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S846
ESTRO 36 2017
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EP-1591 Evaluation of noninvasive eye fixation system
on Cyberknife radiotherapy of orbital’s tumors
A. Skrobala
1,2
, M. Adamczyk
1
, P. Janiga
3
, A. Jodda
1
, J.
Litoborska
1
, E. Czajka
3
, J. Dura
3
, P. Milecki
2,3
1
Greater Poland Cancer Centre, Medical Physics
Department, Poznan, Poland
2
University of Medical Science, Department of
Electroradiology, Poznan, Poland
3
Greater Poland Cancer Centre, Ist Radiotherapy
Department-, Poznan, Poland
Purpose or Objective
Purpose of this study was to evaluate noninvasive eye
fixation system on CyberKnife-based stereotactic
radiotherapy (CK-based SRT) by the
planning and
treatment parameters in patients group suffering from
orbital’s tumors: ocular melanoma and orbital metastases.
Treatment plans for patients with orbital’s tumor
undergoing CK-based SRT are often challenging due to the
close proximity of optic apparatuses.
Material and Methods
Feasibility of the eye fixation system was evaluated in the
present study using data of 15 patients treated by 1 do 14
with median 5 fractions. The treated PTV volume ranged
from 0.73-37.59 cm
3
(median 2.83 cm
3
, mean 7.15 cm
3
, ±
SD 11.98). The prescription dose ranged from 20-50 Gy
with median value 50 Gy prescribed to the 80% isodose.
The eye fixation system was the polymetric device which
was attached to the mask system in cranio-caudal
orientation and placed in front of the diseased eye
(visualization of the system at figure 1 left). The patient
was looking at the black point placed at the arm of the
eye’s fixation system. The proper position of eye during
the imaging and treatment was fixed and the position of
the system can be easily adjusted and fixed to the suitable
position for any patients. The position of the system was
defined by CT and used during treatment delivery. CK-
based SRT of orbital’s tumors were evaluated by PTV
coverage, conformity index (CI), total number of monitor
units (MU), number of beams and the treatment time and
the maximum dose to ipsilateral optic nerve were likewise
to assess delivery efficiency.
Results
The optical fixation system was well tolerated by all
patients and the stable position of the eye was obtained.
The system can be used during planning and treatment
without any interference with the photon beam, doses to
the eye’s fixation system ranged from 0.03 – 3.71 Gy
(median 0.97 Gy, mean 1.15 Gy, ± SD 1.11). Figure 1
showed the treatment plan of one patient treated on the
CK-based SRT using the eye’s fixation system. Average
treatment parameters of 15 total orbital’s lesions (Table
1).
Figure 1. CK-based SRT treatment plan displayed in the
axial plane of the patients with a medial orbital tumor in
the right eye and multiple beam trajectories.
Table 1. Average treatment parameters of 15 total
orbital’s
lesions.
Conclusion
The results of this study and good clinical outcomes
demonstrated the feasibility of the eye fixation devices
for CK-based SRT without the need of implementing
fiducial markers. Two years follow up reported that the
salvage therapy (enucleation) was unneeded in all cases.
CK-based SRT appeared to be a relatively safe technique
in treating orbital’s lesions within or near optic
apparatuses. CK-based SRT using fixation system provides
excellent tumor coverage without delivering excessive
dose to critical anterior structure and provided that the
dose to the optic apparatuses were limited. The long-term
safety of this treatment remains to be confirmed.
EP-1592 Higher biological dose to heart and lung in
IMPT of medulloblastoma patients due to increased LET
E. Rørvik
1
, L.F. Fjæra
1
, C.H. Stokkevåg
2
, S. Thörnqvist
1,2
,
K.S. Ytre-Hauge
1
1
University of Bergen, Department of Physics and
Technology, Bergen, Norway
2
Haukeland University Hospital, Department of Oncology
and Medical Physics, Bergen, Norway
Purpose or Objective
For medulloblastoma patients, proton therapy offers
increased dose conformity compared to conventional
radiation therapy. There is however growing concern
about the clinical consequences of the enhanced linear
energy transfer (LET) delivered to the normal tissue
surrounding the tumor volume. In these patients, the
biological dose received to the lung and heart may be
higher than reflected by treatment plans based on the
clinical practice of using a constant relative biological
effectiveness (RBE) of 1.1. The aim of this study was
therefore to investigate the biological dose to the heart
and lung following craniospinal Intensity-modulated
proton therapy (IMPT) using LET-based models for the RBE
of protons.
Material and Methods
An intensity modulated proton therapy (IMPT) treatment
plan was generated in a commercial treatment planning
system(Eclipse, Varian Medical Systems) applying two
cranial fields and two spinal fields. The dose prescription