Deep learning MRI-only synthetic-CT generation for pelvis, brain and head and neck cancers.

BACKGROUND AND PURPOSE: MRI-only planning relies on dosimetrically accurate synthetic-CT (sCT) generation to allow dose calculation. Here we validated the dosimetric accuracy of sCTs generated using a deep learning algorithm for pelvic, brain and head and neck (H&N) cancer sites using variable MRI data from multiple scanners. METHODS: sCT generation models were trained using a cycle-GAN algorithm, using paired MRI-CT patient data. Input MRI sequences were: T2 for pelvis, T1 with gadolinium (T1Gd) and T2 FLAIR for brain and T1 for H&N. Patient validation sCTs were generated for each site (49 - pelvis, 25 - brain and 30 - H&N). VMAT plans, following local clinical protocols, were calculated on planning CTs and recalculated on sCTs. HU and dosimetric differences were assessed, including DVH differences and gamma index (2 %/2mm). RESULTS: Mean absolute error (MAE) HU differences were; 48.8 HU (pelvis), 118 HU (T2 FLAIR brain), 126 HU (T1Gd brain) and 124 HU (H&N). Mean primary PTV D95% dose differences for all sites were < 0.2 % (range: -0.9 to 1.0 %). Mean 2 %/2mm and 1 %/1mm gamma pass rates for all sites were > 99.6 % (min: 95.3 %) and > 97.3 % (min: 80.1 %) respectively. For all OARs for all sites, mean dose differences were < 0.4 %. CONCLUSION: Generated sCTs had excellent dosimetric accuracy for all sites and sequences. The cycle-GAN model, available on the research version of a commercial treatment planning system, is a feasible method for sCT generation with high clinical utility due to its ability to use variable input data from multiple scanners and sequences.

The role and potential of using quantitative MRI biomarkers for imaging guidance in brain cancer radiotherapy treatment planning: A systematic review.

Background and purpose: Improving the accuracy of brain tumour radiotherapy (RT) treatment planning is important to optimise patient outcomes. This systematic review investigates primary studies providing clinical evidence for the integration of quantitative magnetic resonance imaging (qMRI) biomarkers and MRI radiomics to optimise brain tumour RT planning. Materials and methods: PubMed, Scopus, Embase and Web of Science databases were searched for all years until June 21, 2022. The search identified original articles demonstrating clinical evidence for the use of qMRI biomarkers and MRI radiomics for the optimization of brain cancer RT planning. Relevant information was extracted and tabulated, including qMRI metrics and techniques, impact on RT plan optimization and changes in target and normal tissue contouring and dose distribution. Results: Nineteen articles met the inclusion criteria. Studies were grouped according to the qMRI biomarkers into: 1) diffusion-weighted imaging (DWI) and perfusion-weighted imaging (PWI; five studies); 2) diffusion tensor imaging (DTI; seven studies); and 3) MR spectroscopic imaging (MRSI; seven studies). No relevant MRI-based radiomics studies were identified. Integration of DTI maps offers the potential for improved organs at risk (OAR) sparing. MRSI metabolic maps are a promising technique for improving delineation accuracy in terms of heterogeneity and infiltration, with OAR sparing. No firm conclusions could be drawn regarding the integration of DWI metrics and PWI maps. Conclusions: Integration of qMRI metrics into RT planning offers the potential to improve delineation and OAR sparing. Clinical trials and consensus guidelines are required to demonstrate the clinical benefits of such approaches.

Assessment of CBCT-based synthetic CT generation accuracy for adaptive radiotherapy planning.

