Anthracycline chemotherapy and its effects on left ventricular mechanics: insights into the PROACT PLUS study

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): South Tees Research and Development Fund

Background

Anthracyclines continue to form the backbone of chemotherapy treatment for breast cancer and lymphoma. However, their use has been directly associated with dose-dependent cardiotoxicity. Most studies to date have focused on the effects of high dose anthracyclines on left ventricular (LV) systolic function with a particular interest in peak global longitudinal strain (GLS). Not much attention has been directed to the effects of lower dose anthracyclines and other strain parameters of LV systolic and diastolic function.

Purpose

In this prospective study, we performed a comprehensive 2-dimensional echocardiographic assessment on the effects of anthracyclines on both the LV systolic and diastolic strain measures. We focused on the changes in the LV end-systolic (ES) GLS, myocardial GLS (myoGLS), global radial strain (GRS), global circumferential strain (GCS), myocardial GCS (myoGCS), twist and torsion. Additionally, peak systolic (PS), ES, early-diastolic (ED), and late-diastolic (LD) strain-rates were measured.

Methods

Patients with a new diagnosis of breast cancer or lymphoma undergoing anthracycline chemotherapy (any dose) were recruited between October 2018 to March 2020. Echocardiograms were performed pre-chemotherapy (V1) and 1 month post treatment (V2). These were analysed offline using vendor-independent software (TomTec 2D CPA). The study was ethically approved by the Health Research Association (REC reference 18/EM/0177).

Results

A total number of 62 were recruited into the study of which 7 patients passed away during treatment and 5 failed to attend their follow-up appointment at V2. Of the remaining patients, 6 dropped their LV ejection fraction (EF) to < 53% at V2 (G1). In these patients, a significant reduction in the LV ES-GLS (-19.3% vs. -15.3%, p = 0.0041), myoGLS (-16.8% vs. -12.8%, p = 0.0014), LV longitudinal PS strain-rate (-1 1/s vs. 0.78 1/s, p = 0.0063), and LV longitudinal ED strain-rate (1.1 1/s vs. 0.67 1/s, p = 0.026) was seen from V1 to V2. There was no statistically significant change in the other systolic and diastolic strain parameters in this group of patients. In patients with a normal EF at V2 (G2), a reduction in the LV ES-GLS (-20.8% vs. -19.9%, p = 0.013) and myoGLS (-17.9% vs. -16.9%, p = 0.012) was also seen from V1 to V2. Additionally, a deterioration in the LV radial ED strain-rate (-1.37 1/s vs. -1.2 1/s, p = 0.009), LV longitudinal ED strain-rate (0.98 1/s vs. 0.85 1/s, p = 0.01), and LV circumferential ED strain rate (1.62 1/s vs. 1.33 1/s, p = 0.045) was observed.

Conclusion

In G1, a more extensive deterioration (>15%) in the LV ES-GLS, myoGLS, and longitudinal ED strain-rate was evident when compared to G2. The additional reduction in LV early diastolic strain-rate in both patient groups highlights the global insult that anthracyclines can pose on both LV systolic and diastolic function. However, whether these findings translate into future development of cardiotoxicity is not yet known.

Right ventricular mechanics in anthracycline chemotherapy: insights into the PROACT PLUS study

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): South Tees Research and Development Fund

Background

Anthracyclines are highly effective chemotherapy agents used in the treatment of many breast and haematological malignancies. However, one of the well-recognised associated risks with their use includes cardiotoxicity which can lead to heart failure and poor prognosis. Most studies have focused on the effects of these agents on the left ventricular systolic function. Right ventricular (RV) mechanics in anthracycline chemotherapy have so far been neglected.

Purpose

The PROACT PLUS study is an observational, prospective, cohort study which assesses the effects of anthracyclines on the RV systolic and diastolic measures using 2 dimensional conventional echocardiography and speckle tracking imaging (STE).

