Chapter 11
Oncology: Nursing management in cancer care
239
for the periphery of the tumour to be reoxygenated repeatedly
because tumours shrink from the outside inward. This process
increases the radiosensitivity of the tumour, thereby increas-
ing tumour cell death (Yarbro, Hansen-Frogge & Goodman,
2005).
External radiation
External beam radiation therapy (EBRT) is the most commonly
used form of radiation therapy. The energy utilised in EBRT is
either generated from a linear accelerator or from a unit that
generates energy directly from a core source of radioactive
material such as a GammaKnife™ unit. Through computerised
software programs, both approaches are able to shape an invisi-
ble beam of highly charged electrons to penetrate the body and
target a tumour with pinpoint accuracy. Depending on the size,
shape and location of the tumour, different energy levels are
generated to produce a carefully shaped beam that will destroy
the targeted tumour, yet spare the surrounding healthy tissue
and vital organs in an effort to reduce the treatment toxicities
for the patient. With advances in computer technology, these
beams can be shaped to a two-dimensional or three-dimen-
sional shape to conform to the exact shape of the tumour as
measured by imaging studies such as positron emission tomogra-
phy (PET), CT or MRI scans. Recent treatment enhancements
in EBRT include the ability to direct different energy levels at
different angles directed at the tumour, called intensity modu-
lated radiation therapy (IMRT), which enables higher doses to
be delivered to the tumour while sparing the important healthy
structures surrounding the tumour. IMRT can be administered
as standard daily fractions or as ‘hyperfractionated’ twice daily
fractions, which shortens the duration of the patient’s treat-
ment schedule. Image-guided radiation therapy (IGRT) uses
continuous monitoring of the tumour with ultrasound or CT
scans during the treatment to allow for automatic adjustment
of the target as the tumour changes shape or position, again
in an effort to spare the healthy surrounding tissue and reduce
side effects (Sharpe, Craig & Moseley, 2007).
The most recent treatment enhancements now include
respiratory-gating, where the treatment delivery is actually
synchronised with the patient’s respiratory cycle, enabling the
beam to be adjusted as the tumour moves (Dawson & Jaffray,
2007).
Gamma rays are one of the oldest forms of energy used in
EBRT. This energy is produced from the spontaneous decay
of naturally occurring radioactive elements such as cobalt 60.
The gamma rays also deliver this radiation dose beneath the
skin surface, sparing skin tissue from adverse effects.
Stereotactic body radiotherapy (SBRT) is another form of
EBRT using higher doses of radiation to penetrate very deeply
into the body to control deep-seated tumours that cannot be
treated by other approaches such as surgery. SBRT is delivered
with considerably higher treatment fraction doses over a short
span of time, usually 1 to 5 treatment days, in contrast to 6 to
8 weeks for conventional EBRT (Timmerman et al., 2007).
Proton therapy is another very different approach to EBRT.
The advantage of proton therapy is that it is capable of deliv-
ering its high-energy dose to a deep-seated tumour, with no
energy exiting through the patient’s healthy tissue behind
the tumour, allowing for treatment of deep tumours in close
proximity to critical structures such as the heart or major blood
vessels (Thornton et al., 2007).
prophylactically to prevent leukaemic infiltration to the brain
or spinal cord.
Palliative radiation therapy is used to relieve the symptoms
of metastatic disease, especially when the cancer has spread
to brain, bone or soft tissue, or to treat oncological emer-
gencies such as superior vena cava syndrome or spinal cord
compression.
Two types of ionising radiation—electromagnetic rays
(x-rays and gamma rays) and particles (electrons [beta par-
ticles], protons, neutrons and alpha particles)—can lead to
tissue disruption. The most harmful tissue disruption is the
alteration of the DNA molecule within the cells of the tissue.
Ionising radiation breaks the strands of the DNA helix, leading
to cell death. Ionising radiation can also ionise constituents
of body fluids, especially water, leading to the formation of
free radicals and irreversibly damaging DNA. If the DNA is
incapable of repair, the cell may die immediately, or it may
initiate cellular suicide (apoptosis), a genetically programmed
cell death (Bruner et al., 2006). Cells are most vulnerable to
the disruptive effects of radiation during DNA synthesis and
mitosis (early S, G2 and M phases of the cell cycle). Therefore,
those body tissues that undergo frequent cell division are most
sensitive to radiation therapy. These tissues include bone
marrow, lymphatic tissue, epithelium of the gastrointestinal
tract, hair cells and gonads. Slower-growing tissues or tissues
at rest are relatively radioresistant (less sensitive to the effects
of radiation). Such tissues include muscle, cartilage and con-
nective tissues. However, it is important to remember that
radiation therapy is a localised treatment, and only the tissues
that are within the treatment field will be affected by the radi-
ation therapy.
A radiosensitive tumour is one that can be destroyed by
a dose of radiation that still allows for cell regeneration in
the normal tissue. Tumours that are well oxygenated also
appear to be more sensitive to radiation. In theory, there-
fore, radiation therapy may be enhanced if more oxygen
can be delivered to tumours. In addition, if the radiation
is delivered when most tumour cells are cycling through
the cell cycle, the number of cancer cells destroyed (cell-
killing) is maximal. Radiation sensitivity is also enhanced in
tumours that are smaller in size and that contain cells that are
rapidly dividing (highly proliferative) and poorly differenti-
ated (no longer resembling the tissue of origin) (Bruner et al.,
2006).
Certain chemicals, including chemotherapy agents, act as
radio-sensitisers and sensitise more hypoxic (oxygen-poor)
tumours to the effects of radiation therapy. Combinations of
chemotherapy and radiation therapy are typically used to take
advantage of the radio-sensitising effects of chemotherapy and
achieve an improved survival benefit while minimising side
effects of such therapy. Radiation is delivered to tumour sites
by external or internal means.
Radiation dosage
The radiation dosage is dependent on the sensitivity of the
target tissues to radiation and on the tumour size. The lethal
tumour dose is defined as the dose that will eradicate 95% of
the tumour yet preserve normal tissue. The total radiation
dose is delivered over several weeks to allow healthy tissue to
repair and to achieve greater cell kill by exposing more cells
to the radiation as they begin active cell division. Repeated
radiation treatments over time (fractionated doses) also allow
