A multi-institutional meningioma MRI dataset for automated multi-sequence image segmentation.

Meningiomas are the most common primary intracranial tumors and can be associated with significant morbidity and mortality. Radiologists, neurosurgeons, neuro-oncologists, and radiation oncologists rely on brain MRI for diagnosis, treatment planning, and longitudinal treatment monitoring. However, automated, objective, and quantitative tools for non-invasive assessment of meningiomas on multi-sequence MR images are not available. Here we present the BraTS Pre-operative Meningioma Dataset, as the largest multi-institutional expert annotated multilabel meningioma multi-sequence MR image dataset to date. This dataset includes 1,141 multi-sequence MR images from six sites, each with four structural MRI sequences (T2-, T2/FLAIR-, pre-contrast T1-, and post-contrast T1-weighted) accompanied by expert manually refined segmentations of three distinct meningioma sub-compartments: enhancing tumor, non-enhancing tumor, and surrounding non-enhancing T2/FLAIR hyperintensity. Basic demographic data are provided including age at time of initial imaging, sex, and CNS WHO grade. The goal of releasing this dataset is to facilitate the development of automated computational methods for meningioma segmentation and expedite their incorporation into clinical practice, ultimately targeting improvement in the care of meningioma patients.

Incidence and imaging characteristics of difficult to detect retrospectively identified brain metastases in patients receiving repeat courses of stereotactic radiosurgery.

PURPOSE: During stereotactic radiosurgery (SRS) planning for brain metastases (BM), brain MRIs are reviewed to select appropriate targets based on radiographic characteristics. Some BM are difficult to detect and/or definitively identify and may go untreated initially, only to become apparent on future imaging. We hypothesized that in patients receiving multiple courses of SRS, reviewing the initial planning MRI would reveal early evidence of lesions that developed into metastases requiring SRS. METHODS: Patients undergoing two or more courses of SRS to BM within 6 months between 2016 and 2018 were included in this single-institution, retrospective study. Brain MRIs from the initial course were reviewed for lesions at the same location as subsequently treated metastases; if present, this lesion was classified as a "retrospectively identified metastasis" or RIM. RIMs were subcategorized as meeting or not meeting diagnostic imaging criteria for BM (+ DC or -DC, respectively). RESULTS: Among 683 patients undergoing 923 SRS courses, 98 patients met inclusion criteria. There were 115 repeat courses of SRS, with 345 treated metastases in the subsequent course, 128 of which were associated with RIMs found in a prior MRI. 58% of RIMs were + DC. 17 (15%) of subsequent courses consisted solely of metastases associated with + DC RIMs. CONCLUSION: Radiographic evidence of brain metastases requiring future treatment was occasionally present on brain MRIs from prior SRS treatments. Most RIMs were + DC, and some subsequent SRS courses treated only + DC RIMs. These findings suggest enhanced BM detection might enable earlier treatment and reduce the need for additional SRS.

The ASNR-MICCAI Brain Tumor Segmentation (BraTS) Challenge 2023: Intracranial Meningioma.

Meningiomas are the most common primary intracranial tumor in adults and can be associated with significant morbidity and mortality. Radiologists, neurosurgeons, neuro-oncologists, and radiation oncologists rely on multiparametric MRI (mpMRI) for diagnosis, treatment planning, and longitudinal treatment monitoring; yet automated, objective, and quantitative tools for non-invasive assessment of meningiomas on mpMRI are lacking. The BraTS meningioma 2023 challenge will provide a community standard and benchmark for state-of-the-art automated intracranial meningioma segmentation models based on the largest expert annotated multilabel meningioma mpMRI dataset to date. Challenge competitors will develop automated segmentation models to predict three distinct meningioma sub-regions on MRI including enhancing tumor, non-enhancing tumor core, and surrounding nonenhancing T2/FLAIR hyperintensity. Models will be evaluated on separate validation and held-out test datasets using standardized metrics utilized across the BraTS 2023 series of challenges including the Dice similarity coefficient and Hausdorff distance. The models developed during the course of this challenge will aid in incorporation of automated meningioma MRI segmentation into clinical practice, which will ultimately improve care of patients with meningioma.

