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. , . Nuclear
Medicine and PET/CT: Technology and Techniques. 7thEd. 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.
