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Dear all,
We are Medical Physicists of an Athenian
hospital and we are looking for comments on the design of a 18 MeV linear
accelerator maze door. The maze is designed 9 meters long to cope with a
workload of 1080 Gy/week at isocenter and reach a level of 20 ìSv/week at the
maze entrance door. We have calculated a shielding of 12 cm Polyethylene + 2 cm
of 5% Borated Polyethylene + 2.5 cm Pb in this order from inside to outside. The
main references we used were NCRP Reports 51 and 79, ICRP Report 188 and
“Shielding Techniques for Radiation Oncology Facilities” by Patton McGinley,
1998, Medical Physics Publishing, Madison, Whisconsin. 1.
Do you have any
idea whether our calculated values are reasonable? 2.
Do you think
that the order of the shielding materials is correct or the high-Z material
should be placed first followed by the hydrogenous
material? 3.
McGinley states
that for maze lengths above 3 meters the scattered x-rays can be ignored and
only capture gamma rays should be considered, while NCRP Report 51, 79 don’t
mention any method to estimate the capture gamma rays but on the contrary they
shield the door against first and second reflection of gamma rays. What’s your
opinion? 4. Can you suggest recent literature concerning maze door design for 18 MeV LINACS? For personal replies, please contact us at molfetas@mail.kapatel.gr Thanks in
advance |