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S787
ESTRO 36 2017
_______________________________________________________________________________________________
3
Kangbuk Samsung Hopital, Radiation Oncology, Seoul,
Korea Republic of
Purpose or Objective
Tissue equivalent material commonly used in the electron
radiation therapy was developed its own by using a 3-
dimensional printer (3DP). We fabricated a customized
bolus using a 3DP and evaluated for usefulness and
accuracy of the Customized Bolus.
Material and Methods
Treatment with an electron beam 20MeV according to the
virtual Clinical Target Volume (CTV) and Organ at Risk
(OAR) planed with a treatment plan system (TPS). The 3D
printed customized bolus was then fabricated Bolus A, B
and C, respectively, and its quality and clinical feasibility
were evaluated by visual inspection and by assessing
dosimetric parameters such as Dose Volume Histogr(DVH),
D
max
, D
min
, D
mean
, V
90%
, and V
80%
. Test electron field was
measured using Gafchromic
TM
EBT3 film. And then was
scanned by using a film scanner and compared with TPS
data by applying Gamma (γ) analysis to verify their
geometric accuracy.
Results
In all cases, the CTV volume is encompassed within 90% of
the prescribed dose 3Gy. There was a difference in the
CTV volume, D
max
up to 0.12Gy, D
min
up to 0.09Gy, D
mean
up
to 0.12Gy. In the OAR volume, D
max
up to 0.29Gy, D
min
up
to 1.24Gy, D
mean
up to 0.66Gy. The dose distribution
difference between the measured and TPS dose was within
3%/3mm criteria with Gamma evaluation for EBT3 film.
The pass rate for the test were 92.46%, 95.23%, 98.41% for
Bolus A, B and C, respectively. It showed a more than 90%
pass
rate.
Conclusion
In this study, we fabricated a customized starchy bolus in
powdered form using a 3DP to dose build up and evaluated
for usefulness and accuracy of the Customized Bolus. The
result showed that 3D printed customized bolus could
significantly improve the dose homogeneity in the CTV and
reduce the dose in the OAR for patients treated with
electron therapy effective in clinical trials.
EP-1489 Effect of the thermoplastic mask on patient
skin dose in tomotherapy
V. Ravaglia
1
, A. Giuliano
2
1
San Luca Hospital, Medical Physics, Lucca, Italy
2
Istituto Nazionale di Fisica Nucleare INFN- Pisa, Pisa,
Pisa, Italy
Purpose or Objective
The Treatment Planning Systems (TPS) do not accurately
model skin dose, and several studies in vivo have
demonstrated that the TPS overestimates skin dose in
tomotherapy treatments. The bolus effect due to
thermoplastic masks, which are commonly used in
Tomotherapy head & neck (H&N) treatments, has
sometimes been reported in literature. The aim of this
study was to report results of in vivo measurements of skin
dose in tomotherapy using EBT3 Gafchromic films with and
without thermoplastic mask.
Material and Methods
Surface dose measurements were performed with the
application of EBT3 pieces of size 2x2 cm
2
. Films were read
with a flatbed scanner Epson 10000XL and images were
analyzed using the red channel calibration. Preliminarily,
reproducibility of surface dose measurements was
assessed on Cheese phantom, then the thermoplastic mask
effect was investigated using fine, normal and coarse
calculation dose grids on phantom (see Figure 1). Skin
doses were measured in vivo with the application of
radiochromic film pieces directly on the skin of patients
or in the inner side of thermoplastic mask, if used during
the treatment. The target lesions included H&N, brain and
sarcoma. For each patient films were located in 1 to 3
reproducible points and measurements were repeated on
average for three fractions. Measured doses were
compared with doses calculated with the TPS using fine
grid.
Results