PURPOSE: Cone-beam CT (CBCT)-based synthetic CT (sCT) dose calculation has the potential to make the adaptive radiotherapy (ART) pathway more efficient while removing subjectivity. This study assessed four sCT generation methods using 15 head-and-neck rescanned ART patients. Each patient's planning CT (pCT), rescan CT (rCT), and CBCT post-rCT was acquired with the CBCT deformably registered to the rCT (dCBCT). METHODS: The four methods investigated were as follows: method 1-deformably registering the pCT to the dCBCT. Method 2-assigning six mass density values to the dCBCT. Method 3-iteratively removing artifacts and correcting the dCBCT Hounsfield units (HU). Method 4-using a cycle general adversarial network machine learning model (trained with 45 paired pCT and CBCT). Treatment plans were created on the rCT and recalculated on each sCT. Planning target volume (PTV) and organ-at-risk (OAR) structures were contoured by clinicians on the rCT (high-dose PTV, low-dose PTV, spinal canal, larynx, brainstem, and parotids) to allow the assessment of dose-volume histogram statistics at clinically relevant points. RESULTS: The HU mean absolute error (MAE) and minimum dose gamma index pass rate (2%/2 mm) were calculated, and the generation time was measured for 15 patients using the rCT as the comparator. For methods 1-4 the MAE, gamma index analysis, and generation time were as follows: 59.7 HU, 100.0%, and 143 s; 164.2 HU, 95.2%, and 232 s; 75.7 HU, 99.9%, and 153 s; and 79.4 HU, 99.8%, and 112 s, respectively. Dose differences for PTVs and OARs were all <0.3 Gy except for method 2 (<0.5 Gy). CONCLUSION: All methods were considered clinically viable. The machine learning method was found to be most suitable for clinical implementation due to its high dosimetric accuracy and short generation time. Further investigation is required for larger anatomical changes between the CBCT and pCT and for other anatomical sites.

The benefit of MR-only radiotherapy treatment planning for anal and rectal cancers: A planning study.

INTRODUCTION: Limited evidence exists showing the benefit of magnetic resonance (MR)-only radiotherapy treatment planning for anal and rectal cancers. This study aims to assess the impact of MR-only planning on target volumes (TVs) and treatment plan doses to organs at risks (OARs) for anal and rectal cancers versus a computed tomography (CT)-only pathway. MATERIALS AND METHODS: Forty-six patients (29 rectum and 17 anus) undergoing preoperative or radical external beam radiotherapy received CT and T2 MR simulation. TV and OARs were delineated on CT and MR, and volumetric arc therapy treatment plans were optimized independently (53.2 Gy/28 fractions for anus, 45 Gy/25 fractions for rectum). Further treatment plans assessed gross tumor volume (GTV) dose escalation. Differences in TV volumes and OAR doses, in terms of Vx Gy (organ volume (%) receiving x dose (Gy)), were assessed. RESULTS: MR GTV and primary planning TV (PTV) volumes systematically reduced by 13 cc and 98 cc (anus) and 44 cc and 109 cc (rectum) respectively compared to CT volumes. Statistically significant OAR dose reductions versus CT were found for bladder and uterus (rectum) and bladder, penile bulb, and genitalia (anus). With GTV boosting, statistically significant dose reductions were found for sigmoid, small bowel, vagina, and penile bulb (rectum) and vagina (anus). CONCLUSION: Our findings provide evidence that the introduction of MR (whether through MR-only or CT-MR pathways) to radiotherapy treatment planning for anal and rectal cancers has the potential to improve treatments. MR-related OAR dose reductions may translate into less treatment-related toxicity for patients or greater ability to dose escalate.

Patient position verification in magnetic-resonance imaging only radiotherapy of anal and rectal cancers.

BACKGROUND AND PURPOSE: Magnetic resonance (MR)-only treatment pathways require either the MR-simulation or synthetic-computed tomography (sCT) as an alternative reference image for cone beam computed tomography (CBCT) patient position verification. This study assessed whether using T2 MR or sCT as CBCT reference images introduces systematic registration errors as compared to CT for anal and rectal cancers. MATERIALS AND METHODS: A total of 32 patients (18 rectum,14 anus) received pre-treatment CT- and T2 MR- simulation. Routine treatment CBCTs were acquired. sCTs were generated using a validated research model. The local clinical registration protocol, using a grey-scale registration algorithm, was performed for 216 CBCTs using CT, MR and sCT as the reference image. Linear mixed effects modelling identified systematic differences between modalities. RESULTS: Systematic translation and rotation differences to CT for MR were -0.3 to + 0.3 mm and -0.1 to 0.4° for anal cancers and -0.4 to 0.0 mm and 0.0 to 0.1° for rectal cancers, and for sCT were -0.4 to + 0.8 mm, -0.1 to 0.2° for anal cancers and -0.6 to + 0.2 mm, -0.1 to + 0.1° for rectal cancers. CONCLUSIONS: T2 MR or sCT can successfully be used as reference images for anal and rectal cancer CBCT position verification with systematic differences to CT <±1 mm and <±0.5°. Clinical enabling of alternative modalities as reference images by vendors is required to reduce challenges associated with their use.

Factors That Predict the Success of Laparoscopic Common Bile Duct Exploration for Choledocholithiasis: A 10-Year Study.

