Affordable Access

Publisher Website

An in-vivo dosimetry procedure for Elekta step and shoot IMRT

Authors
Journal
Physica Medica
1120-1797
Publisher
Elsevier
Volume
30
Issue
4
Identifiers
DOI: 10.1016/j.ejmp.2013.11.005
Keywords
  • Imrt In-Vivo Dosimetry
  • Electronic Portal Imaging Device
  • Dosimetry
  • Radiotherapy
Disciplines
  • Computer Science
  • Medicine

Abstract

Abstract Purpose The aim of this work was to extend an in-vivo dosimetry (IVD) method, previously developed by the authors for 3D-conformal radiotherapy, to step and shoot IMRT treatments for pelvic tumors delivered by Elekta linacs. Materials and methods The algorithm is based on correlation functions to convert EPID transit signals into in-vivo dose values at the isocenter point, Diso. The EPID images were obtained by the so-called “IMRT Dosimetric Weighting” mode as a superposition of many segment fields. This way each integral dosimetric image could be acquired in about 10 s after the end of beam delivery and could be processed while delivering the successive IMRT beams. A specific algorithm for Diso reconstruction especially featured for step and shoot IMRT was implemented using a fluence inhomogeneity index, FI, introduced to describe the degree of beam modulation with respect to open beams. A γ-analysis of 2D-EPID images obtained day to day, resulted rapid enough to verify the plan delivery reproducibility. Results Fifty clinical IMRT beams, planned for patients undergoing radiotherapy of pelvic tumors, were used to irradiate a homogeneous phantom. For each beam the agreement between the reconstructed dose, Diso, and the TPS computed dose, Diso,TPS, was well within 5%, while the mean ratio R = Diso/Diso,TPS resulted for 250 tests equal to 1.006 ± 0.036. The same beams were checked in vivo, i.e. during patient treatment delivery, obtaining 500 tests whose average R ratio resulted equal to 1.011 ± 0.042. The γ-analysis of the EPID images with 5% 3 mm criteria supplied 85% of the tests with pass rates γmean ≤ 0.5 and Pγ<1 ≥ 90%.

There are no comments yet on this publication. Be the first to share your thoughts.

Statistics

Seen <100 times
0 Comments

More articles like this

111. In vivo dosimetry and IMRT

on Reports of Practical Oncology... Jan 01, 2003

Dosimetry limitations and a dose correction method...

on Physics in Medicine and Biolog... Feb 07, 2006

aSi-EPID transit signal calibration for dynamic be...

on Medical & Biological Engineeri... Jan 01, 2013

Deliverable navigation for multicriteria step and...

on Physics in Medicine and Biolog... Jan 07, 2013
More articles like this..