829 / 1096
S813
ESTRO 36
_______________________________________________________________________________________________
Conclusion
The imaging doses on new TrueBeam accelerator is
substantially lower than on previous iX platform.
Manufacturer’s default IGRT protocols could be optimised
to reduce the ESD to the patient without losing the
necessary image quality for patient set-up correction. For
patient set-up with planar kV imaging the bony anatomy is
mostly used and optimization should focus on this aspect.
Therefore, the current approach with anthropomorphic
phantom is more advantageous in optimization over
standard kV quality control phantoms and SNR metrics.
EP-1515 A novel attachment system for cutouts in
kilovoltage x-ray beam therapy
M. Baumgartl
1
, G. Kohler
1
1
University Hospital Basel, Clinic for Radiooncology,
Basel, Switzerland
Purpose or Objective
Customized shielding in superficial and orthovoltage
therapy is a common procedure to spare healthy tissue and
is nowadays mainly based on in-house cutouts attached to
applicators or patients. However, the production of
customized shields could be time consuming and does not
always provide a promising result. Inaccuracies during the
replacement of cutouts may arise if the same applicator is
required to treat different patients or target volumes (TV)
immediately one after the other. An adequate, fast and
reproducible approach of shielding was developed to treat
the TV in the low and medium energy (kV) range for
standard applicators.
Material and Methods
In our department most of the cutouts have a straight-
edged shape. Our developed in-house frame-based system
can be used to attach and remove the cutouts to the
applicator in an easy and fast manner. It is important to
note, that the mounted frame must not interfere with the
radiation field. Hence, the frame has an identical size as
the used applicator. VELCRO® strips were deployed as an
attachment modality between applicator, frame and
cutout. Those were glued to a PMMA frame with the same
size of a standard applicator which attach to VELCRO®
strips elongating around the applicator. The skin facing
side of the frame is also covered with VELCRO® strips. In
addition, cutouts were covered on the one side with
VELCRO® strips and on the other side with a plastic foil,
respectively. Straight-lined cutouts can be adjusted within
seconds to shape TVs.
Results
All used straight-lined shields from our database could be
exactly reproduced contouring 100% of the TV using the
developed attachment system. Nevertheless, the system
increases the distance of the applicator to the patient skin
by non-negligible 8.8mm. This has to be taken into
account by an output factor (OF). A comparison of the
measured and calculated (by the ISL) OFs shows a
maximum deviation of ±3.6% (12keV) and ±0.8% (>12keV)
for our set-up.
Conclusion
Shielding healthy tissue in kilovoltage x-ray beam therapy
using the reusable frame-based system promises a fast
exchange of cutouts. It also ensures a high reproducible
accuracy to irradiate multiple TVs in a row with the same
applicator but with different frames and cutouts.
Moreover, it provides a complete coverage of healthy
tissue of straight-lined TVs. Furthermore, a measured OF
should be considered to the prescribed dose using the
presented frame-based attachment system.
EP-1516 Prediction of secondary cancer risk from
lateral electrons transport from pediatric radiotherapy
A. Chaikh
1
, J. Balosso
2
1
CHU de Grenoble - A.Michallon, Radiothérapie et
physique médicale, Grenoble, France
2
University Hospital of Grenoble- University Grenoble-
Alpes, Department of Radiation Oncology and Medical
physics, Grenoble, France