Dosimetric comparison of graphical optimization and inverse planning simulated annealing for brachytherapy of cervical cancer

Abstract

Purpose Graphical optimization (GO) and inverse planning simulated annealing (IPSA) are the main treatment planning optimization techniques used in patients undergoing 3D brachytherapy treatment. This study aims to compare the dosimetric difference of plans optimized by GO and IPSA in cervical cancer brachytherapy. Material and methods 21 cervical cancer patients data sets consisted of computed tomography (CT) and magnetic resonance imaging (MRI), acquired with the Fletcher applicator in situ were transferred to the Oncentra brachytherapy planning system. For each patient, the treatment plan was initially optimized with GO to reach a maximal D90 tumor dose (6 Gy/fraction, 5 fractions), while keeping the dose to organs at risk (OARs) as low as possible. A second plan was then optimized with IPSA on the same CT images and data set (i.e., contours, catheters, and location of dwell points). Targets and OARs dose volume histograms and irradiation time were compared; data were analyzed with paired t-test; p value < 0.05 was considered statistically significant. Results The plans with both optimizations meet the clinical requirements. The mean D90 of the clinical target volume was comparable for GO and IPSA. Similar values (p > 0.05) of target V100, V150, V200, HI, and CI were registered for GO and IPSA optimizations. Bladder and rectum D1cc and D2cc obtained by GO resulted in larger values than those obtained by IPSA (p = 0.002). V75 for bladder and rectum were slightly higher for IPSA, but without statistical difference (p > 0.05). The irradiation time was comparable (p > 0.05). Conclusions In 3D brachytherapy of cervical cancer, GO and IPSA optimizations do not present a significant difference in target dose coverage; nevertheless, IPSA may reduce the maximum dose to normal tissue when compared with GO.