AbstractID: 8595 Title: Forward-planned vs. Inverse-planned IMRT for Whole Pelvic
Irradiation
Introduction: We have initiated whole-pelvic IMRT for prostate cancer. The IMRT course is 60 Gy to the prostate with 54 Gy to
the seminal vesicles and pelvic lymph nodes. Although the prescribed dose-volume constraints are met with inverse-planned IMRT,
the total number of treatment segments is large. The mean number of segments/patient was 134 for the first three patients. This is
probably due to the large treatment volume which produces a very large solution space and makes the underlying optimization
problem very difficult, reflected in the sub-optimal fluence maps. Treatment times have ranged from 25-40 minutes raising serious
questions about patient immobilization, as well as PTV localization. In addition, less than two patients/hour is probably an
unacceptably low patient volume.
Method: In an attempt to shorten treatment times, we solve this treatment planning problem using forward-planned IMRT and the
same prescribed dose volume constraints. Two resulting plans were compared using both isodose distributions and dose volume
histograms.
Results: An inverse IMRT treatment plan is compared with a forward planned IMRT treatment for the same patient. DVH’s were
very similar. The plans were scored qualitatively as equivalent by the medical staff. However, the forward planned IMRT case was
planned in half the time and required a treatment time of only 10 minutes.
Conclusions: Forward-planned IMRT compares quite favorably with inverse-planned IMRT for this technique. DVH’s are quite
similar, but planning and treatment times are 30%-40% less.