Intracavitary Brachytherapy in Cervical Carcinoma: The Role of F18-FDGPET in Treatment Planning

Objective: concomitant chemoirradiation with cisplatinum and intracavitary brachytherapy (BT) is the standard of care in patients with locally advanced cervix cancer. Treatment planning for BT provides for the use of three dimensional imaging, such as CT scan or MRI. Positron emission Tomography with [18F] FDG currently used in staging and restaging of this malignancy, is an imaging modality that can aid in image- guided radiation treatment planning. The purpose of our feasibility study was to compare two tumour volumes during BT planning, the CT-based and PET/CT-based clinical target volume (CTVs), in order to evaluate the value of functional imaging in BT planning and if it could be related to a CT standard data set. Moreover a correlation with some clinical data after a median follow up of 47 months is reported. Methods: From June 2007 to May 2010, thirteen women with advanced cervical carcinoma were enrolled into the study. All the patients had a pretreatment PET/CT for staging. All BT fractions have been planned by CT scan and, in the first (BT1) and in the fourth fraction (BT4), FDG-PET/CT was also employed. Two volumes (CTVs) were defined: a CTVstandard, based on clinical information and on CT scan; and a CTVPET-influenced, created with the additional information brought by PET scan. Results: We compared the dimension of the two volumes and the intersection of CTVstandard and CTVPET-influenced at BT1 and BT4. A non-parametric sum rank test was used to determine the statistical significance for comparison of the two series of volumes (CTVstandard and CTVPET-influenced at BT1 and BT4). All patients completed the protocol, but out of 26 attempts of double CTVdefinition, only for 21 cases a comparison between CTVstandard and CTVPET-influenced was made. For two patients at the first BT fraction PET was negative. In the 21 valuable cases, considering both fractions together (BT1 and BT4), the difference between CTVstandard (25.8 ± 7.5 ml) and CTVPET-influenced (21.6 ± 9.5 ml) was statistically significant (p=0.01). In our small population the changes of GTVPET was unpredictable with residual tracer uptake areas often located far from the applicator and not consistent with clinical evaluation and or CT information. Conclusions: Even if the results of the study are preliminary because of the limited number of patients, our data suggests that PET scan cannot be used to define target volume in BT plan as the only source of information. It could be necessary an integration preferably with MRI for much more individualized brachytherapy treatment.