Thursday, March 11, 2021

Radiation Dose and Contrast Agent Reduction In Abdominal CT Examination with Low Tube Voltage

A Phantom Study

Thinh Xuan Tran, MD.

Objectives

The purpose of study was to investigate image quality and radiation dose of multi-detector computed tomography (MDCT) examination on an abdominal phantom using a standard protocol and a low tube voltage (kV) protocol with the low contrast agent dose at different tube current-time products (mAs).

Materials and Methods

The cylindrical phantom of a 10 cm thick and 30 cm diameter was done from the minced pork roll and used as the abdominal CT scan. The center of the phantom was a contrast enhanced injection syringe of the 40 mm diameter as a target object. The inside of the phantom contained a smaller cylinder module with the 8 cm diameter of low HU tissue equivalent background material.

The contrast-enhanced phantom CT examination was performed by using with different tube voltage protocols of 120 kV and 80 kV at different tube currents 250-650 mAs. The volume CT dose index (CTDIvol), CT number, image noise, contrast to noise ratio (CNR) and dose length product (DLP) were recorded. Image quality is semiquantitatively assessed by two blinded radiologists using a five-point scale. The differences between mean values of CNR, image noise and scores of LCD (low contrast detectability) obtained at 120 kV with 300 mAs and 80 kV with 250-650 mAs were compared respectively. The SPSS version 18 software was used to analyze all statistical data. A statistically significant difference when P value < 0.05 was considered.

Results

The radiation dose was reduced by 38% at 80 kV and 650 mAs. The values obtained at 80 kV and 250-650 mAs, compared to the values obtained with 120 kV at 300 mAs. The iodine CT number with 80 kV at 650 mAs was significantly higher (P=0.006) while the noise value obtained at 80 kV with 650 mAs was higher than that obtained at 120 kV with 300 mAs but no significantly difference (P=0.052). For quality image, there were no significantly differences in mean values of CNR and mean scores of LCD. The CNRs obtained between two protocols 120 kV at 300 mAs and 80 kV at 650 mAs were 69.37 and 65.13 (P=0.091). The mean scores of LCD assigned at 120 kV with 300 mAs and 80kV with 450-650 mAs (P>0.05).

Conclusions

The radiation dose can be significantly reduced by up to 38% at low tube voltage protocol of 80kV and with reduced contrast agent dose of 16% while maintaining compatible image quality without degradation of CNR and LCD. The study has shown the greatest benefits in children, small sized adults and contrast CT examinations.

Keywords: computed tomography, radiation dose, low tube voltage, low contrast agent dose and image quality.

Sunday, October 29, 2017

Medical book and UEMLE steps 1,2,3 examination

https://www.facebook.com/notes/717918348321821/?pnref=story

Tuesday, March 21, 2017

Volumetric modulated arc therapy

Introduction

Volumetric modulated arc therapy (VMAT) was first introduced in 2007 and described as a novel radiation technology designed to deliver treatment quickly and accurately. If appropriate for the treatment of cancer, it can reduce the number of patient visits and greatly improving recovery time. Volumetric Modulated Arc Therapy (VMAT) can be used for treating various types of cancer as prostate, head and neck tumors, as well as a range of other cancerous tumors (1).

All of them used data of Varian accelerators with its implementation of VMAT called RapidArc® (Varian Medical Systems, Inc., USA) and either prototypes of planning or optimizing systems or Varian’s Eclipse™. The ability to generate complex dose distributions is highly dependent on the optimization algorithm and capabilities of the delivery system used for treatment (2) [16, 17].

Image courtesy of Varian Medical Systems (3)

The main advantages of Volumetric Modulated Arc Therapy (VMAT) are precision and speed. Volumetric Modulated Arc Therapy (VMAT) focuses the radiation on the tumor while protecting healthy tissues (1). Each Volumetric Modulated Arc Therapy (VMAT) may reduce treatment times to as little as two minutes (3). Faster treatments improve the accuracy of radiation delivery, in addition to improving patient convenience and quality of life.