BACKGROUND: Laparoscopic common bile duct exploration (LCBDE) can be performed to treat choledocholithiasis at the time of laparoscopic cholecystectomy. The aim of this study was to identify factors that predict the success of LCBDE. MATERIALS AND METHODS: A retrospective audit was performed on patients who underwent LCBDE for the management of choledocholithiasis at Northern Health between 2008 and 2018. RESULTS: A total of 513 patients were identified with an overall success rate of 90.8%. Most LCBDE were done through a transcystic approach with the remainder through a choledochotomy. When comparing patients with a successful operation to those that were unsuccessful, univariate analysis demonstrated significant differences in preoperative white cell count and number of duct stones found. Age and elevated nonbilirubin liver function tests were found to be significant factors associated with the failure of LCBDE on multivariate analysis. The likelihood of a failed operation in those with multiple stones was observed to be almost halved compared with patients with single stone although this did not reach significance [odds ratio (OR): 0.53, 95% confidence interval (CI): 0.28-1.01, P=0.055]. Multivariate analysis indicated that unsuccessful procedures (OR: 10.13, 95% CI: 4.34-23.65, P<0.001) and multiple duct stones (OR: 3.79, 95% CI: 1.66-8.67, P=0.002) were associated with an increased risk of severe complications. CONCLUSIONS: A single impacted stone may be more difficult to remove, however complications were more likely to be associated with multiple duct stones. With no other clinically relevant predictive factors, and because of the high success of the procedure and the low morbidity, LCBDE remains an option for all patients with choledocholithiasis.

Should Common Bile Duct Exploration for Choledocholithiasis Be a Specialist-Only Procedure?

Background: Common bile duct exploration (CBDE) is performed uncommonly. Issues surrounding its uptake in the laparoscopic era include perceived difficulty and lack of training. We aim to determine the success of CBDE performed by "specialist" and "nonspecialist" common bile duct (CBD) surgeons to determine whether there is a substantial difference in success and safety. Methods: A 10-year retrospective audit was performed of patients undergoing CBD exploration for choledocholithiasis. Northern Health maintains an on-call available "specialist" CBD surgeon roster to aid with CBDE. Results: Five hundred fifty-one patients were identified, of which 489/551 (88.7%) patients had stones successfully cleared. Specialists had a higher success rate (90.8% versus 82.6%, P = .008), associated with a longer surgical time. Method (transcystic or transductal), approach (laparoscopic or open), and indication for operation were similar between groups. There was no significant difference in complications. To be confident of a surgeon having an 80% success rate, 70 procedures over 10 years were required, however, an "in-control" 50% success rate may only require 1 procedure per year. Conclusion: While specialist CBDE surgeons have improved success rates, nonspecialist general surgeons also have a good and comparable success rate with an equivalent complication rate. With realistic annual targets, nonspecialist CBD surgeons should be encouraged to perform CBDE in centers without specialist support.

Toward genetic modification of plant-parasitic nematodes: delivery of macromolecules to adults and expression of exogenous mRNA in second stage juveniles.

Plant-parasitic nematodes are a continuing threat to food security, causing an estimated 100 billion USD in crop losses each year. The most problematic are the obligate sedentary endoparasites (primarily root knot nematodes and cyst nematodes). Progress in understanding their biology is held back by a lack of tools for functional genetics: forward genetics is largely restricted to studies of natural variation in populations and reverse genetics is entirely reliant on RNA interference. There is an expectation that the development of functional genetic tools would accelerate the progress of research on plant-parasitic nematodes, and hence the development of novel control solutions. Here, we develop some of the foundational biology required to deliver a functional genetic tool kit in plant-parasitic nematodes. We characterize the gonads of male Heterodera schachtii and Meloidogyne hapla in the context of spermatogenesis. We test and optimize various methods for the delivery, expression, and/or detection of exogenous nucleic acids in plant-parasitic nematodes. We demonstrate that delivery of macromolecules to cyst and root knot nematode male germlines is difficult, but possible. Similarly, we demonstrate the delivery of oligonucleotides to root knot nematode gametes. Finally, we develop a transient expression system in plant-parasitic nematodes by demonstrating the delivery and expression of exogenous mRNA encoding various reporter genes throughout the body of H. schachtii juveniles using lipofectamine-based transfection. We anticipate these developments to be independently useful, will expedite the development of genetic modification tools for plant-parasitic nematodes, and ultimately catalyze research on a group of nematodes that threaten global food security.

