The Pharmacokinetics and Safety of Tucatinib in Volunteers with Hepatic Impairment.

BACKGROUND AND OBJECTIVE: Tucatinib, a highly selective tyrosine kinase inhibitor of the human epidermal growth factor receptor 2 (HER2) approved for HER2-positive metastatic breast cancer, is cleared by hepatic metabolism and subsequent biliary excretion. Liver disease can alter drug disposition and pharmacokinetics (PK). The objective of this study is to characterize PK and safety of tucatinib in volunteers with hepatic impairment. METHODS: This Phase 1 study compared the PK and safety of a single 300-mg oral dose of tucatinib in volunteers with mild, moderate, and severe hepatic impairment (Child-Pugh A/B/C) to healthy volunteers matched for sex, age, and body mass index. Pharmacokinetic parameters were determined for tucatinib and its predominant metabolite ONT-993. RESULTS: Compared with healthy volunteers, tucatinib exposure was similar in volunteers with mild impairment and increased in those with moderate or severe impairment without reaching statistical significance. Respective fold increases in geometric mean ratios for AUC0-t and AUC0-∞ were 1.13 and 1.15 in moderate impairment, and 1.43 and 1.61 in severe impairment compared with healthy volunteers. Three treatment-emergent adverse events (nausea, dermatitis, and increased transaminases) were reported in three volunteers and showed no obvious association with hepatic impairment status. CONCLUSION: The 1.61-fold geometric mean ratio AUC0-∞ increase in volunteers with severe hepatic impairment supports the recommendation in the tucatinib prescribing information to reduce the dose from 300 mg twice daily to 200 mg twice daily in patients with severe impairment; no dose adjustment is recommended for patients with mild or moderate hepatic impairment. This trial (NCT03722823) was registered on October 29, 2018.

Evaluation of Safety and Clinically Relevant Drug-Drug Interactions with Tucatinib in Healthy Volunteers.

BACKGROUND AND OBJECTIVE: Tucatinib is approved for treatment of human epidermal growth factor receptor 2-positive metastatic breast cancer. Understanding potential drug-drug interactions (DDIs) informs proper dosing when co-administering tucatinib with other therapies. The aim of this study was to evaluate DDIs between tucatinib and metabolizing enzymes and transporters in healthy volunteers. METHODS: Parts A-C assessed the impact of itraconazole (cytochrome P450 [CYP] 3A4 inhibitor), rifampin (CYP3A4/CYP2C8 inducer), or gemfibrozil (CYP2C8 inhibitor) on the pharmacokinetics of a single 300 mg dose of tucatinib administered orally and its primary metabolite, ONT-993. Parts D and E assessed the effect of steady-state tucatinib on the pharmacokinetics of repaglinide (CYP2C8 substrate), tolbutamide (CYP2C9 substrate), midazolam (CYP3A4 substrate), and digoxin (P-glycoprotein substrate). RESULTS: Tucatinib area under the concentration-time curve from time 0 extrapolated to infinity (AUC0-inf) increased by ~ 1.3- and 3.0-fold with itraconazole and gemfibrozil, respectively, and decreased by 48% with rifampin, indicating that tucatinib is metabolized primarily by CYP2C8, and to a lesser extent via CYP3A. Tucatinib was a strong inhibitor of CYP3A (midazolam AUC0-inf increased 5.7-fold), a weak inhibitor of CYP2C8 and P-glycoprotein, and had no impact on CYP2C9-mediated metabolism in humans. Tucatinib was well tolerated, alone and with co-administered drugs. CONCLUSION: The potential DDIs identified here may be mitigated by avoiding concomitant use of tucatinib with strong CYP3A inducers, moderate CYP2C8 inducers, CYP3A substrates with a narrow therapeutic window (modifying substrate dose where concomitant use is unavoidable), and strong CYP2C8 inhibitors (decreasing tucatinib dose where concomitant use is unavoidable), or by reducing the dose of P-glycoprotein substrates with a narrow therapeutic window. TRIAL REGISTRATION: This trial (NCT03723395) was registered on October 29, 2018.

