Comparison of manual and inverse optimization for CT guided interstitial brachytherapy in locallyadvanced cervical cancer

Objective To investigate the dosimetric difference between inverse planning simulated annealing (IPSA) and manual optimized plan for isodose line in interstitial brachytherapy for locally advanced cervical cancer and to provide a better optimization method for clinical application. Methods A total of 104 patients with cervical cancer were enrolled in this study. They received pelvic external beam radiotherapy and interstitial brachytherapy in five fractions. Both IPSA and manual optimized plan for isodose line were used to optimize the dose in each fraction. Dose volume parameters of the two plans were compared to analyze the dosimetric outcome by paired t-test. Results There were no significant differences in mean D90 and D100 for high-risk clinical target volume (HR-CTV) and D90 for intermediate-risk clinical target volume (IR-CTV) between the two groups (P>0.05). The IPSA group had a significantly higher D100 for IR-CTV than the manual optimized group (58.36±2.06 Gy vs. 53.99±2.17 Gy, P=0.025). For organs at risk, the IPSA group had a significantly lower mean rectum D2cc and a significantly higher bladder D2cc than the manual optimized group (68.53±2.85 Gy vs. 71.77±1.79 Gy, P=0.002; 80.49±3.36 Gy vs. 78.71±2.64 Gy, P=0.034). There was no significant difference in sigmoid D2cc between the two groups (P>0.05). The IPSA group had significantly higher relative dose homogeneity index (HI) and conformity index (CI) of radiation dose for target volume than the manual optimized group (P<0.05), and there was no significant difference in overdose volume index (OI) between the two groups (P=0.107). Conclusions Compared with manual optimized plan for isodose line, IPSA can improve the dose distribution of tumor tissue, reduce mean rectum D2cc, and increase CI and HI, so it is a preferable optimized treatment planning method in clinical application. Key words: Cervical cancer; Interstitial brachytherapy; Inverse planning simulated annealing; Isodose manual optimized method; Dosimetr