Methods

From October 2018 to March 2020, patients with a new diagnosis of lymphoma or breast cancer undergoing anthracycline chemotherapy were recruited into the PROACT PLUS study. Echocardiography was performed pre-chemotherapy (V1) and 1 month post chemotherapy (V2). Using vendor-independent software (TomTec Imaging Systems, 2D Cardiac Performance Analysis, Unterschleisshiem, Germany), offline analysis of tricuspid annular plane systolic excursion (TAPSE), RV fractional area change (FAC), tricuspid annular systolic velocity (S’), RV global longitudinal strain (RV GLS), RV myocardial longitudinal strain (RV myoGLS), RV free wall strain (RV FWS), RV- and RV free wall peak systolic (PS) strain-rates, end-systolic (ES) strain-rates, early-diastolic (ED) strain-rates and late-diastolic (LD) strain-rates were measured. This study was ethically approved by the Health Research Association (REC reference 18/EM/0177).

Results

62 patients were recruited into this study. Of these, 7 passed away during treatment and 5 failed to attend their follow-up appointment at V2. Of the remaining patients, a significant deterioration in the RV GLS (-25.4% vs. -22.5%, p < 0.0001), RV myoGLS (-22.4% vs. -20.9%, p = 0.005), RV ED strain-rate (1.08 1/s vs. 0.9 1/s, p = 0.01) and RV free wall ED strain-rate (1.24 1/s vs. 1.07 1/s, p = 0.02) was seen between V1 and V2. No statistical significant change was observed in the conventional and other strain measures of RV function. A total number of 6 patients developed left ventricular systolic dysfunction at V2 with ≥ 10% drop in the LV ejection fraction (LVEF) to < 53%. In this group of patients, there was a statistical significant reduction in the RV FWS (-25.5% vs. -22.7%, p = 0.03) which was not evident in the group of patients with preserved LVEF.

Conclusion

These findings suggest that adverse effects of anthracyclines are not purely confined to the LV, and RV systolic and diastolic changes are evident during treatment with anthracyclines, emphasising the global effect of these agents. A comprehensive RV assessment needs to be taken into consideration during the assessment of cardiotoxicity in patients undergoing chemotherapy treatment.

Atrial mechanics in anthracycline chemotherapy: insights into a prospective study

Funding Acknowledgements

Type of funding sources: Public hospital(s). Main funding source(s): South Tees Research and Development Fund

Background

In cancer treatment, detection of anthracycline induced cardiotoxicity (AIC) has been dependent on serial cardiac imaging to identify a reduction in left ventricular ejection fraction (LVEF) and more recently LV global longitudinal strain (GLS). However, studies have failed to assess the adverse effects of these agents on other cardiac chambers such as the left (LA) and right atria (RA).

Purpose

The PROACT PLUS study is an observational, prospective, cohort study investigating the effects of anthracyclines on the left and right atrial mechanics using 2 dimensional speckle tracking echocardiography (STE). We hypothesize that anthracyclines can affect the heart as a whole rather than solely affecting the LV.

Methods

From October 2018 to March 2020, patients with a new diagnosis of lymphoma or breast cancer receiving anthracycline chemotherapy were recruited into this study. Echocardiography was performed pre-chemotherapy (V1) and 1 month post-chemotherapy (V2). LA and RA volumes, LA (4-chamber)- and RA GLS, reservoir strains (RS), conduit strains (CS), contractile strains (CoS), peak-systolic (PS) strain-rates, early-diastolic (ED) strain-rates, and late-diastolic (LD) strain-rates were measured offline using vendor-independent software. This study was ethically approved by the Health Research Association (REC reference 18/EM/0177).

Results

A total number of 62 patients were recruited into this study. Unfortunately, 7 patients passed away during their treatment and 5 failed to attend their follow-up appointment at V2. From V1 to V2, there was a significant deterioration in the LA CS (-18.1% vs. -14.5%, p = 0.02) and LA ED strain-rate (-1.24 1/s vs. -0.86 1/s, p = 0.001). There was no other statistical significant change in the LA volume or other strain parameters. Additionally, there was a statistically significant decline in RA GLS (34.9% vs. 30.8%, p = 0.029), RA RS (41.1% vs. 37.1%, p = 0.03), RA CS (-23.8 vs. -20.6, p = 0.05), and RA ED strain-rate (-1.17 vs. -0.99, p = 0.02) with no significant change in the RA volume and other measures of RA strain.

