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10.0 Gy, 12.5 Gy in part II. The DQA is performed by measuring the abso-
lute dose at different points by an IC within the cheese phantom (3%diff).
In part I two MVCT scans, H&N/sternum and abdomen/pelvis, are per-
formed, the shifts applied are the average of the 2 registrations.
Results:
Sparing of OARs with adequate coverage of PTV is feasible re-
specting the prescribed dose and dose limits. DQA confirmed the agreement
between expected and actually delivered dose. The CT Simulation time is
2 h, 1 week is given for processing, the delivery time is less than 35’.
Conclusion:
The protocol is clinically feasible for using HT to deliver TMI
associated with TLI treatment, it may be a novel approach to increase ra-
diation dose with low risk of severe toxicity.
http://dx.doi.org/10.1016/j.ejmp.2016.01.141A.138
USING CONE BEAM CT (CBCT) TO DOSE TRACKING
F. Marcocci
*
, E. Mezzenga, E. Menghi.
IRST, Meldola, Italy
Introduction:
CBCT is a X-ray tube integral with a flat panel that allow to
obtain a fast 3D image of the patient before dose delivering. It could be a
useful tool to monitor the anatomical changes that occur during the
course of radiotherapy. Anatomical changes could cause a difference
between the calculated dose on CT and the dose actually delivered
producing some difference in organ and target DVH. Dose Tracking
means calculating dose on daily CBCT, back project it on first CT by an
elastic registration and finally obtaining real DVH vs planned DVH. It is
thus possible to give to the oncology radiotherapist an instrument to
decide if re-planning is required. However CBCT has some open question,
mainly correctness of dose calculation on CBCT and correctness of elastic
deformation. The first question reflects electron density estimated by
CBCT and the second is the focus of recent studies. This paper aims to
evaluate the correctness of the dose calculation on CBCT and a pilot dose
tracking case will be presented.
Materials and Methods:
XVI is the CBCT system of Elekta Synergy LINAC.
XVI has two filter F0 and F1 (bow tie filter) and some collimator which differ
in the size. Only F1 filter and M15, M20, L20 collimator are used. Dosi-
metric accuracy was evaluated as a function of Kv and mAs choosing the
right value to obtain the best congruency between CT and CBCT dose cal-
culated on a phantom. For each choice of Kv and mAs and for each collimator
an HU-density curve was calibrated. Finally the optimized procedure on
CBCT was used to dose tracking on a pilot patient. Elastic registrations using
ROI drawn by radiotherapist as control ROI guided deformation of calcu-
lated dose in CBCT on CT.
Results:
2%-2 mm gamma analysis shows an agreement between dose cal-
culated on CT and on CBCT for every preset and every collimator over 92.5%.
Particularly good agreement there is using M20 or M15 collimator with
120 Kv and 264 mAs (97.8%, 99.7%).
Conclusion:
CBCT is a useful tool to monitor dosimetric impact due to an-
atomical changes.
http://dx.doi.org/10.1016/j.ejmp.2016.01.142A.139
DIFFUSION AND SENSITIVITY CHARACTERISTICS OF A CHEMICALLY
CROSS-LINKED PVA-FRICKE GEL DOSIMETER
A. Marini
* , a ,L. Lazzer
i a ,C. Corrad
i a ,M.G. Cascon
e a ,M. Marrale
c ,S. Gallo
c ,L. Tranchina
c ,M. Brai
c ,C. Gagliardo
d ,F. d’Errico
a , b .a
Dipartimento di
Ingegneria Civile e Industriale, Università di Pisa, Pisa, Italy;
b
School of Medicine,
Yale University, New Haven, CT, USA;
c
Dipartimento di Fisica e Chimica,
Università degli Studi di Palermo, Palermo, Italy;
d
Sezione di Scienze
Radiologiche, Dipartimento di Biopatologia e Biotecnologie Mediche, Università
degli Studi di Palermo, Palermo, Italy
Introduction:
Current radiotherapy techniques implement treatment plans
based on volumetric distributions of dose with complex shapes and sharp
gradients. The agreement between these plans and the dose that is truly
delivered is very challenging to verify. Thus, there is the need for a dosi-
metric system that is truly three dimensional, sensitive to radiation in each
point and tissue equivalent. In this framework, great interest is encoun-
tered by radio-chromic gel dosimeters.