Volumetric Modulated Arc Therapy (VMAT) uses photons (W-rays) generated by a medical linear accelerator. The VMAT technique allows beam-on during a full gantry rotation of 360° with simultaneous modulation of the multileaf collimator (MLC) and a variation of gantry rotation speed as well as dose rate (4). Very small beams with varying intensities are aimed at a tumor and then rotated 360 degrees around the patient (4). This results in attacking the target in a complete 3D (three-dimensional) manner, radiation therapist will be able to see the tumour during patient´s treatment and target it directly.

Volumetric Modulated Arc Therapy (VMAT) Treatment involves three basic steps: diagnosis, treatment planning, and treatment delivery. As part of the diagnosis, the medical team generates 3D diagnostic images (usually CT and/or PET) of the patient’s anatomy and then uses these images to specify the dose of radiation needed to treat the tumor (3). This article aims to discuss the current use of VMAT techniques in clinical process of radiation therapy that can be divided into as simulation and patient data acquisition, treatment planning and treatment delivery.

Simulation and patient data acquisition

The process of virtual simulation and data acquisition can be summarized in the following steps:

• Determination of the patient’s treatment position.

• Setting references on the patient’s skin.

• Acquisition of CT data and transfer to the virtual simulation workstation.

• Volume definition, which consists of delineation of target volumes (tumors) and of healthy surrounding structures (normal tissues and organs at risk).

• Determination of the treatment isocenter with respect to the references.

• Choice of plan parameters such as number of fields, energy, field size and orientation.

Modern treatment planning systems (TPSs) incorporate packages for virtual simulation. In consequence, it is possible to transfer the CT data to the TPS and carry out the volume definition, virtual simulation and treatment planning in a single integrated system. CT simulators offer important advantages over conventional simulators, allowing for complex and accurate treatment planning based on 3D data sets.
References

M Teoh, CH Clark, K Wood, S Whitak, et.al. Volumetric modulated arc therapy: a review of current literature and clinical use in practice. Br J Radiol. 2011 Nov; 84(1007): 967–996.

Palma DA, Verbakel WF, Otto K, Senan S: New developments in arc radiation therapy: a review. Cancer Treat Rev 2010, 36: 393-399

Cleveland Clinic. Volumetric modulated arc therapy. Mars, 2017. http://my.clevelandclinic.org/health/articles/volumetric-modulated-arc-therapy

Wolff D, Stieler F, Welzel G, Lorenz F, Abo-Madyan Y, et al. Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer. Radiother Oncol 2009, 93: 226-33.

Sunday, January 24, 2016

Cod liver oil intake and the risk of hypertensive disorder in pregnancy

A science paper is published at VJMP (Vietnam Journal of Medicine and Pharmacy) in 2015

http://vjmp.vn/noi-dung-tap-chi-3/fish-consumption-and-cod-liver-oil-intake-withthe-risk-of-hypertensive-disorders-in-pregnancy-337.htm

Fish consumption and cod liver oil intake withthe risk of hypertensive disorders in pregnancy

Thinh Tran Xuan¹, Bryndis E. Birgisdottir¹, Thorhallur I. Halldorsson¹

Inga Thorsdottir¹, Reynir T. Geirsson²

¹Unit for Nutrition Research, Landspitali National University Hospital & Faculty of Human Nutrition, University of Iceland, 101 Reykjavik, Iceland.

²Department of Obsterics and Gynecology, Landspitali National University Hospital & Faculty of Medicine, University of Iceland, 101 Reykjavik, Iceland

ABSTRACT

Gestational hypertension and preeclampsia are common hypertensive disorders in pregnancy, associated with substantial morbidity and mortality for both mother and infants. A number of dietary factors have been related to hypertensive disorders in pregnancy. Fish consumption, fish liver oil supplements during pregnancy might be associated with gestational hypertension or preeclampsia.

Objectives

To examine the association between fish consumption and intake of cod liver oil with hypertensive disorders in pregnancy.

Methods

This retrospective cohort study was conducted at Landspitali National University Hospital, Reykjavik, Iceland in 1998. A total of 491 pregnant Icelandic women who gave birth at Landspitali National University Hospital in Reykjavik, aged 20-40, of normal weight before pregnancy were randomly selected from maternal records. Information on frequency of fish and cod liver oil consumption during pregnancy was collected from maternal records. We used gestational hypertension is defined as systolic blood pressure (SBP) ≥ 140 mmHg and/or a diastolic blood pressure (DBP) ≥ 90 mmHg as a primary outcome measure. Systolic and diastolic, isolated systolic, and isolated diastolic hypertension were used as secondary outcome measures.

