Assessment of Plan IQ Feasibility DVH for head and neck treatment planning

Designing a radiation plan that optimally delivers both target coverage and normal tissue sparing is challenging. There are limited tools to determine what is dosimetrically achievable and frequently the experience of the planner/physician is relied upon to make these determinations. Plan IQ software provides a tool that uses target and organ at risk ( OAR ) geometry to indicate the difficulty of achieving different points for organ dose–volume histograms ( DVH ). We hypothesized that Plan IQ Feasibility DVH may aid planners in reducing dose to OAR s. Methods and materials Clinically delivered head and neck treatments (clinical plan) were re‐planned (re‐plan) putting high emphasis on maximally sparing the contralateral parotid gland, contralateral submandibular gland, and larynx while maintaining routine clinical dosimetric objectives. The planner was blinded to the results of the clinically delivered plan as well as the Feasibility DVH s from Plan IQ . The re‐plan treatments were designed using 3‐arc VMAT in Raystation (RaySearch Laboratories, Sweden). The planner was then given the results from the Plan IQ Feasibility DVH analysis and developed an additional plan incorporating this information using 4‐arc VMAT ( IQ plan). The DVH s across the three treatment plans were compared with what was deemed “impossible” by Plan IQ 's Feasibility DVH (Impossible DVH ). The impossible DVH (red) is defined as the DVH generated using the minimal dose that any voxel outside the targets must receive given 100% target coverage. Results The re‐plans performed blinded to Plan IQ Feasibilty DVH achieved superior sparing of aforementioned OAR s compared to the clinically delivered plans and resulted in discrepancies from the impossible DVH s by an average of 200–700 cG y. Using the Plan IQ Feasibility DVH led to additional OAR sparing compared to both the re‐plans and clinical plans and reduced the discrepancies from the impossible DVH s to an average of approximately 100 cG y. The dose reduction from clinical to re‐plan and re‐plan to IQ plan were significantly different even when taking into account multiple hypothesis testing for both the contralateral parotid and the larynx ( P < 0.004 for all comparisons). No significant differences were observed between the three plans for the contralateral parotid when considering multiple hypothesis testing. Conclusions Clinical treatment plans and blinded re‐plans were found to suboptimally spare OAR s. Plan IQ could aid planners in generating treatment plans that push the limits of OAR sparing while maintaining routine clinical target coverage goals.