A colleague says: "Protons are used in radiotherapy instead of photons because each…

PHYSICS · Subjective · 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

A colleague says: "Protons are used in radiotherapy instead of photons because each gray of proton dose kills more cancer cells than a gray of photon dose; protons simply do more damage per gray." Using the one clinical number stated for each beam (a

150\,\mathrm{MeV}

proton beam's Bragg peak at about

16\,\mathrm{cm}

in water, essentially no dose beyond; a

6\,\mathrm{MV}

photon beam still giving about

40

per cent of its maximum dose at

20\,\mathrm{cm}

), say whether the colleague's claim is correct, and give the real reason protons are chosen.

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