AJR 2001; 177:1083-1089
© American Roentgen Ray Society
Imaging Findings After Radiotherapy to the Pelvis
Revathy B. Iyer1,
Anuja Jhingran2,
Hassan Sawaf1 and
Herman I. Libshitz1
1
Department of Diagnostic Radiology, #57, The University of Texas M. D.
Anderson Cancer Center, 1515 Holcombe Blvd., Houston, TX 77030-4009.
2
Department of Radiation Oncology, The University of Texas M. D. Anderson
Cancer Center, Houston, TX 77030-4009.
Received March 13, 2001;
accepted after revision May 1, 2001.
Address correspondence to R. B. Iyer.
Introduction
Radiotherapy is the primary treatment modality for some pelvic
malignancies, particularly cervical cancer. It is used in conjunction with
chemotherapy to downstage pelvic malignancy before therapy and may be used
palliatively to control advanced or metastatic tumors in the pelvis.
Complications related to radiation therapy are uncommon. However, because of
the number of patients treated and the relatively long latency period for
radiation injury, the ability to recognize characteristic radiation-induced
pelvic tissue changes on follow-up images is important. These changes include
bone and soft-tissue injury as well as gastrointestinal and genitourinary
tract injury. Complex fistulas may also develop. Neurologic injury after
radiation is rare because of the relative radioresistance of peripheral nerves
in the pelvic field. In this article, we describe some common and some unusual
changes that may be seen in patients who have had pelvic radiation
therapy.
Therapeutic Technique
Pelvic cancers typically treated with radiation alone (usual dose, 30-70
Gy) or in conjunction with other therapies include colorectal, bladder, and
prostate cancer as well as gynecologic malignancies. Cervical cancers
generally are treated with definitive radiation therapy in cases in which the
primary lesion is large or has spread beyond the cervix. Standard treatment
usually includes external beam therapy as well as brachytherapy. External beam
therapy is applied as anteroposterior and posteroanterior fields or as four
fields (anteroposterior, posteroanterior, and right and left lateral) to the
pelvis in incremental daily doses, which total 45 Gy overall (Fig.
1A,1B).
Intracavitary radiation focused on the cervix is also frequently used, with
doses up to 80-95 Gy [1].
Colorectal cancers are often treated with radiation and chemotherapy,
preferably before surgery, with doses of approximately 50 Gy to decrease the
incidence of local recurrence after surgery. Surgery may cause small-bowel
loops to adhere in the pelvis and result in vascular alterations, thus
increasing the likelihood of late radiation enteritis. Radiation is also used
frequently in patients with bladder cancer and men with prostate
carcinoma.
Genitourinary Changes
The overall incidence of urologic complications after pelvic irradiation is
reported to be approximately 21%. However, in a series reported by Dean and
Lytton [2], only 2.5% of such
complications could be ascribed to the effects of radiation alone. They found
that the development of urologic complications was related to the radiation
dosage and previous bladder operations. The incidence of radiation cystitis is
reported to range from 3% to 12%, again depending on the dose to the bladder
[2,
3]
(Fig. 2). The risk of ureteral
stenosis in cervical cancer is 1.0%, 1.2%, 2.2%, and 2.5% at 5, 10, 15, and 20
years, respectively [4].
Ureteral injury may not become apparent for many years after therapy, and,
therefore, continued surveillance of renal function in these patients is
necessary (Fig.
3A,3B).
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Fig. 2. —CT scan of pelvis of 43-year-old woman who presented with
massive hematuria; she had been treated for stage IIB cervical cancer with
definitive radiation therapy to pelvis 2 years earlier. Results of cystoscopy
and biopsy indicated radiation-induced hemorrhagic cystitis that eventually
required cystectomy. CT scan of pelvis obtained after clot removal reveals air
and high-density fluid in bladder compatible with imaging appearance of blood.
Increased perirectal and perivesical fat is due to radiation.
