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

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New Scenarios in Radiotherapy
A.01
DOSIMETRIC COMPARISON OF 3D-CONFORMAL RADIOTHERAPY,
INTENSITY-MODULATED RADIOTHERAPY AND VOLUMETRIC-
MODULATED ARC THERAPY FOR UPPER ABDOMINAL TUMORS
N. Adorante *, F. Perrotti, S. Giancaterino, A. De Nicola, A. Vinciguerra,
P. Bagalà, D. Genovesi, M.D. Falco. Ospedale Clinicizzato S.S. Annunziata,
Radioterapia, Chieti, Italy
Introduction: The aim of the present study was to compare volumetric
modulated arc therapy (VMAT), intensity-modulated radiotherapy (IMRT)
and 3D-conformal radiotherapy (3DCRT) in their ability to spare organs at
risk (OARs) and to cover planning target volume (PTV) in upper abdomi-
nal cancer treatments.
Materials and methods: Two adjuvant pancreatic cancer and four adju-
vant gastric cancer patients were retrospectively analyzed: these cases were
planned with 3DCRT, conventional step-and-shoot 7-field IMRT and single
arc VMAT technique. Conformity index (CI), homogeneity index (HI), and
gradient index (GI) were analyzed for each technique. In addition we evalu-
ated: monitor units (MU), actual delivery time, PTV and OARs doses. All
generated plans for each patient consisted of 50.4 Gy to be delivered to PTV
in 28 fractions.
Results: The VMAT and IMRT plans exceeded the 3D-CRT technique in terms
of PTV dose conformation and OARs sparing. In particular, for kidneys and
liver the dose sparing was improved by VMAT and IMRT (‹V12› = 50% and
‹V30› = 22%, in VMAT and IMRT plans versus ‹V12› = 62% and ‹V30› = 45%
in 3DCRT plans, for kidneys and liver respectively). VMAT exhibited a better
mean CI (0.62 ± 0.06) and mean GI (1.0 ± 0.2) than the other techniques
(IMRT: mean CI [0.56 ± 0.05], mean GI [1.2 ± 0.1] and 3DCRT mean CI
[0.39 ± 0.06], mean GI [1.3 ± 0.2]). No differences were observed in HI
between the techniques. MU and treatment delivery time were reduced
in VMAT treatments (388 MU and 1.5 minutes versus 522 MU and 10
minutes, for VMAT and IMRT respectively).
Conclusions: Our study showed an improved OARs sparing by VMAT
and IMRT for upper abdominal cancer treatments. The better conformity
index (CI), gradient index (GI) and the reduction in MU and in treatment
delivery time confirmed the advantages of VMAT with respect to
the other techniques. These preliminary results must be confirmed
in larger and prospective study in an effort to evaluate the overall
treatment plan quality and to understand the clinical relevance of these
benefits.
A.02
DOSIMETRY IN TOTAL BODY IRRADIATION: A MEASUREMENT SET TO
CHARACTERIZE THE TREATMENT TECHNIQUE
S. Andreoli *, C. Bianchi, P. Colleoni, M. Fortunato. A.O. Papa Giovanni XXIII,
Bergamo, Italy
Introduction: Since 1999, at our hospital, 165 patients subjected them-
selves to total body irradiation (TBI) with 6 MV and using AP-PA geometry.
This experience highlighted the importance of a fixed and consistent ge-
ometry: in this way it is possible to use the patient statistics to predict the
dose to the next patient. To improve the patient comfort and to not use
lead lung shielding anymore, we want to move to a LL geometry, with com-
pensator thicknesses. The aim of this work is to define a phantom
measurement set to characterize the new treatment technique and to be
able to predict the patient dose.
Materials and methods: Measurements are made in TBI geometry using
a 6EX Varian unit and a dedicated table with 1 cm spoiler. Water equiva-
lent slab phantom and anthropomorphic RANDO phantom are used, entrance
and exit doses are measured by diodes and slabs are used for compensa-
tion. Using water equivalent slab phantom, the doses, the correction factor
for different patient thickness and the compensator dosimetric character-
ization are determined. With RANDO phantom the correlation between the
lung thickness and the water equivalent thickness was achieved. Diodes’
outcome is corrected when the compensator is used on them. These mea-
surements were made taking into account the on/off axis body region
position. Finally a TBI was simulated on RANDO phantom to validate the
method.
Results: The range of correction factor for different patient thicknesses is
1.03–0.75 from 8 to 50 cm water thickness on axis, the value changes up
to 8% off axis. For more than 4 cm compensation, the correction factor of
diodes’ outcome ranges from 0.97 to 0.93 for water equivalent thickness
from 8 to 32 cm. There is a linear correlation between the ratio lung/total
thickness and the scaling factor of lung thickness to obtain the water equiv-
alent thickness. The treatment simulation showed good accuracy with dose
differences less than 3%.
Conclusion: This measurement set allows to predict the MU, doses and the
compensator thickness to obtain the desired midline dose.
A.03
REPRODUCIBILITY AND SENSITIVITY OF IQM: A REAL-TIME MONITORING
DEVICE FOR COMPLEX RADIOTHERAPY TREATMENTS
C. Arilli C. Talamonti L. Marrazzo M. Casati A. Compagnucc
S. Calusi L. Fedeli L. Liv S. Pallotta a Medical Physics Unit, AOU Careggi,
Firenze, Italy; b Department of Clinical and Experimental Biomedical Sciences
Mario Serio, University of Florence, Firenze, Italy; c Radiotherapy Unit, AOU
Careggi, Firenze, Italy
Introduction: The aim of this study was to evaluate the output signal re-
producibility and sensitivity in detecting small errors on delivery parameters
of IMRT step and shoot treatments of the integrated quality monitoring (IQM)
device (iRT Systems GmbH, Koblenz, Germany).
Material and methods: IQM is a monitoring online delivery system
composed of a large ionization chamber with a gradient applied on
electrode plate providing a spatially variant collection yield. A calculation
algorithm predicts the signal by receiving data from the treatment
planning system. The global and intra-fraction repeatability were checked
by delivering with an Elekta Precise linac (6 MV), for about 2 hours, the
same treatment field composed of 17 small fields (4 × 4 cm2) and
by analyzing the output signal for the entire treatment and for each
single field respectively. Inter-fraction repeatability was evaluated by
delivering three IMRT plans (head and neck, prostate and an IMRT
sample plan) for more than 70 times in a period of 30 days. 5 types of
errors were induced in the IMRT clinical plans for head and neck,
prostate and the index quadrant by modifying the number of delivered
MU and by introducing deviations in linac leaf positions. The correlation
between IQM signal variations and 3D, 2D gamma and DVH parameters
has been studied.
Results: The global and local intra-fraction repeatability were 0.04% and
between 0.3% and 0.17%, respectively. The mean inter-fraction repeatabil-
ity was 0.36%, 0.28% and 0.15% for head and neck, prostate and sample plan
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