Performance and beam characteristics of the Siemens Primus linear accelerator

Siemens Primus is a small footprint, klystron driven medical linear acceler ator incorporating a compact solid state modulator. A double focused multil eaf collimator (MLC) replaces the lower jaw. The first Primus in the world was installed at St. Jude Children's Research Hospital in early 1997 with x -ray energies of 6 and 15 MV and electron energies of 8, 10, 12, 15, 18, an d 21 MeV. The 10 cm depth dose for a 100 cm SSD 10X10 cm(2) beam is 68% and 77% for 6 and 15 MV x rays, respectively. For both x-ray energies, beam fl atness is slightly better than the manufacturers specification of 3% and be am symmetry is considerably better than 1%. The double focus design of the MLC produces a sharp penumbra (5-7 mm at 6 MV and 6-8 mm at 15 MV), increas ing modestly with beam size. MLC leaf leakage is less than 1.25%. The depth s of the 80% depth dose for the six electron energies of 8, 10, 12, 15, 18, and 21 MeV are 2.6, 3.2, 4.0, 4.9, 6.0, and 7.4 cm, respectively. Beam fla tness is typically 2%-3% for all electron energies except 21 MeV, where it reaches 4% for a 25X25 cm(2) cone. Electron beam symmetry is better than 1% for all energies except 21 MeV, where it is equal to 1%. The results are s tored electronically and may be retrieved using anonymous ftp from the Amer ican Institute of Physics, Physics Auxiliary Publication Service. (C) 1999 American Association of Physicists in Medicine. [S0094-2405(99)01605-3].