Tucatinib Inhibits Renal Transporters OCT2 and MATE Without Impacting Renal Function in Healthy Subjects.

Tucatinib is a potent tyrosine kinase inhibitor selective for human epidermal growth factor receptor 2 (HER2) approved by the US Food and Drug Administration for the treatment of HER2-positive metastatic breast cancer and in development for other HER2-positive solid tumors. Modest, reversible serum creatinine (SCr) elevations have been observed in tucatinib clinical trials. SCr is conveyed by the renal drug transporters organic cation transporter 2 (OCT2) and multidrug and toxin extrusion protein 1 (MATE1) and 2-K (MATE2-K) and can increase in the presence of inhibitors of these transporters. In vitro, tucatinib inhibited OCT2-, MATE1-, and MATE2-K-mediated transport of metformin, with IC50 values of 14.7, 0.340, and 0.135 µM, respectively. Tucatinib also inhibited OCT2- and MATE1-mediated transport of creatinine, with IC50 values of 0.107 and 0.0855 µM, respectively. A phase 1 study with metformin administered orally in the absence and presence of tucatinib was conducted in 18 healthy subjects. Renal function was assessed by measuring glomerular filtration rate (GFR; based on iohexol plasma clearance) and endogenous markers (SCr, cystatin C-based estimated glomerular filtration rate [eGFR]) with and without tucatinib. Metformin exposure increased (1.4-fold) and renal clearance decreased (29.99-17.64 L/h) with tucatinib, with no effect on metformin maximum concentration. Creatinine clearance transiently decreased 23% with tucatinib. GFR and eGFR, which are unaffected by OCT2 and/or MATE1/2-K transport, were unchanged with tucatinib. These data demonstrate that tucatinib inhibits OCT2- and MATE1/2-K-mediated tubular secretion of creatinine, which may manifest as mild SCr elevations that are not indicative of renal impairment.

Tucatinib, Trastuzumab, and Capecitabine for HER2-Positive Metastatic Breast Cancer.

BACKGROUND: Patients with human epidermal growth factor receptor 2 (HER2)-positive metastatic breast cancer who have disease progression after therapy with multiple HER2-targeted agents have limited treatment options. Tucatinib is an investigational, oral, highly selective inhibitor of the HER2 tyrosine kinase. METHODS: We randomly assigned patients with HER2-positive metastatic breast cancer previously treated with trastuzumab, pertuzumab, and trastuzumab emtansine, who had or did not have brain metastases, to receive either tucatinib or placebo, in combination with trastuzumab and capecitabine. The primary end point was progression-free survival among the first 480 patients who underwent randomization. Secondary end points, assessed in the total population (612 patients), included overall survival, progression-free survival among patients with brain metastases, confirmed objective response rate, and safety. RESULTS: Progression-free survival at 1 year was 33.1% in the tucatinib-combination group and 12.3% in the placebo-combination group (hazard ratio for disease progression or death, 0.54; 95% confidence interval [CI], 0.42 to 0.71; P<0.001), and the median duration of progression-free survival was 7.8 months and 5.6 months, respectively. Overall survival at 2 years was 44.9% in the tucatinib-combination group and 26.6% in the placebo-combination group (hazard ratio for death, 0.66; 95% CI, 0.50 to 0.88; P = 0.005), and the median overall survival was 21.9 months and 17.4 months, respectively. Among the patients with brain metastases, progression-free survival at 1 year was 24.9% in the tucatinib-combination group and 0% in the placebo-combination group (hazard ratio, 0.48; 95% CI, 0.34 to 0.69; P<0.001), and the median progression-free survival was 7.6 months and 5.4 months, respectively. Common adverse events in the tucatinib group included diarrhea, palmar-plantar erythrodysesthesia syndrome, nausea, fatigue, and vomiting. Diarrhea and elevated aminotransferase levels of grade 3 or higher were more common in the tucatinib-combination group than in the placebo-combination group. CONCLUSIONS: In heavily pretreated patients with HER2-positive metastatic breast cancer, including those with brain metastases, adding tucatinib to trastuzumab and capecitabine resulted in better progression-free survival and overall survival outcomes than adding placebo; the risks of diarrhea and elevated aminotransferase levels were higher with tucatinib. (Funded by Seattle Genetics; HER2CLIMB ClinicalTrials.gov number, NCT02614794.).