A Deep Learning-Based Computer Aided Detection (CAD) System for Difficult-to-Detect Brain Metastases.

PURPOSE: We sought to develop a computer-aided detection (CAD) system that optimally augments human performance, excelling especially at identifying small inconspicuous brain metastases (BMs), by training a convolutional neural network on a unique magnetic resonance imaging (MRI) data set containing subtle BMs that were not detected prospectively during routine clinical care. METHODS AND MATERIALS: Patients receiving stereotactic radiosurgery (SRS) for BMs at our institution from 2016 to 2018 without prior brain-directed therapy or small cell histology were eligible. For patients who underwent 2 consecutive courses of SRS, treatment planning MRIs from their initial course were reviewed for radiographic evidence of an emerging metastasis at the same location as metastases treated in their second SRS course. If present, these previously unidentified lesions were contoured and categorized as retrospectively identified metastases (RIMs). RIMs were further subcategorized according to whether they did (+DC) or did not (-DC) meet diagnostic imaging-based criteria to definitively classify them as metastases based upon their appearance in the initial MRI alone. Prospectively identified metastases (PIMs) from these patients, and from patients who only underwent a single course of SRS, were also included. An open-source convolutional neural network architecture was adapted and trained to detect both RIMs and PIMs on thin-slice, contrast-enhanced, spoiled gradient echo MRIs. Patients were randomized into 5 groups: 4 for training/cross-validation and 1 for testing. RESULTS: One hundred thirty-five patients with 563 metastases, including 72 RIMS, met criteria. For the test group, CAD sensitivity was 94% for PIMs, 80% for +DC RIMs, and 79% for PIMs and +DC RIMs with diameter <3 mm, with a median of 2 false positives per patient and a Dice coefficient of 0.79. CONCLUSIONS: Our CAD model, trained on a novel data set and using a single common MR sequence, demonstrated high sensitivity and specificity overall, outperforming published CAD results for small metastases and RIMs - the lesion types most in need of human performance augmentation.

Impact of Race on Outcomes of High-Risk Patients With Prostate Cancer Treated With Moderately Hypofractionated Radiotherapy in an Equal Access Setting.

Background: Moderately hypofractionated radiotherapy (MHRT) is an accepted treatment for localized prostate cancer; however, limited MHRT data address high-risk prostate cancer (HRPC) and/or African American patients. We report clinical outcomes and toxicity profiles for individuals with HRPC treated in an equal access system. Methods: We identified patients with HRPC treated with MHRT at a US Department of Veterans Affairs referral center. Exclusion criteria included < 12 months follow-up and elective nodal irradiation. MHRT included 70 Gy over 28 fractions or 60 Gy over 20 fractions. Acute and late gastrointestinal (GI) and genitourinary (GU) toxicities were graded using Common Terminology Criteria for Adverse Events, version 5.0. Clinical endpoints, including biochemical recurrence-free survival (BRFS), distant metastases-free survival (DMFS), overall survival (OS), and prostate cancer-specific survival (PCSS) were estimated using Kaplan-Meier methods. Clinical outcomes, acute toxicity, and late toxicity-free survival were compared between African American and White patients with logistic regression and log-rank testing. Results: Between November 2008 and August 2018, 143 patients with HRPC were treated with MHRT and followed for a median of 38.5 months; 82 (57%) were African American and 61 were White patients. Concurrent androgen deprivation therapy (ADT) was provided for 138 (97%) patients for a median duration of 24 months. No significant differences between African American and White patients were observed for 5-year OS (73% [95% CI, 58%-83%] vs 77% [95% CI, 60%-97%]; P = .55), PCSS (90% [95% CI, 79%-95%] vs 87% [95 % CI, 70%-95%]; P = .57), DMFS (91% [95% CI, 80%-96%] vs 81% [95% CI, 62%-91%]; P = .55), or BRFS (83% [95% CI, 70%-91%] vs 71% [95% CI, 53%-82%]; P = .57), respectively. Rates of acute grade 3+ GU and GI were low overall (4% and 1%, respectively). Late toxicities were similarly favorable with no significant differences by race. Conclusions: Individuals with HRPC treated with MHRT in an equal access setting demonstrated favorable clinical outcomes that did not differ by race, alongside acceptable rates of acute and late toxicities.