Quality of recovery assessment of day case and multiday stay patients undergoing elective laparoscopic cholecystectomy.

Objectives: Many laparoscopic cholecystectomy operations are performed with at least overnight admission. Current research shows that laparoscopic cholecystectomy is safe and feasible to do as a day case. Patient centred outcomes are less well understood. Material and Methods: Elective laparoscopic cholecystectomy patients at a single metropolitan hospital in Melbourne, Australia were surveyed 24 hours after surgery using the 15-question Quality of Recovery (QoR-15) survey. A comparison was made between day case surgeries and multi-day surgeries. Results: One hundred and eight patients were recruited consisting of 34 day case and 74 multi-day patients. Patient groups did not differ in terms of age, sex or postoperative morbidity. The multi-day group had a higher proportion of comorbid patients (p-value = 0.03). There was no significant dif- ference in overall QoR-15 score between the two groups, although there was an observed trend towards a higher score in the day case group (132.0 vs 127.9, p= 0.147). QoR-15 individual question results showed that day cases rated significantly better for sleep quality and for less feelings of anxiety or worry. The differences narrowed when comparing patient groups as they were booked (intention-to-treat). There were no identified sub-groups that had a significantly higher score if admitted multi-day. Conclusion: Quality of recovery following day case laparoscopic cholecystectomy is just as good, if not better, than multi-day cases. Laparoscopic cholecystectomy as a day case is both safe and economically superior to multi-day management. This gives further weight to current recommendations suggesting that the majority of laparoscopic cholecystectomy operations could be performed as day cases.

Multicentre, deep learning, synthetic-CT generation for ano-rectal MR-only radiotherapy treatment planning.

BACKGROUND AND PURPOSE: Comprehensive dosimetric analysis is required prior to the clinical implementation of pelvic MR-only sites, other than prostate, due to the limited number of site specific synthetic-CT (sCT) dosimetric assessments in the literature. This study aims to provide a comprehensive assessment of a deep learning-based, conditional generative adversarial network (cGAN) model for a large ano-rectal cancer cohort. The following challenges were investigated; T2-SPACE MR sequences, patient data from multiple centres and the impact of sex and cancer site on sCT quality. METHOD: RT treatment position CT and T2-SPACE MR scans, from two centres, were collected for 90 ano-rectal patients. A cGAN model trained using a focal loss function, was trained and tested on 46 and 44 CT-MR ano-rectal datasets, paired using deformable registration, respectively. VMAT plans were created on CT and recalculated on sCT. Dose differences and gamma indices assessed sCT dosimetric accuracy. A linear mixed effect (LME) model assessed the impact of centre, sex and cancer site. RESULTS: A mean PTV D95% dose difference of 0.1% (range: -0.5% to 0.7%) was found between CT and sCT. All gamma index (1%/1 mm threshold) measurements were >99.0%. The LME model found the impact of modality, cancer site, sex and centre was clinically insignificant (effect ranges: -0.4% and 0.3%). The mean dose difference for all OAR constraints was 0.1%. CONCLUSION: Focal loss cGAN models using T2-SPACE MR sequences from multiple centres can produce generalisable, dosimetrically accurate sCTs for ano-rectal cancers.

Infection by cyst nematodes induces rapid remodelling of developing xylem vessels in wheat roots.

Cyst nematodes induce host-plant root cells to form syncytia from which the nematodes feed. Comprehensive histological investigation of these feeding sites is complicated by their variable shape and their positions deep within root tissue. Using tissue clearing and confocal microscopy, we examined thick (up to 150 µm) sections of wheat roots infected by cereal cyst nematodes (Heterodera avenae). This approach provided clear views of feeding sites and surrounding tissues, with resolution sufficient to reveal spatial relationships among nematodes, syncytia and host vascular tissues at the cellular level. Regions of metaxylem vessels near syncytia were found to have deviated from classical developmental patterns. Xylem vessel elements in these regions had failed to elongate but had undergone radial expansion, becoming short and plump rather than long and cylindrical. Further investigation revealed that vessel elements cease to elongate shortly after infection and that they later experience delays in secondary thickening (lignification) of their outer cell walls. Some of these elements were eventually incorporated into syncytial feeding sites. By interfering with a developmental program that normally leads to programmed cell death, H. avenae may permit xylem vessel elements to remain alive for later exploitation by the parasite.

Intravascular ultrasound-guided laparoscopic division of the median arcuate ligament.