A Multicenter Phase I Study Evaluating Dual PI3K and BRAF Inhibition with PX-866 and Vemurafenib in Patients with Advanced BRAF V600-Mutant Solid Tumors.

Purpose: The objectives of the study were to evaluate the safety of daily oral PX-866 in combination with twice daily vemurafenib and to identify potential predictive biomarkers for this novel combination.Experimental Design: We conducted a phase I, open-label, dose-escalation study in patients with advanced BRAF V600-mutant solid tumors. PX-866 was administered on a continuous schedule in combination with vemurafenib. Patients underwent a baseline and on-treatment biopsy after 1-week of PX-866 monotherapy for biomarker assessment.Results: Twenty-four patients were enrolled. The most common treatment-related adverse events were gastrointestinal side effects. One dose-limiting toxicity (DLT) of grade 3 rash and one DLT of grade 3 pancreatitis were observed in cohort 2 (PX-866 6 mg daily; vemurafenib 960 mg twice daily) and cohort 3 (PX-866 8 mg daily; vemurafenib 960 mg twice daily), respectively. Of 23 response-evaluable patients, seven had confirmed partial responses (PR), 10 had stable disease, and six had disease progression. Decreases in intratumoral pAKT expression were observed following treatment with PX-866. Patients who achieved PRs had higher rates of PTEN loss by IHC (80% vs. 58%) and pathogenic PTEN mutations and/or deletions (57% vs. 25%). Two patients with durable PRs had an increase in intratumoral CD8+ T-cell infiltration following treatment with PX-866.Conclusions: PX-866 was well tolerated at its maximum tolerated single-agent dose when given in combination with a modified dose of vemurafenib (720 mg twice daily). Response to treatment appeared to be associated with PTEN loss and treatment with PX-866 seemed to increase CD8+ T-cell infiltration in some patients. Clin Cancer Res; 24(1); 22-32. ©2017 AACR.

Knowledge, attitudes and practices of Australian medical students towards influenza vaccination.

BACKGROUND: Annual influenza vaccination is recommended but not compulsory for healthcare workers in Australia, including medical students. A quarter of healthcare workers are estimated to have an influenza infection in any given year, with a subsequent transmission risk to colleagues and patients. During clinical placements, medical students are also at risk of influenza. While compliance with other vaccination requirements are high, influenza vaccine uptake of healthcare workers and medical students remain low globally. We aimed to explore medical students' influenza vaccination rates, attitudes, knowledge and intended practices at a large Australian university. METHOD: A 35 item self-administered online survey was distributed to medical students enrolled at a large Australian university (UNSW Australia) in April/May 2014. The survey examined the knowledge, attitudes and practices of medical students towards influenza vaccination and identified factors associated with vaccine uptake. RESULTS: Of the 606 students, 53.8% (95%CI 49.8-57.8%) receiving their most recent influenza vaccine in 2014. Self-protection was the most common motivator (83%) and inconvenience (64%) the most common barrier to vaccination, despite access to on campus clinics. Students generally held positive attitudes to the influenza vaccine and vaccination recommendations, though some misconceptions existed. The majority (61%) were in support of mandatory influenza vaccination policies for medical students. Significant predictors of influenza vaccination included living on campus, clinical experience, awareness of vaccination recommendations and agreeing that vaccination was important for medical students, while those with perceived time constraints were less likely to be vaccinated. CONCLUSION: Misconceptions and access to influenza vaccine were barriers to uptake of influenza vaccine by medical students. Medical programs need to emphasise the benefits of influenza vaccination in the protection of healthcare workers and patient safety across the medical education program. Our results suggesting majority support for mandatory influenza vaccination may represent a shifting perspective in the medical community.

