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129 Approach to the Cancer Patient 1203

residual disease is outside the treatment field, it is left several terms under the umbrella term SRT. SRS (stereo-
VetBooks.ir untreated and recurrence is likely; this is referred to as a tactic radiosurgery) treats the CNS, brain and spine.
Despite having surgery in the name, the procedure is
geographic miss. The risk increases with multiple sur-
geries by means of distortion of normal tissue structures.
tic body radiation therapy) treats all other structures
Placement of hemoclips (radiopaque clips) at the mar- noninvasive,and no surgery is involved. SBRT (stereotac-
gins of the resected tissue benefits treatment planning, than the brain and spine. SRT is used to treat tumors that
decreasing the likelihood of a geographic miss. The would otherwise be considered inoperable and classi-
majority of radiation‐induced adverse effects are often cally it is not used to address microscopic disease. At
mild and self‐limiting. Advanced imaging developments present, SRT use in veterinary patients is expanding
have enhanced our ability to delineate tumor tissue beyond the initially treated bone tumors, central and
extent and have led to improved treatment outcomes peripheral nervous system tumors.
and fewer patient side‐effects.
Radiopharmaceuticals
Intensity‐Modulated Radiation Therapy (IMRT) Radiopharmaceuticals are radioactive substances used to
The majority of radiation treatments in veterinary oncol- image and/or treat particular cancers. One example is
ogy are delivered with radiation beams of uniform inten- iodine‐131, a frequently employed treatment of thyroid
sity in a static field. Collimators are used to limit the adenoma/carcinoma in the cat. Samarium‐153 and
treatment beam and provide a rectangular treatment related compounds have been used for treatment of
field. Further development has led to the more complex multilobular osteochondrosarcoma, and osteosarcoma.
multileaf collimator (MLC) which is made of many metal
slats capable of independent movement to shape the Palliative Medical Care
field. IMRT has the ability to specifically modulate the
weights of small segments within an individual radiation Metronomic Chemotherapy
beam. This is referred to as intensity distribution, and Metronomic chemotherapy, which is intended to pre-
allows the beam to conform to the three‐dimensional vent tumor angiogenesis, is based on frequent, low‐dose,
shape of complex tumor target volumes. This technique continuous cytotoxic drug administration lacking the
of RT delivers a nonuniform fluence (beam intensity) to rest period included with conventional chemotherapy. It
the patient, allowing optimization of dose distribution to results in minimal toxicity, is often cost‐effective, and
the target volume while sparing critical tissues. The convenient. In veterinary medicine, metronomic therapy
MLC uses the superimposition of many subfields that has become an affiliate to many protocols and usually
deliver the prescribed dose. The use of IMRT has per- combines an orally administered cytotoxic chemothera-
mitted the radiation oncologist to treat tumors (nasal peutic agent with an NSAID. It is most frequently applied
and prostate) that would otherwise be difficult to control in the treatment of visceral hemangiosarcoma (HSA),
without significant patient side‐effects. transitional cell carcinoma of the urinary bladder, nasal
tumors, and metastatic cancers.
Stereotactic Radiation Therapy
Stereotactic radiosurgery (SRS) involves precision deliv- Pain Management
ery of one or several high doses of radiation to the target
(tumor) by means of a linear accelerator with a sophisti- It is often difficult for clients to recognize the signs of
cated treatment planning system, delivery, and position- pain or discomfort in their pets. Unrelieved pain is a
ing device (frame). The conformal nature of SRS permits major cause of suffering in patients with cancer.
avoidance of toxicity to normal surrounding tissues. The Veterinarians managing cancer patients must be vigilant
CyberKnife® Radiosurgery System delivers radiation about monitoring for and providing relief from pain,
through a manipulated robot‐mounted linear accelera- whether caused by the neoplastic process itself or coinci-
tor. At present, SRS is primarily utilized in select canine dental in nature. Providing adequate management of
osteosarcoma patients and veterinary patients with cen- pain is central to oncologic care and will improve the
tral and peripheral nervous system tumors. Stereotactic quality of life of the animal patient.
radiation therapy (SRT) involves precision delivery of
one or several high doses of radiation therapy delivered Palliative Radiation Therapy
to the target (tumor) by means of a linear accelerator
with a sophisticated treatment planning system, delivery, Palliative radiation therapy (PRT) is the administration
and positioning device(s). Most linear accelerators are of a radiotherapy dose in a smaller number of treatments
floor mounted and revolve 360 degrees around the (fractions) than would be used in the delivery of curative
patient. The conformal nature of SRT permits avoidance intent RT (CRT); however, the fraction dose is higher
of toxicity to normal surrounding tissues. There are and less percise than SRT. The appeal of PRT lies in