Conclusion

These findings support our hypothesis that anthracyclines exert their cardiotoxic effects on all cardiac chambers including the atria. Whether these changes lead to subsequent permanent structural abnormalities in the atria hence increasing the future risk of atrial arrhythmias, or whether these changes predate subsequent cardiac dysfunction and poor prognosis, remains unknown. Long-term follow up and assessment of atrial mechanics is crucial in better understanding of AIC to help guide the future monitoring and management of patients undergoing cancer treatment.

Oral Healthcare Implications of Dedicated Online Communities: A Computational Content Analysis of the r/Dentistry Subreddit

The current study explores communication expressed by participants in a subreddit surrounding oral health care, moderated by dentists and dental hygienists. The corpus was analyzed through Leximancer, a computer-assisted program used for computational content analyses of large data sets. Users' personal disclosures about ongoing dental concerns, advice about others' self-care, and the role of interpersonal communication with and among health care providers emerged as dominant themes. The findings suggest that online communities may serve an important role that dentists are unable to fill in their limited interactions with individual patients. Such interaction spaces may therefore offer a fertile environment for future interventions to promote beneficial practices and achieve positive health-related outcomes.

The effects of doxorubicin on left and right atrial mechanics in patients with lymphoma

Background

Despite the associated dose-dependent cardiotoxicity, anthracyclines continue to form the backbone of modern chemotherapy regimens. Speckle Tracking Echocardiography (STE) has been a popular method of quantifying cardiac function but most studies have focused on left ventricular function. Research into the effects of anthracyclines on left atrial (LA) and right atrial (RA) function continues to be neglected.

Purpose

To investigate the effects of doxorubicin, a commonly used anthracycline, on both the LA and RA systolic and diastolic strain and strain-rate parameters in two groups of patients with lymphoma: Group 1 (G1) with a conventional drop in ejection fraction (EF <53%), and Group 2 (G2) without.

Methods

We retrospectively studied 46 patients treated for lymphoma between 2015 and 2018; G1 (n=12) and G2 (n=34). Echocardiograms performed at baseline (T0), mid-chemotherapy (T1), and post-chemotherapy (T2), were analysed by using offline vendor-independent software (TomTec, 2D Cardiac Performance Analysis). Using 2D STE, LA and RA reservoir, conduit and contractile strains, systolic and diastolic strain-rates were measured. Multi-level longitudinal model was used for statistical analysis.This study was ethically approved by the Health Research Association (REC Reference 18/SS/0139).

Results

Median age was 64 years (IQR 51–74 years) in G1, and 65 years (IQR 57–73 years) in G2. In G1, there was no significant change in LA reservoir strain with time, however a significant decline with an average mean difference of −7.52 was seen between T0 to T2 (p=0.016) in G2. LA conduit strain did not significantly change in either group with incremental doses of doxorubicin. However, LA contraction strain was seen to significantly increase in G1 between T1 to T2 (p=0.045) with an average change of 7.23. LA peak systolic strain rate, and late diastolic strain rate did not show any significant change with time in both groups. Yet, a significant increase was seen in LA early diastolic strain rate between T0 to T2 (p=0.017) in G1 but not G2. No significant changes were seen in the RA strain parameters in both groups.

Conclusion

In patient with a reduction in LV function, a significant change was noted in the left atrial contraction strain and early diastolic strain rate with incremental doses of doxorubicin. These changes shows the close relationship between the LA and LV, and the importance of LA in providing a compensatory mechanism for a decline in LV function secondary to anthracycline cardiotoxicity.

Funding Acknowledgement

Type of funding source: None

A single dose of zoledronate preserves bone mineral density for up to 2 years after a second course of romosozumab

This phase 2 study evaluated the efficacy and safety of transitioning to zoledronate following romosozumab treatment in postmenopausal women with low bone mass. A single dose of 5 mg zoledronate generally maintained the robust BMD gains accrued with romosozumab treatment and was well tolerated.

INTRODUCTION

Follow-on therapy with an antiresorptive agent is necessary to maintain the skeletal benefits of romosozumab therapy. We evaluated the use of zoledronate following romosozumab treatment.

