PCI) is used to decrease the probability of developing brain metastases in patients with small cell lung cancer and has been linked to deleterious cognitive effects. Although no well-established imaging markers for these effects exist, previous studies have shown that structural and metabolic changes in the brain can be detected with MRI and PET. This study used an image processing technique called texture analysis to explore whether global changes in brain glucose metabolism could be characterized in PET images. Methods: 18F-FDG PET images of the brain from patients with small cell lung cancer, obtained before and after the administration of PCI, were processed using texture analysis. Texture features were compared between the pre- and post-PCI images. Results: Multiple texture features demonstrated statistically significant differences before and after PCI when texture analysis was applied to the brain parenchyma as a whole. Regional differences were also seen but were not statistically significant. Conclusion: Global changes in brain glucose metabolism occur after PCI and are detectable using advanced image processing techniques. These changes may reflect radiation-induced damage and thus may provide a novel method for studying radiation-induced cognitive impairment.

Preliminary Clinical Evaluation of Intrafraction Prostate Displacements for Two Immobilization Systems.

Immobilization systems and their corresponding set-up errors influence the clinical target volume to the planning target volume (CTV-PTV) margins, which is critical for hypofractionated prostate stereotactic body radiotherapy (SBRT). This preliminary study evaluates intrafraction prostate displacement for two immobilization systems (A and B). Six consecutive patients having localized prostate cancer and implanted prostate marker seeds were studied. Planar X-ray images were acquired pre- and post-treatment to find the intrafraction prostate displacement. The average absolute displacements (lateral, longitudinal, vertical) were 0.9 ± 0.4 mm, 1.7 ± 0.1 mm, 1.3 ± 0.3 mm (system A), and 0.5 ± 0.2 mm, 0.6 ± 0.1 mm, 0.8 ± 0.3 mm (system B), with average three-dimensional displacements of 2.6 ± 0.2 mm (system A) and 1.3 ± 0.2 mm (system B). The computed CTV-PTV margins (lateral, longitudinal, vertical) were 2.5 mm, 2.5 mm, 3.6 mm and 1.4 mm, 1.6 mm, 2.4 mm for systems A and B, respectively. This suggests that the immobilization system influences intrafraction prostate displacement and, therefore, the margins applied. However, the margins found for both systems are comparable to the margins used for hypofractionated prostate SBRT.

A simple knowledge-based tool for stereotactic radiosurgery pre-planning.

We studied the dosimetry of single-isocenter treatment plans generated to treat a solitary intracranial lesion using linac-based stereotactic radiosurgery (SRS). A common metric for evaluating SRS plan quality is the volume of normal brain tissue irradiated by a dose of at least 12 Gy (V12), which is important because multiple studies have shown a strong correlation between V12 and incidence of radiation necrosis. Unrealistic expectations for values of V12 can lead to wasted planning time. We present a model that estimates V12 without having to construct a full treatment plan. This model was derived by retrospectively analyzing 50 SRS treatment plans, each clinically approved for delivery using circular collimator cone arc therapy (CAT). Each case was re-planned for delivery via dynamic conformal arc therapy (DCAT), and then scaling arguments were used to extend dosimetric data to account for different prescription dose (PD) values (15, 18, 21, or 24 Gy). We determined a phenomenological expression for the total volume receiving at least 12 Gy (TV12) as a function of both planning target volume (PTV) and PD: T V 12 / 1 c c = n ∗ P D / 1 G y + d ∗ P T V / 1 c c a ∗ P D / 1 G y c , where a , c , n , d are fit parameters, and a separate set of values is determined for each plan type. In addition, we generated a sequence of plots to clarify how the relationship between conformity index (CI) and TV12 depends on plan type (CAT vs DCAT), PTV, and PD. These results can be used to suggest realistic plan parameters and planning goals before the start of treatment planning. In the absence of access to more sophisticated pre-planning tools, this model can be locally generated and implemented at relatively low cost with respect to time, money, and expertise.

Regional Changes in Brain 18F-FDG Uptake After Prophylactic Cranial Irradiation and Chemotherapy in Small Cell Lung Cancer May Reflect Functional Changes.

