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

32 / 146

Purpose: In this study, we investigated Ru-106/Rh-106 pediatric applica-
tors (BEBIG, Germany) by utilizing two dosimetry equipments: a dedicated
PTW Optidos dosimeter and a new synthetic diamond detector devel-
oped at the laboratories of Rome “Tor Vergata” University, commercialized
by PTW as microDiamond (mD) and characterized for the present appli-
cation by the National Institute of Ionizing Radiation Metrology – ENEA-
INMRI. The aim of this work was to compare depth-dose profiles with the
ones provided by the manufacturer.
Materials and methods: A BEBIG Ru-106 plaque type CCX was placed in
a homemade water phantom on a dedicated PMMA support. Depth dose
rate measurements were collected through a PTW-Optidos and two mD
detectors. Measurements were performed along the central axis of the
plaque. The results have been compared with the calibration data provid-
ed by the manufacturer.
Results: The mD current integrated over 20 s resulted in charge measure-
ments from about 0.5 to 15 pC in the depth range from 10 mm to 1.51 mm.
In general, measurement repeatability was below 0.5% and reproducibil-
ity was within 2%, including detector positioning errors and differences
between the results from two different mD detectors. Both PTW-Optidos
and mD relative dose distributions showed a good agreement with the ma-
nufacturer’s data, with differences within 4% up to a distance of 8 mm from
the plaque surface. Reference dose rate measured by mD at 2 mm depth
was found about 19% lower than the manufacturer’s value, but still within
the 95% confidence interval. A larger deviation (about −30%) was achieved
using the PTW-Optidos dosimeter.
Conclusions: The differences observed between measured and nominal dose
rate values indicate that a verification of the manufacturer’s data should
always precede the clinical use of Ru-106 eye-plaques. This work has also
shown the suitability of microDiamond to perform accurate relative and
absolute dosimetry of such eye-plaques.
A.90
ACTIVE BREATHING CONTROL (ABC) APPLIED TO LEFT BREAST CANCER
(LBC): DOSIMETRIC RESULTS AFTER 50 PATIENTS AT SPEDALI CIVILI OF
BRESCIA
B. Ghedi L. Spiazz R. Cavagnin N. Pasinetti L. Cost L. Pegurri
R. Moretti a U.O. Fisica Sanitaria, A.O. Spedali Civili Di Brescia, Brescia, Italy;
b Istituto Del Radio, A.O. Spedali Civili Di Brescia, Brescia, Italy
Introduction: The toxic effect of radiation therapy (RT) for the heart has
been extensively documented for LBC patients. Adjuvant chemotherapy regi-
mens may exacerbate the problem, with the use of proven cardio-toxic drugs.
We studied the impact of the implementation of ABC system, a medical
device to reproducibly suspend the patients breathing at the moderate deep
inspiration breath-hold, on the heart, left anterior descending artery (LAD)
and ipsilateral lung dose.
Methods and materials: 50 patients with stages 0–III LBC have been en-
rolled since May 2012. They underwent RT with ABC: the prescription dose
was 50 Gy plus a boost in 88% and 2.75 Gy up to 44 Gy plus a boost in 22%.
For each patient, a free breathing (FB) and a breath hold CT were taken. Two
plans with tangent fields were elaborated. For each patient, the two DVHs
were compared and analyzed using two SW: (1) A homemade Planning Re-
porting Orienteering (PRO)-DVH SW, which elaborates Bio-DVH (equivalent
dose volume histograms for 25 fractions) that allows comparison regardless
of the treatment schedule. (2) The Bioplan (Biological Evaluation of radio-
therapy treatments PLANs) forNTCP calculations of cardiacmortality, according
to the relative seriality model, using D50 = 52.3 Gy, γ = 1.28, s = 1 as param-
eters. PRO-DVH was used to compare the average Bio-DVH as well.
Results: Analyzing the plans performed with FB and ABC, we obtain a com-
parable coverage of the PTV, while the cardiac mortality is significantly
reduced in terms of NTCP with the use of ABC (p < 0.01 for a t-test, paired
samples, two tailed). The same results for the reduction of mean, max and
mean LAD dose. There is no significant difference in the ipsilateral lung dose.
Conclusion: The clinical implementation of ABC gave encouraging dosi-
metric results and is now routinely adopted in our Institution for compliant
LBC patients with significant LAD exposure in radiation fields.
