Kilovoltage peak

Kilovoltage peak (kVp) is the peak voltage applied to the X-ray tube. It determines the highest energy of X-ray photon. It is responsible for the acceleration of electrons from the cathode to the anode. It also determines tube current in space charge region. 

Increase in kVp shifts the X-ray spectrum to right. The radiation dose to the patient is directly proportional to the square of kV. However, it must be remembered that in practical purposes where a different kVp is used in different cases (say for e.g. low kV in mammography as compared to chest X-ray), other factors like mA and film focus distance (FFD) play a role and a complex relation exist to the patient dose (patient dose in mammography is much more than a chest X-ray).

Increasing the kVp will decrease the contrast seen between soft tissue and bone ².