Chemotherapy followed by prophylactic cranial irradiation (PCI) is associated with increased survival in patients with small cell lung cancer but is associated with fatigue and cognitive impairment. This retrospective study evaluated regional differences in 18F-FDG uptake by the brain before and after PCI. The null hypothesis was that direct toxic effects on the brain from PCI and chemotherapy are symmetric; thus, asymmetric deviations may reflect functional changes due to therapy. Methods: Electronic medical records from 2013 to 2016 were reviewed for patients with small cell lung cancer, MRI of brain negative for metastasis, and 18F-FDG PET/CT scans before and after PCI. As the standard of care, patients received first-line chemotherapy or chemoradiation to the thorax followed by PCI. The 18F-FDG PET/CT scans nearest the PCI were selected. Sixteen patients met these initial criteria. Commercially available PET software was used to register and subtract the PET scans before and after PCI to obtain difference maps. Occipital and cerebellar regions were excluded from the final statistical analysis given the known high variability and misregistration. The χ2 test was used to analyze the data. Results: Two patients had 18F-FDG uptake differences only in the occipital and cerebellar regions. The software registration failed on 1 patient's scans. Therefore, 13 patients were included in the final analysis. Nine of 13 patients demonstrated significant unilateral changes in only 1 region of the brain, and 3 of 13 showed significant changes unilaterally in 2 regions. The χ2 test revealed a significant unilateral regional difference on a patient level (χ2 = 6.24, P = 0.025). The most commonly affected brain region was the frontal lobe. Conclusion: Significantly more patients had unilateral than bilateral regional differences (both increases and decreases) in 18F-FDG uptake in the brain before and after PCI. This finding suggests that differences in unilateral distribution are related to functional changes, since direct toxicity alone from PCI and chemotherapy would be symmetric. The frontal region was the most commonly affected, suggesting a potential contributing etiology for cognitive impairment and decreased executive function after therapy.

Failure modes and effects analysis for ocular brachytherapy.

PURPOSE: The aim of the study was to identify potential failure modes (FMs) having a high risk and to improve our current quality management (QM) program in Collaborative Ocular Melanoma Study (COMS) ocular brachytherapy by undertaking a failure modes and effects analysis (FMEA) and a fault tree analysis (FTA). METHODS AND MATERIALS: Process mapping and FMEA were performed for COMS ocular brachytherapy. For all FMs identified in FMEA, risk priority numbers (RPNs) were determined by assigning and multiplying occurrence, severity, and lack of detectability values, each ranging from 1 to 10. FTA was performed for the major process that had the highest ranked FM. RESULTS: Twelve major processes, 121 sub-process steps, 188 potential FMs, and 209 possible causes were identified. For 188 FMs, RPN scores ranged from 1.0 to 236.1. The plaque assembly process had the highest ranked FM. The majority of FMs were attributable to human failure (85.6%), and medical physicist-related failures were the most numerous (58.9% of all causes). After FMEA, additional QM methods were included for the top 10 FMs and 6 FMs with severity values > 9.0. As a result, for these 16 FMs and the 5 major processes involved, quality control steps were increased from 8 (50%) to 15 (93.8%), and major processes having quality assurance steps were increased from 2 to 4. CONCLUSIONS: To reduce high risk in current clinical practice, we proposed QM methods. They mainly include a check or verification of procedures/steps and the use of checklists for both ophthalmology and radiation oncology staff, and intraoperative ultrasound-guided plaque positioning for ophthalmology staff.

Automated survey of 8000 plan checks at eight facilities.

PURPOSE: To identify policy and system related weaknesses in treatment planning and plan check work-flows. METHODS: The authors' web deployed plan check automation solution, PlanCheck, which works with all major planning and record and verify systems (demonstrated here for mosaiq only), allows them to compute violation rates for a large number of plan checks across many facilities without requiring the manual data entry involved with incident filings. Workflows and failure modes are heavily influenced by the type of record and verify system used. Rather than tackle multiple record and verify systems at once, the authors restricted the present survey to mosaiq facilities. Violations were investigated by sending inquiries to physicists running the program. RESULTS: Frequent violations included inadequate tracking in the record and verify system of total and prescription doses. Infrequent violations included incorrect setting of patient orientation in the record and verify system. Peaks in the distribution, over facilities, of violation frequencies pointed to suboptimal policies at some of these facilities. Correspondence with physicists often revealed incomplete knowledge of settings at their facility necessary to perform thorough plan checks. CONCLUSIONS: The survey leads to the identification of specific and important policy and system deficiencies that include: suboptimal timing of initial plan checks, lack of communication or agreement on conventions surrounding prescription definitions, and lack of automation in the transfer of some parameters.

Registration of on-board X-ray images with 4DCT: a proposed method of phase and setup verification for gated radiotherapy.

