2. Radiation Therapy
• The treatment of benign and malignant
diseases with ionizing radiation
• GOAL: to deliver a precisely measured
dose of irradiation to a defined tumor
volume with minimal damage to
surrounding healthy tissue
3. • This results in:
– eradication of tumor
– high quality of life
– prolongation of survival
– allows for effective palliation or
prevention of symptoms of
cancer, with minimal morbidity
• Over the past 20 years, advances have
been made in imaging and treatment
delivery, allowing for improved targeting
and increased sparing of normal tissues
5. • Different irradiation doses are
required for tumor
control, depending on tumor type
and the number of cells present
• Varying radiation doses can be
delivered to specific portions of the
tumor (periphery versus central
portion) or to the tumor bed in cases
in which all gross tumor has been
surgically removed
6. • Treatment portals must adequately
cover all treatment volumes plus a
margin
8. • Curative
– when there is a probability of long-
term survival after adequate
therapy
– some adverse effects of
therapy, although
undesirable, may be acceptable
9. • Palliative
– when there is no hope of survival
for extended periods, radiation
can be used to palliate
symptoms, primarily pain
– Lower doses of irradiation (75% to
80% of curative dose) can control
the tumor and palliate symptoms
without excessive toxicity
11. • A boost is the additional dose
administered through small portals to
residual disease
– It is given to obtain the same probability
of control as for subclinical aggregates
• Radiosensitivity is the degree and
speed of response
– This measure of susceptibility of cells to
injury or death by radiation depends on
cancer diagnosis and its inherent
biologic activity
12. – It is directly related to reproductive
capability of the cell
• Role of oxygen
– Oxygen must be present at the time of
radiation's maximal killing effect
– Poor circulation with resultant hypoxia
can reduce cellular radiosensitivity
– Giving multiple, daily doses allows
reoxygenation and enhances
radiosensitivity
– The dose should allow for repair of
normal tissues
13. • Cellular response can be modified
by:
– changing the dose rate
– manipulating the process of cell repair
– recruiting cells into replication cycle
– using hyperthermia (above 104 F [40
C])
• Radioresistance
– The lack of tumor response to radiation
because of tumor characteristics (slow-
growing tumor, less responsive), tumor
cell proliferation, and circulation
14. – Radiation is most effective during the
mitotic stage of the cell cycle
• Radioresistant tumors
– Many tumors are resistant to
radiation, such as squamous
cell, ovarian, soft tissue sarcoma, and
gliomas
– Many other tumors can become
resistant after a period of time
– Normal radioresistant tissues include
mature
bone, cartilage, liver, thyroid, muscle, br
16. • There are generally two types of
radiation and several techniques in
which radiation is delivered
• The two types of radiation include
external (or teletherapy) and internal
(or brachytherapy)
17. • Teletherapy
– most commonly delivered through a
linear accelerator machine
• Brachytherapy
– uses seeds, wires, or catheters to
deliver radiation directly to or adjacent
to the tumor bed
– This technique delivers less radiation to
adjacent normal tissue, but requires
direct tumor access
