| PROSTATE BRACHYTHERAPY
Mr Anthony Flynn, Mr J A Evans and Dr D V Ash Cookridge Hospital, Leeds |
The Brachytherapy Group at Cookridge Hospital Leeds has recently completed an extensive study into the dosimetry of iodine-125 seeds prostate brachytherapy.
Prostate brachytherapy, an option for the treatment of early stage prostate cancer, involves the permanent implantation of radioactive seeds into the prostate under ultrasound and fluoroscopic guidance. The method was first described in the early 1980s but it has taken some years for long-term reports on large numbers of patients to become available. So far there have been relatively few reports from Europe because the method was taken up here more recently. Prostate brachytherapy started in Leeds in 1995 and after a gradual build up there are now about 200 patients treated annually with a total of over 1400 cases. This study analysed 667 patients with a median follow up of 31 months (18 to 98.2 months) in order to identify factors could affect PSA relapse free survival (PSA-RFS). For this group of 667 patients, 557 showed no evidence of PSA relapse, 20 had a clinical relapse and only 10 died from prostate cancer. 15 other patients died from other causes.
Prostate tumours can be divided into low, intermediate and high risk groups depending mainly on the initial PSA value and the tumour type (Gleason score). In this study the respective PSA-RFS is 84.3%, 73.9% and 52.6% for low, intermediate and high risk groups respectively.
The impact of radiation dose on PSA-RFS was investigated, based on post implant dosimetry analysis. The “D90”, which is defined as the dose received by 90% of the prostate volume, is one hitherto generally accepted measure of dose received by the prostate. In contrast to other published studies, the Leeds study has not shown any significant effect of “D90” on the probability of achieving biochemical control. We think this could be because the position of any areas of low dosage tends to be in parts of the prostate where malignant cells are unlikely. Also, some PSA relapses are not due to local recurrence but to distant dissemination. In view of this, the study suggests that other dosimetry parameters may be more useful than “D90”.
Analysis of PSA-RFS according to year of implant demonstrates a year on year improvement. This is likely to be due to better patient selection and improvement in technique. Actuarial PSA-RFS for patients implanted between 1998 and 2001 is 86.3% compared with 74.9% for the whole population of patients and 31% for patients treated between 1995 and 1998. This effect has been demonstrated by others and confirms that there is a learning curve and that new developments in ultrasound and planning computers can have a significant effect on outcome. The provision of mentoring by experienced teams should allow the learning curve to be considerably shortened for those who have recently started or are about to start an implant programme.
The study also examined whether MRI imaging and fusion of MRI and CT images would be better than the more usual CT image alone for post-implant analysis. It concluded that the benefit was not significant. Although the prostate can be defined more easily on MRI the seeds are more difficult to see so the net benefit is marginal.
The project work was carried out by Bashar Al-Qaisieh, Research Physicist in the Medical Physics Department at the Cookridge Hospital, Leeds and supervised by Dr D Ash (Clinical Oncologist), A Flynn (Clinical Scientist) and J A Evans (Clinical Scientist). It was supported jointly by the Prostate Research Campaign UK and the Cookridge Hospital Prostate Cancer Research and Education Fund.
Research summary, 03 January 2005
Project G2002/05.