Conventional radiotherapy technique uses multiple beams of radiation with the same intensity to treat the tumor leading to excessive high radiation dose of the normal tissues in the beam path. Intensity-modulated radiotherapy (IMRT) is able to modulate the beam intensity through multiple small beams (beamlets) within the radiation beam such as when the radiation goes through the normal tissues, its intensity decreases and when it hit the cancer, its intensity increases. Such physical properties allow IMRT to conform the radiation dose to the cancer delivering a high radiation dose to improve the chance for cure while sparing the adjacent normal tissues. The tumor is usually treated with a safety margin to decrease the chance of missing the tumor because of patient movement during treatment and the difficulty to reproduce the same treatment position every day.
Image-guided radiotherapy (IGRT) is a special technique of radiation delivery that combines the normal sparing property of IMRT with daily imaging before each radiation treatment. Imaging of the tumor during treatment allows us to precisely target the tumor and decrease the volume of normal tissue in the safety margin. As a result, IGRT allows further sparing of normal tissues and possibly escalating radiation dose to the cancer to kill it completely in some cancer that may be more resistant to radiation such as cancer of the kidney. As the cancer shrinks during the treatment, we can re-plan the treatment to spare more normal tissues from radiation. The normal tissue sparing of IMRT and IGRT allows elderly cancer patients to tolerate radiation treatment better especially when radiotherapy is combined with chemotherapy to increase the patient chance for cure.
Complications following head and neck cancer radiation such as hearing loss, damage to the jaw bone, swallowing difficulty requiring a feeding tube or resulting in aspiration of food into the lungs, hoarse voice, and dry mouth may be minimized with IMRT and IGRT. Damage to the lungs, heart, small bowels, and bones may also be reduced following radiation of the chest and abdomen with these new radiotherapy techniques. All other normal organs close to the tumor may be spared from serious toxicity giving the patient a chance for better quality of life.
Two figures will be added in this section to illustrate the ability of IGRT to spare the normal tissues (lung) and tumor shrinkage during treatment (head and neck cancer)