DOse volume effects and Fibrosis in the corpora cavernosa After Radiotherapy for prostate cancer
A pilot study

Erectile dysfunction (ED) is a side effect after external beam radiotherapy
(EBRT) for prostate cancer, affecting 50% to 60% of pre-treatment potent
patients. Radiation dose to the corpora cavernosa has the potential to be an
important factor in ED after EBRT. Several studies have tried to elucidate the
etiology of ED after radiotherapy by using Doppler ultrasound. These studies
demonstrated a reduced flow in the cavernosal arteries and venous leakage of
the corpora cavernosa in men with ED after EBRT. It is very well possible that
the decrease of flow in cavernous arteries is caused by an occlusion higher up,
in the IPAs. Untill now, there is no report analyzing dose-volume effects
between radiation dose in the IPAs and ED after radiotherapy. Our hypothesis is
that the inflow of blood into the corpora cavernosa is reduced by
radiation-induced fibrosis (RIF) in the IPAs providing the inflow. By use of
MRI it is possible to visualize the IPAs.

The first objective of this study is to test the hypothesis that a higher dose
to the IPAs and corpora cavernosa is correlated to ED after EBRT. The second
objective is to test the hypothesis that RIF in the IPAs and corpora cavernosa
is correlated to ED after EBRT.

Part A

At first MRI scans will be taken of 5 patients suffering from ED after EBRT.
These MRI scans will be performed to see if it is possible to detect RIF in the
IPAs and corpora cavernosa.

Part B

Before starting EBRT the International Index of Erectile function (IIEF) 26
questionnaire will be filled out and a MRI scan will be performed. This MRI
scan will be matched with the planning CT scan. The IPAs and corpora cavernosa
will be contoured on the matched CT-MRI scan.
An IIEF questionnaire will be sent to the patients at 1 and 2 years after EBRT.

If it is possible to detect RIF in Part A of the present study, then the MRI
scans will be repeated at 1 and 2 years after EBRT. Two radiologists, blinded
for the IIEF scores, will assess whether fibrosis in the IPAs and corpora
cavernosa has occured.

One or three MRI scans will be made of each patients. This will require I.V.
gadolinium chelate contrast. This is a very safe form of contrast, which hardly
ever causes side-effects. The benefit for the patient is small, although extra
informatin about the tumor could be attained with the MRI scan.
The IIEF has to be filled out one or three times. This takes about 10 minutes.
The patient population of this study is the same patient population that might
benefit from this study in the future.