Characterization of Radiographic and Molecular Changes in Mouse Brain after FLASH Irradiation

PURPOSE/OBJECTIVE(S)

Despite refinements in treatment platforms such as incorporation of high-resolution imaging and real time motion tracking, the amount of radiation dose delivered safely to a particular tissue type is limited by both tissue intrinsic and extrinsic factors. FLASH radiotherapy (RT), delivery of relatively high radiation dose at dose rates several orders of magnitude higher than that of conventional (CONV) dose-rates, may change that paradigm due to normal tissue sparing characteristics of FLASH RT. Our Radiation Oncology Physics division developed a novel FLASH kV x-ray cabinet system for preclinical laboratory research. Here we utilize this technology to establish optimal radiation parameters for FLASH effect in brain tissue of a murine model. A range of total radiation dose and dose rates that are considered to be within the window for FLASH effect are being investigated. We have identified several measurable and clinically meaningful toxicity outcomes, including radiation necrosis and blood brain barrier integrity, to assess FLASH effects in brain tissue.

MATERIALS/METHODS

A high-capacity rotating anode x-ray tube was implemented for FLASH irradiation, operating at 150 kVp with 0.025 mm Cu added filtration. A custom 3D printed immobilization tool was designed to reproducibly position animals for stereotactic irradiation of the brain. Dose and dose rate measurements were performed with calibrated radiographic film in kV solid water. Conventional dose rate irradiations were delivered using a standard laboratory irradiator (SARRP) operating at the same kVp and filtration. The depth-dose gradients in solid water were compared between the irradiators. Healthy 8-week-old C57BL6J mice were then irradiated with graded doses of FLASH and CONV x-rays (10- 60 Gy) using a single 1-cm wide AP field. Dose was prescribed to the center of the brain, at a depth of 3.25 mm. RT-induced necrosis is being monitored by serial biweekly MR imaging using a 7-T preclinical MRI machine. Histopathological changes will be assessed through H&E staining of harvested brain at 3-months post-irradiation (n = 5 per arm). FITC-Dextran infusion will be performed prior to necropsy to assess blood-brain barrier integrity.

RESULTS

Animal setup for stereotactic FLASH brain irradiation was reproducible to within 0.5mm. Measured dose rates were 75.6 Gy/s for FLASH and 3.8 Gy/min for conventional irradiations. At 5-mm depth in solid water, the PDDs agreed to within 4% between SARRP and FLASH Irradiator. Biweekly T1 post and T2 weighted image acquisition is currently underway. Histology and FITC-Dextran data will be presented when available.

CONCLUSION

We have successfully designed a high-precision platform to study x-ray FLASH effects in mice brain model. Evaluation of dose window for brain FLASH effect and molecular mechanisms of this phenomenon is an important step in the potential translation of FLASH RT for brain irradiation.

Local Hemodynamic Conditions Associated with Focal Changes in the Intracranial Aneurysm Wall

BACKGROUND AND PURPOSE

Aneurysm hemodynamics has been associated with wall histology and inflammation. We investigated associations between local hemodynamics and focal wall changes visible intraoperatively.

MATERIALS AND METHODS

Computational fluid dynamics models were constructed from 3D images of 65 aneurysms treated surgically. Aneurysm regions with different visual appearances were identified in intraoperative videos: 1) "atherosclerotic" (yellow), 2) "hyperplastic" (white), 3) "thin" (red), 4) rupture site, and 5) "normal" (similar to parent artery), They were marked on 3D reconstructions. Regional hemodynamics was characterized by the following: wall shear stress, oscillatory shear index, relative residence time, wall shear stress gradient and divergence, gradient oscillatory number, and dynamic pressure; these were compared using the Mann-Whitney test.

RESULTS

Hyperplastic regions had lower average wall shear stress (P = .005) and pressure (P = .009) than normal regions. Flow conditions in atherosclerotic and hyperplastic regions were similar but had higher average relative residence time (P = .03) and oscillatory shear index (P = .04) than thin regions. Hyperplastic regions also had a higher average gradient oscillatory number (P = .002) than thin regions. Thin regions had lower average relative residence time (P < .001), oscillatory shear index (P = .006), and gradient oscillatory number (P < .001) than normal regions, and higher average wall shear stress (P = .006) and pressure (P = .009) than hyperplastic regions. Thin regions tended to be aligned with the flow stream, while atherosclerotic and hyperplastic regions tended to be aligned with recirculation zones.

CONCLUSIONS

Local hemodynamics is associated with visible focal wall changes. Slow swirling flow with low and oscillatory wall shear stress was associated with atherosclerotic and hyperplastic changes. High flow conditions prevalent in regions near the flow impingement site characterized by higher and less oscillatory wall shear stress were associated with local "thinning" of the wall.

