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The Use of Radiation Therapy as a Viable Treatment Option in the Feline
Gastrointestinal Lymphoma Patient
Jaclyn Christensen
Tarleton State University
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Abstract
The treatment of gastrointestinal lymphoma in cats usually focuses on the use of
chemotherapeutic drugs along with steroid therapy. Historically, this is the best method
of achieving the greatest survival time in these patients. The objective of this study was to
determine if survival times would increase when also using radiation therapy.
The results of this study showed that cats treated with chemotherapy and steroids
alone had a median survival time of less than 9.6 months. Comparatively, cats treated
with radiation therapy in conjunction with chemotherapy and steroids had a median
survival time of 11.8 months. This indicates that feline gastrointestinal lymphoma
patients could achieve a greater survival time when using radiation therapy in conjunction
with chemotherapeutic drugs and steroid therapy.
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Table of Contents
Introduction………………………………………………………….……………………4
The Problem Statement…….………………………………………………………..…….4
Purpose of study/significance of study……………………………………………………5
Hypotheses………………………………………………………………………………...5
Research Questions……………………………………………………………………..…5
Assumptions…………………………………………..…………………………………...5
Limitations………………………………………………………………………………...6
Delimitations………………………………………………………………………………6
Definitions…………………………………………………………………………………6
Literature Review……………………………………………………………………….....7
Methodology………………………………………………………………………………8
Data Analysis…………………………………………………………………………….10
Findings………………………………………………………………………..………...11
Summary and Conclusions………………………………………………………………11
Implications of Findings…………………………………………………………………11
Recommendations………………………………………………………………………..12
References………………………………………………………………………………..13
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Introduction
Feline gastrointestinal lymphoma is a common form of neoplasia seen in cats.
Survival time varies dependent upon the severity of the grade. Small cell GI lymphoma
carries the longest median survival time of 20.5 months. Intermediate cell GI lymphoma
has a median survival time of 7 months, and large cell GI lymphoma has a median
survival time of only 45 days. To achieve these survival times clinicians often use
chemotherapeutic drugs, alongside steroid therapy.
This study examined previous research to determine if survival times will increase
when radiation therapy is initiated. This research strongly suggested that radiation
therapy increases survival time, indicating that radiation should be considered by the
clinician overseeing feline gastrointestinal lymphoma cases.
Statement of Problem
Feline gastrointestinal (GI) lymphoma is a common cancer in feline patients.
Unfortunately, the long term prognosis is often poor with a short survival time. The
common treatment of choice is chemotherapy, in conjunction with steroid therapy. With
advances in veterinary medicine, radiation therapy is widely available and used often in
the treatment of the canine lymphoma patient. The proposed study will evaluate if
radiation therapy, when used in conjunction with chemotherapy and steroids will improve
the survival time in felines with GI lymphoma. Through this, a new viable treatment
option may become available to extend the life of feline gastrointestinal lymphoma
patients.
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Purpose of Study
The diagnosis of feline gastrointestinal lymphoma is devastating to pet owners.
Ultimately, owners face the reality that their pet is terminal. Many owners choose to
intervene medically to prolong their pet’s life as much as possible. This medical
intervention includes the use of chemotherapeutic agents as well as steroid therapy.
Although somewhat effective, these treatments provide only a short median survival
time. The purpose of this study is to evaluate the use of radiation therapy in feline
gastrointestinal lymphoma patients. The ultimate goal is to provide an increase in
survival time with the use of radiation, thus giving owners another treatment option.
Hypothesis
H01 states that there will be an increase in the median survival time in feline patients
treated with combination therapies, including steroids, chemotherapy, and radiation.
Research Questions
1. How will radiation therapy effect the median survival time in feline GI
lymphoma patients also treated with chemotherapy and steroids?
2. How sensitive are lymphoma cells to radiation therapy?
Assumptions
1. For the purpose of this study, it is assumed that the research used to collect data
was performed by individuals educated and capable of providing accurate results.