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Gastrointestinal Changes
The overall incidence of chronic radiation injury to the bowel after
radiotherapy to the pelvis is about 1-5%
[5]. The most important risk
factor for injury to the gastrointestinal tract is the dose of radiation
given. A study of patients with prostate cancer showed that doses of more than
70 Gy raised the likelihood of rectal bleeding after therapy
[6]. Some chemotherapeutic
agents, such as adriamycin and bleomycin, also potentiate the effects of
radiation [5,
6]. Rapidly proliferating
cells, such as those in the mucosa of the small intestine, are most
radiosensitive and, therefore, at highest risk for acute injury, which occurs
within weeks of therapy and is rarely studied radiographically. The changes in
the vascular and interstitial connective tissues are more insidious, and the
initial injury leads to progressive ischemia of the intestinal wall
[5]. Chronic radiation
enteritis may develop months or years after therapy, and imaging does play a
role in the evaluation of these patients.
The ileum is the most frequently injured segment of the small intestine
because of its location in the pelvis. Submucosal edema and fibrosis are seen
at barium examinations as thickening and straightening of small-bowel folds
and separation of adjacent loops. CT can directly reveal bowel wall thickening
related to submucosal edema (Fig.
4A,4B).
Fluoroscopic evaluation may show single or multiple areas of stenosis and
small-bowel obstruction. Altered peristalsis may also be encountered. Fibrotic
changes in the mesentery may cause fixation of bowel loops; in this condition,
the loops appear angulated and tethered at small-bowel follow-through
examination. Increased density in the mesentery may be evident at CT
[5].
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Fig. 4A. —31-year-old woman with stage IB cervical cancer treated 2
years earlier with 40-Gy dose of whole-pelvis and intracavitary radiation.
Since therapy, patient had experienced long history of gastrointestinal
complaints, including weight loss, diarrhea, and recurrent bowel obstruction.
Small-bowel series shows small-bowel loops with thickened folds
(arrows) in pelvis related to chronic radiation enteritis.
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Fig. 4B. —31-year-old woman with stage IB cervical cancer treated 2
years earlier with 40-Gy dose of whole-pelvis and intracavitary radiation.
Since therapy, patient had experienced long history of gastrointestinal
complaints, including weight loss, diarrhea, and recurrent bowel obstruction.
CT scan also shows radiation-related thickening of bowel wall (straight
arrow) and presacral soft tissues (curved arrows).
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Radiation damage to the colon can also be shown radiographically. Loss of
distensibility with strictures of various lengths and degrees of narrowing may
be encountered. Widening of the presacral space may also be seen
(Fig. 5). Barium studies may
show mucosal changes such as ulceration, pseudopolypoid protrusions, or
contour irregularities ranging from tiny serrations to ragged margins and even
circumferential lesions simulating malignancy (Figs.
6A,6B,6C,7,8A,8B).
Complex fistulas may also develop
[7]
(Fig. 9). The possibility of
radiation-induced colon cancers has been suggested
[6].
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Fig. 6B. —60-year-old woman treated 2 years earlier for cervical cancer
with definitive radiation. CT scan (B) and barium enema (C)
obtained 3 years after A show rectosigmoid ulceration (arrow)
that proved to be benign.
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Fig. 6C. —60-year-old woman treated 2 years earlier for cervical cancer
with definitive radiation. CT scan (B) and barium enema (C)
obtained 3 years after A show rectosigmoid ulceration (arrow)
that proved to be benign.
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Fig. 7. —40-year-old woman who had been treated for cervical cancer.
Double-contrast barium enema shows narrowing and contour irregularity of
redundant transverse colon (arrow), which had been included in
radiation field during therapy.
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Fig. 8A. —52-year-old woman who received 60-Gy whole-pelvis radiation
and 15-Gy intracavitary radiation therapy for cervical cancer. Baseline barium
enema obtained before therapy shows normal rectosigmoid.
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Fig. 8B. —52-year-old woman who received 60-Gy whole-pelvis radiation
and 15-Gy intracavitary radiation therapy for cervical cancer. Barium enema
obtained approximately 6 months after therapy reveals ulcerated stricture of
rectosigmoid and widening of presacral space. Note clips in region of
cervix.
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Fig. 9. —62-year-old woman treated with definitive radiation therapy
20 years earlier for stage IIB cervical cancer. Barium enema shows complex
fistulas (arrows), including rectovaginal and rectovesical fistulas.
b = bladder, v = vagina.
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The rectum is relatively radioresistant but is involved most commonly
because of its fixed location near organs in the pelvis that are frequently
targeted for radiotherapy [5]
(Fig. 10). The use of
large-volume balloon catheters should be avoided because of the risk of
perforation [7].