Median arcuate ligament syndrome is a rare and poorly understood condition that can have a significant impact on the quality of life of patients. Diagnosis is often difficult and delayed because of the need to exclude other pathologic processes. Treatment strategies traditionally involve open or laparoscopic division of the median arcuate ligament, with or without vascular reconstruction. This report portrays a case of median arcuate ligament syndrome with compression of two visceral arteries and distal embolic complications. A novel hybrid technique is described using intravascular ultrasound technology to aid in laparoscopic median arcuate ligament division. This allowed real-time intravascular visualization of the compressive segment, guided release of the ligament fibers, and demonstrated confirmation of decompression.

A Single, Shared Triploidy in Three Species of Parasitic Nematodes.

The root-knot nematodes of the genus Meloidogyne are important and damaging parasites capable of infecting most flowering plants. Within this genus, several species of the Meloidogyne incognita group show evidence of paleopolyploidy in their genomes. We used our software tool POInT, the Polyploidy Orthology Inference Tool, to phylogenetically model the gene losses that followed that polyploidy. These models, and simulations based on them, show that three of these species (M. incognita, M. arenaria and M. javanica) descend from a single common hybridization event that yielded triplicated genomes with three distinguishable subgenomes. While one of the three subgenomes shows elevated gene loss rates relative to the other two, this subgenome does not show elevated sequence divergence. In all three species, ancestral loci where two of the three gene copies have been lost are less likely to have orthologs in Caenorhabditis elegans that are lethal when knocked down than are ancestral loci with surviving duplicate copies.

An Acute General Surgical Unit (AGSU) Negates the Impact of the Tokyo Guidelines 2018 (TG18) Diagnostic Criteria for the Treatment of Acute Cholecystitis.

PURPOSE: The Tokyo Guidelines 2018 (TG18) were developed to aid diagnosis and treatment for acute cholecystitis. The benefits of being treated in an acute general surgical unit (AGSU) include earlier diagnosis and treatment. This study aims to define the usefulness of TG18 before and after the introduction of AGSU. METHODOLOGY: Patients who underwent cholecystectomy at Northern Health were audited retrospectively and assessed for TG18 diagnostic criteria and outcomes between 1 February 2012 and 1 February 2014 (one-year pre- and post-AGSU). RESULTS: Five hundred and eighty-seven patients underwent emergency cholecystectomy with 203 (34.6%) patients having a suspected diagnosis, and 234 (39.9%) patients with a definitive diagnosis of acute cholecystitis using TG18 diagnostic criteria. After the introduction of AGSU, time from imaging to operation improved from 2.5 to 1.7 days (p = 0.012). There were more operations occurring during in-hours following AGSU implementation (75.8% vs. 62.7%, p < 0.001). Maximum pre-operative CRP of >26.6 mg/L had a higher likelihood of Clavien-Dindo complication grade 3 or 4 (OR 3.86, 95%CI 1.18-12.63, p = 0.027) compared with TG18 definitive diagnosis criteria (OR 1.50, 95%CI 0.46-4.91, p = 0.501). Surprisingly, there was a trend towards higher complications and readmissions for patients operated within 24 h, although this trend was not significant. CONCLUSION: Patients with suspected acute cholecystitis should be stratified clinically and with CRP in an AGSU with TG18 adding little value in a busy metropolitan unit.

Correction to: An Acute General Surgical Unit (AGSU) Negates the Impact of the Tokyo Guidelines 2018 (TG18) Diagnostic Criteria for the Treatment of Acute Cholecystitis.

The original article can be found online.

A Systematic Review of the Clinical Implementation of Pelvic Magnetic Resonance Imaging-Only Planning for External Beam Radiation Therapy.