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2. It is also assumed that when referring to “chemotherapy”, the specific drugs being
used are those that are traditionally given during the treatment of lymphoma and
may vary depending on patient response.
Limitations
1. Lack of previous research available on this specific topic limits this study.
2. This study is limited because only one feline GI lymphoma patient could be used
for radiation therapy.
Delimitations
1. This study generalized feline GI lymphoma, rather than evaluating each grade and
the individual response.
Definitions
Chemotherapy- Chemotherapy or chemotherapeutic agents are a variety of
cytotoxic drugs that are given to patients during the treatment of different types of
neoplasia.
Lymphoma- Lymphoma is a malignant cancer within the lymphatic system and
lymph nodes.
Median Survival Time- Median survival time is the time in which fifty percent of
an observed group is alive and fifty percent of the same group is deceased.
Neoplasia- Neoplasia (or cancer) is an abnormal growth of cells.
Radiation- Radiation is a therapy in which high energy particles (X-Rays, Gamma
Rays, etc.) are used to damage cancer cells.
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Literature Review
Feline gastrointestinal lymphoma will fall into one of three categories including
low-grade, intermediate/high grade, or large cell lymphoma. With the use of
chemotherapy alone, the median survival time is 615 days for low-grade, 210 days for
intermediate/high grade, and 45 days for large cell lymphomas (Barrs & Beatty, 2012).
Prior to the introduction of effective chemotherapy, human patients with
advanced-stage lymphoma were often treated with radiation therapy alone. Currently,
radiation therapy is being used in a consolidative fashion to initially involved sites, sites
of bulky disease, or sites that failed to respond completely to chemotherapy (Hoppe &
Aleman, 2011). In one study, human patients who relapsed or had only a partial response
to chemotherapy were treated with radiation therapy. Eighty-six percent of the patients
responded to radiation, with a median survival time of 17 months (Safwat, Bayoumy, ElSharkawy, Shaaban, Mansour & Kamel, 2003).
In a retrospective study medical records of 11 cats with gastrointestinal
lymphoma were evaluated to determine the efficacy of radiation therapy. The cats had
different grades of lymphoma, and all had been previously treated with various
chemotherapy protocols. Ten of the eleven cats responded to radiation. The median
survival time in this group of cats was 355 days, with 25% of the cats still alive at 1,000
days (Parshley, LaRue, Kitchell, Heller & Dhaliwal, 2010).
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Methodology
Research Design
Experimental doses of radiation were given to a feline diagnosed with GI
lymphoma. A total of two fractions (or doses) of radiation were given once daily for two
consecutive days. The feline patient was placed under general anesthesia for
approximately 45 minutes (which included induction, treatment, and recovery) and was
treated with a dose of 2.5 gray given over 20 minutes. The entire abdominal cavity was
treated. The feline patient was then checked every two weeks via abdominal ultrasound to
check for progression versus a response.
The independent variable of this study was the use and dose of radiation. The
dependent variable was the lymphoma and it’s response.
Sample Population
One domestic short-haired feline was used. The feline was a 14 year old, neutered
male. The feline had been diagnosed with intermediate grade GI lymphoma and treated
with chemotherapy 8 months prior to radiation. Prior to beginning radiation, the feline
had stopped responding to chemotherapy and the GI lymphoma had returned.
This feline was chosen because he had been diagnosed with the most common
type of GI lymphoma seen in cats. He was also chosen because his response time to
chemotherapy was of an average time frame. Additionally, he was chosen due to the
owner’s willingness and content to participate.
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Informed Consent
Owner’s consent was given for the feline to take part in radiation therapy. All
treatments were performed in the presence of a veterinary radiation oncologist.
Anesthesia was maintained and the feline was monitored by a veterinary anesthesiologist.
Confidentiality
By reading this study, the reader agrees to keep all data, technology or other
information about the University and researchers confidential. Written permission is
required in order to re-produce any information herein until the date of publication.
