Physica Medica: European Journal of Medical Physics - Volume 32 - Supplement 1 - February 2016

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Conclusion: The results confirm that the use of beam directions crossing
OARs with a high degree of inter-fractional variation should be mini-
mized for actively scanned carbon ion beams. However, it is useful to stress
that results obtained are patient-dependent and more statistics is needed
to draw a general conclusion.
A.168
DOSIMETRIC ASSESSMENT OF 3D-PRINTED APPLICATORS FOR HIGH DOSE
RATE BRACHYTHERAPY
A. Vavassori R. Ricotti A. Bazani F. Pansini R. Spot D. Ciardo
V. Sammarc F. Cattan R. Orecchia B.A. Jereczek-Fossa a Department
of Radiation Oncology, European Institute of Oncology, Milan, Italy; b Unit of
Medical Physics, European Institute of Oncology, Milan, Italy; c Department of
Oncology and Hemato-oncology, University of Milan, Milan, Italy; d Tecniche
di Radiologia Medica, per Immagini e Radioterapia, University of Milan, Milan,
Italy
Purpose: Feasibility and dosimetric study of 3D-printed cylindrical and skin
mould applicators for high dose rate brachytherapy (HDR-BRT) using ac-
rylonitrile butadiene styrene (ABS).
Materials and methods: Three cylindrical applicators with a single 2.5 mm
catheter channel and a 1 mm radial slit for radiochromic film support were
3D printed (HP3DX100, Hamlet) using ABS plastic. The reference config-
uration (20% infill percentage) had the slit in contact with the channel; the
test configurations had the slit at 6.3 mm distance from the channel axis
(20% and 40% infill). Depth dose profiles were measured by Gafchromic EBT3
films when the 192Ir source passing through the catheter channel deliv-
ered 2 Gy at 10 mm distance from the channel axis.
Four skin moulds with 4 parallel catheter channels spaced-out at 10 mm,
with 5 mm distance between the axis of the channel and the surface were
3D printed using ABS. Two geometrical shapes were compared to the com-
mercial Freiburg Flap applicator (Nucletron): a group of 16 semi-spheres
reproducing the actual Freiburg geometry (10% infill) and a parallelepi-
ped applicator (10%, 20% and 40% infill). A dose of 2 Gy to the surface at
5 mm distance from the channel axis was delivered using a 192Ir source.
Surface dose distributions were measured with Gafchromic EBT3 films and
evaluated using gamma index analysis (dose difference criteria of 3%,
distance-to-agreement criteria of 3 mm and 10% dose threshold).
Results: The radiation attenuation profiles were comparable in all the cy-
lindrical configurations. Dose attenuation was not sensitive to the density
of the material. Surface dose distribution comparison of the 3D printed skin
mould applicator with the Freiburg Flap showed an overall gamma index
passing rate greater than 90%.
Conclusion: ABS 3D-printed applicators are a reliable solution for patient-
specific HDR-BRT of superficial lesions. Further assessment of 3D printing
techniques and materials is required for clinical development.
A.169
RADIOBIOLOGICAL ANALYSIS FOR EVALUATION OF SIB
HYPOFRACTIONATED TREATMENT IN H&N DISEASE
L. La Rosa, A. Occhipinti, A. Pedalino *, A. Rabito. UOS Fisica Sanitaria – ASP7,
Ragusa, Italy
Introduction: In this work we have analysed a method to calculate a SIB
hypofractionated treatment, starting from the prescription of a conven-
tional treatment including a sequential boost (1.8–2 Gy/fraction).
To calculate the SIB hypofractionated treatment we have started from the
biological equivalent dose (BED) calculation: we have estimated BED value
for tumoural tissues (BEDt) and normal tissues (BEDsani).
Materials and methods: We have analysed cases of patients with head and
neck disease. We have started from the conventional treatment prescrip-
tion and, according to the isoeffect theory, we have calculated the SIB
hypofractionated treatment, evaluating BEDt and BEDsani.
To estimate, froma statistical point of view, the effects of the hypofractionated
treatment compared to the conventional treatment including the sequen-
tial boost, two radiobiological quantities have been used: TCP (tumour control
probability) and NTCP (normal tissue complication probability).
