Comparison of IPSA with dose-point optimization and manual optimization for interstitial template brachytherapy for gynecologic cancers

Abstract

Purpose: To compare inverse planning simulated annealing (IPSA) algorithm with the dose-point optimized (DPO) plan and manual/graphically optimized (GrO) plan for interstitial template brachytherapy for gynecologic cancers.

Methods and materials: The data set of 10 consecutive patients was selected for this dosimetric study. For each patient, three plans were calculated: DPO, GrO, and IPSA. Dose-volume parameters from the three plans were compared to analyze the dosimetric outcome.

Results: Coverage of the clinical target volume (CTV) with GrO plan and IPSA algorithm was significantly better (mean V(100) of 88.8% and 89.1%; p=0.006) as compared with DPO plan (83.7%; p=0.62). Similarly, mean D(90) was same in both GrO plan and IPSA, 3.96±0.23 and 3.96±0.15Gy, respectively. DPO plans were homogeneous with homogeneity index being 0.82 as compared with 0.68±0.05 of GrO plan and 0.71±0.04 of IPSA. However, IPSA resulted in high conformity with conformity index of 0.78 as compared with 0.72 (p=0.001) and 0.68 (p≤0.001) for GrO and DPO plans, respectively. The dose to rectum (3.3±1.06Gy) and bladder (3.17±0.5Gy) was generally high for DPO plan. GrO plan reduced the dose to the rectum (2.91±0.63; p=0.011) and bladder (2.89±0.63Gy; p=0.003) significantly. IPSA resulted in a further reduction of the dose to rectum (2.79±0.67Gy; p=0.046) and bladder (2.81±0.67Gy; p=0.035), however with no statistical significance as compared with GrO plan.

Conclusion: IPSA resulted in significant sparing of normal tissues without compromising CTV coverage as compared with DPO plan. However, IPSA did not show any significant improvement either in CTV coverage or in normal tissue sparing as compared with GrO plan. IPSA was found to be superior in terms of homogeneity and conformity as compared with GrO plan.