Pilot study on the use of a radiopaque hydrogel during breast conserving surgery with full-thickness closure for target definition and positioning of boost or partial breast irradiation.

Breast conserving surgery (BCS) followed by breast radiotherapy has been shown
to be as effective as ablative therapy in the treatment of early stage breast
cancer patients. In BCS there is a shift towards the use of full-thickness
closure (FTC), or oncoplastic techniques in general. This development creates
challenges in breast radiotherapy target definition. Quality of target
definition for radiotherapy after FTC is imprecise. We hypothesize that
instillation of a radiopaque hydrogel during FTC of the lumpectomy cavity will
reduce inter-observer variability during target definition for boost or partial
breast irradiation. Also, we hypothesize that it will increase the accuracy of
patient positioning during radiation delivery.

Primary objective: Estimate the Conformity Index (Cx) of target definition.
Secondary objectives: Estimate the distance between the center of mass (dCOM)
of the observers* target volumes, Cavity Visualisation Score (CVS), feasibility
of the hydrogel marker instillation, stability of the hydrogel marker volume
over time, comparison of target volumes defined by clips and hydrogel, adverse
events, ease of use, motion of hydrogel marker/clips over time, the feasibility
of patient positioning based on the hydrogel marker on cone beam computed
tomography (CBCT) and planar kV images made on a conventional linac and a
Cyberknife and the accuracy of this procedure compared to positioning based on
the surgical clips.

Cross sectional interventional study, with a retrospective matched control
group, on the inter-observer variability of 6 measures applied to 60 patients
across 5 observers. All 5 observers will rate all 60 patients. Interventional
group of 20 patients will get hydrogel + clips. Matched control group of 40
patients gets standard clips only. The positioning accuracy will be assessed in
a subset of 10 patients from the intervention group. Study will be performed
combined in a large secondary hospital (Franciscus Gasthuis, Rotterdam) and a
tertiary hospital (Erasmus MC, Rotterdam)

5-10ml of Iodined PolyEthyleneGlycol, brandname *TraceIT* will be left behind
just before FTC by stepwise instillation and coating the lumpectomy cavity
walls. All patients will undergo a CT at 3 times (post-op (day of surgery), 4
weeks (regular planning CT), and 2.5± 0.5months). In addition, for research
purposes regular CBCT images that monitor the patient positioning during
radiotherapy will be used. Optionally, patients undergo a test session at the
CyberKnife.

Tolerance of the investigational product is expected to be good based on
existing safety data. Radiation dose of the extra study images is negligible
with regards to total radiation dose of the radiotherapy treatment.
Furthermore, target definition and patient positioning may be improved by this
new technique, with possibly lower radiation dose to healthy tissue and fewer
geographical misses. We conclude that the benefits of the treatment when used
as intended considerably outweigh the risks.