Rape-a Nightmare for Victim, Dilemma for Certifier and a Challenge for Society

Violence against women is a global phenomenon, represented in various forms and magnitude. Rape is also considered as the wicked act of violence against women by every civilized society. This article encompasses three-dimensional approach of the problem. The immediate, delayed and remote physical and mental tauuma sustained by victim, the difficulties and inadequacies in medical examination and certification, deficiencies investigation and laboratory set up and unrealistic and unsympathetic attitude of our society towards the victim are highlighted. Some measures to combat this crime and to lessen the misery of the victim are also suggested.

Gold nanotriangles: scale up and X-ray radiosensitization effects in mice

In the past decade, there has been considerable interest in radiosensitization using gold nanoparticles that accumulate specifically in cancerous tissue while sparing normal tissues. Despite this interest, it remains unclear which nanoparticle morphologies, cellular uptake, or cytoplasmic distribution elicit optimal radiosensitization. We introduce gold nanotriangles (AuNTs) as a possible X-ray radiotherapy sensitizer. In this study, we first explored a large-scale synthetic method for the production of high quality monodisperse AuNTs. Second, we conducted in vitro and in vivo experiments to evaluate the effect of PEGylated AuNTs (pAuNTs) on cellular uptake, cytotoxicity, bio-distribution, and radiosensitization on radiation-resistant human Glioblastoma Multiforme (GBM) cells. Our results suggest that the new scale up synthesis methodology consistently produced high quality AuNTs and pAuNTs which had nonspecific cellular uptake without any obvious cytotoxicity and exhibited excellent radiosensitization.

Wall Mechanical Properties and Hemodynamics of Unruptured Intracranial Aneurysms

BACKGROUND AND PURPOSE

Aneurysm progression and rupture is thought to be governed by progressive degradation and weakening of the wall in response to abnormal hemodynamics. Our goal was to investigate the relationship between the intra-aneurysmal hemodynamic conditions and wall mechanical properties in human aneurysms.

MATERIALS AND METHODS

A total of 8 unruptured aneurysms were analyzed. Computational fluid dynamics models were constructed from preoperative 3D rotational angiography images. The aneurysms were clipped, and the domes were resected and mechanically tested to failure with a uniaxial testing system under multiphoton microscopy. Linear regression analysis was performed to explore possible correlations between hemodynamic quantities and the failure characteristics and stiffness of the wall.

RESULTS

The ultimate strain was correlated negatively to aneurysm inflow rate (P = .021), mean velocity (P = .025), and mean wall shear stress (P = .039). It was also correlated negatively to inflow concentration, oscillatory shear index, and measures of the complexity and instability of the flow; however, these trends did not reach statistical significance. The wall stiffness at high strains was correlated positively to inflow rate (P = .014), mean velocity (P = .008), inflow concentration (P = .04), flow instability (P = .006), flow complexity (P = .019), wall shear stress (P = .002), and oscillatory shear index (P = .004).

CONCLUSIONS

In a study of 8 unruptured intracranial aneurysms, ultimate strain was correlated negatively with aneurysm inflow rate, mean velocity, and mean wall shear stress. Wall stiffness was correlated positively with aneurysm inflow rate, mean velocity, wall shear stress, flow complexity and stability, and oscillatory shear index. These trends and the impact of hemodynamics on wall structure and mechanical properties should be investigated further in larger studies.

Tissue biomarkers for prostate cancer radiation therapy

Prostate cancer is the most common cancer and second leading cause of cancer deaths among men in the United States. Most men have localized disease diagnosed following an elevated serum prostate specific antigen test for cancer screening purposes. Standard treatment options consist of surgery or definitive radiation therapy directed by clinical factors that are organized into risk stratification groups. Current clinical risk stratification systems are still insufficient to differentiate lethal from indolent disease. Similarly, a subset of men in poor risk groups need to be identified for more aggressive treatment and enrollment into clinical trials. Furthermore, these clinical tools are very limited in revealing information about the biologic pathways driving these different disease phenotypes and do not offer insights for novel treatments which are needed in men with poor-risk disease. We believe molecular biomarkers may serve to bridge these inadequacies of traditional clinical factors opening the door for personalized treatment approaches that would allow tailoring of treatment options to maximize therapeutic outcome. We review the current state of prognostic and predictive tissue-based molecular biomarkers which can be used to direct localized prostate cancer treatment decisions, specifically those implicated with definitive and salvage radiation therapy.

The interplay between inflammation and oxidative stress in carcinogenesis

Emerging data suggest that primary dysfunction in the tumor microenvironment is crucial for carcinogenesis. These recent findings make a compelling case for targeting the milieu for cancer chemoprevention as well as therapy. The stroma is an integral part of its physiology, and functionally, one cannot totally dissociate the tumor surrounding from the tumor cells. A thorough understanding of the tumor and stroma will aid us in developing new treatment targets. In this review, we shed light at the key aspects of the carcinogenic process and how oxidative stress and inflammation contribute to this process. We dissect the connection between metastasis and oxidative stress and focus on the key players in the tumor microenvironment that leads to inflammation, oxidative stress and DNA damage. Moreover, we consider the role of inflammation in disease, specifically cancer and metastasis. Finally, we discuss the potential applications in prognosis and cancer treatment.

