title: Patient geometry-driven information retrieval for IMRT treatment plan quality control.
abstract: OBJECTIVE
  Intensity modulated radiation therapy (IMRT) treatment plan quality depends on the planner's level of experience and the amount of time the planner invests in developing the plan. Planners often unwittingly accept plans when further sparing of the organs at risk (OARs) is possible. The authors propose a method of IMRT treatment plan quality control that helps planners to evaluate the doses of the OARs upon completion of a new plan.
  
  
  METHODS
  It is achieved by comparing the geometric configurations of the OARs and targets of a new patient with those of prior patients, whose plans are maintained in a database. They introduce the concept of a shape relationship descriptor and, specifically, the overlap volume histogram (OVH) to describe the spatial configuration of an OAR with respect to a target. The OVH provides a way to infer the likely DVHs of the OARs by comparing the relative spatial configurations between patients. A database of prior patients is built to serve as an external reference. At the conclusion of a new plan, planners search through the database and identify related patients by comparing the OAR-target geometric relationships of the new patient with those of prior patients. The treatment plans of these related patients are retrieved from the database and guide planners in determining whether lower doses delivered to the OARs in the new plan are feasible.
  
  
  RESULTS
  Preliminary evaluation is promising. In this evaluation, they applied the analysis to the parotid DVHs of 32 prior head-and-neck patients, whose plans are maintained in a database. Each parotid was queried against the other 63 parotids to determine whether a lower dose was possible. The 17 parotids that promised the greatest reduction in D50 (DVH dose at 50% volume) were flagged. These 17 parotids came from 13 patients. The method also indicated that the doses of the other nine parotids of the 13 patients could not be reduced, so they were included in the replanning process as controls. Replanning with an effort to reduce D50 was conducted on these 26 parotids. After replanning, the average reductions for D50 of the 17 flagged parotids and nine unflagged parotids were 6.6 and 1.9 Gy, respectively. These results demonstrate that the quality control method has accurately identified not only the parotids that require dose reductions but also those for which dose reductions are marginal. Originally, 11 of out the 17 flagged parotids did not meet the Radiation Therapy Oncology Group sparing goal of V(30 Gy) < 50%. Replanning reduced them to three. Additionally, PTV coverage and OAR sparing of the original plans were compared to those of the replans by using pairwise Wilcoxon p test. The statistical comparisons show that replanning compromised neither PTV coverage nor OAR sparing.
  
  
  CONCLUSIONS
  This method provides an effective quality control mechanism for evaluating the DVHs of the OARs. Adoption of such a method will advance the quality of current IMRT planning, providing better treatment plan consistency.
authors.affiliation: Department of Radiation Oncology and Molecular Radiation Science, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21231, USA. bwu10@jhmi.edu
authors.forename: Binbin
authors.initials: B
authors.lastname: Wu
authors.forename: Francesco
authors.initials: F
authors.lastname: Ricchetti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Sanguineti
authors.forename: Misha
authors.initials: M
authors.lastname: Kazhdan
authors.forename: Patricio
authors.initials: P
authors.lastname: Simari
authors.forename: Ming
authors.initials: M
authors.lastname: Chuang
authors.forename: Russell
authors.initials: R
authors.lastname: Taylor
authors.forename: Robert
authors.initials: R
authors.lastname: Jacques
authors.forename: Todd
authors.initials: T
authors.lastname: McNutt
mesh_terms: D005240:Feasibility Studies; D006801:Humans; D011786:Quality Control; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000592:standards*; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*