Effect of Large Prostate Volume on Efficacy and Toxicity of Moderately Hypofractionated Radiation Therapy in Patients With Prostate Cancer.

Purpose: To evaluate the effect of prostate volume on outcomes after moderately hypofractionated radiation therapy (mHFRT) for prostate cancer. Methods and Materials: Prostate cancer patients treated with mHFRT at a Veteran's Affairs Medical Center from August 20, 2008, to January 31, 2018, were identified. Patients were placed into a large prostate planning target volume (LPTV) cohort if their prostate PTV was in the highest quartile. Acute/late genitourinary (GU) and gastrointestinal toxicity events among patients with and without LPTV were compared. Multivariable analyses estimated the effect of factors on toxicity. Overall survival, biochemical recurrence-free survival, and freedom from late GU/gastrointestinal toxicity of patients with and without LPTV were estimated via Kaplan-Meier. Results: Four hundred and seventy-two patients were included. Ninety-three percent received 70 Gy in 2.5 Gy fractions; 75% received androgen deprivation therapy. Median follow-up was 69 months. Patients with LPTV (PTV >138.4 cm3) had a higher late 2 + GU toxicity compared with those without (59% vs 48%, P = .03). Earlier time to late 2 + GU toxicity was associated with LPTV (hazard ratio 1.36; 95% confidence interval [CI], 1.00-1.86; P = .047), androgen deprivation therapy use (hazard ratio 1.60; 95% CI, 1.13-2.27; P = .01), and higher baseline American Urologic Association symptom score (odds ratio 1.03; 95% CI, 1.02-1.05; P < .001). At 2 years, freedom from late 2 + GU toxicity was 46% (95% CI, 47%-54%) for those with LPTV versus 61% (95% CI, 55%-65%) for those without (P = .04). Late grade 3 GU toxicity was 7% for those with LPTV and 4% for those without. No differences in overall survival or biochemical recurrence-free survival were observed between patients with or without LPTV. Conclusions: LPTV did not affect efficacy of mHFRT for prostate cancer; however, it was associated with increased risk and earlier onset of late grade 2 + GU toxicity.

A Pooled Toxicity Analysis of Moderately Hypofractionated Proton Beam Therapy and Intensity Modulated Radiation Therapy in Early-Stage Prostate Cancer Patients.

PURPOSE: Data comparing moderately hypofractionated intensity modulated radiation therapy (IMRT) and proton beam therapy (PBT) are lacking. We aim to compare late toxicity profiles of patients with early-stage prostate cancer treated with moderately hypofractionated PBT and IMRT. METHODS AND MATERIALS: This multi-institutional analysis included patients with low- or intermediate-risk biopsy-proven prostate adenocarcinoma from 7 tertiary referral centers treated from 1998 to 2018. All patients were treated with moderately hypofractionated radiation, defined as 250 to 300 cGy per daily fraction given for 4 to 6 weeks, and stratified by use of IMRT or PBT. Primary outcomes were late genitourinary (GU) and gastrointestinal (GI) toxicity. Adjusted toxicity rates were calculated using inverse probability of treatment weighting, accounting for race, National Comprehensive Cancer Network risk group, age, pretreatment International Prostate Symptom Score (GU only), and anticoagulant use (GI only). RESULTS: A total of 1850 patients were included: 1282 IMRT (median follow-up 80.0 months) and 568 PBT (median follow-up 43.9 months). Overall toxicity rates were low, with the majority of patients experiencing no late GU (56.6%, n = 1048) or late GI (74.4%, n = 1377) toxicity. No difference was seen in the rates of late toxicity between the groups, with late grade 3+ GU toxicity of 2.0% versus 3.9% (odds ratio [OR] 0.47; 95% confidence interval 0.17-1.28) and late grade 2+ GI toxicity of 14.6% versus 4.7% (OR 2.69; confidence interval 0.80-9.05) for the PBT and IMRT cohorts, respectively. On multivariable analysis, no factors were significantly predictive of GU toxicity, and only anticoagulant use was significantly predictive of GI toxicity (OR 1.90; P = .008). CONCLUSIONS: In this large, multi-institutional analysis of 1850 patients with early-stage prostate cancer, treatment with moderately hypofractionated IMRT and PBT resulted in low rates of toxicity. No difference was seen in late GI and GU toxicity between the modalities during long-term follow-up. Both treatments are safe and well tolerated.

