168Comparison of recent new recommendations for electron beam dosimetry

168Comparison of recent new recommendations for electron beam dosimetry

$45 166 167 IS THERE A NEED FOR A LEGISLATIVE LEVEL BESIDES A TOLERANCE AND ACTION LEVEL IN QUALITY ASSURANCE A MULTI-PURPOSE SOLID P H A N T O M ...

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$45

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IS THERE A NEED FOR A LEGISLATIVE LEVEL BESIDES A TOLERANCE AND ACTION LEVEL IN QUALITY ASSURANCE

A MULTI-PURPOSE SOLID P H A N T O M IgOR P O S T A L

H.J. van Kleffens', G. Meijer ') and B.J. Mijnbe~-~) l) University Hospital Utrecht, The Netherlands 2) The Netherlands Cancer Institute, Amsterdam, The Netherlands

E. Pintye, I. Gomole, J. lzewska, J. Novotny, J. Van Dam, A. Dntreix

Fullfilling the EC-Directive 84/466 in national legislation it is required for all EC-coun~es to define quality criteria for the equipment used for patient treatment with ionizing radiation. The government of The Netherlands has supported a project, initiated by the Netherlands Society on Clinical Physics, which aims at defining and implementing minimum requirements for the equipment used in nuliotherapy in The Netherlands. A~ a consequence these minimum requirements can be used by the government as criteria to judge whether or not a specific device is authorized for radiotherapy. So legislation can serve as an immanent to prohibit the use of degraded equipment and to guarantee a specific degee of qnality.ln daily practice a tolerance level and an action level are commonly applied in quality control protocols. Tolerance levels are the limits for specific parameters below which the equipment involved is in an excellent condition. These limits are applied during acceptance tests and commissioning procedures. The action level used in quality control procedures is the limit which requires a corrective action, when this limit has been crossed, in order to bring the equipment back in a condition which fullfilis the tolerance level. However, it might happen that a parameter (temporarely) exceeds such an action level. It might therefore be worthwile to define a third level, the legislative level, describing the utmost limit which under no circumstances may be exceeded. This level might be applied by the government as criterion for auditing purposes to prevent usage of equipment in an unacceptable condition. This approach is currently under discussion in The Netherlands.

168 COMPARISON OF I~CEI~J~I~WI~COMI~HDATION8 ELECTRON BEI~J4DOSIMETRY

T L D A N D FILM A U D I T - FEASIBILITY STUDY -

U. H. Ga.~uisber8, Dept. Radiotherapy, Leuven, BELGIUM A multi-purpose solid phantom was designed and manufactured

for an easy dosimetric check in the clinical work. The aim is to check the output ratio, beam symmetry and flatness to compare with wedge, inlganogenei~ and oblique phantom surf~e with a calculation by treatment planning systems for eeCo and megavoltase x-ray beams in non-reference conditions. The phantom is made of poly~wene (p = 1.0474 g/can3). Thermolumineacent powder (Desmarquest, France) and films (Kodak X-OMAT V) were used to compare data with the resoits measured by ionisation chamber. The number of the TLD samples per control procedure is 16, and the number of films is 9. The inserts for inhomogeneity are wood and air. The f e ~ ' b ~ has been assessed by measurements performed on Alcyon cobalt unit and Satume linear a~r~elerator (6MV, 18MV, 25MV) with PCL-3 TLD reader and film de~itometer VIDAR VXR-12 (Poseidon software). Results fi'om TI.J3 samples and films are in good agreement with the ionisation chamber measurement. Data have shown that the multipurpose phantom is m~table for postal external andit and local quafity assurance for high energy photon beams.

169 FOR

A Nisbet and D I Thwaites D e p a r t m e n t of M e d i c a l P h y s i c s and M e d i c a l Engineering, University of Edinburgh, Western General Hospital, Edinburgh, Scotland, UK New r e c o m m e n d a t i o n s for e l e c t r o n d o s i m e t r y have been formulated recently by a number of national and internatlonal groups, including the new UK electron dosimetry Code of Practice and the recent AAPM and IAEA recommendations for parallel-plate chamber dosimetry of electron beams. These new recommendations are reviewed and compared. The practical applicatlon of each has been investigated over a range of electron beam energies. Particular a t t e n t i o n h a s b e e n p a i d to t h e d i f f e r e n t approaches employed for parallel-plate chamber calibration and to any changes or differences in m e t h o d s a n d d a t a to be u s e d b o t h at c a l i b r a t i o n and in the m e a s u r e m e n t s in the electron beams. The resulting d e t e r m i n a t i o n of d o s e s is compared, both b e t w e e n the new sets of recommendations and to other already existing dosimetry protocols.

THE

IPEMB

UK

NATIONAL

ELECTRON

BEAM

D O S I M E T R Y INTERCOMPARISON

NISBET,A. and THWAITES,D. Department of Medical Physics, Western General Hospital, University of Edinburgh, Edinburgh, OK The Institution of Physics and Engineering in Medicine and Biology(IPEMB) have been funded by the U.K. Department of Health to carry out a national electron beam dosimeWy intercomparison involving all radiotherapy centres in the counU-y possessing electron beam treatment facilities. Around 90% of UK radiotherapy centres now have electron treatment facilities, a significant number of which are relatively new to electrons and to the very different dosimetry considerations involved. In dapar~ents where the use of electrons has been well developed and integrated with photon treatments up to 20°/0 of patients typically have some treatments with electrons. It is widely accepted that the potential for problems in elactron beam dosimetry is significantly greater than for megavoltage photons. The remit of the projact has therefore been to develop a methodology for clinical electron beam dosimetry audit, including an element of procedural audit, and using this, to collect data on a national scale to quantify the consistency in current UK practice. The methodology employed will be described and the overall results from the study presented