title: Dosimetric verification of IMAT delivery with a conventional EPID system and a commercial portal dose image prediction tool.
abstract: OBJECTIVE
  The electronic portal imaging device (EPID) is a system for checking the patient setup; as a result of its integration with the linear accelerator and software customized for dosimetry, it is increasingly used for verification of the delivery of fixed-field intensity-modulated radiation therapy (IMRT). In order to extend such an approach to intensity-modulated arc therapy (IMAT), the combined use of an EPID system and a portal dose image prediction (PDIP) tool has been investigated.
  
  
  METHODS
  The dosimetric behavior of an EPID system, mechanically reinforced to maintain its positional stability during the accelerator gantry rotation, has been studied to assess its ability to measure portal dose distributions for IMAT treatment beams. In addition, the PDIP tool of a commercial treatment planning system, commonly used for static IMRT dosimetry, has been validated for simulating the PDIs of IMAT treatment fields. The method has been applied to the delivery verification of 23 treatment fields that were measured in their dual mode of IMRT and IMAT modalities.
  
  
  RESULTS
  The EPID system has proved to be appropriate for measuring the PDIs of IMAT fields; additionally the PDIP tool was able to simulate these accurately. The results are quite similar to those obtained for static IMRT treatment verification, although it was necessary to investigate the dependence of the EPID signal and of the accelerator monitor chamber response on variable dose rate.
  
  
  CONCLUSIONS
  Our initial tests indicate that the EPID system, together with the PDIP tool, is a suitable device for the verification of IMAT plan delivery; however, additional tests are necessary to confirm these results.
authors.affiliation: Servizio di Fisica Sanitaria, Arceispedale S. Maria Nuova, Reggio Emilia 42100, Italy. iori.mauro@asmn.re.it
authors.forename: Mauro
authors.initials: M
authors.lastname: Iori
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Cagni
authors.forename: Marta
authors.initials: M
authors.lastname: Paiusco
authors.forename: Peter
authors.initials: P
authors.lastname: Munro
authors.forename: Alan E
authors.initials: AE
authors.lastname: Nahum
mesh_terms: D000465:Algorithms; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D011874:Radiometry / Q000295:instrumentation*; D011879:Radiotherapy Dosage; D020266:Radiotherapy, Conformal / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012984:Software; D014963:X-Ray Intensifying Screens