The use of magnetic resonance (MR) imaging scans alone for radiation therapy treatment planning (MR-only planning) has been highlighted as one method of improving patient outcomes. Recent technologic advances have meant that introducing MR-only planning to the clinic is becoming a reality, with several specialist radiation therapy clinics using this technique for treatment. As such, substantial efforts are being made to introduce this technique into wide-spread clinical implementation. A systematic review of publications investigating the clinical implementation of pelvic MR-only radiation therapy treatment planning was undertaken following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. The Medline, Embase, Scopus, Science Direct, Cumulative Index to Nursing and Allied Health Literature, and Web of Science databases were searched (timespan: all years to January 2, 2019). Twenty-six articles met the inclusion criteria. The studies were grouped into the following categories: (1) MR acquisition and synthetic computed tomography generation verification, (2) MR distortion quantification and phantom development, (3) clinical validation of patient treatment positioning in an MR-only workflow, and (4) MR-only commissioning processes. Key conclusions from this review are (1) MR-only planning has been implemented clinically for prostate cancer treatments; (2) a substantial amount of work remains to translate MR-only planning into widespread clinical implementation for all pelvic sites; (3) MR scanner distortions are no longer a barrier to MR-only planning, but they must be managed appropriately; (4) MR-only-based patient positioning verification shows promise, but limited evidence is reported in the literature and further investigation is required; and (5) a number of MR-only commissioning processes have been reported, which can aid centers as they undertake local commissioning; however, this needs to be formalized in guidance from national bodies.

Axillary radiotherapy for nodal lymphoma: What CTV expansion is required to account for absence of pre-chemotherapy treatment position FDG PET-CT?

Involved site lymphoma radiotherapy clinical target volumes (CTV) require expansion in the absence of treatment-position pre-chemotherapy PET-CT. This prospective imaging study evaluates CTV contouring for axillary lymphoma using diagnostic imaging compared with co-registered treatment-position PET-CT. Generous expansion axially and cranio-caudally is required to encompass pre-chemotherapy disease without treatment-position pre-chemotherapy PET-CT.

Evaluation of clinical target volume expansion required for involved site neck radiotherapy for lymphoma to account for the absence of a pre-chemotherapy PET-CT in the radiotherapy treatment position.

BACKGROUND AND PURPOSE: Involved site radiotherapy clinical target volume (CTV) for lymphoma requires an expansion to account for the absence of radiotherapy treatment-position pre-chemotherapy imaging, which is not widely implemented. This prospective imaging study aims to quantify CTV expansion required for neck radiotherapy. MATERIALS AND METHODS: 10 patients from a prospective single centre imaging study underwent a pre-chemotherapy FDG-PET-CT in both the diagnostic and radiotherapy treatment position, and subsequently received neck radiotherapy post-chemotherapy. CTVINRT and CTVdiagPET were delineated on the planning CT, following co-registration of the radiotherapy position PET-CT and side-by-side assessment of diagnostic PET-CT respectively. RESULTS: Intra-observer variability was limited, with delineation of CTVINRT highly reproducible and slightly lower for CTVdiagPET (mean DICE 0.88 and 0.8 respectively). Superiorly, CTVdiagPET varied by -10 to +15mm from CTVINRT. Inferiorly, CTVdiagPET varied by -18 to +6mm from CTVINRT. Comparing CTVINRT and CTVdiagPET in the axial plane, the mean DICE was 0.74. Mean sensitivity index was 0.75 (range 0.59-0.91), showing that on average 75% of the CTVINRT was encompassed by the CTVdiagPET. CONCLUSIONS: In the absence of treatment-position PET-CT, CTV expansion cranially and caudally by 10mm and 18mm respectively, along with generous contouring in the axial plane, was required to encompass pre-chemotherapy disease.

Evaluation of High Dosages of Oral Meloxicam in American Kestrels ( Falco sparverius ).

To evaluate the toxicity of short-term high doses of meloxicam in American kestrels ( Falco sparverius ), 32 male captive-born, 1- to 4-year-old American kestrels were randomly assigned to 4 groups: 3 groups treated with meloxicam (n = 9 per group) and a control group (n = 5). Meloxicam was administered orally via feeding tube in the proventriculus at 2, 10, and 20 mg/kg every 12 hours for 7 days for the treatment groups, while the control group received saline solution. The birds were evaluated for the presence of clinical signs, abnormalities in the complete blood cell count and in the plasma biochemical panel for the 20-mg/kg group, and gross and histopathologic lesions. No clinical signs or mortality were observed in any group. No significant differences of clinical relevance were found in results of the packed cell volume, total solids, and biochemical panel, and no evidence of renal toxicity was found in the treatment or control groups. A significant correlation was found between hepatic lipidosis and meloxicam dose (P = .02). Two of 9 birds in the 20-mg/kg group developed gastric ulcers, although this result was not significant. None of the birds in the 2- and 10-mg/kg groups had similar lesions. Finally, meloxicam dosages up to 20 mg/kg did not result in nephrotoxicity in American kestrels. Further toxicologic studies to evaluate hepatotoxicity and gastrotoxicity of meloxicam in avian species are needed.