A photon beam has its dose maximum at and a percentage depth dose of per cent at

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Nuclear medicine, dosimetry and radiotherapy · Nuclear medicine, dosimetry and radiotherapy

Life at Thermal Energy, Ch Echoes, precession and the therapeutic beam

Problem

6\,\mathrm{MV}

photon beam has its dose maximum at

1.5\,\mathrm{cm}

and a percentage depth dose of

67

per cent at

10\,\mathrm{cm}

. A tumour centred

10\,\mathrm{cm}

deep is prescribed

1.8\,\mathrm{Gy}

per fraction. ((a)) With a single beam, what dose must be given at the depth of maximum? ((b)) Instead, two beams enter from opposite sides of a patient

20\,\mathrm{cm}

thick, and each gives half the prescription at the tumour. What dose does each beam give at its own maximum, counting that beam alone?

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