title: Algorithms used in heterogeneous dose calculations show systematic differences as measured with the Radiological Physics Center's anthropomorphic thorax phantom used for RTOG credentialing.
abstract: OBJECTIVE
  To determine the impact of treatment planning algorithm on the accuracy of heterogeneous dose calculations in the Radiological Physics Center (RPC) thorax phantom.
  
  
  METHODS
  We retrospectively analyzed the results of 304 irradiations of the RPC thorax phantom at 221 different institutions as part of credentialing for Radiation Therapy Oncology Group clinical trials; the irradiations were all done using 6-MV beams. Treatment plans included those for intensity-modulated radiation therapy (IMRT) as well as 3-dimensional conformal therapy (3D-CRT). Heterogeneous plans were developed using Monte Carlo (MC), convolution/superposition (CS), and the anisotropic analytic algorithm (AAA), as well as pencil beam (PB) algorithms. For each plan and delivery, the absolute dose measured in the center of a lung target was compared to the calculated dose, as was the planar dose in 3 orthogonal planes. The difference between measured and calculated dose was examined as a function of planning algorithm as well as use of IMRT.
  
  
  RESULTS
  PB algorithms overestimated the dose delivered to the center of the target by 4.9% on average. Surprisingly, CS algorithms and AAA also showed a systematic overestimation of the dose to the center of the target, by 3.7% on average. In contrast, the MC algorithm dose calculations agreed with measurement within 0.6% on average. There was no difference observed between IMRT and 3D CRT calculation accuracy.
  
  
  CONCLUSIONS
  Unexpectedly, advanced treatment planning systems (those using CS and AAA algorithms) overestimated the dose that was delivered to the lung target. This issue requires attention in terms of heterogeneity calculations and potentially in terms of clinical practice.
authors.affiliation: Radiological Physics Center, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA. sfkry@mdanderson.org
authors.forename: Stephen F
authors.initials: SF
authors.lastname: Kry
authors.forename: Paola
authors.initials: P
authors.lastname: Alvarez
authors.forename: Andrea
authors.initials: A
authors.lastname: Molineu
authors.forename: Carrie
authors.initials: C
authors.lastname: Amador
authors.forename: James
authors.initials: J
authors.lastname: Galvin
authors.forename: David S
authors.initials: DS
authors.lastname: Followill
mesh_terms: D000465:Algorithms; D002173:Cancer Care Facilities; D003406:Credentialing; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000532:radiotherapy*; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D018787:Radiation Oncology; D011859:Radiography; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal; D050397:Radiotherapy, Intensity-Modulated; D012189:Retrospective Studies; D013909:Thorax