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ESTRO 36 2017
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generated from the Boolean sum volume of the rectum
and bladder obtained from all CB-CT’s. For the rectum,
the mean ± standard deviation displacement was 0.8 ± 0.3
cm. For the bladder, this was 1.5 ± 0.5 cm. In a second
step, these contours will be transposed on the original
plan and dose-volume histograms (DVH) will be calculated
and combined, to produce single mean DVH representative
of the dose actually delivered over the entire treatment
course.
Conclusion
Despite a strict treatment protocol, important variation in
rectal and especially bladder filling was observed. This
resulted in PRV margins of 0.8 and 1.5 cm for rectum and
bladder, respectively, which is not clinically possible.
Therefore, truly adaptive radiotherapy is needed,
depending heavily on automatization.
EP-1840 Verification of accurate movement of 6DoF
Couch using Yonsei QA Set.
D. Jung
1
, H. Park
1
, J. Yoon
1
, S. Lee
1
, J. Kim
1
, J. Cho
1
1
Yonsei Cancer Center, Radiation Oncology, Seoul, Korea
Republic of
Purpose or Objective
Yonsei QA Set was established to verify the movement
accuracy
of
image-guided
6DoF(Six
Degree
of Freedom) Couch and to evaluate its usefulness.
Material and Methods
Two sets of linear accelerators equipped with 6DoF Couch
and CBCT were used. Using the established QA Set, each
CBCT image was obtained over 15 times through the
Penta-Guide Phantom installed with off-set shift values
along six translational (Translation; TX, TY, TZ) and
rotational (Rotation, Pitch; RX, Roll; RY, Yaw; RZ)
directions. Using this method, we compared the reference
image and the registration image, and we analyzed the
error calculated by measuring the positional accuracy of
the modified 6DoF Couch.
Results
Image-guided comparison of reference image
and registration image demonstrated a correlation of
0.993, revealing high calibration accuracy
.
Error between the modified off-set value of 6DoF Couch
and the measured value along translational directions
were 0.25±0.18 mm in the TX direction, 0.25±0.25 mm in
the TY direction, and 0.36±0.2 mm in the TZ direction.
Misalignments along the rotational axis were 0.18±0.08°
in the RX direction, 0.26±0.09° in the RY direction, and
0.11±0.08° in the RZ direction. The correlation value
among the rotational directions was significant at 0.958.
Conclusion
Using the Yonsei QA Set, we were able to verify the error
of 6DoF Couch along both the translational and rotational
directions in a very simple method. This system would be
useful in performing Daily IGRT QA of 6DoF Couch.
EP-1841 CASPIR Trial: Interim analysis of prostatic
calculi as an alternative to fiducial markers for IGRT
A.G.M. O'Neill
1
, R. King
1
, S. Jain
1
, A.R. Hounsell
1
, J.M.
O'Sullivan
1
1
Queens University Belfast, Centre for Cancer Research &
Cell Biology, Belfast, United Kingdom
Purpose or Objective
Image guided Radiotherapy (IGRT) for prostate cancer
(PCA) frequently employs surgically implanted fiducial
markers (FMs). However, it is estimated that up to 35% of
prostate radiotherapy patients have prostatic calculi (PC)
visible on treatment cone beam CTs (CBCT). PCs
represent a potential alternative to implanted fiducials.
The purpose of this clinical trial is to directly compare FMs
with PCs as an aid to prostate IGRT. Preliminary results
are reported.
Material and Methods
We designed a single institution ethically approved
prospective clinical trial investigating the feasibility of
using prostate calcifications as natural FMs for IGRT.
Patients planned for standard prostate radical EBRT +/-
brachytherapy are eligible for the study. Following written
informed consent, and prior to CT planning, 3 gold fiducial
markers are inserted into the prostate by the trans-
perineal route under TRUS guidance. PCs within the PTV
are contoured. All participants are aligned for EBRT
according to FM positions using daily CBCT image guidance
on a Varian TrueBeam linac. Off-line, a single experienced
user analyses CBCTs using Image Registration in Eclipse
(version 13.6). Random and systematic treatment set-up
errors are determined based on FMs, PCs (where present),
prostate gland (PG) and bony landmarks (BL) and CTV-PTV
margins derived for each data set.
Results
To date 25 participants have been recruited. 12
participants have PCs contoured, 6 of whom have
completed radiotherapy. Based on 2982 individual image
registrations the PTV margins required based on each
reference structure are summarised in Table 1.
Table
1
Conclusion
The maximum difference between the CTV-PTV
(PC)
margin
and CTV-PTV
(FM)
margin is 1.3mm in the X or L/R
dimension. This is less than the maximum difference
between CTV-PTV
(FM)
and CTV-PTV
(BL)
for the same
dimension (1.7mm) and comparable to the difference
between CTV-PTV
(FM
and CTV-PTV
(PG)
.
Preliminary results
from this study demonstrate some evidence to
support
the
use of PCs as an alternative to FMs for prostate IGRT.
Recruitment is ongoing with a target of 30 participants
with
PCs.
EP-1842 Comparison between infrared marker and
surface imaging for DIBH of left-sided breast treatments
A. Tini
1
, I. Pytko
1
, A. Moreira
1
, J. Sharpe
1
, C. Winter
1
, M.
Guckenberger
1
, C. Linsenmeier
1
1
University Hospital Zürich, Department of Radiation
Oncology, Zurich, Switzerland
Purpose or Objective