Imaging Effects of Radiation Therapy in the Abdomen and Pelvis: Evaluating “Innocent Bystander” Tissues

Abstract

Accurate interpretation of posttherapeutic images obtained in radiation oncology patients requires familiarity with modern radiation therapy techniques and their expected effects on normal tissues. Three-dimensional conformal external-beam radiation therapy techniques (eg, intensity-modulated radiation therapy, stereotactic body radiation therapy), although they are designed to reduce the amount of normal tissue exposed to high-dose radiation, inevitably increase the amount of normal tissue that is exposed to low-dose radiation, with the potential for resultant changes that may evolve over time. Currently available internal radiation therapy techniques (eg, arterial radioembolization for hepatic malignancies, brachytherapy for prostate cancer and gynecologic cancers) also carry risks of possible injury to adjacent nontargeted tissues. The sensitivity of tissues to radiation exposure varies according to the tissue type but is generally proportional to the rate of cellular division, with rapidly regenerating tissues such as intestinal mucosa being the most radiosensitive. The characteristic response to radiation-induced injury likewise varies according to tissue type, with atrophy predominating in epithelial tissue whereas fibrosis predominates in stromal tissue. Moreover, changes in irradiated tissues evolve over time: In the liver, decreased attenuation at computed tomography and increased signal intensity at T2-weighted magnetic resonance imaging reflect hyperemia and edema in the early posttherapeutic period; later, veno-occlusive changes alter the hepatic enhancement pattern; and finally, fibrosis develops in some patients. In the small bowel, wall thickening and mucosal hyperenhancement predominate initially, whereas luminal narrowing is the most prominent feature of chronic enteropathy. Correlation of posttherapeutic images with images used for treatment planning may be helpful when interpreting complex cases.

Tumor response assessment by MRI following stereotactic body radiation therapy for hepatocellular carcinoma

“…These include ring-like [20] T2-weighted high intensity and arterial enhanced signals, corresponding with an altered inflammatory zone with veno-occlusive damage [20]. These perilesional changes can mimic tumor progression, especially when the tumor arterial enhancement persists on the first imaging controls.…”

MDCT findings in small bowel obstruction: implications of the cause and presence of complications on treatment decisions

“…By contrast, chronic radiation enteropathy may develop months to years after radiation exposure and manifests as luminal narrowing and stricture formation secondary to fibrosis, which can also lead to SBO [32].…”

“…Within the gastrointestinal tract, the small bowel is most susceptible to the effect of radiation due to its rapid cellular turnover [32]. Acute radiation enteropathy occurs in the first few days or weeks after exposure and is characterized by mucosal hyperenhancement and bowel wall thickening, which can result in acute SBO (Fig.…”

Radiation-Induced Liver Injury Mimicking Metastatic Disease in a Patient With Esophageal Cancer

“…14,15 Subsequent atrophy, fibrosis, or both of incidentally radiated liver parenchyma have been reported on long-term follow-up. 15 This case exhibits the reported imaging and clinical laboratory findings of focal radiation-induced liver injury. Although the patient remained asymptomatic, posttherapy laboratories showed rising liver enzymes with near normalization 2 months after completion of radiation therapy.…”