title: Adaptive beamlet-based finite-size pencil beam dose calculation for independent verification of IMRT and VMAT.
abstract: OBJECTIVE
  The use of sophisticated dose calculation procedure in modern radiation therapy treatment planning is inevitable in order to account for complex treatment fields created by multileaf collimators (MLCs). As a consequence, independent volumetric dose verification is time consuming, which affects the efficiency of clinical workflow. In this study, the authors present an efficient adaptive beamlet-based finite-size pencil beam (AB-FSPB) dose calculation algorithm that minimizes the computational procedure while preserving the accuracy.
  
  
  METHODS
  The computational time of finite-size pencil beam (FSPB) algorithm is proportional to the number of infinitesimal and identical beamlets that constitute an arbitrary field shape. In AB-FSPB, dose distribution from each beamlet is mathematically modeled such that the sizes of beamlets to represent an arbitrary field shape no longer need to be infinitesimal nor identical. As a result, it is possible to represent an arbitrary field shape with combinations of different sized and minimal number of beamlets. In addition, the authors included the model parameters to consider MLC for its rounded edge and transmission.
  
  
  RESULTS
  Root mean square error (RMSE) between treatment planning system and conventional FSPB on a 10 × 10 cm(2) square field using 10 × 10, 2.5 × 2.5, and 0.5 × 0.5 cm(2) beamlet sizes were 4.90%, 3.19%, and 2.87%, respectively, compared with RMSE of 1.10%, 1.11%, and 1.14% for AB-FSPB. This finding holds true for a larger square field size of 25 × 25 cm(2), where RMSE for 25 × 25, 2.5 × 2.5, and 0.5 × 0.5 cm(2) beamlet sizes were 5.41%, 4.76%, and 3.54% in FSPB, respectively, compared with RMSE of 0.86%, 0.83%, and 0.88% for AB-FSPB. It was found that AB-FSPB could successfully account for the MLC transmissions without major discrepancy. The algorithm was also graphical processing unit (GPU) compatible to maximize its computational speed. For an intensity modulated radiation therapy (∼12 segments) and a volumetric modulated arc therapy fields (∼90 control points) with a 3D grid size of 2.0 × 2.0 × 2.0 mm(3), dose was computed within 3-5 and 10-15 s timeframe, respectively.
  
  
  CONCLUSIONS
  The authors have developed an efficient adaptive beamlet-based pencil beam dose calculation algorithm. The fast computation nature along with GPU compatibility has shown better performance than conventional FSPB. This enables the implementation of AB-FSPB in the clinical environment for independent volumetric dose verification.
authors.affiliation: Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
authors.forename: Justin C
authors.initials: JC
authors.lastname: Park
authors.affiliation: Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
authors.forename: Jonathan G
authors.initials: JG
authors.lastname: Li
authors.affiliation: Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
authors.forename: Lahcen
authors.initials: L
authors.lastname: Arhjoul
authors.affiliation: Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
authors.forename: Guanghua
authors.initials: G
authors.lastname: Yan
authors.affiliation: Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
authors.forename: Bo
authors.initials: B
authors.lastname: Lu
authors.affiliation: Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
authors.forename: Qiyong
authors.initials: Q
authors.lastname: Fan
authors.affiliation: Department of Radiation Oncology, University of Florida, Gainesville, Florida 32610-0385.
authors.forename: Chihray
authors.initials: C
authors.lastname: Liu
mesh_terms: D000465:Algorithms; D003196:Computer Graphics / Q000295:instrumentation; D006801:Humans; D008962:Models, Theoretical; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods; D050397:Radiotherapy, Intensity-Modulated / Q000379:methods*; D013997:Time Factors