All perfect praise be to Allah, The Lord of The Worlds; and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
In principle, Islamic Sharia permits plastic surgery that aims at concealing defects, as indicated in the Prophetic Sunnah; AbdurRahman ibn Tarafah said that his grandfather Arfajah ibn As'ad who had his nose cut off at the battle of al-Kilab got a silver nose, but it developed a stench, so the Prophet (PBUH) ordered him to get a gold nose.{Abu Dawud}.
The International Islamic Fiqh Academy sanctioned hair transplant in case of hair loss. Its resolution No.(173)/2007 stated: "Sharia permits the necessary and needed plastic surgery with the purpose of concealing the defects resulting from burns, accidents, diseases and the like. For example, dermatoplasty and hair transplant for women who suffer from hair loss."
In conclusion, it is permissible to donate hair to victims of cancer in order to conceal the defects resulting from chemotherapy. This provided that no material compensation is taken in return because Sharia highly values man`s dignity; therefore, it doesn`t sanction making any part of his body a commodity in a commutative contract. And Allah knows best.
