Towards Adaptive Radiotherapy (ART) for Cervical Cancer:
CT-study of the effect of full and empty bladder on the position of the uterus

Radiotherapy (RT) combined with chemotherapy is the first choice of treatment
in women with inoperable cervical cancer. The position of the uterus has a
daily variation, which is particularly dependent from the amount of bladder
filling. Therefore, patients customly are instructed to have a full bladder
during radiotherapy. Despite this instruction, the bladder filling shows
considerable daily variation, and thus also the position of the uterus and
tumor. The position of the bladder can daily be visualized on the linear
accelerator by a Cone-Beam CT-scan (CBCT), but the quality of CBCT is mostly
not good enough to distinguish the uterus and tumour. Uterus and tumour can
little better visualized on a conventional radiotherapy treatment planning
CT-scan. Non-invasive gold standard for visualizing the tumour nowadays is
T2-weighted MRI.
The present standard of care is to make just one RT treatment plan based on
just one plannings-CT-scan. To account for daily position variation, the
radiation oncologists takes a wide margin around the uterus.
However, if we would make more RT treatment plans in advance, based on
CT-scans with a full and with an empty bladder, one could daily choose a more
appropriate plan adapted to bladder filling as daily assessed by CBCT: Adaptive
Radiotherapy (ART). Next, thanks to ART, future margins around the uterus could
be reduced, thereby improving the precision of radiotherapy and reducing the
risk of late radiation complications.

Goal: Towards implementation of ART in women with cervical cancer to increase
RT precision and reduce the risk of late radiation complications.

Study question: What is the effect of bladder filling on the position of the
uterus and tumour in women who have radiotherapy for cervical cancer?

Prospective cohort study

Nature and extent of the burden:
(1) Three Visicoil* fiducial 3 mm gold-markers will be placed in the cervix
uteri, preferably during the standard investigation under anesthesia, or as an
out-patient clinic procedure.
(2) The extra CT-scan with empty bladder will take 15 minutes extra plus a
reduced dose (70 ml) standard iodine intravenous contrast agent. The extra
CT-scan gives minimal extra radiation burden (15 mSv) compared to the
subsequent radiotherapy (80.000 mSv).
(3) Five cone-beam CT scans will be made on the on the linear accelerator
during the first week of radiotherapy; the extra dose (25 mSv) will be
subrtracted from the daily radiation dose,
(4) Each week, a T2 weighted MRI will be made without i.v. contrast (20 min per
scan; no radiation burden; 5 scans).

Gain for the patient:
(1) The use of fiducial gold markers may allow a better tumor localization and
patient position verification on cone-beam CT,
(2) A minor advantage of lowering the radiation dose by 15mSv per MRI.