A.91
A TOOL TO CHECK BRACHYTHERAPY TREATMENT TIME: A STATISTICAL
APPROACH
M. Giacometti *, L. Tesei, L. Vicenzi, S. Costantini, M. Cardinali,
S. Maggi. Azienda Ospedaliera Universitaria Ospedali Riuniti, Ancona, Italy
Introduction: Verification of treatment time accuracy is one of the spe-
cific activities of medical physicist. In external beam planning this issue
has been faced for both 3DCRT and now for IMRT. Instead brachytherapy
has not received the same attention, given the simplicity of the technique
and the reduced diffusion. The aim of this work is to evaluate a possible
approach for the verification of the correctness of BRT treatment times.
Materials and methods: Our department is equipped with a microSelectron
therapy unit and Oncentra v.4.1SP2 TPS, both by Nucletron Elekta. In this
work we considered gynecological treatments, 195 with cylindrical appli-
cator and 69 with Fletcher applicator, performed from 2011 until today.
For each plan we recorded: source Air kerma strength (mGy m2/h), volume
of the PTV enclosed within 90% isodose of prescription (V90, cc), prescrip-
tion dose (cGy) and treatment time (s); following, we calculated the
parameter F obtained as treatment time multiplied by activity and divided
by prescription dose.
Results: Data relating to the two types of treatment were analyzed sepa-
rately. We applied a linear fit to the F parameter as a function of V90; the
R2 values of 0.9593 and 0.9503 relate to fit for, respectively, treatments with
cylindrical and Fletcher applicator. Following, we analyzed the distribu-
tion of per cent difference between time calculated by TPS and time obtained
from the linear fit. In both cases we got a Gaussian distribution with mean
and standard deviation (−0.1%, 4.2%) and ( −0.3%, 4.2%) for cylindrical and
Fletcher applicator, respectively.
Conclusion: This work shows that, assuming the same criteria for volume
contouring, it is possible to obtain a parameter F statistically correlated to
V90. The per cent difference between the time calculated by TPS and the
one estimated using the linear fit shows a Gaussian distribution with a stan-
dard deviation of 4%, thus suggesting a tool to evaluate BRT treatment time’s
accuracy.
A.92
EPID-BASED IN-VIVO DOSIMETRY FOR PROSTATE CANCER TREATED BY
VOLUMETRIC ARC THERAPY: PRELIMINARY CLINICAL RESULTS
S. Giancaterino A. De Nicola N. Adorante P. Bagalà F. Perrotti
S. Menna A. Fidanzio A. Piermattei D. Genovesi M.D. Falco
a Department of Radiation Oncology, SS Annunziata Hospital, Chieti, Italy;
b Istituto di Fisica e Unità Operativa di Fisica, Sanitaria Università Cattolica del
S. Cuore, Roma, Italy
Purpose: The purpose of this study is to report the in-vivo dosimetry (IVD)
results obtained using the SOFTDISO software (Best Medical Italy) during
VMAT prostate cancer treatments.
Materials and methods: The SOFTDISO software reconstructs the dose at
the isocenter (Diso) in the patient from the transit signal acquired by the
EPID and allows the comparison between EPID images obtained during the
therapy fractions. In particular for each beam and fraction, the ratios, R,
between the dose reconstructed at the isocenter point Diso in single-arc
VMAT plans and the dose calculated by the treatment planning system
Diso,TPS (generally about 2 Gy for fraction) obtained by Oncentra Masterplan
were computed. The acceptance criteria were: 0.95 < R < 1.05. Moreover the
γ-analysis (2%-2 mm) between portal images was reported. 15 patients with
prostate cancer were treated with 6 MV photon beam delivered by an Elekta
Synergy Agility. Our protocol required, for each patient, 5 consecutive IVDs
in the first 5 treatment sessions after a cone beam CT (CBCT) based set-
up correction and the IVD test once weekly afterward for the rest of the
treatment course when the CBCT scan was not acquired.
Results: The IVD procedure supplied 110 tests and the average R was equal
to 1.004 ± 0.024 (1 SD), in a range between 0.948 and 1.059. The global R
value for each single patient was well within the 5% tolerance level. The
γ-analysis between EPID images yielded P(γ < 1) > 97% in 80% of the tests.
The remaining 20% of the tests gave P(γ < 1) > 93%; they were mainly related
to the sessions where the CBCT scans were not performed indicating that
small set-up variations occurred.
e27 Abstracts/Physica Medica 32 (2016) e1–e70