Reduction of Intra-Dosimetrist Variation, and Improvement of Overall Plan Quality as Assessed by Dose-Volume Histograms, Through Training and Implementation of Advanced Optimization Tools

Abstract

Our Cancer Center network comprises a research Cancer Center as well as 10 independent community practices, with 18 total Dosimetrists. Many steps have been taken to increase treatment planning standardization, while dosimetry techniques and practices across the system have remained independent, with limited use of advanced optimization tools, knowledge-based planning (KBP) and multi-criteria optimization (MCO). With the objective to improve standardization of techniques, identify best practices, and improve overall quality, we implemented an in-house dosimetry plan challenge and solicited participation from 18 dosimetrists within the network.We anonymized an existing intermediate risk prostate adenocarcinoma clinical T1c N0 M0 patient dataset with physician drawn target contours (prostate plus proximal 1cm seminal vesicles) and normal structures, to create an identical test case for each dosimetrist. Clinically relevant planning objectives were provided in addition to instructions to produce a plan of clinical quality, committing typical clinical time/effort, using only standard optimization tools. Following submission of all plans, the results were discussed with the dosimetry team, including evaluations of dose-volume histograms (DVH). Instruction was provided on the advanced optimization tools KBP and MCO. Dosimetrists were instructed to repeat the challenge with the explicit instruction to use KBP and MCO. KBP/MCO plan results were compared to the plan results without KBP/MCO use to show the overall impact of advanced tools on achieved plan quality and intra-dosimetrist variation. All plans were explicitly normalized to the PTV D100% = 95% to allow direct comparison of DVHs.All initial plans submitted by 16 dosimetrists met the prescribed objectives outlined for clinical practice. However, plans demonstrated a wide range of acceptable dose-volume histograms. In addition to visual evaluation of the DVHs, multiple dose points for the Target (PTV), Rectum and Bladder, were exported for comparison between groups of plans. The group average achieved bladder doses were reduced from 52.8%Rx to 41.9%Rx, 23.9%Rx to 15.5%Rx, and 6.3%Rx to 5.5%Rx at D15%, D30%, and D60% respectively. The group average achieved rectal doses were reduced from 62.3%Rx to 45.8%Rx, 49.3%Rx to 32.7%Rx, and 33.9%Rx to 19.9%Rx at D10%, D20%, and D40% respectively. Similarly, the standard deviations also showed marked decrease with those for the bladder reduced from 0.084 to 0.044, 0.067 to 0.02, and 0.014 to 0.010 for D15%, D30%, and D60% respectively, and those for rectum reduced from 0.106 to 0.0690, 0.109 to 0.066, 0.086 to 0.038 at D10%, D20%, and D40% respectively.Standardization of clinical treatment planning objectives and consistent use of advanced optimization tools can improve overall planning quality and reduce intra-dosimetrist variation of treatment planning results based on clinical DVH metrics.