METHODS

This phase 2, dose-finding study enrolled postmenopausal women with low bone mineral density (BMD). Subjects who received various romosozumab doses or placebo from months 0-24 were rerandomized to denosumab (60 mg SC Q6M) or placebo for 12 months, followed by open-label romosozumab (210 mg QM) for 12 months. At month 48, subjects who had received active treatment for 48 months were assigned to no further active treatment and all other subjects were assigned to zoledronate 5 mg IV. Efficacy (BMD, P1NP, and β-CTX) and safety were evaluated for 24 months, up to month 72.

RESULTS

A total of 141 subjects entered the month 48-72 period, with 51 in the no further active treatment group and 90 in the zoledronate group. In subjects receiving no further active treatment, lumbar spine (LS) BMD decreased by 10.8% from months 48-72 but remained 4.2% above the original baseline. In subjects receiving zoledronate, LS BMD was maintained (percentage changes: - 0.8% from months 48-72; 12.8% from months 0-72). Similar patterns were observed for proximal femur BMD in both groups. With no further active treatment, P1NP and β-CTX decreased but remained above baseline at month 72. Following zoledronate, P1NP and β-CTX levels initially decreased but approached baseline by month 72. No new safety signals were observed.

CONCLUSION

A zoledronate follow-on regimen can maintain robust BMD gains achieved with romosozumab treatment.

Romosozumab or alendronate for fracture prevention in East Asian patients: a subanalysis of the phase III, randomized ARCH study

Romosozumab, a sclerostin antibody, exerts dual effect to increase bone formation and decrease bone resorption. Among high-risk postmenopausal East Asian women, romosozumab followed by alendronate was associated with lower incidences of fractures vs alendronate alone. Romosozumab demonstrates potential to address an unmet need in osteoporosis management in Asia.

INTRODUCTION

Romosozumab, a sclerostin antibody, exerts dual effect to increase bone formation and decrease bone resorption. The global ARCH study demonstrated superiority of romosozumab followed by alendronate in reducing fracture risk in high-risk postmenopausal osteoporotic women vs alendronate alone. We report outcomes among ARCH East Asian patients.

METHODS

In ARCH, 4093 postmenopausal osteoporotic women with fragility fracture were randomized 1:1 to monthly romosozumab 210 mg or weekly alendronate 70 mg for 12 months, both followed by open-label alendronate. Primary endpoints were incidence of new vertebral fracture (VF) at 24 months and clinical fracture at primary analysis (confirmed fractures in ≥ 330 patients and all patients had opportunity to attend month 24 visit). This post hoc analysis was not powered to detect fracture-rate differences.

RESULTS

This analysis included 275 patients from Hong Kong, Korea, and Taiwan. Romosozumab followed by alendronate reduced risk of new VFs at 24 months by 60% (P = 0.11) and clinical fractures at primary analysis by 44% (P = 0.15) vs alendronate alone. Romosozumab followed by alendronate significantly increased mean bone mineral density at 24 months from baseline by a further 9.0%, 3.3%, and 3.0% at the lumbar spine, total hip, and femoral neck vs alendronate alone. Adverse event (AE) rates, including positively adjudicated serious cardiovascular AEs (1.6% vs 1.4% at 12 months for romosozumab vs alendronate), were similar across treatment groups.

CONCLUSIONS

Consistent with the global analysis, romosozumab followed by alendronate was associated with lower incidences of new vertebral, clinical, non-vertebral, and hip fractures vs alendronate alone among East Asian patients.

P1383 The effects of doxorubicin on left and right ventricular strain in patients with lymphoma: insights from a retrospective study

Funding Acknowledgements

South Tees Research and Development Fund (UK)

Background

Anthracyclines are a cornerstone in the management of lymphoma. However, their use is associated with cardiotoxicity. Speckle tracking echocardiography (STE) has been established as a valid measure of quantifying cardiac function. However, most studies to this date have focused predominantly on left ventricular (LV) global longitudinal strain (GLS) with only a limited number assessing the right ventricle (RV) and other LV strain parameters.

