Study of the feasibility of needle path optimization in 3D brachytherapy for cervical cancer

Objective: To compare the dosimetric differences between free-hand method and virtually optimized method for implanting needles in intracavitary and interstitial combined brachytherapy (IC/IS BT) of cervical cancer, and to explore the improvement space of the existing interstitial brachytherapy plan. Methods: High-dose-rate cervical cancer IC/IS BT plans (short for Treatment-Plan) of 18 cases were retrospectively analyzed. For each treatment plan, Nucletron Oncentra 3D brachytherapy planning system was utilized to redesign the virtually optimized insertion method IC/IS BT plan (short for Optimized-Plan). Dose volume histogram was adopted to evaluate the dose distribution in high-risk clinical target areas and exposure dose to organ at risk (OAR). The plan execution efficiency between two plans was also assessed. Results: Comparing these two plans, the differences in conformity and uniformity of dose distribution of the target area were statistically significant (P = 0.000, 0.008). The differences of D_{0.01 cm³}, D_{1 cm³}, D_{2 cm³} and D_{5 cm³} in bladder, rectum, sigmoid and small bowel were all statistically significant (all P < 0.05). Optimized-Plan could reduce the D_{2 cm³} of bladder, rectum, sigmoid and small bowel by 60.41, 36.43, 27.53 and 12.43 cGy, respectively. The execution time for the Treatment-Plan and Optimized-Plan were (857.92 ± 243.39) s and (804.53 ± 239.13) s with statistical significance (P < 0.001). Conclusions: Compared with the free-hand method, virtually optimized method yields more conformable coverage of the target area and more uniform dose distribution. At the same time, the doses of each OAR are reduced to different degrees and the execution time of the plan is also shortened. (authors)