1 Radiation Therapy Flashcards
Sulfhydryl components
scavenge free radicals
Administering a dose in fractions with adequate time between applications allows
the repair of sublethal damage
and the repopulation of tissue cells.
Tumors often have poorly developed
blood vessels intermittent blood flow
Dose range for solid tumor cure
60 to 80 Gy,
Preventive (adjuvant) doses
45–60 Gy in 1.8–2 Gy fractions (for breast, head, and neck cancers.)
In North America, Australia, and Europe, the typical fractionation schedule
for adults is 1.8 to 2 Gy per day, five days a week, For children, a typical fraction size may be 1.5 to 1.8 Gy per day
External beam radiation therapy fails
to eradicate the primary tumor in 1 out of 3 patients
E of protons used in proton therapy
190MeV with range 25cm (Bragg-Peak)
the most common form of radiotherapy
External beam radiotherapy or teletherapy
Kilovoltage (“superficial”) X-rays
treating skin cancer and
superficial structures. 50 to 200 kV
Megavoltage (“deep”) X-rays
treat deep-seated tumors
(e.g. bladder, bowel, prostate, lung, or brain). 1 to 25 MV. Most common in therapy and produced in linac and Co units (Co-60 teletherapy machine)
diagnostic X-rays
20 to 150 kV
orthovoltage X-rays
200 to 500 kV
supervoltage X-rays
500 to 1000 kV
Intensity Modulated Radiation Therapy
intensity modulation is achieved by moving the leaves in the MLC(Multi-Leaf Collimator) during the course of treatment, thereby delivering a radiation field with a non-uniform (i.e. modulated) intensity in beamlets
3D Conformal Radiation Therapy
utilizes sophisticated computer technologies such as CT scans and MRI images to view tumors in three dimensions (3D)-width, height and depth. With superior tumor imaging, patient treatment plans can be created with greater precision.
Neutron Capture Therapy
the patient is injected with a tumor localizing drug containing a non-radioactive isotope that has a high cross section for slow neutron capture.;patient is radiated with epithermal neutrons, which after losing energy as they penetrate tissue, are
absorbed by the injected isotope, which then emits high-energy charged particles that deposit their kinetic energy locally,
thereby resulting in the killing of cancer cells.
Isotopes Used in Neutron Capture Therapy
boron-10 only - BNCT
The BNCT Reaction
10B+n=7Li+4He+Gamma (0.477 MEv)
B agents used clinically
Sodium borocaptate (BSH); Boronophenylalanine (BPA)
BNCT Dose Components
1H(n,gamma)2H, 14N(n,p)14C; fast neutrons from recoil. D=CFD(boron)+RBE(N)D(N)+RBE(R)D(R)+RBE(gamma)D(gamma)
Brachytherapy or Endocurietherapy
Implanting radioactive sources into or close to tumor 50-70 Gy in 5-9
days is common
common for temporary implants in Interstitial therapy
Iridium-192
iodine- 125 in Interstitial therapy
common for permanent implants total prescribed dose of 160 Gy, with 80 Gy delivered in the first 60 days.most effective in slow-growing tumors
Radio-Immuno Therapy
administration of a radionuclide conjugated
to a monoclonal antibody for therapeutic intent
Radioimmunotherapy Limitations
Bone marrow toxicity, poor tumor penetration, poor tumor antigen/receptor expression: Iodine-131, alpha emitters: Ac-225(7MEV alpha, milked from 229 Th cow), Th-227 (6MEV alpha), U-230, At-211
cancer Societal Cost
106b
cancer survival rate
40%
Radiograph- x-ray
Intensity of diagnostic x-rays (10 - 150
keV) attenuated in body
Computed Tomography
Spatial distribution of attenuation coefficients in body
Magnetic Resonance Imaging:
Spatial distribution of proton density in body
CT or CAT Scan
shows organs of interest at selected levels
of the body. They are visual equivalent of bloodless slices of anatomy, with each scan being a single slice. source of the x-ray beam encircles or rotate around the patient. X-rays passing through the body are
detected by an array of detectors. Information from the detectors is computer processed and then displayed as an image on a video screen.
CT vs MRI
MRI has no radiation, and good for soft tissue difference recognition. A longer time than CT and more expensive.
Technetium-99m
half life of 6 hours, gamma emitter from Mo cow. Scan is done 2-3 h after injection, takes about 30 min
SPECT
uses radioactive tracers and scanner can give information about blood flow to tissues and chemical reactions (metabolism) in the body. Antibodies can be labeled with radioactive tracers and attach to a tumor.
Positron Annihilation
β+ + β-=2γ with E= 2*0.511 MEv
PET tracer for Cerebral blood flow
Positron emission tomography. 15O in water tracer
FDG
Most used PET tracer. Tracer for 18F for glucose metabolism. Taken up by tumors.
CT and SPECT
CT gives an image of an anatomical structure while SPECT gives info about the metabolism and functions of organs.
SPECT
Single-photon emission computed tomography
Dual-Modality Imaging
Structural Imaging (CT, MRI) + Functional Imaging (SPECT, PET)