Purpose

Using 2D STE, we assessed the effects of anthracyclines on LV and RV strain parameters, focusing on LV endocardial (GLS), LV myocardial GLS (myoGLS), LV radial strain (GRS), RV endocardial (RV GLS), myocardial GLS (RV myoGLS), and RV free wall strain (RVFWS).

Methods

We retrospectively collected data on patients treated for lymphoma between 2015-2018. Two groups (G) were defined: those with a conventional drop in LV ejection fraction (EF), (G1, n = 11) and those without (G2, n = 24). Echocardiograms were performed pre-chemotherapy (T0), mid-treatment (T1), and post-chemotherapy (T2) and were analysed offline using vendor-independent software (TomTec 2D CPA). LV and RV strain analysis was performed in both groups. This study was ethically approved by Health Research Association (REC Reference 18/SS/0139).

Results

Mean age was 61 ± 16 years (G1) and 65 ± 12 years (G2). 18% (G1) and 17% (G2) of patients had a history of IHD in each group. Mean cumulative dose of doxorubicin was 280 ± 31 mg/m2 (G1) and 280± 48mg/m2 (G2). In both groups, there was no significant change in LV or RV strain parameters from T0 to T1. In G1, between T1 and T2, patients exhibited a significant deterioration in LV GLS (-19.7 ± 2.6% vs.-15.6 ± 2.5% p < 0.0005), and LV myoGLS (-17.3 ± 2.2% vs. -14.1 ± 2.9% p = 0.02). There was also a measurable decline in RV strain parameters between T1 to T2 (RV GLS, -23.1 ± 4.7% vs. -18.8 ± 4.2% p = 0.028) and (RV myoGLS -21.5 ± 5.2% vs -17.3 ± 3.6% p = 0.013). When analysed from T0 to T2, the changes in RV strain were more marked; RV GLS (-25.2 ± 4.9% vs. -18.8 ± 4.2% p = 0.005), RV myoGLS (-22.4 ± 5.2% vs-17.3 ± 3.6% p = 0.005), and RVFWS (-28.8 ± 5.7% vs. -20.9 ± 6.7% p = 0.001). In G2, no change was observed in LV GLS (-20.4 ± 2.3% vs. -19.6 ± 2.8% p = 0.66), LV myoGLS (-18.8 ± 2.5% vs. -17.5 ± 3.1% p = 0.18), RV GLS (-24.2 ± 2.3% vs. -23.1 ± 2.7% p = 0.42), RV myoGLS (-22.4 ± 2.9% vs. -20.6 ± 2.8% p = 0.09), RVFWS (-26.7 ± 4.6% vs. -25.2 ± 3.6% p = 1.0). GRS did not significantly change in either G1 or G2 during treatment.

Conclusion

In patients with a reduction in LVEF, this analysis demonstrated a significant reduction in LV strain parameters secondary to anthracycline treatment. Novel strain parameters did not change in the normal EF group, or predate EF/GLS decline in those with reduced LVEF. Measurable RV dysfunction was noted in those with LV deterioration, highlighting the global cardiac insult of anthracycline treatment. Preventative and monitoring strategies in cardio-oncology should not overlook RV function.

Bone mineral density gains with a second 12-month course of romosozumab therapy following placebo or denosumab

Romosozumab is a therapy that stimulates bone formation and reduces bone resorption. In this study of postmenopausal women with low BMD, a second course of romosozumab following a period off treatment or on denosumab increased or maintained BMD, respectively, and was well tolerated, providing insight into treatment sequence options.

INTRODUCTION

In patients with high fracture risk, therapies that stimulate bone formation provide rapid BMD gains; currently available agents, parathyroid hormone receptor agonists, are limited to a 2-year lifetime exposure and generally used for a single treatment course. However, for long-term osteoporosis management, a second treatment course may be appropriate. Romosozumab, a therapy with the dual effect of increasing bone formation and decreasing bone resorption, reduces fracture risk within 12 months. Here, we report efficacy and safety of a second romosozumab course.