Current gated radiation therapy starts with simulation 4DCT images of a patient with lung cancer. We propose a method to confirm the phase of 4DCT for planning and setup position at the time of treatment. An intensity-based rigid algorithm was developed in this work to register an orthogonal set of on-board projection X-ray images with each phase of the 4DCT. Multiple DRRs for one of ten 4DCT phases are first generated and the correlation coefficient (CC) between the projection X-ray image and each DRR is computed. The maximum value of CC for the phase is found via a simulated annealing optimization process. The whole process repeats for all ten phases. The 4DCT phase that has the highest CC is identified as the breathing phase of the X-ray. The phase verification process is validated by a moving phantom study. Thus, the method may be used to independently confirm the correspondence between the gating phase at the times of 4DCT simulation and radiotherapy delivery. When the intended X-ray phase and actual gating phase are consistent, the registration of the DRRs and the projection images may also yield the values of patient shifts for treatment setup. This method could serve as the 4D analog of the conventional setup film as it provides both verification of the specific phase at the time of treatment and isocenter positioning shifts for treatment delivery.

Patient positioning using implanted gold markers with the Novalis Body system in the thoracic spine.

OBJECTIVE: To evaluate the effectiveness of implanted gold marker registration compared with bony fusion alignment for patient positioning using the Novalis Body system. METHODS: Eighteen treatment fractions of stereotactic spinal radiotherapy were analyzed for three patients who each had three implanted gold seeds placed near their spinal lesions before radiotherapy. At each treatment session, the registration was first performed using bony fusion and then verified by another bony fusion, followed by registration with implanted markers. The software reported the calculated shifts for both methods. In addition, the actual three-dimensional coordinate positions of the markers were read using PTDReader software. Implanted marker positions were analyzed for variations in individual maker coordinate displacement, interseed distances, and area transcribed by them. Measured positional differences between the two fusion methods were applied to actual treatment plans to assess the resulting dosimetric differences in the treatment plans. RESULTS: Both fusion algorithms were shown to localize the patient well, within 1.5 mm, but the implanted marker fusion consistently related less deviation from the planned isocenter, by approximately 0.5 mm, than did the bony fusion. Exceptions to this localization occurred when the average interseed distances were less than 3.0 cm and resulted in the two registration methods being equivalent. Implanted spine markers were also shown to have less than 0.7 mm deviation from the planned marker coordinates, indicating no migration of the seeds. Dose distributions were found to be highly dependant on differences in fusion method, with spinal cord doses up to 350% greater with bony fusion than with implanted markers. CONCLUSION: Implanted markers used with the Novalis Body system have been shown to be more effective in patient positioning than the bony fusion method in the thoracic spine.

Lung tumor tracking in fluoroscopic video based on optical flow.

Respiratory gating and tumor tracking for dynamic multileaf collimator delivery require accurate and real-time localization of the lung tumor position during treatment. Deriving tumor position from external surrogates such as abdominal surface motion may have large uncertainties due to the intra- and interfraction variations of the correlation between the external surrogates and internal tumor motion. Implanted fiducial markers can be used to track tumors fluoroscopically in real time with sufficient accuracy. However, it may not be a practical procedure when implanting fiducials bronchoscopically. In this work, a method is presented to track the lung tumor mass or relevant anatomic features projected in fluoroscopic images without implanted fiducial markers based on an optical flow algorithm. The algorithm generates the centroid position of the tracked target and ignores shape changes of the tumor mass shadow. The tracking starts with a segmented tumor projection in an initial image frame. Then, the optical flow between this and all incoming frames acquired during treatment delivery is computed as initial estimations of tumor centroid displacements. The tumor contour in the initial frame is transferred to the incoming frames based on the average of the motion vectors, and its positions in the incoming frames are determined by fine-tuning the contour positions using a template matching algorithm with a small search range. The tracking results were validated by comparing with clinician determined contours on each frame. The position difference in 95% of the frames was found to be less than 1.4 pixels (approximately 0.7 mm) in the best case and 2.8 pixels (approximately 1.4 mm) in the worst case for the five patients studied.

A deformable lung tumor tracking method in fluoroscopic video using active shape models: a feasibility study.

