SU‐E‐T‐243: Analysis of Planner Dependence in IMRT

Purpose: To establish trends in the observed variations within large sets of IMRT treatment plans. Past data of comparable treatments are statistically analyzed to identify clinical preferences and establish best practices for future decision‐making processes. Methods: We propose three statistical measures of variations in the DVH of 100 head and neck cancer patients from IU‐Simon Cancer Center: a) Standard deviation for delivered dose, std(D), to specific volumes, b) standard deviation for volume, std(V), receiving a specific of dose, and c) a steepness measure for DVH and 1‐standard deviation at specific dose points as a measure for falloff preference. Results: The three methods show considerable variation amongst DVHs: a) Negligible dose deviation until 70% volume, a steady increase to std(D)=22% at 100% volume, followed by a steady decrease to std(D)=0% at 115% volume. On the other hand, b) standard deviation of volume is rather constant at 3% until at high volumes (100%), where it increases to 15%. c) Average steepness of DVH over the 100 patients is negligible until 94% dose, after which it falls steadily to −13 at 104% dose. It then steadily climbs back to 0 at 110% dose. This change depicts the dose falloff on a typical DVH. The 1 standard deviation spread is most evident between 96% and 110% dose, with a maximum of 7.2 at 103% dose. Furthermore, there is a ripple effect at 85% dose with a standard deviation of 1.8 that is distinct from the usual trend. Conclusion: Unanimous decisions for DVHs exist only at lower values of volume and dose. However, significant variations are found in the falloff region of the DVH. For this region, the increased variations in the steepness suggest that individual preferences are more divergent. A closer unanimity in future decision‐making may lead to enhanced planner independence of IMRT treatments. Joint Purdue‐IU Seed Grant.