METHODS

In this phase 2, dose-finding study, postmenopausal women with low bone mass (T-score ≤ - 2.0 and ≥ - 3.5) received romosozumab or placebo (month 0-24) followed by placebo or denosumab (month 24-36); participants then received a year of romosozumab (month 36-48).

RESULTS

Of 167 participants who entered the month 36-48 period, 35 had been initially randomized to romosozumab 210 mg monthly. In participants who received romosozumab 210 mg monthly followed by placebo, a second romosozumab course (n = 19) increased BMD by amounts similar to their initial treatment (month 0-12) at the lumbar spine (12.4%; 12.0%, respectively) and total hip (6.0%; 5.5%, respectively). Following denosumab, a second romosozumab course (n = 16) increased BMD at the lumbar spine (2.3%) and maintained BMD at the total hip. Safety profiles were similar between first and second romosozumab courses.

CONCLUSIONS

After 12 months off-treatment, a second romosozumab course again led to rapid and large BMD gains. Following denosumab, BMD gains with romosozumab were smaller than with initial treatment. No new safety findings were observed during the second course.

Pixel-to-pixel variation on a calibrated PILATUS3-based multi-energy soft x-ray detector

A multi-energy soft x-ray pin-hole camera based on the PILATUS3 100 K x-ray detector has recently been installed on the Madison Symmetric Torus. This photon-counting detector consists of a two-dimensional array of ∼100 000 pixels for which the photon lower-threshold cutoff energy E _c can be independently set for each pixel. This capability allows the measurement of plasma x-ray emissivity in multiple energy ranges with a unique combination of spatial and spectral resolution and the inference of a variety of important plasma properties (e.g., T _e, n _Z, Z _eff). The energy dependence of each pixel is calibrated for the 1.6-6 keV range by scanning individual trimbit settings, while the detector is exposed to fluorescence emission from Ag, In, Mo, Ti, V, and Zr targets. The resulting data for each line are then fit to a characteristic "S-curve" which determines the mapping between the 64 possible trimbit settings for each pixel. The statistical variation of this calibration from pixel-to-pixel was explored, and it was found that the discreteness of trimbit settings results in an effective threshold resolution of ΔE < 100 eV. A separate calibration was performed for the 4-14 keV range, with a resolution of ΔE < 200 eV.

Simulation, design, and first test of a multi-energy soft x-ray (SXR) pinhole camera in the Madison Symmetric Torus (MST)

A multi-energy soft x-ray pinhole camera has been designed and built for the Madison Symmetric Torus reversed field pinch to aid the study of particle and thermal-transport, as well as MHD stability physics. This novel imaging diagnostic technique combines the best features from both pulse-height-analysis and multi-foil methods employing a PILATUS3 x-ray detector in which the lower energy threshold for photon detection can be adjusted independently on each pixel. Further improvements implemented on the new cooled systems allow a maximum count rate of 10 MHz per pixel and sensitivity to the strong Al and Ar emission between 1.5 and 4 keV. The local x-ray emissivity will be measured in multiple energy ranges simultaneously, from which it is possible to infer 1D and 2D simultaneous profile measurements of core electron temperature and impurity density profiles with no a priori assumptions of plasma profiles, magnetic field reconstruction constraints, high-density limitations, or need of shot-to-shot reproducibility. The expected time and space resolutions will be 2 ms and <1 cm, respectively.

BRCA1 through Its E3 Ligase Activity Regulates the Transcription Factor Oct1 and Carbohydrate Metabolism

The tumor suppressor BRCA1 regulates the DNA damage response (DDR) and other processes that remain incompletely defined. Among these, BRCA1 heterodimerizes with BARD1 to ubiquitylate targets via its N-terminal E3 ligase activity. Here, it is demonstrated that BRCA1 promotes oxidative metabolism by degrading Oct1 (POU2F1), a transcription factor with proglycolytic and tumorigenic effects. BRCA1 E3 ubiquitin ligase mutation skews cells toward a glycolytic metabolic profile while elevating Oct1 protein. CRISPR-mediated Oct1 deletion reverts the glycolytic phenotype. RNA sequencing (RNAseq) confirms deregulation of metabolic genes downstream of Oct1. BRCA1 mediates Oct1 ubiquitylation and degradation, and mutation of two ubiquitylated Oct1 lysines insulates the protein against BRCA1-mediated destabilization. Oct1 deletion in MCF-7 breast cancer cells does not perturb growth in standard culture, but inhibits growth in soft agar and xenograft assays. In primary breast cancer clinical specimens, Oct1 protein levels correlate positively with tumor aggressiveness and inversely with BRCA1. These results identify BRCA1 as an Oct1 ubiquitin ligase that catalyzes Oct1 degradation to promote oxidative metabolism and restrict tumorigenicity. Mol Cancer Res; 16(3); 439-52. ©2018 AACR.