A Randomized, Phase II Trial of Cetuximab With or Without PX-866, an Irreversible Oral Phosphatidylinositol 3-Kinase Inhibitor, in Patients With Metastatic Colorectal Carcinoma.

BACKGROUND: The phosphotidylinositol-3 kinase (PI3K)/serine-threonine kinase/mammalian target of rapamycin signaling pathway is frequently altered in colorectal cancer (CRC). PX-866 is an oral, irreversible, pan-isoform inhibitor of PI3K. This randomized phase II study evaluated cetuximab with or without PX-866 in patients with metastatic, anti-epidermal growth factor receptor-naive, KRAS codon 12 and 13 wild-type CRC. PATIENTS AND METHODS: Patients with metastatic CRC who had received both oxaliplatin and irinotecan were randomized (1:1) to cetuximab (400 mg/m2 loading then 250 mg/m2 weekly) with or without PX-866 (8 mg orally daily; arms A and B, respectively). The primary endpoint was progression-free survival (PFS). Secondary endpoints included objective response rate, overall survival (OS), toxicity, and correlation of relevant biomarkers with efficacy outcomes. RESULTS: A total of 85 patients were enrolled. The median PFS was 59 days versus 104 days for arms A (cetuximab + PX-866) and B (cetuximab alone), respectively (P = .77). OS between the 2 arms (266 vs. 333 days for arm A vs. B) were similar (P = .83). Overall toxicity, including treatment-related toxicity, was higher in arm A compared with arm B, especially in terms of all-grade nausea (66% vs. 37%), vomiting (50% vs. 29%), diarrhea (64% vs. 18%), and rash (66% vs. 37%). Grade 3 diarrhea occurred in 19% of patients in Arm A and 0% in Arm B. PIK3CA mutations and PTEN loss by immunohistochemistry were infrequently seen. CONCLUSION: The addition of PX-866 to cetuximab did not improve PFS, objective response rate, or OS in patients with metastatic CRC. The combination arm had greater toxicity and may have been harmful in this study.

A randomized, phase 2 trial of docetaxel with or without PX-866, an irreversible oral phosphatidylinositol 3-kinase inhibitor, in patients with relapsed or metastatic head and neck squamous cell cancer.

INTRODUCTION: The phosphotidylinositol-3 kinase (PI3K)/serine-threonine kinase (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is frequently altered in head and neck squamous cell cancer (HNSCC). PX-866 is an oral, irreversible, pan-isoform inhibitor of PI3K. Preclinical models revealed synergy with docetaxel and a phase 1 trial demonstrated tolerability of this combination. This randomized phase 2 study evaluated PX-866 combined with docetaxel in patients with advanced, refractory HNSCC. METHODS: Patients with locally advanced, recurrent or metastatic HNSCC who had received at least one and no more than two prior systemic treatment regimens were randomized (1:1) to a combination of docetaxel (75mg/m(2) IV every 21days) with or without PX-866 (8mg PO daily; Arms A and B, respectively). The primary endpoint was progression free survival (PFS). Secondary endpoints included objective response rate (RR), overall survival (OS), toxicity, and correlation of biomarker analyses with efficacy outcomes. RESULTS: 85 patients were enrolled. There was a non-significant improvement in response rate in the combination arm (14% vs. 5%; P=0.13). Median PFS was 92days in Arm A and 82days in Arm B (P=0.42). There was no difference in OS between the two arms (263 vs. 195days; P=0.62). Grade 3 or higher adverse events were infrequent, but more common in the combination arm with respect to diarrhea (17% vs. 2%), nausea (7% vs. 0%), and febrile neutropenia (21% vs. 5%); grade 3 or higher anemia was more frequent in arm B (7% vs. 27%). PIK3CA mutations or PTEN loss were infrequently observed. CONCLUSION: The addition of PX-866 to docetaxel did not improve PFS, RR, or OS in patients with advanced, refractory HNSCC without molecular pre-selection.

A multicenter phase 1 study of PX-866 and cetuximab in patients with metastatic colorectal carcinoma or recurrent/metastatic squamous cell carcinoma of the head and neck.