Results

The prevalence of gestational hypertension and preeclampsia was 21% and 3%, respectively. Fish consumption was not associated with hypertensive disorders in pregnancy. Intake of fish liver oil was, however, positively associated with combined gestational hypertension (SBP) ≥ 140 and (DBP) ≥ 90. Using this definition women consuming one table spoon (≈ 9g) a day or more had an adjusted odds ratio of 6.3 (95% confidence interval: 2.2, 17.9) of having pregnancy hypertension compared to those with no intake. This association appeared to be driven by a relative shift from isolated diastolic hypertension to combined systolic and diastolic hypertension as overall fish liver oil was not associated with hypertension defined as (SBP) ≥ 140 and/or (DBP) ≥ 90.

Conclusions

No association was found between fish consumption and hypertensive disorders in pregnancy. Our results suggest that high (≈ 9 g/day) intake of fish liver oil may affect the severity of gestational hypertension. These findings are in line with previous reports from Iceland were high consumption of fish liver oil has been associated with hypertensive disorders in pregnancy.

Keywords

Fish, fish liver oil, n-3 PUFA, gestational hypertension, preeclampsia and hypertensive disorders in pregnancy.

Sunday, February 15, 2015

TheraSphere® (Yttrium-90) on Hepatocellular Carcinoma (HCC)

Introduction

TheraSphere® is Yttrium-90 microspheres radioembolization useful for liver cancer treatment and used generally to treat patients with hepatocellular carcinoma (HCC) and liver metastases (1). In this paper, we become to discuss it, how to activate Yttrium-90 on the hepatocellular carcinoma, information of nuclide, radiation and the half-life. We also will analyze physiological features of Yttrium-90 on hepatocellular carcinoma cells and its side effects on the patient.

How to activate Yttrium-90 on hepatocellular carcinoma

TheraSphere (Yttrium-90 microspheres) are radioactive particles as a form of radiation treatment for unresectable HCC. TheraSphere is supplied in 0.5 mL of sterile, pyrogen-free water contained in a 0.3-mL V-bottom vial secured within a 12-mm clear acrylic vial shield. Yttrium-90 microspheres are administered by intra-arterial hepatic injection preferentially flow to tumor (Figure 1.), to patients with unresectable HCC who can have appropriately positioned hepatic arterial catheters (2).

Figure 1. Yttrium-90 microspheres are injected into the hepatic arteries preferentially flow to tumor (5).

The Yttrium-90 microspheres are trapped in tumors at the precapillary alveolar level. Patients can be released after infusion of the microspheres, since the Yttrium-90 decays only by beta-emission. Beta radiation is delivered internally to tumor at site of active growth. After administration, the bremsstrahlung radiation (electromagnetic radiation) is produced from the beta minus-interaction in the body, can be imaged and used to determine qualitative distribution in the liver (1).

A suspension of appropriately calibrated Yttrium-90 microspheres injected via the hepatic artery preferentially lodge in the peritumoral vessels, a process termed embolization, by which tumors are deprived of their nutrient arterial supply (3).

Information of nuclide, radiation and half-life

TheraSphere consists of nonbiodegradable glass microspheres (mean diameter of 25 μm) with yttrium-90 as an integral constituent of the glass. Yttrium-90 have the element´s atomic number (Z=39) and number of neutrons (N=51) and the atomic mass (A=90) (1). Yttrium-90 is a pure beta emitted radionuclide, produced by neutron and decays to stable zirconium-90 with a physical half-life of 64.1 hours (2.67 days). The average energy of beta emission from the yttrium-90 is 0.9367 MeV, with a mean tissue penetration of 2.5 mm and a maximum of 10 mm (2).

One gigabecquerel (1GBq or 27mCi) delivers a total absorbed radiation dose of 50Gy/kg of tissue or per kilogram of targeted liver tissue provides a dose of 50Gy. In therapeutic use, in which the isotope decays to infinity, 94% of the radiation is delivered in 11 days (3).