Multi-energy x-ray detector calibration for T and impurity density (n) measurements of MCF plasmas

Soft x-ray detection with the new "multi-energy" PILATUS3 detector systems holds promise as a magnetically confined fusion (MCF) plasma diagnostic for ITER and beyond. The measured x-ray brightness can be used to determine impurity concentrations, electron temperatures, n_e²Z_eff products, and to probe the electron energy distribution. However, in order to be effective, these detectors which are really large arrays of detectors with photon energy gating capabilities must be precisely calibrated for each pixel. The energy-dependence of the detector response of the multi-energy PILATUS3 system with 100 K pixels has been measured at Dectris Laboratory. X-rays emitted from a tube under high voltage bombard various elements such that they emit x-ray lines from Zr-Lα to Ag-Kα between 1.8 and 22.16 keV. Each pixel on the PILATUS3 can be set to a minimum energy threshold in the range from 1.6 to 25 keV. This feature allows a single detector to be sensitive to a variety of x-ray energies, so that it is possible to sample the energy distribution of the x-ray continuum and line-emission. PILATUS3 can be configured for 1D or 2D imaging of MCF plasmas with typical spatial energy and temporal resolution of 1 cm, 0.6 keV, and 5 ms, respectively.

Development of a high resolution x-ray spectrometer for the National Ignition Facility (NIF)

A high resolution (E/ΔE = 1200-1800) Bragg crystal x-ray spectrometer is being developed to measure plasma parameters in National Ignition Facility experiments. The instrument will be a diagnostic instrument manipulator positioned cassette designed mainly to infer electron density in compressed capsules from Stark broadening of the helium-β (1s²-1s3p) lines of krypton and electron temperature from the relative intensities of dielectronic satellites. Two conically shaped crystals will diffract and focus (1) the Kr Heβ complex and (2) the Heα (1s²-1s2p) and Lyα (1s-2p) complexes onto a streak camera photocathode for time resolved measurement, and a third cylindrical or conical crystal will focus the full Heα to Heβ spectral range onto an image plate to provide a time integrated calibration spectrum. Calculations of source x-ray intensity, spectrometer throughput, and spectral resolution are presented. Details of the conical-crystal focusing properties as well as the status of the instrumental design are also presented.

Multi-energy SXR cameras for magnetically confined fusion plasmas (invited)

A compact multi-energy soft x-ray camera has been developed for time, energy and space-resolved measurements of the soft-x-ray emissivity in magnetically confined fusion plasmas. Multi-energy soft x-ray imaging provides a unique opportunity for measuring, simultaneously, a variety of important plasma properties (T_e, n_Z, ΔZ_eff, and n_e,fast). The electron temperature can be obtained by modeling the slope of the continuum radiation from ratios of the available brightness and inverted radial emissivity profiles over multiple energy ranges. Impurity density measurements are also possible using the line-emission from medium- to high-Z impurities to separate the background as well as transient levels of metal contributions. This technique should be explored also as a burning plasma diagnostic in-view of its simplicity and robustness.

