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Dosimetric evaluation of a new collimator insert system for stereotactic radiotherapy

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The prototype of a stereotactic collimator set developed in our department is evaluated for clinical use. This set consists of three cylindrical blocks mounted on a tray which slides in the wedge insert of a Siemens Primus accelerator. Each block has a collimating hole along its long axis to produce radiation fields of circular cross-section at the isocentre plane with diameters of 15 mm, 20 mm and 25 mm. Different geometric and dosimetric quality assurance tests were performed and results are found within the limits set for stereotactic radiotherapy. Dosimetry results measured using Kodak EDR-2 radiographic film and a pinpoint ion chamber also show good agreement with corresponding results calculated by Monte Carlo simulation of the linear accelerator head and the collimators. Measured dosimetry data were used to adapt a conventional PLATO treatment planning system for stereotactic radiotherapy using the prototype collimator set. Treatment planning system calculations and film measurements for treatment of an intracranial lesion in an anthropomorphic head phantom using coplanar 180° arcs are compared and found to agree within 2 mm. This supports the accuracy of dose delivery using the prototype stereotactic collimators. Despite their increased penumbra (2.5–3.5 mm relative to 2–2.5 mm for commercially available collimators) the ease of construction makes the proposed stereotactic collimators an interesting alternative for accomplishing cost effective stereotactic treatments.


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Volume 80, Issue 954June 2007
Pages: 389-e124

© The British Institute of Radiology


  • ReceivedAugust 10,2005
  • RevisedAugust 28,2006
  • AcceptedSeptember 11,2006
  • Published onlineJanuary 28,2014


This work was partly supported by the EU and the Greek Ministry of Education, in the framework of the Scientific Programme “Herakleitos” and by the Special Research Account of the University of Athens.