Geographic Limitations
This study was conducted in a temperature and humidity controlled environment.
Temperature was maintained between 68 and 72 degrees Fahrenheit. Relative humidity
was maintained between 30% and 70%. There were no geographic limitations.
Data Collection
The patient had an abdominal ultrasound examination performed the day prior to
receiving radiation therapy. The patient was then monitored every two weeks via
abdominal ultrasound to determine the response. The ultrasound findings were
documented in the patient’s medical record.
Instrumentation
The patient was treated with an Accuray Tomotherapy radiation machine. The
machine was calibrated and the planning was performed by a veterinary radiation
oncologist.
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Data Analysis
Diagram A
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
Chemotherapy
Alone
Chemo + Radiation
200
days
400
days
600
days
800
days
1000
days
Overall survival time of GI lymphoma cats based on treatment choice
(Based on the findings of previous studies)
Diagram B
Week # Following Radiation
Ultrasound Findings
0
Abnormal stomach layering and enlarged
lymphnodes, progressive lymphoma
indicated
2
Normal ultrasound, lymphoma in remission
4
Normal ultrasound, lymphoma in remission
6
Normal ultrasound, lymphoma in remission
8
Normal ultrasound, lymphoma in remission
10
Normal ultrasound, lymphoma in remission
Ultrasound findings of the feline GI lymphoma patient treated with radiation
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Findings
The average median survival time of a feline gastrointestinal patient treated with
chemotherapy and steroids alone is 290 days. In the retrospective study performed by
Parshley, LaRue, Kitchell, Heller & Dhaliwal, the median survival time was 355 days.
In the performed experiment, the feline treated with radiation responded and was
in remission at the time the study concluded, after the 10th week following radiation.
Summary and Conclusions
Evidence from this study suggests that radiation therapy, when used in
conjunction with chemotherapy and steroids, will increase the overall survival time in
feline GI lymphoma patients. Somewhere between 86-91% of lymphoma patients (human
or animal) should see a response to radiation therapy, indicating that lymphoma cells are
sensitive to radiation therapy.
Implications of the Findings
This research suggests that radiation may be a reasonable treatment option for
feline GI lymphoma patients that have either relapsed, or do not fully respond to
chemotherapy. This implication was determined by retrospectively evaluating the
survival times of feline GI lymphoma patients that were treated with chemotherapy alone
versus feline GI lymphoma patients that were treated with chemotherapy and radiation
therapy. The response rate of patients treated with radiation was notably high, and an
increase in survival time was recorded. Thus, radiation therapy should be considered in
the treatment plan of feline GI lymphoma patients.
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Recommendations
Further research is necessary to provide stronger evidence indicating the benefit
of radiation therapy in regards to feline GI lymphoma treatment. Larger study groups
should be used to determine the benefits on a larger scale. Varying radiation doses should
also be considered to find the highest tolerable dose that provides the longest remission
time.
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References
Barrs, V., Beatty, J. (2012). Feline alimentary lymphoma: Diagnostics, therapy,
prognosis. Journal of Feline Medicine and Surgery. 14(191-201).
Hoppe, R., Aleman, B. (2011). Background and rationale for radiotherapy in advancedstage lymphoma. Radiotherapy for Hodgkin Lymphoma. 3(1), 540-552.
Parshley, D.L., LaRue, S.M., Kitchell, B., Heller, D., Dhaliwal, R.S. (2011). Abdominal
irradiation as a rescue therapy for feline gastrointestinal lymphoma: a
retrospective study of 11 cats. Journal of Feline Medicine and Surgery. 13(63).
Safwat, A., Bayoumy, Y., El-Sharkawy, N., Shaaban, K., Kamel, A. (2003). The
potential palliative role of irradiation. Radiotherapy and Oncology. 69(2003), 3336.
Safwat, A. (2000). The role of low dose irradiation in the treatment of lymphoma.
Radiotherapy and Oncology. 56(2000), 1-8.