Local Tumor Control and Patient Outcome Using Stereotactic Body Radiation Therapy for Hepatocellular Carcinoma: iRECIST as a Potential Substitute for Traditional Criteria.

OBJECTIVE. The purpose of this study was to investigate whether, compared with traditional criteria, the modified Response Evaluation Criteria in Solid Tumors version 1.1 for immune-based therapeutics (iRECIST) improves prediction of local tumor control and survival in patients with hepatocellular carcinoma (HCC) treated with stereotactic body radiotherapy (SBRT). MATERIALS AND METHODS. Fifty-one HCC lesions (mean size, 3.1 cm) treated with SBRT in 41 patients (mean age, 67 years) were retrospectively included. Each patient underwent CT or MRI before SBRT and at least once after SBRT. Best overall response was categorized using Response Evaluation Criteria in Solid Tumors version 1.1 (RECIST 1.1), iRECIST, World Health Organization (WHO) criteria, modified Response Evaluation Criteria in Solid Tumors (mRECIST), and European Association for the Study of the Liver (EASL) criteria. Lesions were then classified as local tumor control (i.e., stable disease, partial response, or complete response) or local treatment failure (i.e., progressive disease) by each tumor response criteria. Proportions of local tumor control were compared using the McNemar exact test. The 1-year overall survival was estimated using the Kaplan-Meier method. RESULTS. The median follow-up after SBRT was 21.0 months. The local tumor control rate was 94.1% (48/51) by iRECIST, 88.2% (45/51) by RECIST 1.1, 72.5% (37/51) by WHO criteria, 80.4% (41/51) by mRECIST, and 72.5% (37/51) by EASL criteria. The local tumor control rate was significantly higher according to iRECIST compared with WHO (p = 0.0010) and EASL (p = 0.0225) criteria. The 1-year survival rate for patients with local tumor control according to iRECIST (86.4%) was higher (although not statistically significant) compared with the 1-year survival rate for patients with local tumor control according to the other response criteria. CONCLUSION. iRECIST may provide more robust interpretation of HCC response after SBRT, yielding improved prediction of local tumor control and 1-year survival rates compared with traditional criteria.

Radiation Therapy for Pancreatic Cancer: Executive Summary of an ASTRO Clinical Practice Guideline.