Transcription factor Oct1 is a somatic and cancer stem cell determinant

Defining master transcription factors governing somatic and cancer stem cell identity is an important goal. Here we show that the Oct4 paralog Oct1, a transcription factor implicated in stress responses, metabolic control, and poised transcription states, regulates normal and pathologic stem cell function. Oct1^HI cells in the colon and small intestine co-express known stem cell markers. In primary malignant tissue, high Oct1 protein but not mRNA levels strongly correlate with the frequency of CD24^LOCD44^HI cancer-initiating cells. Reducing Oct1 expression via RNAi reduces the proportion of ALDH^HI and dye efflux^HI cells, and increasing Oct1 increases the proportion of ALDH^HI cells. Normal ALDH^HI cells harbor elevated Oct1 protein but not mRNA levels. Functionally, we show that Oct1 promotes tumor engraftment frequency and promotes hematopoietic stem cell engraftment potential in competitive and serial transplants. In addition to previously described Oct1 transcriptional targets, we identify four Oct1 targets associated with the stem cell phenotype. Cumulatively, the data indicate that Oct1 regulates normal and cancer stem cell function.

Understanding the mechanisms that control stem cell function is a fundamental prerequisite both for the full application of stem cells to regenerative medicine and for a full understanding of the relationship between stem cells and cancer. In this study we show that a transcription factor known as Oct1 is a central regulator of normal and cancer stem cell function. We show that high Oct1 levels are associated with stem cells in multiple normal and malignant settings. Altering Oct1 expression, up or down, correspondingly alters multiple stem cell parameters, as well as stem cell function. We highlight known and identify new target genes Oct1 binds to that are consistent with a role in stem cell function.

A modification of flattening filter free linac for IMRT

PURPOSE

This study investigates the benefits of a modified flattening filter free (FFF) linac over the standard (STD) linac equipped with the flattening filter. Energy and angular spread of the electron beam of the FFF linac were modified. Modification of FFF beam parameters is explored to maximize the monitor unit efficiency and to minimize the head scatter in IMRT delivery for large target volumes or targets lying away from the central axis.

METHODS

The EGSnrc code is used to model FFF and STD linacs and study basic beam properties for both linac types in various beam configurations. Increasing energy of FFF linac results in similar beam attenuation properties and maximized dose rate compared to STD linac. Matching beam attenuation properties allows a more direct exploration of beam flatness of FFF linac in regard to IMRT delivery, especially away from the central axis where the effective dose rate is considerably smaller than the one at the central axis. Flatness of open beam dose profile of FFF linac is improved by increasing the angular spread of the electron beam. The resulting dose rate within the treatment field and outside of the field (peripheral dose) are characterized and compared to the unmodified FFF and STD linacs,

RESULTS

In order to match beam penetration properties, the energy of FFF is adjusted from 6.5 to 8.0 MeV for small to medium field sizes and from 6.5 to 8.5 MeV for larger ones. Dose rate of FFF vs STD linac increased by a factor of 1.9 (6.5 MeV) and 3.4-4.1 (8.0-8.5 MeV). Adjusting the mean angular spread of the electron beam from 0 degrees to 5 degrees-10 degrees resulted in complete flattening of photon beam for field sizes between 10 x 10 cm2 and 15 x 15 cm2 and partial flattening for field sizes from 15 x 15 cm2 to 30 x 30 cm2. Values of angular spread > or =14 degrees are not recommended as they exceed the opening of the primary collimator, affecting the area at the edges of the field. FFF fields of sizes smaller than 6 x 6 cm2 are already flat and beam flattening is not necessary. Overall, the angular spread of 5 degrees-10 degrees is sufficient and can satisfactorily flatten open beam dose profiles even for larger field sizes. Increasing the electron beam angular spread amounts to a slight decrease of dose rate of FFF linac. However, for angular spread, 5 degrees-10 degrees dose rate factor of FFF vs STD is still about 1.6-2.6, depending on the field size (and the adjusted energy). Similarly, in case of peripheral dose, a moderate increase in dose can be observed for angular spread of 5 degrees-10 degrees and for field sizes 10 x 10 cm2 to 30 x 30 cm2. Lastly, beam flatness of not modified FFF linac can be conveniently described by an analytical function representing a ratio of STD vs FFF doses: 1 + b|r|(n).

CONCLUSIONS

A modified FFF beamline with increased energy and electron beam angular spread results in satisfactory flattened beam and high dose rate within the field. Peripheral dose remaining at similar (or smaller) level than that of STD linac for the same delivered dose within the treatment field.