A Comparison of Forward Planning vs. Inverse Planning Simulated Annealing for Accelerated Partial Breast Irradiation Multi Channel Catheter Brachytherapy

Abstract

Provide a comparison and educate those planning Accelerated Partial Breast Irradiation (APBI) multi channel catheter brachytherapy with either forward or inverse planning systems for a skin distance of less than 7mm. The following will demonstrate, in this particular study, which of the two planning processes is more beneficial for the patient. Prior to this study, the participating clinic used Inverse Planning Simulated Annealing (IPSA) for all of its APBI multi channel catheter brachytherapy planning purposes. In order to make a comparison of the forward planning and the IPSA results, a selection of 3 out of 56 patients were chosen that had a skin distance of less than 7mm. These three patients A,B, and C then received a planning CT and were contoured identically. Firstly for all 3 of the patients the forward plan was completed. The next step was to place the catheters in the 4 channels and then activate all of the possible dwell positions. During the forward planning process, points were then dropped on the outer edge of the PTVeval in order to normalize and optimize the prescription dose of 340cGy to these selected points. Then using the NSABP 39 protocol, a set of predetermined information is compared to the outcome of the current plan and can then be changed in order to fall within the guidelines. The plan was then adjusted by different methods including graphical manipulation and changing or eliminating the manual weighting of the dwells. This process was completed until the planner and doctor were satisfied with the outcomes of the stated criteria. In regards to IPSA based planning, first the catheters are reconstructed but then the input IPSA presets are used and a plan is created. This plan was then adjusted by simply changing the dose and weight to various targets and OAR's. This process was again completed until the criteria were met. Patients A, B, and C were then evaluated and compared for certain previously determined criteria. Table 1 shows the planning structure evaluation for all of the patients. As it is shown for 2/3 patients, the V150 and maximum rib dose were lower for the forward planing process. For all 3 of the patients, the V200 and whole breast evaluations were also lower for the forward planning process. On the other hand, 2/3 patients had a lower maximum skin dose with IPSA. Finally the V90 and the time to plan were almost equivalent for both the forward and IPSA planning process. From these results, it can be concluded that forward planning could be as good as or even better in certain circumstances than IPSA. Despite this study only containing 3 patients, it still provides insight into using the more appropriate planning process to benefit the patient. This study shows that forward planning is as good or even better than using IPSA for treatment planning of APBI multi catheter brachytherapy in a selected class of patients. Therefore, for an initial start-up clinic using the IPSA based planning would be easier. Then once experience has been gained by the planner, using forward planning could be accomplished. In order to continue this study, all of the patients at this particular institution will be planned with both forward and IPSA planning processes and a comparison will be made in order to choose the best plan for each patient.Table 1Planning Structure EvaluationPATIENT APATIENT BPATIENT CMANUALIPSAMANUALIPSAMANUALIPSAV150 OF PTV_EVAL (cc)19.0322.1419.0924.5319.0718.29V200 OF PTV_ EVAL (cc)4.847.374.458.313.894.02V90 OF PTV_EVAL91.56%91.88%90.45%92.75%91.19%91.52%WHOLE BREAST EVAL43.42%44.90%19.70%20.96%35.71%35.82%MAX RIB DOSE (cGy)481456351393368391MAX SKIN DOSE (cGy)443462480454453386TIME TO PLAN20:28.0014:14.0013:15.0014:26.0012:05.0010:33.00 Open table in a new tab