IMRT for the treatment of prostate cancer: a comparison of a forward-planned technique and an inverse-planned technique utilizing a dose gradient method.

Radiation therapy has been a major treatment option for patients with prostate cancer with documented efficacy over the last 30 years. Recent research has shown a correlation between improved local control, disease-free survival, and overall survival and dose delivered. Excessive dose to the rectum is one of the leading causes of morbidity in the treatment of prostate cancer. The RTOG and others have suggested dose limitations based on various treatment parameters. Intensity-modulated radiation therapy (IMRT) is becoming more widely used, with the goal of improving dose coverage while limiting morbidity. In an effort to evaluate our inverse-planning technique relative to our forward-planned technique based on rectal dose, 2 plans were generated on 10 patients. One plan was generated with 9-field forward planning, using 2 posterior obliques to decrease dose to the rectum. The other plan utilized inverse IMRTplanning. To evaluate dose to the rectum, we compared the dose gradient from the posterior edge of the prostate across the anterior third of the rectal wall. This gradient, which is not part of the IMRT planning objectives, proved useful in assessing plan differences, and led to new dose objectives for certain IMRT plans.