• implant dose coverage at 4 weeks, comparing CT and MRI versus CT alone
  

• implant edema at time of implant and at 2 and 4 weeks
  

This study addresses three major sources of post-implant dosimetry inaccuracy for permanent prostate implants: post-operative edema, prostate contour delineation, and dose calculation method. It is hypothesized that a pragmatic edema model can minimize the first uncertainty, co-registered CT + MR images the second, and an improved dose calculation algorithm the third.

Detailed objectives are to:

• measure and model the effects of edema on dosimetry;
• evaluate CT + MR image registration methods;
• compare dosimetry for CT alone vs. CT + MRI using the contemporary TG-43 dose calculation method;
• set up a Monte Carlo code that makes full use of the information in CT + MR images to perform implant dose calculations;
• compare prostate dosimetry for the Monte Carlo vs. the simpler TG-43 method;
• develop an analytical post-implant dose calculation algorithm for routine clinical use (Monte Carlo is too slow on a single-CPU brachytherapy planning computer); and finally
• assess the performance of the new algorithm.

Of the estimated 250,000 new cases of prostate cancer in North America in 2004, most are early stage disease as a consequence of PSA testing. Permanent prostate implant therapy is a major option for this group, as long-term clinical studies indicate a cure rate equal to surgery and external beam radiotherapy, but with fewer complications. By dealing with dosimetric inaccuracies, a proven treatment can reach its full potential.