caa a22 4500 445304162 CHVBK 20180317142607.0 cr unu---uuuuu 170323e20100301xx s 000 0 eng 10.1007/s13246-010-0004-x doi (NATIONALLICENCE)springer-10.1007/s13246-010-0004-x Intensity modulated radiation therapy (IMRT) surface dose measurements using a PTW advanced Markus chamber [Elektronische Daten] [F. Chen, R. Gupta, P. Metcalfe] A new PTW advanced Markus ionization chamber has been implemented in IMRT fields, to measure surface dose at ICRU and ICRP reference depth of 0.07mm [ICRU Report 39, Determination of dose equivalents resulting from external radiation sources, 1985; ICRP Publication 60, 1990 recommendations of the International Commission on Radiological Protection, 1991]. This chamber has a small radius with a revised guard ring design, therefore less prone to surface over-response effects. The over response correction for advanced Markus chamber is 3.3%, which is significantly smaller than 10.1% which was the original Markus chamber over response. After over response correction, the surface dose can be accurately measured by either data extrapolation or by adding one layer of plastic sheet protector to the top of Markus chamber. The surface dose measurements for small fields, e.g 3×3cm, the polarity effect of advanced Markus chamber is 12%, which is significantly higher than the 5% polarity effect of the original Markus. For a 12×12cm field size, surface dose (at 0.07mm) measured by advanced Markus chamber is 19.8% for open field and 19.2% for an unmodulated step-and-shoot IMRT field. The variation in surface dose due to intensity modulated IMRT fields has also been investigated. For an intensity modulated, step-wedge IMRT field, surface dose varies from 15.7±1% for the highest intensity segment to 26.9±1% for the lowest intensity segment. The results of chamber measurements have been compared against EBT type GAFCHROMIC® film results. Australasian College of Physical Scientists and Engineers in Medicine, 2010 Surface dose nationallicence IMRT nationallicence Markus chamber nationallicence Gafchromic film nationallicence Chen F. Department of Radiation Oncology Medical Physics, Westmead Cancer Care Center, 2145, Westmead, NSW, Australia aut Gupta R. Department of Medical Physics, St George Cancer Care Center, Kogarah, NSW, Australia aut Metcalfe P. Center for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia aut Australasian Physical & Engineering Sciences in Medicine Springer Netherlands 33/1(2010-03-01), 23-34 0158-9938 33:1<23 2010 33 13246 https://doi.org/10.1007/s13246-010-0004-x text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s13246-010-0004-x text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Chen F. Department of Radiation Oncology Medical Physics, Westmead Cancer Care Center, 2145, Westmead, NSW, Australia aut NATIONALLICENCE 700 1- Gupta R. Department of Medical Physics, St George Cancer Care Center, Kogarah, NSW, Australia aut NATIONALLICENCE 700 1- Metcalfe P. Center for Medical Radiation Physics, University of Wollongong, Wollongong, NSW, Australia aut NATIONALLICENCE 773 0- Australasian Physical & Engineering Sciences in Medicine Springer Netherlands 33/1(2010-03-01), 23-34 0158-9938 33:1<23 2010 33 13246 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer