Overview of Radiation Theraphy Flashcards
- use of high level radiation (megavoltage) to destroy cancer cells
Radiation Therapy
- has its greatest effects on tissues that divide rapidly such as cancer cells. it destroys the cell ability to divide or multiply (law of bergonie and tribondeau)
Radiation Therapy
with each treatment more of the cancer cells and the tumor..
shrinks
reason for side effects of radiotheraphy
damage to healthy cells
curative also called
radical radiotherapy
in this treatment, rad dose is given so high that some side effects are unavoidable
curative (radical radiotherapy)
can be used as treatment alone or be given in combination with chemotherapy, surgery and other forms of treatment
radiation
considered emergency cases in radiotherapy
- bone metastasis with spinal cord compression
- cases with profuse bleeding (i.e. cervical cancer)
- mass obstructing the lungs
- brain metastasis
aim of radiotherapy
to deliver a PRECISE measured dose of radiation to DEFINED tumor volume
members of radiotherapy team
- radiation oncologist
- medical physicist/dosimetrist
- radiotherapy technologist
immobilization devices:
- alpha cradle
- thermoplastic mask
2 forms of radiation therapy
- external radiation therapy (teletherapy)
2. internal radiation therapy (brachytherapy)
goal of radiotherapy
- curative (cure from cancer)
- pallative (relieve symptoms)
in this treatment, doses of rad. are given to a carefully defined area through a machine that directs the high-energy rays or particles from outside the body at the cancer and the normal tissues surrounding it.
external radiation therapy (teletherapy)
___ places the source of high-energy rays inside the body, as close as possible to the cancer cells.
internal radiation therapy (brachytherapy)
this delivers very intense radiation to a small area of the body and limits the dose to normal tissue
internal radiation therapy (brachytherapy)
this is used typically include radium, cesium, iodine, and phosphorus, and they are implanted for only a short time or left in place permanently.
radioactive substances
unit of absorbed dose
Gray (Gy)
will assure the delivery of the exact prescribed dose.
detailed measurement
dose of radiation determination:
- size tumor
- extent tumor
- grade of tumor
- response to radiation
the largest amount of dose that can be accepted without the production of injurious symptoms
tolerance dose
factors affecting tolerance dose
- dose rate
- volume irradiated
- sensitivity of the tissues
- amount of recovery, w/c can take place bet. fractions
the dose that can be tolerated by normal tissue in the treatment zone varies with the total time over w/c the dose is given.
dose rate
the higher the dose rate
the greater the late damage potential
the smaller volume to be treated
the higher the total dose which may be tolerated
increase the chance of radiation damage to cells.
good oxygenation
many of the cells within a large cell mass where there is no organized blood supply is
hypoxic
less oxygenated and therefore less sensitive to radiation
tumor cells
if the number of cells doubles within the time interval bet. two fraction, treatment may __ (cell doubling time)
fail
a planned series of fractions of total dose.
fractionation
this allows recovery of normal cells while depleting the number of surviving tumor cells
fractionation
dose prescribed: 6040 cGy
total treatment days: 33 days
breast
dose prescribed: 5040 cGy
total treatment days: 28 days
gyne (cervic, uterus, ovary)
dose prescribed: 3000 cGy
total treatment days: 10 days
whole brain & bone mets
would lead to an overall treatment period w/c is significantly longer than intended
missed treatments
at a survival disadvantage if treatment duration is lengthened
some patients (head & neck)
the cell kinetic change and there is a potential for very rapid repopulation
once some cells are killed
- once-daily doses given 5 days per week
- recovery period at the weekend
conventional fractionated course
once, twice or three times weekly treatments with higher dose of radiation.
less than 5 fractions per week
potential for late radiation damage increase with fraction doses.
less than 5 fractions per week
reasons for lowered fractionation regimes
- fewer visits and less traveling time for patients
- shortage of treatment machine
- clinical indication (for every sensitive tumor - skin lymphomas)
shortening the treatment course duration but giving a high number of small fractions.
hyperfractionation
given to tumors with a fast cell-doubling time such as 5 days
hyperfractionation
may result in more acute injury but an unchanged potential for late damage
hyperfractionation
target volume is separated into 3 distinct regions:
- gross tumor volume (GTV)
- clinical target volume (CTV)
- planning target volume (PTV)
denotes the demonstrable tumor
gross tumor volumegross tumor volume
denotes the GTV and subclinical disease (region to account for uncertainties in microscopic tumor spread)
clinical target volume
denotes the CTV and includes margins for geometric/postion uncertainties. Usually 1.5cm physical margin are set around the CTV.
planning target volume
is the volume of tissue enclosed by an isodose surface, selected and specified by the radiation oncologists as being appropriate to achieve the purpose of treatment.
treated volume
is always larger than the PTV and usually has a simpler shape.
treated volume
is the volume of tissue that receives a dose considered significant in relation to tissue tolerance.
irradiated volume
overview of treatment process
- initial consultation with Rad Onco
- informed consent process (Rad Onco)
- simulation stage (RadioTherapy tech)
- - determine patient position
- - acquire x-ra or ct scan
- - tatto process
- - documentation - planning stage (Rad Onco & Med Phy)
it is necessary to make the marks permanent since this will be the basis for body alignment during the treatment
Tattoo process
simulation worksheet (filled out by the Radiation Therapist) is also called as
simulation form
data would be needed by the Medical Physicist for the planning stage
simulation worksheet or simulation form
he will draw/contour the treatment fields on the acquired images as well as dose prescription
radiation oncologist
he would do a lot of calculations considering the tolerance dose of the part to be treated as well as its surrounding tissues
Medical Physicist
he would have __ working days to complete everything for the patient to start the treatment
Medical Physicist
3-5 days
can hurt normal cells, causing side effects.
high doses of radiation
is usually temporary and will disappear gradually when therapy is complete
side effects
generally limited to the region of the body being treated
side effects
skin becomes painful, red, itchy, and blistered
radiation dermatitis
rad. can affect the membranes of the mouth and/or gastrointestinal tract, causing discomfort while swallowing
nutritional problems
most common side effects of radiation therapy
fatigue or weakness