PURPOSE: This guideline systematically reviews the evidence for treatment of pancreatic cancer with radiation in the adjuvant, neoadjuvant, definitive, and palliative settings and provides recommendations on indications and technical considerations. METHODS AND MATERIALS: The American Society for Radiation Oncology convened a task force to address 7 key questions focused on radiation therapy, including dose fractionation and treatment volumes, simulation and treatment planning, and prevention of radiation-associated toxicities. Recommendations were based on a systematic literature review and created using a predefined consensus-building methodology and system for grading evidence quality and recommendation strength. RESULTS: The guideline conditionally recommends conventionally fractionated or stereotactic body radiation for neoadjuvant and definitive therapy in certain patients and conventionally fractionated regimens for adjuvant therapy. The task force suggests a range of appropriate dose-fractionation schemes and provides recommendations on target volumes and sequencing of radiation and chemotherapy. Motion management, daily image guidance, use of contrast, and treatment with modulated techniques are all recommended. The task force supported prophylactic antiemetic medication, and patients may also benefit from medications to reduce acid secretion. CONCLUSIONS: The role of radiation in the management of pancreatic cancer is evolving, with many ongoing areas of active investigation. Radiation therapy is likely to become even more important as new systemic therapies are developed and there is increased focus on controlling local disease. It is important that the nuances of available data are discussed with patients and families and that care be coordinated in a multidisciplinary fashion.

The role of external beam radiotherapy in the treatment of hepatocellular cancer.

Hepatocellular carcinoma (HCC) is increasing in incidence and mortality. Although the prognosis remains poor, long-term survival has improved from 3% in 1970 to an 18% 5-year survival rate today. This is likely because of the introduction of well tolerated, oral antiviral therapies for hepatitis C. Curative options for patients with HCC are often limited by underlying liver dysfunction/cirrhosis and medical comorbidities. Less than one-third of patients are candidates for surgery, which is the current gold standard for cure. Nonsurgical treatments include embolotherapies, percutaneous ablation, and ablative radiation. Technological advances in radiation delivery in the past several decades now allow for safe and effective ablative doses to the liver. Conformal techniques allow for both dose escalation to target volumes and normal tissue sparing. Multiple retrospective and prospective studies have demonstrated that hypofractionated image-guided radiation therapy, used as monotherapy or in combination with other liver-directed therapies, can provide excellent local control that is cost effective. Therefore, as the HCC treatment paradigm continues to evolve, ablative radiation treatment has moved from a palliative treatment to both a "bridge to transplant" and a definitive treatment.

Triphasic contrast enhanced CT simulation with bolus tracking for pancreas SBRT target delineation.

PURPOSE: Bolus-tracked multiphasic contrast computed tomography (CT) is often used in diagnostic radiology to enhance the visibility of pancreas tumors, but is uncommon in radiation therapy pancreas CT simulation, and its impact on gross tumor volume (GTV) delineation is unknown. This study evaluates the lesion conspicuity and consistency of pancreas stereotactic body radiation therapy (SBRT) GTVs contoured in the different contrast phases of triphasic CT simulation scans. METHODS AND MATERIALS: Triphasic, bolus-tracked planning CT simulation scans of 10 consecutive pancreas SBRT patients were acquired, yielding images of the pancreas during the late arterial (LA), portal venous (PV), and either the early arterial or delayed phase. GTVs were contoured on each phase by a gastrointestinal-specialized radiation oncologist and reviewed by a fellowship-trained abdominal radiologist who specializes in pancreatic imaging. The volumes of the registered GTVs, their overlap ratio, and the 3-dimensional margin expansions necessary for each GTV to fully encompass GTVs from the other phases were calculated. The contrast difference between tumor and normal pancreas was measured, and 2 radiation oncologists rank-ordered the phases according to their value for the lesion-contouring task. RESULTS: Tumor-to-pancreas enhancement was on average much larger for the LA and PV than the delayed phase or early arterial phases; the LA and PV phases were also consistently preferred by the radiation oncologists. Enhancement differences among the phases resulted in highly variable GTV volumes with no observed trends. Overlap ratios ranged from 18% to 75% across all 3 phases, improving to 43% to 91% when considering only the preferred LA and PV phases. GTV expansions necessary to encompass all GTVs ranged from 0.3 to 1.8 cm for all 3 phases, improving slightly to 0.1 to 1.4 cm when considering just the LA and PV phases. CONCLUSIONS: For pancreas SBRT, we recommend combining the GTVs from a multiphasic CT simulation with bolus-tracking, including, at a minimum, a Boolean "OR" of the LA and PV phases.