BACKGROUND: This phase I, dose-finding study determined the safety, maximum tolerated dose (MTD)/recommended phase 2 dose (RP2D), and antitumor activity of PX-866, a phosphatidylinositol 3-kinase inhibitor, combined with cetuximab in patients with incurable colorectal cancer or squamous cell carcinoma of the head and neck. METHODS: PX-866 was administered at escalating doses (6-8 mg daily) combined with cetuximab given at a 400 mg/m(2) loading dose followed by 250 mg/m(2) weekly. A "3 + 3" study design was used. Prior therapy with anti-EGFR therapies, including cetuximab, was allowed. RESULTS: Eleven patients were enrolled. The most frequent treatment-emergent adverse event was diarrhea (90.1%), followed by hypomagnesemia (72.2%), vomiting (72.2%), fatigue (54.5%), nausea (54.5%), rash (45.5%) and peripheral edema (40%). No dose limiting toxicities were observed. The RP2D was 8 mg, the same as the single-agent PX-866 MTD. Best responses in 9 evaluable patients were: 4 partial responses (44.4%), 4 stable disease (44.4%), and 1 disease progression (11.1%). The median progression free survival was 106 days (range: 1-271). CONCLUSION: Treatment with PX-866 and cetuximab was tolerated with signs of anti-tumor activity. Further development of this combination is warranted.

A randomized, phase 2 trial of Docetaxel with or without PX-866, an irreversible oral phosphatidylinositol 3-kinase inhibitor, in patients with relapsed or metastatic non-small-cell lung cancer.

INTRODUCTION: The phosphotidylinositol-3 kinase/serine-threonine kinase (AKT)/mammalian target of rapamycin signaling pathway is frequently altered in non-small-cell lung cancer (NSCLC). PX-866 is an oral, irreversible, pan-isoform inhibitor of phosphotidylinositol-3 kinase. Preclinical models revealed synergy with docetaxel and a phase 1 trial demonstrated tolerability of this combination. This randomized phase 2 study evaluated PX-866 combined with docetaxel in patients with advanced, refractory NSCLC. METHODS: Patients with locally advanced, recurrent, or metastatic NSCLC who had received at least one and no more than two prior systemic treatment regimens were randomized (1:1) to a combination of docetaxel (75 mg/m intravenous every 21 days) with or without PX-866 (8 mg orally daily; arms A and B, respectively). The primary end point was progression-free survival (PFS). Secondary end points included objective response rate, overall survival (OS), toxicity, and correlation of biomarker analyses with efficacy outcomes. RESULTS: A total of 95 patients were enrolled. Median PFS was 2 months in arm A and 2.9 months in arm B (p = 0.65). Objective response rates were 6% and 0% in arms A and B, respectively (p = 0.4). There was no difference in OS between the two arms (7.0 versus 9.2 months; p = 0.9). Grade 3 or higher adverse events were infrequent, but more common in the combination arm with respect to diarrhea (7% versus 2%), nausea (4% versus 0%), and vomiting (7% versus 0%). PIK3CA mutations or PTEN loss were infrequently observed. CONCLUSION: The addition of PX-866 to docetaxel did not improve PFS, response rate, or OS in patients with advanced, refractory NSCLC without molecular preselection.

Evaluating dosimetric accuracy of flattening filter free compensator-based IMRT: measurements with diode arrays.