In order to address the limitations of gels based on natural matrices, some
investigators have proposed dosimeters based on poly vinyl alcohol (PVA)
made by freezing-thawing cycles. Even though these gels have a low dif-
fusion rate, they are also difficult to prepare and they have low sensitivity.
Furthermore, depending on the gelation temperature they can only be read
out by MRI. We hereby present a PVA gel that is chemically crosslinked,
and that offers high sensitivity and low diffusion. These gels can be read
out with optical techniques.
Materials and Methods:
The proposed gel contains 10% w/v of PVA and
is crosslinked by adding glutaraldehyde (GTA). A common formulation gelatin
gel was also prepared and studied for comparison. Both gels contain Xylenol
Orange and the “Fricke” chemical dosimeter: 25 mM sulphuric acid and
0.5 mM iron ammonium sulphate.
Absorbance measurements were done to assess sensitivity and diffusion
coefficient of the gel.
Results:
The dose response of our dosimeter is linear between 0 and 30 Gy
and its sensitivity is equal to 0.073 Gy
−
1
. The diffusion coefficient of the PVA-
based gel is 0.23 mm
2
/h. These characteristics were compared to gelatin
and to data available for so called PVA hydrogels and cryogels.
Conclusions:
Our dosimeter made with PVA and crosslinked with GTA
showed a sensitivity that is comparable to gelatin, and greater than PVA
hydrogels. The diffusion coefficient is 0.23 mm
2
/h, against 0.56 and 0.14 of
gelatine and cryogels.
http://dx.doi.org/10.1016/j.ejmp.2016.01.143A.140
ALANINE/ESR DOSIMETRY FOR TOTAL BODY IRRADIATION USING AN
ANTHROPOMORPHIC PHANTOM
M. Marrale
* , a , b , c ,V. Salamone
d ,S. Gall
o a , b , e ,A. Longo
a , b ,S. Panzeca
a , b , c ,C. Stancampiano
d ,B. Abbate
c , f ,V. Caputo
c , f ,F. D’Errico
g , h ,M. Brai
a , b , c .a
Dipartimento di Fisica e Chimica, Università di Palermo, Palermo, Italy;
b
Istituto Nazionale di Fisica Nucleare (INFN) Gruppo V SEZ. Catania, Catania,
Italy;
c
Scuola di Specializzazione in Fisica Medica, Università di Palermo,
Palermo, Italy;
d
Struttura Complessa di Radiodiagnostica e Radioterapia, Azienda
Ospedaliera Universitaria Policlinico di Catania, Catania, Italy;
e
PH3DRA
Laboratories, Dipartimento di Fisica e Astronomia, Università di Catania, Catania,
Italy;
f
Unità Operativa Complessa di Fisica Medica, ARNAS Ospedale Civico di
Palermo, Palermo, Italy;
g
Dipartimento di Ingegneria Civile e Industriale,
Università di Pisa, Pisa, Italy;
h
Yale University, Yale, USA
Introduction:
Total Body Irradiation (TBI) is a technique widely used in
the radiation blood-oncology in the treatment of patients that need bone
marrow transplantation or peripheral stem cell transplantation.
This technique has some limitations such as the lack of homogeneity of
the dose distribution (which may show variations of 20% in the different
areas), irradiation of critical organs such as the lungs, the liver, the intes-
tine and the eye-lens which can receive a dose comparable to that nominal
and require appropriate shielding and a proper evaluation of the dose ab-
sorbed by them.
The positive outcome of this type of radiation therapy is strictly related
to a precise and accurate measurement of the distribution of the dose de-
livered to the patient in the various body districts.
In this work we performed an analysis by mean of Electron Spin Reso-
nance (ESR) with alanine dosimeters of the doses absorbed in TBI treatment
by using and anthropomorphic phantom.
Materials and Methods:
ESR measurements were performed through the
use of commercial alanine pellets. The dosimeters were irradiated with a
clinical linear accelerator for the construction of the calibration curve and
these values were used for dose calculation of the irradiation of dosim-
eters in an anthropomorphic phantom. Dose measurements were also
performed through a diode.
Results:
The response of alanine as function of dose is found to be linear.
The alanine dose measurements in phantom were compared with those
obtained by a diode. Estimated doses with alanine are significantly com-
parable with the measurements performed with the diode. An
underestimation of about 5% was observed with respect the doses planned
by the TPS.
Conclusions:
Alanine dosimetric system present several advantages such
as: tissue equivalence, linearity of its dose–response over a wide range, high
e41
Abstracts/Physica Medica 32 (2016) e1–e70