Digital tomosynthesis for respiratory gated liver treatment: clinical feasibility for daily image guidance.

PURPOSE: Breath-hold (BH) treatment minimizes internal target volumes (ITV) when treating sites prone to motion. Digital tomosynthesis (DTS) imaging has advantages over cone-beam CT (CBCT) for BH imaging: BH-DTS scan can be completed during a single breath-hold, whereas BH-CBCT is usually acquired by parsing the gantry rotation into multiple BH segments. This study evaluates the localization accuracy of DTS for BH treatment of liver tumors. METHODS: Both planning CT and on-board DTS/CBCT images were acquired under BH, using the planning CT BH window as reference. Onboard imaging data sets included two independent DTS orientations (coronal and sagittal), and CBCT images. Soft tissue target positioning was measured by each imaging modality and translated into couch shifts. Performance of the two DTS orientations was evaluated by comparing target positioning with the CBCT benchmark, determined by two observers. RESULTS: Image data sets were collected from thirty-eight treatment fractions (14 patients). Mean differences between the two DTS methods and the CBCT method were <1 mm in all directions (except the lateral direction with sagittal-DTS: 1.2 mm); the standard deviation was in the range of 2.1-3.5 mm for all techniques. The Pearson correlation showed good interobserver agreement for the coronal-DTS (0.72-0.78). The interobserver agreement for the sagittal-DTS was good for the in-plane directions (0.70-0.82), but poor in the out-of-plane direction (lateral, 0.26). CONCLUSIONS: BH-DTS may be a simpler alternative to BH-CBCT for onboard soft tissue localization of the liver, although the precision of DTS localization appears to be somewhat lower because of the presence of subtle out-of-plane blur.

Comparing digital tomosynthesis to cone-beam CT for position verification in patients undergoing partial breast irradiation.

PURPOSE: To evaluate digital tomosynthesis (DTS) technology for daily positioning of patients receiving accelerated partial breast irradiation (APBI) and to compare the positioning accuracy of DTS to three-dimensional cone-beam computed tomography (CBCT). METHODS AND MATERIALS: Ten patients who underwent APBI were scanned daily with on-board CBCT. A subset of the CBCT projections was used to reconstruct a stack of DTS image slices. To optimize soft-tissue visibility, the DTS images were reconstructed in oblique directions so that the tumor bed, breast tissue, ribs, and lungs were well separated. Coronal and sagittal DTS images were also reconstructed. Translational shifts of DTS images were obtained on different days from the same patients and were compared with the translational shifts of corresponding CBCT images. Seventy-seven CBCT scans and 291 DTS scans were obtained from nine evaluable patients. RESULTS: Tumor beds were best visible in the oblique DTS scans. One-dimensional positioning differences between DTS and CBCT images were 0.8-1.7 mm for the six patients with clips present and 1.2-2.0 mm for the three patients without clips. Because of the limited DTS scan angle, the DTS registration accuracy along the off-plane direction is lower than the accuracy along the in-plane directions. CONCLUSIONS: For patients receiving APBI, DTS localization offers comparable accuracy to CBCT localization for daily patient positioning while reducing mechanical constraints and imaging dose.

Clinical evaluation of positioning verification using digital tomosynthesis and bony anatomy and soft tissues for prostate image-guided radiotherapy.

