Page 241 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

220 PART III Therapeutic Modalities for the Cancer Patient

and sarcomas in cats respond comparably to nasal tumors in dogs: blepharospasm, conjunctivitis, and keratoconjunctivitis sicca
48 Gy administered in 4 Gy fractions over 4 weeks resulted in a (KCS). 169,170 KCS may be temporary or permanent, depending
169,171
164
on the dose administered and the sensitivity of the patient.
1- and 2-year survival rates of 44.3% and 16.6%, respectively.
VetBooks.ir The histologic type and clinical stage of the tumor did not affect KCS is treated with artificial tears and steroids to prevent corneal
the prognosis.
ulceration. If corneal ulceration is present, healing may be delayed
Nine dogs with recurrent nasal tumors previously treated with as a result of radiation damage to the corneal stem cells. 172 Late
3D-CRT (median 50 Gy) were reirradiated. 165 The overall MST effects include vascular changes, which may have subtle effects on
from initial treatment was 31 months with an increased incidence vision but in most cases do not result in blindness. Radiation-
of late effects. Retreatment becomes a more viable option with induced cataracts may occur and the latent period is related to
new modalities, such as IMRT and SRT, that can better spare local dose. 173 As with other cataracts, these can be removed with phaco-
normal tissues. emulsification. When treating nasal or facial tumors, it may be
The response to feline nasal planum SCC is affected by the necessary for the eye to receive the full treatment dose. At doses
tumor stage. 166 Cats with T1 tumors had 1- and 5-year survival above 40 Gy, degenerative angiopathy of retinal vessels can prog-
rates of 85% and 56%, respectively, and the mean ST was 53 ress over 2 years and result in retinal degeneration. 172 Optic nerve
months (the median was not reached). However, larger, more axonal degeneration has been reported to occur secondary to the
invasive tumors showed a less favorable response when treated retinal changes. 172 IMRT and SRT allow greater sparing of ocular
with 40 Gy in 4 Gy fractions over 3.5 weeks. 166 Tumor control tissues, resulting in diminished acute and late toxicities. 9,123
should be improved by reducing the dose per fraction and increas-
ing the total dose. For small, superficial SCC lesions of the nasal Tumors in the Cranial Vault
planum in cats, strontium (Sr)-90 plesiotherapy is a viable option.
Because Sr-90 emits a low-energy β-particle, very high doses can Brain tumors can be treated successfully with RT and/or surgery
be administered to the surface of a lesion without unacceptable (see Chapter 31). In the treatment of brain tumors, surgery may
complications or damage to underlying tissue. In one study, 49 be indicated to relieve life-threatening clinical signs. Although
cats with SCC of the nasal planum were administered a median of appropriate studies are still needed, reported STs after radiation
128 Gy in a single fraction with a complete response rate of 88% for brain tumors in dogs with less severe neurologic signs are fre-
and median PFI of 1710 days. 167 Larger, invasive SCC lesions are quently comparable to surgery alone. 174 Adjuvant RT is indicated
usually not amenable to treatment with Sr-90. 167 in patients with incomplete surgical resection; RT alone should be
performed in dogs and cats with cancer at surgically inaccessible
Radiation Considerations sites or in locations where surgical morbidity is high.
Canine and feline sinonasal tumors are challenging to treat with
radiation because they are anatomically complex with frequent Efficacy of Treatment
involvement of the nasal sinuses, cribriform plate, and nasophar- Published STs of canine brain tumors treated with RT compare
ynx. The geometry of the nasal cavity is problematic, because the favorably to surgery, although directly comparable data is lacking
target is larger caudally than rostrally, making it difficult to achieve and combinations of surgery and RT may be superior to either
even dose distribution. The dose sculpting benefits of inverse modality alone. There is little published information on irradiation
treatment planning used for IMRT and SRT make these modali- of nonpituitary feline brain tumors, because most feline menin-
ties the treatment of choice for nasal tumors. Regardless of radia- giomas are effectively treated surgically. 175 Nevertheless, radiation
tion modality used, clients should be advised of the potential for outcomes for cats appear comparable to canine brain tumors, and
persistent nasal symptoms and long-term radiation effects. RT should be considered when the tumor location is not amena-
ble to surgical resection. In one study, 46 dogs with brain tumors
Treatment-Related Toxicities associated with neurologic disease were treated with RT alone 176 ;
After treatment with 3D-CRT, radiation toxicities of nasal tumors the MST was 23.3 months with 1- and 2-year survival rates of
are similar to those described previously for the oral cavity, with 69% and 47%, respectively. No prognostic clinical factors were
mucositis affecting the oral cavity and tongue, and dry to moist identified. The outcome in this study was superior to those from
desquamation of skin. Regardless of radiation modality used, previous reports in which the MST was about 1 year. 177–179 Dif-
the nasal cavity will never be completely normal after turbinate ferences may be due to improved treatment planning capabilities,
destruction from the tumor and from radiation damage. In dry which was supported by a study of 31 dogs treated with 3D-CRT
environments, room humidifiers can make patients more com- that had an MST of 19 months. 180 In another study also involving
fortable, and intermittent antibiotics may be necessary to treat 31 dogs with meningioma, postoperative RT improved the MST
periodic bouts of rhinitis. Fungal infections after the treatment of from 7 months with surgery alone to 16.5 months with surgery
nasal tumors has also been reported. Long-term use of pentoxi- followed by RT. 181
9
fylline and vitamin E are recommended to help mitigate radiation Thirty dogs with image-based diagnoses of intracranial menin-
effects in patients treated with SRT. 168 Nasal discharge, sneezing, giomas were treated with SRT, with most receiving 24 Gy in three
and epistaxis may indicate tumor recurrence and can be challeng- fractions. The overall MST for any cause of death was 561 days
ing to differentiate from posttreatment rhinitis. Deep nasal cul- and treatment was well tolerated. In another study, 39 dogs with
8
ture and sensitivity may help direct antibiotic treatment. If there image-based meningiomas were treated with stereotactic volume-
is no durable clinical response from antibiotic treatment, then a modulated arc RT (VMAT) receiving 33 Gy in five fractions. The
CT is recommended to evaluate for recurrence. 2-year overall survival rate was 74.3% and treatment was well
Ocular radiation complications are extremely common when tolerated. 182
3D-CRT planning is used because of the proximity of the nasal Forty-two dogs with presumed gliomas were treated with
cavity and frontal sinus to the orbit. 169 Effects to the eyes are dose VMAT alone or in combination with temozolomide. The MSTs
related and vary in severity. 170 Acute effects include blepharitis, for RT alone and RT and temozolomide were 383 days and 420