> Near-infrared light can go as deep as 10 centimeters (~ 4 inches) into the human body. This attribute of the infrared light is key to treating cancer anywher

> Near-infrared light can go as deep as 10 centimeters (~ 4 inches) into the human body. This attribute of the infrared light is key to treating cancer anywhere in the human body with this method. As long as the patient is not obese, I assume 10 centimeters of penetration depth are enough to reach any part of the body. Penetration depth and the precision of the desired effect is something that is very important in radiation therapy as well. With radiation therapy you basically shoot small particles at the cancer cells but you also damage surroundings if you don't aim precisely enough. Dependig on the depth of the cancer cells inside the body, different particles are used. The amount of damage the particles deal depends on physical effects. Photons deal most of the damage on the surface. More heavy particles like alpha particles deal most of the damage once they are slowed down inside the body. (See Bragg peak https://en.wikipedia.org/wiki/Bragg_peak https://en.wikipedia.org/wiki/Bragg_peak ).