Session Item

The study was performed to assess and compare the performance of two different RapidArc^TMoptimization algorithms such as PRO and PO by changing the Gantry speed and Dose Rate technical parameters. Additionally, the study aimed to assess the plan quality, agreement between plan delivery and TPS calculation, technical delivery performance using with trajectory log files.

Total five patients selected for this study from each site: Brain, Head and Neck, Hodgkin’s Lymphoma, Advanced Right Lung, Ca cervix. The RapidArc^TMplans were generated using Varian Eclipse TPS v15.6 PRO and PO algorithms with maximum range of Dose Rates (DR) from 100 to 600 MU/min, minimum 0.5 and maximum Gantry Speed (GS) fixed at 6.0 deg/sec. The reference plans were created for all patients by PO algorithm with GS 6.0 deg/sec and DR 600 MU/min, other plans were re-optimized using same dose constraints and objectives, for each patient 24 plans were generated and total 120 plans were created. Pretreatment gamma verification were performed using Portal dosimetry and ArcCheck to assess deliverability and accuracy. Plan quality scores were analyzed using target and OAR’s values. Trajectory log files from Truebeam LINAC controllers were collected and analyzed to verify delivery performance.

The result of the study shows: (i) Plan quality values both algorithms achieved similar results and no significant differences were observed; (ii) Closely similar results of dynamic range MU/deg is achieved across all dose rates with both gantry speed modulation and the values range from 2.244±0.38 and 2.027±0.35 (iii) Total mean Monitor Units (MU) for PO maximum is 14 % higher than the PRO; (iv) Reduced total beam on time is a major benefit of high DR and GS compare to constant DR and GS; (v) DR has higher priority over GS modulation and compensation mechanism adjustment between both algorithms are different for higher DRs. (vi) Pretreatment quality assurance in gamma evaluation (1 % & 1 mm) using Portal dose and ArcCheck analysis shows a maximum difference of 15 % in slow GS compare to max. GS. For both PO and PRO (vii) Trajectory log files maximum deviations observed for gantry positions, MU and DR results for PO and PRO were -0.1 deg, -0.03, 88.17 MU/min and -0.12 deg, -0.03, 83.84 MU/min respectively.

These results show that new PO algorithm is either clinically beneficial or neutral in terms of plan quality and efficiency in comparison to PRO. The parameters GS and DR in optimization engine might be undeviating for those variables and capable of generating plans unaided from the limits chosen. The pattern of DR variation between adjacent Control Points in PO was significantly different than PRO.