A dynamic multi-leaf collimator (DMLC) can be used to track a moving target during radiotherapy. One of the major benefits for DMLC tumor tracking is that, in addition to the compensation for tumor translational motion, DMLC can also change the aperture shape to conform to a deforming tumor projection in the beam's eye view. This paper presents a method that can track a deforming lung tumor in fluoroscopic video using active shape models (ASM) (Cootes et al 1995 Comput. Vis. Image Underst. 61 38-59). The method was evaluated by comparing tracking results against tumor projection contours manually edited by an expert observer. The evaluation shows the feasibility of using this method for precise tracking of lung tumors with deformation, which is important for DMLC-based real-time tumor tracking.

A novel respiratory detection method based on automated analysis of ultrasound diaphragm video.

This paper proposes a novel respiratory detection method based on diaphragm motion measurements using a 2D ultrasound unit. The proposed method extracts a respiratory signal from an automated analysis of the internal diaphragm motion during breathing. The respiratory signal may be used for gating. Ultrasound studies of diaphragm breathing motion were performed on four volunteers. The ultrasound video stream was captured and transferred to a personal computer and decomposed into individual image frames. After straightforward image analysis, region of interest selection, and filtering, the mutual information (MI) and correlation coefficients (CCs) between a selected reference frame and all other frames were computed. The resulting MI and CC values were discovered to produce a signal corresponding to the respiratory cycle in both phase and magnitude. We also studied the diaphragm motion of two volunteers during repeated deep inspiration breath holds (DIBH) and found a slight relaxation motion of the diaphragm during the DIBH, suggesting that the residual motion may be important for treatments delivered at this breathing phase. Applying the proposed respiratory detection method to these ultrasound studies, we found that the MI and CC values demonstrate the relaxation behavior, indicatingthat our method may be used to determine the radiation triggering time for a DIBH technique.

Postprostatectomy target-normal structure overlap volume differences using computed tomography and radioimmunoscintigraphy images for radiotherapy treatment planning.

PURPOSE: The purpose of this study was to analyze regions of uptake in normal structures on postprostatectomy radioimmunoscintigraphy (RIS) images by evaluating differences in the overlap volumes of prostate fossa clinical target volume (CTV) and planning target volume (PTV) using correlative computed tomography (CT) images. MATERIALS AND METHODS: The electronic records of 13 patients who received external beam radiotherapy postprostatectomy and who underwent a vessel-based RIS/CT registration were reviewed. For each patient, the RIS-defined CTV (CTV(RIS)) was compared (in terms of the overlap volume with the surrounding bladder, rectum, pubic symphysis, and penile bulb) with the CT-defined CTV(pre) before this registration and also with CTV(post) (the final target volume used for treatment). Similar analyses were done for PTV(RIS), PTV(pre), and PTV(post) defined in each case to be the corresponding CTV + 1-cm margin. RESULTS: CTV(RIS) overlapped significantly more with the bladder, rectum, and symphysis, but not with the penile bulb, than did either the CTV(pre) or CTV(post). However, the corresponding PTV analyses revealed no significant differences between any of the overlap volumes of any of the PTVs with the bladder, rectum, and penile bulb, but did reveal a significant difference between the PTV(RIS) and PTV(post) overlap volumes with the symphysis compared with PTV(pre) overlap volumes with the symphysis. CONCLUSIONS: On RIS images, there appear to be areas of uptake in the bladder, rectum, and pubic symphysis but not the penile bulb; however, the dosimetric consequences of this uptake for radiation treatment planning are minimal on the bladder, rectum, and penile bulb, but require segmentation for dose reduction to the pubic symphysis.

Spectrum reconstruction from dose measurements as a linear inverse problem.

There are three ways to determine the spectrum of a clinical photon beam: direct measurement, modelling the source and reconstruction from ion-chamber measurements. We focus on reconstruction because the necessary equipment is readily available and it provides independent confirmation of source models for a given machine. Reconstruction methods involve measuring the dose in an ion chamber after the beam passes through an attenuator. We gain information about the spectrum from measurements using attenuators of differing compositions and thicknesses since materials have energy dependent attenuation. Unlike the procedures used in other papers, we do not discretize or parametrize the spectrum. With either of these two approximations, reconstruction is a least squares problem. The forward problem of going from a spectrum to a series of dose measurements is a linear operator, with the composition and thickness of the attenuators as parameters. Hence the singular value decomposition (SVD) characterizes this operator. The right singular vectors form a basis for the spectrum, and, at first approximation, only those corresponding to singular values above a threshold are measurable. A more rigorous error analysis shows with what confidence different components of the spectrum can be measured. We illustrate this theory with simulations and an example utilizing six sets of dose measurements with water and lead as attenuators.