Acute effects of pelvic irradiation on the adult uterus revealed by dynamic contrast-enhanced MRI

Objective:

Pelvic radiation therapy (RT) can influence fertility in female rectal cancer survivors. Data regarding its effects on the adult uterus are scant. This study aims to evaluate the uterus before and after RT, using dynamic contrast-enhanced MRI.

Methods:

Eligible patients (n=10) received RT for rectal cancer, had an intact uterus and underwent dynamic contrast-enhanced MRI before and after RT. Seven patients were pre-menopausal.

Results:

Patients received pelvic RT (median, 50.2 Gy) with concurrent 5-fluorouracil. Five patients were treated with intensity modulated RT (IMRT) and five with a three-field technique. The median D95 of the uterus was 30 Gy; D05 was 48 Gy; and V95 was 97%. The median cervical D95 was 45 Gy; D05, 50 Gy; and V95, 100%. Cervical dose was higher with IMRT than with three-field plans (p≤0.038). On T₂ MRI, the junctional zone was visible in nine patients before and in one after RT (p=0.001). Median cervical length (2.3 vs 3.0 cm) and endometrial thickness (2.6 vs 5.9 mm) were reduced after RT (p≤0.008). In pre-menopausal patients, the volume transfer constant, K_trans, (0.069 vs 0.195, p=0.006) and the extracellular extravascular volume fraction, V_e, (0.217 vs 0.520, p=0.053) decreased.

Conclusion:

Pelvic RT significantly affected uterine anatomy and perfusion. Cervical dose was higher with IMRT than three-field plans, but no attempt was made to constrain the dose.

Advances in knowledge:

Pelvic RT significantly affects the adult uterus. These findings are crucial to understand the potential consequences of RT on fertility, and they lay the groundwork for further prospective studies.As the cure rate in locally advanced rectal cancer continues to improve, understanding the long-term sequelae of therapy is gaining importance. Research has shown that young cancer survivors are concerned about treatment-related effects on fertility, pregnancy and neonatal outcomes 1,2]. Previously, pelvic irradiation, standard in the management of locally advanced rectal cancer, invariably caused sterility in females as a result of acute ovarian failure. Currently, however, the risk of ovarian dysfunction may be greatly reduced by transposing the ovaries to the paracolic gutters before radiation therapy (RT) 3]. Additionally, an increasing number of females undergo embryo or oocyte cryopreservation before receiving RT 4]. These advances prompt the question: if a young female has undergone pelvic RT, can she carry a pregnancy to term?Answering this question requires an understanding of the effects of the pelvic RT on the uterus. Ultrasounds of paediatric cancer survivors suggest that pelvic RT alters uterine volume, distensibility and vasculature, with patients who are younger at the time of RT being the most vulnerable to these effects 5–7]. Additionally, population-based studies of paediatric cancer survivors have demonstrated an association between abdominal and/or pelvic RT and adverse pregnancy and neonatal outcomes, including placental abnormalities, pre-term delivery, low birth weight infants and perinatal mortality 8–11]. However, only sparse data exist regarding the effects of pelvic RT on the adult uterus, which may be more radioresistant.The aim of this study was to use dynamic contrast-enhanced (DCE) MRI to assess the acute effects of RT on the uterus in females treated for locally advanced rectal cancer. A second aim was to compare dosimetric parameters of conventional three-field RT and intensity modulated RT (IMRT) treatment plans.