title: Dosimetric consequences of pancreatic tumor motion when predetermined treatment margins are employed during intensity-modulated radiation therapy.
abstract: OBJECTIVE
  To quantify the dosimetric consequences of pancreatic tumor motion on the pancreatic intensity-modulated radiation therapy (IMRT) plans.
  
  
  METHODS
  Dose map of IMRT plans for 5 patients with pancreatic cancer were measured using a 2D diode array placed on a computer-controlled platform to simulate 2D pancreatic tumor motion. Dosimetric analysis was then performed to obtain IMRT quality assurance (QA) passing rates. The convolution method, which used a motion kernel to simulate 2D pancreatic motion, was also applied to the treatment and phantom verification plans for a wide range of magnitudes of motion (0.8-2.0 cm). The resulting motion-convolved verification dose maps (VDMs) were compared with the dynamic measurements to evaluate IMRT QA passing rates as well as the dose-volume histogram, the V95% of the planning target volume (PTV) and V98% of the clinical target volume (CTV).
  
  
  RESULTS
  While CTV coverage was maintained when the simulated pancreatic tumor drifted inside the PTV with magnitudes of 1.0 cm and 1.5 cm, the V95% of the PTV was reduced by 10% and 17%, respectively. We also found that the differences between the measurements and the static VDMs increased proportional to the amplitude of motion, while the agreement between the measurements and the motion-convolved VDMs was excellent for any magnitude of motion.
  
  
  CONCLUSIONS
  When the 4D technique is not available, predetermined margins must be used carefully to avoid possible under-dose to the target. Additionally, the phantom results show that the kernel convolution method provides an accurate evaluation of the dosimetric impact due to tumor motion and it should be employed in the planning process.
authors.affiliation: Department of Radiation Oncology, University of Pennsylvania School of Medicine, PA, USA. Jiajian.Shen@uphs.upenn.edu
authors.forename: J
authors.initials: J
authors.lastname: Shen
authors.forename: J M
authors.initials: JM
authors.lastname: Metz
authors.forename: T C
authors.initials: TC
authors.lastname: Zhu
authors.forename: J
authors.initials: J
authors.lastname: Panetta
authors.forename: J C
authors.initials: JC
authors.lastname: Finlay
authors.forename: M
authors.initials: M
authors.lastname: Xu-Welliver
authors.forename: J P
authors.initials: JP
authors.lastname: Plastaras
authors.forename: V
authors.initials: V
authors.lastname: Bar Ad
authors.forename: S
authors.initials: S
authors.lastname: Both
mesh_terms: D006801:Humans; D010190:Pancreatic Neoplasms / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D050397:Radiotherapy, Intensity-Modulated / Q000592:standards