PURPOSE: To evaluate on-board digital tomosynthesis (DTS) for patient positioning vs. two-dimensional (2D) radiography and three-dimensional cone beam (CBCT). METHODS AND MATERIALS: A total of 92 image sessions from 9 prostate cancer patients were analyzed. An on-board image set was registered to a corresponding reference image set. Four pairs of image sets were used: digitally reconstructed radiographs vs. on-board orthogonal paired radiographs for the 2D method, coronal-reference DTS vs. on-board coronal DTS for the coronal-DTS method, sagittal-reference DTS vs. on-board sagittal DTS for the sagittal-DTS method, and planning CT vs. CBCT for the CBCT method. The registration results were compared. RESULTS: The systematic errors in all methods were <1 mm/1 degrees . When registering the bony anatomy, the mean vector difference was 0.21 +/- 0.11 cm between 2D and CBCT, 0.11 +/- 0.08 cm between CBCT and coronal DTS, and 0.14 +/- 0.07 cm between CBCT and sagittal DTS. The correlation between CBCT to DTS was stronger (coefficient = 0.92-0.95) than the correlation between 2D and CBCT or DTS (coefficient = 0.81-0.83). When registering the soft tissue, the mean vector difference was 0.18 +/- 0.11 cm between CBCT and coronal DTS and 0.29 +/- 0.17 cm between CBCT and sagittal DTS. The correlation coefficient of CBCT to sagittal DTS and to coronal DTS was 0.84 and 0.92, respectively. CONCLUSION: DTS could provide equivalent results to CBCT when the bony anatomy is used as landmarks for prostate image-guided radiotherapy. For soft tissue-based positioning verification, coronal DTS produced equivalent results to CBCT, but sagittal DTS alone was insufficient. DTS could allow for comparable soft tissue-based target localization with faster scanning time and a lower imaging dose compared with CBCT.

On-board four-dimensional digital tomosynthesis: first experimental results.

The purpose of this study is to propose four-dimensional digital tomosynthesis (4D-DTS) for on-board analysis of motion information in three dimensions. Images of a dynamic motion phantom were reconstructed using acquisition scan angles ranging from 20 degrees (DTS) to full 360 degrees cone-beam computed tomography (CBCT). Projection images were acquired using an on-board imager mounted on a clinical linear accelerator. Three-dimensional (3D) images of the moving target were reconstructed for various scan angles. 3D respiratory correlated phase images were also reconstructed. For phase-based image reconstructions, the trajectory of a radiopaque marker was tracked in projection space and used to retrospectively assign respiratory phases to projections. The projections were then sorted according phase and used to reconstruct motion correlated images. By using two sets of projections centered about anterior-posterior and lateral axes, this study demonstrates how phase resolved coronal and sagittal DTS images can be used to obtain 3D motion information. Motion artifacts in 4D-DTS phase images are compared with those present in four-dimensional CT (4DCT) images. Due to the nature of data acquisition for the two modalities, superior-inferior motion artifacts are suppressed to a greater extent in 4D-DTS images compared with 4DCT. Theoretical derivations and experimental results are presented to demonstrate how optimal selection of image acquisition parameters including the frequency of projection acquisition and the phase window depend on the respiratory period. Two methods for acquiring projections are discussed. Preliminary results indicate that 4D-DTS can be used to acquire valuable kinetic information of internal anatomy just prior to radiation treatment.

A novel digital tomosynthesis (DTS) reconstruction method using a deformation field map.

We developed a novel digital tomosynthesis (DTS) reconstruction method using a deformation field map to optimally estimate volumetric information in DTS images. The deformation field map is solved by using prior information, a deformation model, and new projection data. Patients' previous cone-beam CT (CBCT) or planning CT data are used as the prior information, and the new patient volume to be reconstructed is considered as a deformation of the prior patient volume. The deformation field is solved by minimizing bending energy and maintaining new projection data fidelity using a nonlinear conjugate gradient method. The new patient DTS volume is then obtained by deforming the prior patient CBCT or CT volume according to the solution to the deformation field. This method is novel because it is the first method to combine deformable registration with limited angle image reconstruction. The method was tested in 2D cases using simulated projections of a Shepp-Logan phantom, liver, and head-and-neck patient data. The accuracy of the reconstruction was evaluated by comparing both organ volume and pixel value differences between DTS and CBCT images. In the Shepp-Logan phantom study, the reconstructed pixel signal-to-noise ratio (PSNR) for the 60 degrees DTS image reached 34.3 dB. In the liver patient study, the relative error of the liver volume reconstructed using 60 degrees projections was 3.4%. The reconstructed PSNR for the 60 degrees DTS image reached 23.5 dB. In the head-and-neck patient study, the new method using 60 degrees projections was able to reconstruct the 8.1 degrees rotation of the bony structure with 0.0 degrees error. The reconstructed PSNR for the 60 degrees DTS image reached 24.2 dB. In summary, the new reconstruction method can optimally estimate the volumetric information in DTS images using 60 degrees projections. Preliminary validation of the algorithm showed that it is both technically and clinically feasible for image guidance in radiation therapy.

