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

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stability of radiation induced free radicals, no destructive read-out proce-
dure and these features are.
A.141
NUCLEAR MAGNETIC RESONANCE RELAXOMETRY AND IMAGING FOR
DOSIMETRY WITH AGAROSE FRICKE GEL
M. Marrale G. Collur C. Gagliardo S. Gallo G. Iacoviello
A. Longo L. Tranchina V. Caputo F. D’Errico A.M. Gueli
M. Midir S. Panzec M. Brai 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 Dipartimento di
Biopatologia e Biotencologie Mediche Forensi, Università di Palermo, Palermo,
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 Laboratorio di Fisica e Tecnologie
Relative, UNINETLAB, Università di Palermo, Palermo, Italy; h Dipartimento di
Ingegneria Civile e Industriale, Università di Pisa, Pisa, Italy; i Yale University,
Yale, USA; j Scuola di Specializzazione in Fisica Medica, Università di Catania,
Catania, Italy
Introduction: Fricke Xylenol Gel (FXG) dosimetric system is based on the
radiation induced oxidation of ferrous to ferric ions. In this kind of gels it
can occur that ferrous and ferric ions diffuse in the gel matrix. To pre-
serve the spatial distribution of the dose from diffusion, Fricke gels must
be undergoing measurement within a few hours of their irradiation. Thus,
the spatial integrity of the dose distribution in the Fricke gel is main-
tained. The oxidation of ferrous ions also causes a reduction of the
longitudinal nuclear magnetic relaxation time which can be measured by
means of nuclear magnetic resonance (NMR) instrumentation.
In this work we performed NMR relaxometry and MR imaging investiga-
tions of Fricke Xylenol Gel characterized by gelatinous matrix of Agarose
for possible applications in clinical photon beams used for radiation therapy.
Materials and Methods: NMR relaxometry measurements were per-
formed using an mq-ProFiler single-side relaxometer (Bruker Biospin). MRI
imaging was realized on a 1.5 T Achieva scanner (Philips) with an eight
channel head coil. The gels were irradiated in the clinical dose range (0–
20 Gy) with a Siemens Primus Low linear accelerator.
Results: The main dosimetric features of the NMR signal were investi-
gated. The linearity of the response with dose was observed. In order to
assess the photon sensitivity we analyzed the dependence of NMR relax-
ation time on radiation dose with varying ferrous ammonium sulfate content
inside FXG. The ferrous ammonium sulfate content which maximizes sen-
sitivity is 1.75 mM. Furthermore, signal stability was followed for several
days after irradiation.
Aldo for MRI analysis the dose calibration curves were obtained also with
MRI scanner. Moreover, a depth dose profile was reconstructed.
Conclusions: We can conclude that FXG dosimeters with optimal ferrous
ammonium sulfate content can be regarded as a valuable dosimetric tool
to achieve fast information on spatial dose distribution.
A.142
DOSE VERIFICATION OF VMAT HYPOFRACTIONATED LUNG TREATMENTS
IN MOVING PHANTOM
L. Marrazzo S. Calusi M. Casat P. Bonom L. Livi S. Pallotta
a Medical Physics Unit, Careggi University Hospital, Florence, Italy; b Department
of Biomedical, Experimental and Clinical Sciences, University of Florence,
Florence, Italy; c Radiotherapy Unit, Careggi University Hospital, Florence, Italy
Introduction: Predicting dose to a moving target in lung is challenging.
The aim of this study was to assess whether planning on the average CT
scan (AVGCT) allows for a good representation of the dose distribution de-
livered to the moving target and to quantify the agreement between planned
and delivered dose distribution using a moving phantom and EBT3 films.
Materials and Methods: For 10 patients who received lung SBRT, VMAT
plans generated on the AVGCT were recalculated on each phase of the 4DCT
and the resulting average plan was compared with the original plan. All
patients had an ITV defined using the maximum intensity projection and
a PTV created as a 5 mm isotropic expansion. The mean GTV displace-
ment was 1 cm.
