A reticle retrofit and dosimetric consideration for a linear accelerator.
OBJECTIVE
An imperfect reticle system in an accelerator causes uncertainties in source-skin distance (SSD), off-axis distance (OAD), isocenter, and so forth. A reticle was designed and fabricated, and its implications on x-ray and electron beam dosimetry were investigated.


METHODS
A new reticle frame was dimensioned to fit snugly in the accelerator. The frame was fabricated to carry a pair of adjustable cross wires and to allow the machine operation in the photon and electron modes. The impact of the cross wires on 6 MV photon and 5-10 MeV electron beam parameters such as dose rate (Gy/monitor unit), beam uniformity, surface dose, and so forth, were studied using suitable ion chambers and phantoms.


RESULTS
The retrofitted system offered long-term mechanical stability leading to precise SSD, OAD, and isocenter measurements. Changes introduced by the cross wires on the 6 MV photon and 5-10 MeV electron beams are presented.


CONCLUSIONS
Long-term stability of a reticle in an accelerator is important for an accurate patient setup and for making reliable dosimetric measurements. Beam characteristrics have to be studied whenever modifications on a reticle system are made.
Hudner Oncology Center, Saint Anne's Hospital, Fall River, MA 02721-1798, USA.
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Krithivas
D004867:Equipment Design / Q000592:standards; D010315:Particle Accelerators / Q000295:instrumentation* / Q000592:standards; D011786:Quality Control; D011874:Radiometry / Q000379:methods