18F-FDG-PET/CT guided external beam radiotherapy volumes in inoperable uterine cervical cancer.

Background: In patients with advanced stage cancer of the uterine cervix who undergo irradiation with curative intent, there is the necessity to treat all suspicious nodes on imaging. Our hypothesis was that adding fluorodeoxyglucose positron emission computer tomography/computer tomography (FDG-PET/CT) to the imaging workup would alter the external beam radiotherapy (EBRT) treatment plan, either resulting in an extended external beam radiotherapy (EBRT) field to the para-aortal region or an additional boost to suspicious nodes. Since extended field radiotherapy or additional boost can cause toxicity, our secondary aim was to assess the incidence of severe late bowel toxicity in patients treated with extended para-aortal EBRT-field and boost compared to elective pelvic radiotherapy.

Methods: Eighty-eight patients were enrolled. First, the optimal radiation treatment plan (EBRT and boost) was retrospectively determined based on magnetic resonance imaging (MRI) or FDG-PET/CT. Second, the severe bowel toxicity caused by the extended para-aortal field was assessed, based on the executed radiotherapy.

Results: Based on MRI 8/88 patients would receive EBRT with para-aortic extension, this was 21/88 for FDG-PET/CT. Based on MRI 47/704 lymph node regions would receive additional boost, while based on PET/CT 91/704. Late severe bowel toxicity was seen in 12/84 patients, 6/65 in the group who received elective pelvic irradiation and 6/19 with para-aortal EBRT and boost at common iliac and/or para-aortal lymph nodes. Significant worse overall survival was seen of patients who needed para-aortal irradiation.

Conclusions: Addition of FDG-PET/CT leads to an extension of the elective EBRT volume and more suspicious lymph nodes receive a boost. However, when deciding to intensify radiation therapy, late severe bowel toxicity has to be taken into account.