A Feasibility Study of MR-based target delineation for Radiotherapy Treatment planning For Gastric Cancer

Studies have demonstrated that computed tomography (CT) based clinical target
volume (CTV) delineations of gastric tumours have large variations (up to 19mm)
between observers [1]. On top of that, the treatment area experiences much
intra- and inter-fraction position variation due to oral intake, respiration
and gas filling [2], leading to internal target volume (ITV) margins of 19.2,
13.5 and 7.8mm in respectively medio-lateral, cranio-caudal and
antero-posterior directions. These uncertainties require generous treatment
margins, increasing the radiation dose to normal organs and associated risk for
toxicity. These factors are a serious limitation to the RT treatment.

MRI has superior soft-tissue contrast over (cone-beam) CT, facilitating CTV
determination and detection of organ motion for gastric cancer [3,4].
Integration of MRI in the RT treatment chain, will therefore improve certainty
with regards to the shape and position of the gross tumour volume (GTV) and the
clinical tumour volume (CTV). This increase in certainty will likely lead to
reduction of margins, potentially leading to a clinically significant reduction
of toxicity. Furthermore, it is expected that functional MRI, will allow for
the assessment of treatment response [5].

Primary objective (part 1)
* Establish the feasibility of MR-based target delineation for radiotherapy
treatment planning for gastric cancer.

Secondary objectives (part 2)
* Assess the volumetric differences between clinical target volumes before and
after (partial) gastrectomy.
* Test and (if necessary) develop tools for an MR-based target delineation for
the treatment planning of the stomach, such as software for registration,
margin detection and mid-position determination.
* Evaluate the feasibility to delineate the macroscopic (gross) tumour volume.

Each patient will receive 2 additional MRI exams. The first exam will be
scheduled before gastrectomy and, if applicable, before the start of any
neo-adjuvant therapy. The second MRI will be scheduled 4 * 10 weeks after
resection, but before any postoperative therapy. Both MRI exams will be used to
create a planning dataset on which the clinical target volume (CTV), gross
target volume (GTV, only on pre- operative MRI) and organs-at-risk (OARs) will
be delineated. Both delineation sets will be compared volumetrically. The image
quality will be evaluated, if it is feasible to delineate the clinical and
gross tumour volume.

The study will be divided into two parts. In the first part, 5 patients will be
included. Based on the data of these 5 patients, the feasibility of
constructing a delineation from the acquired MRI-data will be assessed. The
study is considered feasible when the clinical target volume (CTV) and the
organs-at-risk (OARs) can be delineated, the data can be registered to each
other and a reconstructed (mid-position) plannings scan can be assessed and can
be used in treatment planning.

When this is considered feasible, an additional 15 patients will be included in
part 2 of the study, resulting in a total of 20 patients.

The patients will undergo MRI exams at two time points, before and after
(partial) gastrectomy.
The scan duration of the first exam is approximately 50 minutes and the second
scan will be less. The two MRI exams will not be used clinically.

Patients will undergo a MRI exam two additional times. During the MRI exam 15
ml of the contrast agent Dotarem (Gadoteric acid, concentration 0.5M) is
administered intravenously. No adverse effects are known of the administration
of a repeated dose one week after a previous exam. No risk has been reported of
repeated MRI exams.