Digital tomosynthesis of the chest.

Digital tomosynthesis is a technique that generates an arbitrary number of section images of a patient from a single pass of the x-ray tube. It is under investigation for application to a number of clinical detection tasks, and has recently been implemented in commercial devices for chest radiography. Tomosynthesis provides improved visibility of structures in the chest, such as pulmonary nodules, airways, and spine. This review article outlines the components of a typical tomosynthesis system, and presents examples of improved pulmonary nodule detection from a clinical trial in human subjects. Possible implementation strategies for use in chest imaging are discussed.

Fast reconstruction of digital tomosynthesis using on-board images.

Digital tomosynthesis (DTS) is a method to reconstruct pseudo three-dimensional (3D) volume images from two-dimensional x-ray projections acquired over limited scan angles. Compared with cone-beam computed tomography, which is frequently used for 3D image guided radiation therapy, DTS requires less imaging time and dose. Successful implementation of DTS for fast target localization requires the reconstruction process to be accomplished within tight clinical time constraints (usually within 2 min). To achieve this goal, substantial improvement of reconstruction efficiency is necessary. In this study, a reconstruction process based upon the algorithm proposed by Feldkamp, Davis, and Kress was implemented on graphics hardware for the purpose of acceleration. The performance of the novel reconstruction implementation was tested for phantom and real patient cases. The efficiency of DTS reconstruction was improved by a factor of 13 on average, without compromising image quality. With acceleration of the reconstruction algorithm, the whole DTS generation process including data preprocessing, reconstruction, and DICOM conversion is accomplished within 1.5 min, which ultimately meets clinical requirement for on-line target localization.

Automatic registration between reference and on-board digital tomosynthesis images for positioning verification.

The authors developed a hybrid multiresolution rigid-body registration technique to automatically register reference digital tomosynthesis (DTS) images with on-board DTS images to guide patient positioning in radiation therapy. This hybrid registration technique uses a faster but less accurate static method to achieve an initial registration, followed by a slower but more accurate adaptive method to fine tune the registration. A multiresolution scheme is employed in the registration to further improve the registration accuracy, robustness, and efficiency. Normalized mutual information is selected as the criterion for the similarity measure and the downhill simplex method is used as the search engine. This technique was tested using image data both from an anthropomorphic chest phantom and from eight head-and-neck cancer patients. The effects of the scan angle and the region-of-interest (ROI) size on the registration accuracy and robustness were investigated. The necessity of using the adaptive registration method in the hybrid technique was validated by comparing the results of the static method and the hybrid method. With a 44 degrees scan angle and a large ROI covering the entire DTS volume, the average of the registration capture ranges in single-axis simulations was between -31 and +34 deg for rotations and between -89 and +78 mm for translations in the phantom study, and between -38 and +38 deg for rotations and between -58 and +65 mm for translations in the patient study. Decreasing the DTS scan angle from 44 degrees to 22 degrees mainly degraded the registration accuracy and robustness for the out-of-plane rotations. Decreasing the ROI size from the entire DTS volume to the volume surrounding the spinal cord reduced the capture ranges to between -23 and +18 deg for rotations and between -33 and +43 mm for translations in the phantom study, and between -18 and +25 deg for rotations and between -35 and +39 mm for translations in the patient study. Results also showed that the hybrid registration technique had much larger capture ranges than the static method alone in registering the out-of-plane rotations.