Bone and Soft-Tissue Changes
After irradiation, the highly radiosensitive hematopoietic elements of bone
undergo necrosis and fatty marrow replacement; these changes can be detected
on MR images within days of therapy (Fig.
11). Radiation also affects bone cells and vessels by leaving an
acellular, ischemic frame that on radiographs initially appears to be normal
structure [8]. The first
radiographic signs of change, demineralization and osteopenia, develop
approximately 1 year after completion of therapy, and the changes may be
progressive. Small lytic areas in irradiated bone may be difficult to
distinguish from metastatic disease. As ischemic changes progress, the bone is
more likely to fracture. Healing of irradiated bone is also abnormal.
Spontaneous fractures, nonunion of fractures, aseptic necrosis, and bone
resorption may occur [8] (Figs.
12A,12B
and
13A,13B,13C,13D).
Insufficiency fractures are frequently encountered in the sacrum, and patients
present with pain that may be clinically indistinguishable from pain related
to tumor recurrence (Fig.
14A,14B).
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Fig. 11. —43-year-old man treated for rectal cancer. Coronal
T1-weighted MR image of pelvis shows abrupt linear change in marrow signal in
iliac bones bilaterally with fatty marrow inferiorly (arrows)
corresponding to treatment portal.
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Fig. 12B. —76-year-old woman treated 10 years earlier for stage IB
cervical cancer. Conventional radiograph of pelvis obtained 2 years after
A shows right hip replacement and subcapital fracture of left hip.
Sacral and ilial radiation changes are also apparent.
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Fig. 13B. —73-year-old woman treated for cervical cancer 2 years earlier
with radiation therapy. Conventional radiograph of pelvis after therapy
reveals multiple insufficiency fractures (arrows).
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Fig. 13C. —73-year-old woman treated for cervical cancer 2 years earlier
with radiation therapy. CT scans of pelvis also reveal fractures of sacrum,
left iliac bone, and inferior pubic rami (arrows).
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Fig. 13D. —73-year-old woman treated for cervical cancer 2 years earlier
with radiation therapy. CT scans of pelvis also reveal fractures of sacrum,
left iliac bone, and inferior pubic rami (arrows).
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Fig. 14A. —63-year-old woman treated with radiation therapy for stage
IIA cervical cancer 25 years earlier; she had been involved in motor vehicle
accident 1 month before imaging and sustained known pubic fracture. Axial
T1-weighted MR images of pelvis before (A) and after (B)
administration of gadolinium show abnormal signal in right pubis (solid
arrow), which biopsy results confirmed to be radioosteonecrosis. Note
hematoma located posteriorly (open arrow).
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Fig. 14B. —63-year-old woman treated with radiation therapy for stage
IIA cervical cancer 25 years earlier; she had been involved in motor vehicle
accident 1 month before imaging and sustained known pubic fracture. Axial
T1-weighted MR images of pelvis before (A) and after (B)
administration of gadolinium show abnormal signal in right pubis (solid
arrow), which biopsy results confirmed to be radioosteonecrosis. Note
hematoma located posteriorly (open arrow).
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Soft-tissue changes in the pelvis include thickening of the perirectal
fascia and presacral fibrous tissue. Such changes should stabilize
approximately 12 weeks after completion of therapy
[7]. Secondary malignancy in
irradiated tissues is rare, with a reported incidence of 0.1%. Sarcomas may be
of soft-tissue or bony origin
[8] (Fig.
15A,15B).
The latency period for development of radiation-induced malignancy is long,
typically 10 years or more.
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Fig. 15A. —52-year-old woman treated with 40-Gy external beam therapy to
pelvis and intracavitary therapy 14 years earlier for stage IIB cervical
cancer. Enterovaginal fistula was complication of therapy. Conventional
radiograph of pelvis shows lytic destruction of right iliac bone.
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Fig. 15B. —52-year-old woman treated with 40-Gy external beam therapy to
pelvis and intracavitary therapy 14 years earlier for stage IIB cervical
cancer. Enterovaginal fistula was complication of therapy. CT scan shows bony
destruction and surrounding soft-tissue mass. Biopsy revealed high-grade
sarcoma compatible with radiation-induced sarcoma.
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Introduction
Therapeutic Technique