Physiological Features of Yttrium-90 Microsphere

TheraSphere (MDS Nordion, Ottawa, Ontario, Canada) consists of millions of microscopic, radioactive glass Yttrium-90 microspheres (20–30 micrometers in diameter) with yttrium-90 as an integral constituent of the glass (3). The Yttrium-90 microspheres are not biodegradable; they decay only by a pure beta-emission, produced by neutron bombardment of Yttrium-90 in a reactor with a mean tissue penetration of 2.5 mm (2).

The Yttrium-90 microsphere is a high energy beta-emitter, would create a zone of radiation exposure confined to the vicinity of the tumor while maintaining nontumorous hepatic parenchymal exposure to tolerable levels. This forms the premise for radioembolization, also known as selective internal radiation therapy or microsphere brachytherapy (3). In clinical practice, millions of microspheres, measuring 30 micrometers in diameter incorporating yttrium-90, are injected via an intra-arterial catheter to the hepatic arterial supply of the tumor (3).

In patients with non-compromised liver function, the liver can tolerate 30 to 35Gy (1Gy represents the energy absorbed from ionizing radiation equal to 1 J/kg of tissue) when it is presented via uniform radiation fields with conventional fractionation (2).

Characteristics of yttrium-90 Microspheres are shown in table 1. as following (3, 4).

Table 1. Characteristics of Yttrium-90 Microsphere
Parameter	Glass
Trace name	ThereSphere® (MDS, Nordion, Canada)
Radioactive form	⁹⁰Y (Yttrium-90)
Diameter	20-30 μm
Specific gravity	3.6 g/dL
Activity per particle	2500 Bq
Average number of microspheres per administered activity	1.2-8 million
Material	Glass with Yttrium-90 in matrix
Liver tolerance radiation dose	30-35 Gy
FDA Approved	HCC
Recommended dose for liver tumor	2.0-3.0 GBq

Yttrium-90 microspheres can be delivered in a local as segmental or sub-segmental, regional (lobar via the left or right hepatic artery), or whole-liver (via proper hepatic artery) manner, resulting in high radiation doses to arterial-fed tumors while sparing the liver parenchyma, which receives most of its blood supply from the portal vein. This method of radiation treatment provides a safety margin by distributing the radiation in a partial liver volume while treating tumors with tumoricidal doses of radiation. Yttrium-90 microsphere injection provides millions of scattered point sources of radioactivity, as opposed to the uniform fields of external beam radiotherapy. This difference in field properties for a given measure of radiation absorbed dose results in different biological effects (2).

The Side effects

Radioembolization is not without complications; it may lead to post-radioembolization syndrome which includes fatigue, nausea, vomiting, anorexia, fever, abdominal pain and cachexia. More serious adverse events include radiation induced liver toxicity, vascular injury when introducing the catheter, radiation pneumonitis from microspheres shunting around the liver and into the lungs, and gastrointestinal tract ulceration (4).

Absolute contraindications for the use of ⁹⁰Y microspheres include pretreatment with ^99mTc macroaggregated albumin scan demonstrating significant hepatopulmonary shunts, and inability to prevent deposition of the microspheres to the gastrointestinal tract with modern catheter techniques (4).

References

1. Paul E. Christian, Kristen M. Waterstram. Nuclear Medicine and PET/CT: Technology and Techniques. 7^thEd. Hardcover – March 18, 2011.

2. Geschwind JF, Salem R, Carr BI, et al. Yttrium-90 Microspheres for the Treatment of Hepatocellular Carcinoma. Gastroenterology. 2004 Nov;127(5 Suppl 1):194-205.

3. Murthy R, Kamat P, Nuñez R, Salem R. Radioembolization of Yttrium-90 Microspheres for Hepatic Malignancy. Semin Intervent Radiol. 2008 Mar;25(1):48-57.

4. Saad M Ibrahim, Robert J Lewandowski, Kent T Sato, et al. Radioembolization for the treatment of unresectable hepatocellular carcinoma: A clinical review. World J Gastroenterol. Mar 21, 2008; 14(11): 1664-1669.

5. Figure is taken at. http://zoominmedical.com/cancer-tumor-diagram/