title: EPID in vivo dosimetry in RapidArc technique.
abstract: OBJECTIVE
  The aim of the study was to estimate the dose at the reference point applying an aSi-EPID device in the course of patient treatment.
  
  
  METHODS
  The method assumes direct proportionality between EPID signal and dose delivered to the patient reference point during the treatment session. The procedure consists of treatment plan calculation for the actual patient in the arc technique. The plan was realized with an elliptic water-equivalent phantom. An ionization chamber inside the phantom measured the dose delivered to the reference point. Simultaneously, the EPID matrix measured the CU distribution. EPID signal was also registered during patient irradiation with the same treatment plan. The formula for in vivo dose calculation was based on the CU(g) function, EPID signal registered during therapy and the relation between the dose and EPID signal level measured for the phantom. In vivo dose was compared with dose planned with the treatment planning system. Irradiation was performed with a Clinac accelerator by Varian Medical Systems in the RapidArc technique. The Clinac was equipped with an EPID matrix (electronic portal image device) of aSi-1000. Treatment plans were calculated with the Eclipse/Helios system. The phantom was a Scanditronix/Wellhöfer Slab phantom, and the ionization chamber was a 0.6 ccm PTW chamber.
  
  
  RESULTS
  In vivo dose calculations were performed for five patients. Planned dose at the reference point was 2 Gy for each treatment plan. Mean in vivo dose was in the range of 1.96-2.09.
  
  
  CONCLUSIONS
  Our method was shown to be appropriate for in vivo dose evaluation in the RapidArc technique.
authors.affiliation: Centre of Oncology - Maria Sklodowska Curie, Memorial Institute, Branch Gliwice, Radiotherapy and Brachytherapy Planning Department, Poland.
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Slosarek
authors.affiliation: Centre of Oncology - Maria Sklodowska Curie, Memorial Institute, Branch Gliwice, Radiotherapy and Brachytherapy Planning Department, Poland.
authors.forename: Marta
authors.initials: M
authors.lastname: Szlag
authors.affiliation: Centre of Oncology - Maria Sklodowska Curie, Memorial Institute, Branch Gliwice, Radiotherapy and Brachytherapy Planning Department, Poland.
authors.forename: Barbara
authors.initials: B
authors.lastname: Bekman
authors.affiliation: Centre of Oncology - Maria Sklodowska Curie, Memorial Institute, Branch Gliwice, Radiotherapy and Brachytherapy Planning Department, Poland.
authors.forename: Aleksandra
authors.initials: A
authors.lastname: Grzadziel
keywords: Arc technique; Electronic portal imaging device; IMRT; Portal dosimetry; Verification