A motor driven moving phantom was customized with a tissue equiva-
lent volume simulating the lesion, embedded in cork. EBT3 can be inserted
on a coronal plane in the ‘target’ volume. Plans were generated on the AVGCT
with different strategies. Due to the motion of the film relative to linac
isocenter during delivery, the dose calculated on the CT scan cannot be di-
rectly compared to the dose measured on the moving film. To account for
motion, the planned dose was convolved with the motion function.
Results: The variations between the AVGCT plan and the plan recalcu-
lated and averaged on each phase of the 4DCT are extremely moderate. For
none of the DVH parameters any significant correlation was found between
the variation and neither the extent of tumor displacement nor the plan
complexity.
The average γ passing rate (3%/3 mm, 10%th, local) is 93.0% in static and
94.4% in moving phantom and comparable for all the adopted strategies.
The average difference in near minimum dose to the target, which is the
main metric of significance for lung SBRT, is within 2%.
Conclusion: The study on patients shows that AVGCT is adequate for VMAT
planning. The verifications in static and moving phantom show compara-
ble results, thus suggesting that interplay effect is negligible.
A.143
INITIAL EXPERIENCE WITH AN ACTIVE BREATHING COORDINATOR
DEVICE FOR BREATH HOLD RADIOTHERAPY TREATMENT OF BREAST
A. Martignano V. Vanoni E. Magri L. Menegotti A. Valentini
a Department of Medical Physics, Azienda Provinciale per i Servizi Sanitari –
APSS, Trento, Italy; b Department of Radiotherapy, Azienda Provinciale per i
Servizi Sanitari – APSS, Trento, Italy
Introduction: In this work first data on radiation therapy treatments with
the Active Breathing Coordinator (ABC, Elekta) device are analyzed.
Materials and Methods: The ABC device was used to immobilize the breath-
ing motion in a mid-inhale position with a computer controlled valve. The
patients were trained before the simulation CT to establish the patient-
specific volume threshold and breath hold time. A free breathing CT was
also acquired. Two tangential beams treatment plans were created for each
patient: one in breath hold and the other in free breathing. The planned
dose was 50 Gy in 25 fractions. A software was written to analyze ABC soft-
ware logs. Differences in ipsilateral lung volume, left ventricle distance from
the PTV (for left breast treatments), reproducibility of inhale volume and
patient positioning were evaluated. Patient setup reproducibility was veri-
fied by comparing EPID images acquired randomly during the treatment
with DRR generated by the TPS.
Results: Five patients have been evaluated thus far. The inhale breath hold
volume threshold has an average value of 1.34 ± 0.42 L and the breath hold
duration has an average value of 20.8 ± 1.8 s. The average volume in-
crease of the ipsilateral lung using ABC compared to the free breathing
situation is 67.6 ± 22.3%. The mean minimum distance increment of the left
ventricle to the PTV compared to the free breathing situation is of
1.3 ± 0.9 cm. The mean number of breath holds per fraction is 8.5 ± 2.0 and
the mean inhale volume is 1.7 ± 0.5 L. The inter-fraction coefficient of vari-
ation (CV) of the inhale volume among the patients is 3.6 ± 0.7%, while the
mean intra-fraction CV is 3.5 ± 1.2%. The mean random setup error during
the treatment is below 2 mm.
Conclusions: The ABC device is used to reduce respiratory motion in breast
cancer patients. The device has demonstrated very good intra- and inter-
fraction reproducibility of inhale volume and patient setup thus far.
A.144
EVALUATION OF AN INTEGRAL QUALITY MONITOR DEVICE FOR
MONITORING REAL-TIME DELIVERY
G. Mior A. Martignano L. Menegotti A. Valentini a School of Medical
Physics, University of Rome Tor Vergata, Roma, Italy; b Department of Medical
Physics, Azienda Provinciale per i Servizi Sanitari – APSS, Trento, Italy
e42 Abstracts/Physica Medica 32 (2016) e1–e70