Given Dose / Applied Dose = amount of radiation you put in to get a certain amount of radiation to the tumor.   This number has to be higher than the tumor dose

• Depends on the depth of tumor
• Patients size
• The energy of the beam

Tumor Dose – the amount of radiation you want to give to the tumor

• Prescribed by the doctor

Cord Dose – is the amount of radiation the spinal cord receives

• Is only allowed 45 Gy
• Spinal cord starts at foramen magnum and ends at L2

Skin Dose – the amount of radiation the skin receives

• Is a problem if you treat with a modified diagnostic machine
• With higher powered machines you will have skin sparring

Skin sparring –a property of megavoltage irradiation where the maximum dose occurs at some depth beneath the skin surface .The skin doesn’t receive 100% of the radiation because the beam energy is so high that the beam has to slow down before it will have its maximum effect   (Dmax)

•  40% for cobalt machine

•  about 10% for 10 Mev LINAC

( **for the higher energy machines if you want to treat close to the skin surface you would have to place bolus ontop of the area to be treated to slow down the beam)

(**the higher the energy of the machine the more skin will be sparred)

Dmax – the place in the beams path(in the patient) that will receive the most amount of radiation

•  Cobalt machine = .5cm (buildup region)

•  10 Mev LINAC   = 2.5cm (buildup region)

               buildup region – is the space between the skin surface and Dmax

Properties of Radiation

Ionization – is the removal of electron from an atom ( Any process by which a neutral atom gains or loses electrons ,thus acquiring a net charge , as the dissociation of a substance in solution into ions or ion production by the passage of radioactive particles)

• in ionization two ions become unstable and they create and ion pair