PURPOSE: Compensator-based IMRT coupled with the high dose rate flattening filter free (FFF) beams offers an intriguing possibility of delivering an intensity modulated radiation field in just a few seconds. As a first step, the authors evaluate the dosimetric accuracy of the treatment planning system (TPS) FFF beam model with compensators. METHODS: A 6 MV FFF beam from a TrueBeam accelerator (Varian Medical Systems, Palo Alto CA) was modeled in PINNACLE TPS (v. 9.0, Philips Radiation Oncology, Fitchburg WI). Flat brass slabs from 0.3 to 7 cm thick and an 18° brass wedge were used to adjust the beam model. A 2D (MAPCHECK) and 3D (ARCCHECK) diode arrays (Sun Nuclear Corp, Melbourne FL), were investigated for use with the compensator FFF beams. Corrections for diode sensitivity caused by the spectral changes in the beam were introduced. Four compensator plans based on the AAPM TG-119 report were developed. A composite ion chamber measurement, beam by beam MAPCHECK measurements, and a composite ARCCHECK measurement were performed. The array results were analyzed with the same thresholds as in TG-119 report-3%/3 mm with global dose normalization-as well as with the more stringent combinations of the gamma analysis criteria. RESULTS: The FFF beam shows a greater variation of the effective attenuation coefficient with brass thickness due to the prevalence of the low energy photons compared to the conventional 6X beam. As a result, a compromise had to be made while trying to achieve dose agreement for a combination of field sizes, brass thicknesses, and measurement depths (≥5 cm in water). An agreement of measured and calculated dose to within 1% was observed for brass thicknesses up to 2 cm. For the 3 cm slab, an error of up to 2.8% was noted for the field sizes above 10 × 10 cm(2), and up to 3.8% for the 5 × 5 cm(2) field. Both diode arrays exhibit a substantial sensitivity drop as the compensator thickness increases, reaching 10% for a 7 cm brass slab. A simple correction based on the brass thickness along the ray was introduced to counteract this effect. Pooled for five profiles, the average ratio of uncorrected and corrected MAPCHECK to ion chamber readings are 0.966 and 1.008, respectively. With the proper correction, all MAPCHECK measurement to calculation comparisons exhibit 100% γ(3%/3 mm) passing rates with global dose-error normalization. For the TG-119-type plans, the average γ(2%/2 mm) passing rate with local normalization is 94% (range 87.8%-98.3%). The lower ARCCHECK γ-analysis passing rates (corrected for diode sensitivity) are predictable based on the observed PDD discrepancies. However, with the 3%/3 mm thresholds and global normalization, the average γ-analysis passing rate is 96.4% (range 89.9%-100%). CONCLUSIONS: MAPCHECK analysis demonstrates high passing rates with the stringent γ(2%/2 mm) and local normalization criteria combination. The geometry of the ARCCHECK array creates a stress test for the FFF TPS model because of the shallow depth of the entrance diodes and large air cavity. Hence, the ARCCHECK γ-analysis passing rates are lower than with the MAPCHECK, while still on par with TG-119.

Toughening in graphene ceramic composites.

The majority of work in graphene nanocomposites has focused on polymer matrices. Here we report for the first time the use of graphene to enhance the toughness of bulk silicon nitride ceramics. Ceramics are ideally suited for high-temperature applications but suffer from poor toughness. Our approach uses graphene platelets (GPL) that are homogeneously dispersed with silicon nitride particles and densified, at ∼1650 °C, using spark plasma sintering. The sintering parameters are selected to enable the GPL to survive the harsh processing environment, as confirmed by Raman spectroscopy. We find that the ceramic's fracture toughness increases by up to ∼235% (from ∼2.8 to ∼6.6 MPa·m(1/2)) at ∼1.5% GPL volume fraction. Most interestingly, novel toughening mechanisms were observed that show GPL wrapping and anchoring themselves around individual ceramic grains to resist sheet pullout. The resulting cage-like graphene structures that encapsulate the individual grains were observed to deflect propagating cracks in not just two but three dimensions.

Validation of Pinnacle treatment planning system for use with Novalis delivery unit.