Outcomes of preterm infants <29 weeks gestation over 10-year period in Canada: a cause for concern?

OBJECTIVE

To compare risk-adjusted changes in outcomes of preterm infants <29 weeks gestation born in 1996 to 1997 with those born in 2006 to 2007.

STUDY DESIGN

Observational retrospective comparison of data from 15 units that participated in the Canadian Neonatal Network during 1996 to 1997 and 2006 to 2007 was performed. Rates of mortality and common neonatal morbidities were compared after adjustment for confounders.

RESULT

Data on 1897 infants in 1996 to 1997 and 1866 infants in 2006 to 2007 were analyzed. A higher proportion of patients in the later cohort received antenatal steroids and had lower acuity of illness on admission. Unadjusted analyses revealed reduction in mortality (unadjusted odds ratio (UAOR): 0.83, 95% confidence interval (CI): 0.63, 0.98), severe retinopathy (UAOR: 0.68, 95% CI: 0.50 to 0.92), but increase in bronchopulmonary dysplasia (UAOR: 1.61, 95% CI: 1.39 to 1.86) and patent ductus arteriosus (UAOR: 1.22, 95% CI: 1.07 to 1.39). Adjusted analyses revealed increases in the later cohort for bronchopulmonary dysplasia (adjusted odds ratio (AOR): 1.88, 95% CI: 1.60 to 2.20) and severe neurological injury (AOR: 1.49, 95% CI: 1.22 to 1.80). However, the ascertainment methods for neurological findings and ductus arteriosus differed between the two time periods.

CONCLUSION

Improvements in prenatal care has resulted in improvement in the quality of care, as reflected by reduced severity of illness and mortality. However, after adjustment of prenatal factors, no improvement in any of the outcomes was observed and on the contrary bronchopulmonary dysplasia increased. There is need for identification and application of postnatal strategies to improve outcomes of extreme preterm infants.

Targeting DNA damage and repair: embracing the pharmacological era for successful cancer therapy

DNA is under constant assault from genotoxic agents which creates different kinds of DNA damage. The precise replication of the genome and the continuous surveillance of its integrity are critical for survival and the avoidance of carcinogenesis. Cells have evolved an arsenal of repair pathways and cell cycle checkpoints to detect and repair DNA damage. When repair fails, typically cell cycle progression is halted and apoptosis is initiated. Here, we review the different sources and types of DNA damage including DNA replication stress and oxidative stress, the repair pathways that cells utilize to repair damaged DNA, and discuss their biological significance, especially with reference to cancer induction and cancer therapy. We also describe the main methodologies currently used for the detection of DNA damage with their strengths and limitations. We conclude with an outline as to how this information can be used to identify novel pharmacological targets for DNA repair pathways or enhancers of DNA damage to develop improved treatment strategies that will benefit cancer patients.

Radiosensitization of MYC-overexpressing prostate cancer cells by statins

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Background: Studies have shown a link between HMG-CoA reductase inhibitors (statins) and decreased cancer risk in various cancers including prostate cancer. Recent clinical studies have shown improved outcome for men on statin therapy receiving definitive radiation therapy compared to radiation therapy alone for prostate cancer. The oncogene Ras can be inhibited by statin treatment and in turn also result in targeted downregulation of Myc. Inactivation of Myc has been shown to induce tumor regression in transgenic mouse models of different cancers.

Methods: Utilizing both in vitro and in vivo models, we studied in MYC over-expressing prostate cancer cells statin induced cytotoxicity and radiosensitization. We studied the effect of statin treatment with and without radiation treatment on in vitro cell death and clonogenic survival and correlated effects to levels of MYC and phospho-MYC. We constructed mutant cell lines to specifically examine the MYC-dependent effects of statins on prostate cancer cell cytotoxicity and radiosensitization. We performed similar studies in vivo using subcutaneous tumor grafts.

Results: Statin treatment alone of prostate cancer cells resulted in increased cell death and decreased clonegenic survival. Statin treatment further sensitized prostate cancer cells to ionizing radiation as shown through colony formation assays. These cellular effects were associated with decreased levels of active MYC as confirmed by western and phospho-western analysis. Statin-induced cell death and decreased MYC levels could be rescued with the HMG-CoA bypass product mevalonate. Finally, flank tumor graft experiments demonstrated the ability of statins and radiation to delay tumor growth in vivo.

Conclusions: Our preliminary data have implicated MYC as a potential critical target for the cytotoxic effects of statins on prostate cancer cells. The prevalence of MYC overexpression in human prostate cancers is as high as 80%. Thus the ability of statins to radiosensitize MYC overexpressing prostate cancer cells may provide a mechanistic explanation to the improved outcomes for men taking statins while on radiation therapy and now may afford us a molecular biomarker to examine this phenomenon in the clinic.

No significant financial relationships to disclose.