What is Intensity Modulated Radiation Treatment (IMRT) and How Does it Compare to High Dose Rate Brachytherapy?
There are a number of prostate cancer treatment options available including Intensity Modulated Radiation Treatment or IMRT. This is an improvement over standard external beam irradiation in that the beam is dynamically modified during the daily treatment. The daily treatments are given over an eight to nine week period. The treatment machine, called a linear accelerator, delivers a high powered beam of radiation to the body as in standard external beam radiation, but this newer machine is equipped with a special device called a computerized multileaf collimator that shapes the beam during the radiation in accordance with the treatment plan. The shape and speed of the collimator windows determine the intensity of dose to the target. The equipment is rotated around the patient to send radiation beams from different angles to give the tumor a higher dose than the adjacent bladder and rectum. This is definitely an improvement over standard conformal external beam radiation but it still is an external beam which must penetrate pelvic tissues to get to the target in the middle of the pelvis.
In contrast, High Dose Rate brachytherapy is delivered from within the prostate and radiates outward a short distance with a rapid falloff. The term brachytherapy is derived from the Greek brachy which means short distance. The intensity of the dose is modulated by adjusting the time the source stays at each position within the implanted catheter matrix. The radiation dose is modulated at the target not as it enters the body. Finally, it does not have the daily patient set up and prostate motion problems associated with external beam intensity modulated treatment (IMRT). My conclusion is that IMRT is an improvement in external beam radiation treatment but the advantage still goes to High Dose Rate brachytherapy.