At last, we compared the prescribed conventional treatment and the
hypofractionated treatment calculated, basing on the DVH obtained from
the two techniques, for tumours and OAR, and on the TCP and NTCP
calculation.
Results: The accomplished assessments show, as expected, that in
hypofractionated treatment (SIB) we observe increasing TCP values, cor-
responding to a higher probability of tumour local control, as well as a
decreased probability of damaging normal tissues (NTCPsib < NTCPconv).
Conclusions: This method to calculate the SIB hypofractionated treat-
ment appears to be very successful in reducing the overall treatment time
and in achieving a greater effect on the tumour and a reduced impact on
normal tissues.
A.170
DEFORMABLE REGISTRATION AND CONTOURING PROPAGATION OF THE
BOWEL LOOPS ON DAILY MVCTS: EVALUATION OF INTER-OBSERVER
VARIATIONS AND THE IMPACT ON DVHS
L. Perna C. Sini C. Cozzarini G. Agnello G.M. Cattane L.B. Hysin
L. Muren C. Fiorin R. Calandrino a Medical Physics Department, IRCCS
San Raffaele Scientific Institute, Milan, Italy; b Radiotherapy Department, IRCCS
San Raffaele Scientific Institute, Milan, Italy; c Department of Oncology and
Medical Physics, Haukeland University Hospital, Bergen, Norway;d Department
of Medical Physics, Aarhus University/Aarhus University Hospital, Aarhus,
Denmark
Introduction: The bowel loops (BLs) display a complex motion patterns
during RT. To enable motion-inclusive toxicity studies, methods of auto-
matic segmentation play an important role as alternative to manual
delineation. This study aimed to assess the performance of a contour prop-
agation software.
Materials and methods: Four observers contoured the BLs on the plan-
ning kV-CT (kV-BLs) and on a therapy MV-CT (MV-BLs) in eight prostate
patients. After elastic registration, kV-BLs were deformed, using Mimvista
software, to MV-CT (CP-BLs) and then manually corrected (MC-BLs).
The potential of contour propagation method was assessed evaluating:
1) The inter-observer variations of both CP-BLs and MC-BLs relative to MV-
BLs using the DICE.
2) The contouring time.
3) The impact of inter/intra-observer variations on DVH parameters
(V10–V50).
The results were further compared against BL propagation to kV-CTs
Results: Mean DICE between the observers were 0.89 for kV-BLs, 0.82 for
MV-BLs, 0.92 for the reference kV-CT, with significant inter-modality dif-
ferences (Wilcoxon test, p < 0.002). Contour propagation alone generally
failed (average DICE between propagated and manual BLs on MV-CTs/kV-
CTs: 0.56/0.65), missing a large part of the BL volume due to the poor local
contrast between BLs and pelvic fat and the difficulties of recognising
changes in air content. After manual correction, DICE increases to 0.81 for
MV-CTs and 0.90 for kV-CT while reducing contouring time (−48%). Re-
garding the impact on DVHs, significant differences (p < 0.05) were found
between CP-BLs and manual BLs for absolute (V10–V50) but not for rela-
tive volumes, while a very good agreement was generally found for MC-BLs.
Conclusions: The visibility of the bowel on MV-CT was reasonably good
in most of the pelvic cavity emphasising the potential of MV-CTs for quan-
tifying bowel motion during RT. The use of commercial software to propagate
bowel contours from kV-CT to MV-CT followed by manual correction does
not influence the DVHs of the BLs and may replace full manual contouring.
A.171
NEW APPROACH TO BRAIN METASTASES TREATMENT
N. Perna *, G. Scognamillo, M. Lioce, R. Carbonara, L. Rella, A. Nardone. Istituto
Tumori Giovanni Paolo II – IRCCS, Bari, Italy
Introduction: Whole brain radiotherapy (WBRT) has been considered the
standard treatment for brain metastases.
Several studies suggest to combine WBRT with a simultaneous integrated
boost (SIB) using a VMAT technique.
e50 Abstracts/Physica Medica 32 (2016) e1–e70