I. Medical Physics:

Medical Physics is the whole applications of the Physics' principles in Medecine in order to diognose and treat malignant desease. It includes mainly:

For scanning in Nuclear Medicine:
PET (Positron Emission Tomography)

For diagnostic imaging:
X-rays (Radiology),
Ultrasounds, and
MRI (Magnetic Resonance Imaging.

For Radiotherapy treatment:
Brachytherapy (HDR and LDR)
Ionizing radiation (Oncology)

II. Radiation Therapy

Radiation therapy, that is the treatment of cancer, is done by ionizing radiations like neutrons, electrons, γ-rays, and ions such as protons. It is a palliative treatment, that the main goal is to kill cancer cells and shrink tumors. It comes internally, that is Brachytherapy or Curietherapy. and externally by using radiation beams from special machines, or from a particle accelrators. We treat then cancer by protons.
But. why do we vafour Proton therapy?

Protons release most of their energy when they hit the tumor and deliver no exit dose beyond the tumor boundary. Therefore, the dose of radiation conforms to the tumor better and there is less damage to healthy tissue.

While standard particles such as electrons, neutrons, gamma-rays and X-rays used for conventional treatments, lose their energy rapidly in tissues, protons have the major advantage over these conventional radiations to release their energy according to the Bragg peak. This advantage makes protons deliver a precise dose of energy directly to the tumour while reducing adverse effects to adjacent normal tissues. By combining protons with different energies in a single beam, the Bragg peak can be modulated into a plateau that dumps a high dose of radiation throughout the precise depth of the tumour.