For an institution that already owns the licenses, it is economically advantageous and technically feasible to use Pinnacle TPS (Philips Radiation Oncology Systems, Fitchburg, WI) with the BrainLab Novalis delivery system (BrainLAB A.G., Heimstetten, Germany). This takes advantage of the improved accuracy of the convolution algorithm in the presence of heterogeneities compared with the pencil beam calculation, which is particularly significant for lung SBRT treatments. The reference patient positioning DRRs still have to be generated by the BrainLab software from the CT images and isocenter coordinates transferred from Pinnacle. We validated this process with the end-to-end hidden target test, which showed an isocenter positioning error within one standard deviation from the previously established mean value. The Novalis treatment table attenuation is substantial (up to 6.2% for a beam directed straight up and up to 8.4% for oblique incidence) and has to be accounted for in calculations. A simple single-contour treatment table model was developed, resulting in mean differences between the measured and calculated attenuation factors of 0.0%-0.2%, depending on the field size. The maximum difference for a single incidence angle is 1.1%. The BrainLab micro-MLC (mMLC) leaf tip, although not geometrically round, can be represented in Pinnacle by an arch with satisfactory dosimetric accuracy. Subsequently, step-and-shoot (direct machine parameter optimization) IMRT dosimetric agreement is excellent. VMAT (called "SmartArc" in Pinnacle) treatments with constant gantry speed and dose rate are feasible without any modifications to the accelerator. Due to the 3 mm-wide mMLC leaves, the use of a 2 mm calculation grid is recommended. When dual arcs are used for the more complex cases, the overall dosimetric agreement for the SmartArc plans compares favorably with the previously reported results for other implementations of VMAT: gamma(3%,3mm) for absolute dose obtained with the biplanar diode array passing rates above 97% with the mean of 98.6%. However, a larger than expected dose error with the single-arc plans, confined predominantly to the isocenter region, requires further investigation.

Simulation of intrafraction motion and overall geometrical accuracy of a frameless intracranial radiosurgery process.

We conducted a comprehensive evaluation of the clinical accuracy of an image-guided frameless intracranial radiosurgery system. All links in the process chain were tested. Using healthy volunteers, we evaluated a novel method to prospectively quantify the range of target motion for optimal determination of the planning target volume (PTV) margin. The overall system isocentric accuracy was tested using a rigid anthropomorphic phantom containing a hidden target. Intrafraction motion was simulated in 5 healthy volunteers. Reinforced head-and-shoulders thermoplastic masks were used for immobilization. The subjects were placed in a treatment position for 15 minutes (the maximum expected time between repeated isocenter localizations) and the six-degrees-of-freedom target displacements were recorded with high frequency by tracking infrared markers. The markers were placed on a customized piece of thermoplastic secured to the head independently of the immobilization mask. Additional data were collected with the subjects holding their breath, talking, and deliberately moving. As compared with fiducial matching, the automatic registration algorithm did not introduce clinically significant errors (<0.3 mm difference). The hidden target test confirmed overall system isocentric accuracy of < or =1 mm (total three-dimensional displacement). The subjects exhibited various patterns and ranges of head motion during the mock treatment. The total displacement vector encompassing 95% of the positional points varied from 0.4 mm to 2.9 mm. Pre-planning motion simulation with optical tracking was tested on volunteers and appears promising for determination of patient-specific PTV margins. Further patient study is necessary and is planned. In the meantime, system accuracy is sufficient for confident clinical use with 3 mm PTV margins.

Transplanted human bone marrow contributes to vascular endothelium.

Recent evidence indicates that bone marrow is a source of endothelial progenitor cells that are mobilized into the peripheral blood in response to cytokines or tissue injury. Previously, we showed that functional endothelial cells (ECs) can be clonally derived from phenotypically defined hematopoietic stem cells. To determine the EC potential of human bone marrow and peripheral blood stem cells, blood vessels in sex-mismatched transplant recipients were evaluated. EC outcomes were identified by using a combination of immunohistochemistry and XY interphase FISH. Donor-derived ECs were detected in the skin and gut of transplant recipients with a mean frequency of 2% and could readily be distinguished from CD45-expressing hematopoietic stem cells. None of the >4,000 ECs examined had more than two sex chromosomes, consistent with an absence of cell fusion. Y chromosome signals were not detected in sex-matched female recipients, excluding the vertical transmission of male cells. None of the recipients evaluated before hematopoietic engraftment demonstrated donor-derived ECs, indicating a close linkage between the recovery of hematopoiesis and EC outcomes. Transplantable bone marrow-derived endothelial progenitor cells may represent novel therapeutic targets for hematopoietic and vascular disease.