Page 240 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 13 Radiation Oncology 219

fractions to a total dose of 30–36 Gy) and conventionally fraction- xerostomia is not commonly recognized in animals. IMRT tech-
ated (2–4 Gy fractions to as high as 45 Gy or more) protocols were nology should provide improved sparing of salivary glands and in
human patients has resulted in significantly lower proportion of
used with or without surgery or chemotherapy. The median times
VetBooks.ir to first event and MST were 5 and 7 months, respectively. Tumor patients with grade II or worse xerostomia. 147 Osteoradionecrosis,
or development of nonvital bone susceptible to pathologic frac-
recurrence was the first event in only 27% of the dogs, whereas
new metastases or death accounted for the remaining 63%. In ture after RT, is an uncommon complication that can occur in
a retrospective study of 39 dogs with incompletely resected oral any bone in a radiation field, typically years after treatment. The
MM treated with coarsely fractionated RT plus platinum-based mandible is the most susceptible bone to osteoradionecrosis but,
chemotherapy, the MST was 363 days. 142 The dogs received six as with most late effects, the risk can be minimized by administer-
2
weekly fractions of 6 Gy, with cisplatin (10–30 mg/m ) or car- ing radiation in lower doses per fraction. 148 The role of SRT for
2
boplatin (90 mg/m ) administered 1 hour before irradiation. The the treatment of oral tumors is unclear. 149 Human patients who
local recurrence rate was 15% and the median time to metastasis have failed traditional RT regimens are sometimes treated with
was 311 days. 142 Five cats with oral MM were treated with 8 Gy salvage SRT. 149
delivered on days 0, 7, and 21. All died from progressive disease
and the MST was 146 days. 143 Nasal Tumors
Radiation Considerations Nasal tumors (see Chapter 24, Section B) in dogs are difficult to
Reproducibility of treatment fields for oral tumors can be aided control. Surgery, cryosurgery, or immunotherapy alone do not
by positioning and immobilization devices. Depending on the appear to improve survival over no treatment. 150–153 RT provides
size and location of the target, IMRT allows better sparing of sur- the best reported tumor control for canine nasal tumors and likely
rounding normal structures such as the eyes and salivary glands. needs to be part of any curative-intent treatment regimen.
MM may have a low α/β ratio, making them more responsive to
coarsely fractionated protocols. 144 Efficacy of Treatment
RT has long been the standard of care for nasal and sinonasal
Treatment-Related Toxicities tumors. The location is not generally amenable to complete sur-
Treatment toxicity depends on the time-dose-fraction size of the gical resection, and although early reports of orthovoltage radia-
protocol and the specific normal structures in the treatment field. tion pulse surgery showed improved outcomes, 154,155 most reports
For oral tumors, this can include the skin, nasal cavity, and eyes. combining RT and surgery have not demonstrated therapeutic
The major acute complications associated with RT of the oral cav- gain compared with radiation alone. 156,157 Interestingly, over the
ity are mucositis and skin effects. Mucositis always occurs to some past 20 years, advancements in treatment planning technology
degree in patients that have received irradiation to the oral cavity, from point calculations to 2D, 2.5D, and 3D-CRT technologies
pharynx, and/or esophagus. Mucositis typically begins during the have not been associated with improved tumor control or survival.
second week of therapy and reaches a maximum severity during or Megavoltage RT alone planned with 3D-CRT has been reported
shortly after the last week of therapy. Clinical signs include thick- to provide an MST of approximately 1 year. 158–160 Histologic
ened saliva and tenderness of the mouth. Patients may be reluctant subpopulations may be prognostically significant; however, most
to eat or drink and require supportive care. Low-salt foods are less publications are hampered by inadequate patient numbers. Crib-
irritating to the oral mucosa than regular commercial diets. Infre- riform erosion has been associated with a poor prognosis with
quently, placement of a gastrostomy or esophagostomy tube may fractionated RT protocols. 161,162
be necessary to facilitate feeding. Oral mucositis should subside Two publications have evaluated outcome in dogs with nasal
within 2 weeks after therapy. The extent of skin effects will vary tumors treated with IMRT. 122,123 Thirty-one dogs treated with
based on the field size and location. Erythema, hair loss, dry and IMRT were compared with 36 historical controls treated with the
moist desquamation, and swelling of lips can occur. The effects same prescription using 2D treatment planning. The MSTs were
may start late in the course of treatment or shortly after com- 420 days and 410 days, respectively. 123 In another report, 12 dogs
pletion of treatment. Blotting the skin gently with moist towels treated with IMRT to a dose commonly used for 2D or 3D-CRT
can help keep the area clean. Never rub or scrub the area, and an planning had an MST of 446 days. 122 Patient numbers in both
E-collar may be useful to keep the patient from rubbing or paw- studies were low, and there was no stratification for prognostic
ing at the area. Pain management is important for both mucositis factors. Although definitive conclusions cannot be made regarding
and skin effects. tumor control, the decrease in acute effects to the region in both
Rarely, animals treated with chemotherapy subsequent to a studies was profound with minimal grade II and III cutaneous and
course of RT can develop a return of radiation side effects such mucosal toxicity noted. Although the ipsilateral eye could not be
as mucositis or moist desquamation of the skin, a phenomenon spared, minimal side effects to the contralateral eye were noted. 123
known as radiation recall. 145 Radiation recall is a poorly under- SRT has been investigated in 29 dogs with solid nasal tumors
stood phenomenon that can occur with many different anti- with three daily fractions of 10 Gy. Clinical signs improved in
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neoplastic drugs, although it is most commonly associated with all dogs. Acute effects were minimal; however, approximately 10%
doxorubicin, taxanes, and gemcitabine. 145 It is drug specific for of dogs developed significant oronasal or nasocutaneous fistulas.
individual patients and rechallenge does not necessarily induce the The MST was 586 days with 69% and 22% alive 1 and 2 years
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reaction. 145 post-SRT, respectively. Developing patient selection criteria and
Late complications of radiation specific to the oral cavity include modifying normal tissue radiation constraints should be a priority,
osteoradionecrosis, xerostomia, and oronasal fistula development. so late tissue effects can be minimized.
Xerostomia (dryness of the mouth due to salivary dysfunction) Lymphoproliferative nasal tumors in cats respond well and
is a common complication in human patients undergoing RT durably to RT (these are addressed later in the chapter in the sec-
of the head and neck region 146,147 ; however, clinically significant tion on lymphoma; also see Chapter 33, Section B). 163 Carcinomas