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

120 / 146

C.390
ACCURATE MONTE CARLO MODELING OF AN ACTIVITY METER USING
FLUKA
F. Zagni A. Evandri G. Cicoria A. Infantino S. Vichi M.P. Morig
M. Marengo a Medical Physics Department, University Hospital ‘S.Orsola-
Malpighi’, Bologna, Italy; b Montecuccolino Nuclear Engineering Laboratory,
Department of Industrial Engineering, University of Bologna, Bologna, Italy;
c Department of Physics and Astronomy, University of Bologna, Bologna, Italy
Introduction: Monte Carlo codes for simulations of radiation physics ex-
periments are nowadays well suited for the low-energy range, such as for
medical physics applications. In this work we developed and validated the
model of one of the world’s most diffused radionuclide activity meters, a
Capintec CRC-15, using FLUKA.
Materials and Methods: The main geometrical elements and materials of
the ionizing chamber were modeled. Thickness and position of internal com-
ponents were evaluated through both direct measurements of external
dimensions and CT/X-ray imaging. For validation, a set of reference sources
was used: 137Cs (22.7 ± 1.5% MBq), 133Ba (1.3 ± 1.5%), 131I (100 ± 1.5%),
177Lu (196 ± 1.0%), 68Ge “mock 18F” (7.5 ± 1.65%), 57Co (35 ± 3.0%). For each
source, container and filling were suitably modeled as well as the nu-
clides’ full decay schemes. Calibration factors could be evaluated based on
the energy deposited in the Argon gas. Simulation results (statistical
error <1%) were normalized to the response of the modeled 137Cs source.
The sensitivity–source position dependence was also assessed in a range
of 15 cm.
Results: A high accuracy energy–response curve was calculated, as well
as the sensitivity–position curve (maximum discrepancy <4%). The ratios
between simulated and measured relative responses were: 133Ba 1.00 ± 0.03,
68Ge 1.01 ± 0.03, 131I 0.98 ± 0.03, 177Lu 1.03 ± 0.03, 57Co 0.97 ± 0.04.
Conclusion: An accurate model of a widely diffuse activity meter has been
validated for a variety of gamma-emitting nuclides, covering a wide range
of energies and source positions, showing discrepancies below 3% for all
cases. Monte Carlo simulations proved to be a powerful tool for assess-
ment of activity meter’s calibration factors for radionuclides used in
radiopharmacy, in particular for very short lived or non conventional, re-
search radionuclides, and for the easy assessment of geometrical correction
factors.
C.391
EXPERIENCE WITH ALPHA RADIATION THERAPY: PRELIMINARY
PHYSICAL ASSESSMENT ON USING RA-223
F. Zenone C. Gasperi A. Baldoncini G. Belli a UOC Fisica Sanitaria,
AUSL8, Arezzo, Italy; b UOC Medicina Nucleare, AUSL8, Arezzo, Italy
Introduction: We report our experience in two multi-center trials using
Ra-223 to treat prostate cancer related metastasis.
Evaluation of authorized limits for detention of Ra-223, setting the dose
calibrator, radioprotection and waste management, and control of double-
blind (drug vs. placebo) in one of the trials are addressed.
Materials and Methods: Ra-223, mainly alpha-emitter with few gamma
(t1/2 = 11 d), is allotted in 6 mL vials of chloride solution (1 MBq/mL).
The activity limit required for license was estimated accounting on dosage
(50 kBq/kg, every 4 weeks for 6 cycles) and patients planned.
Activity measures are performed with dose calibrator by detecting gamma
emission. It is set by varying its response until it fits the activity of a trace-
able NIST reference source, repeating the procedure 10 times in 3 days.
A spreadsheet calculates the volume to be used based on patient’s weight
and time of injection, also compares the decay correction with that esti-
mated from the producer.
Despite operator’s exposure is low (whole body dose = 0.4 μSv/pz; hands
equivalent dose = 200 μSv/pz), we use lead syringe cover, due to gamma
rays, and shielded cell of manipulation for little release of Rn-219.
The analysis system of liquid waste from patients, who are treated in day-
hospital, was also tested to discharge Ra-223 into the sewage in exemption.
To ensure the double-blind, treatments are registered as hidden to RIS.
Results: Based on patient weight and early delivery of drug (even 10 days)
two vials are shipped. About 50% of the drug, which is patient-specific, has
not been used.
Calibrator accuracy showed an agreement within 1%.
The two methods of decay correction differ by 0.7% at calibration time, and
by ±1.5% maximum in a working day.
Conclusions: The excess of drug supplied increases the activity held daily.
Such aspects must be taken into account for both the request of clearance
and waste management.
It is important to plan the number of patients, the dates of injection and
the limits of authorization.
C.392
PHYSICAL PERFORMANCE OF CLEARPEM, A DEDICATED SCANNER FOR
POSITRON EMISSION MAMMOGRAPHY
A. Zorz S. Morzenti M. Pizzichemi E. De Ponti L. Guerr C. Landoni
E. De Bernardi E. Auffray R. Bugalho J.C.R. Da Silv S. Tavernier
J. Varela P. Lecoq M. Paganoni A. Crespi a A.O. San Gerardo, S.C. Fisica
Sanitaria, Monza, Italy; b Dipartimento di Fisica, Università degli Studi di Milano
Bicocca, Milano, Italy; c A.O. San Gerardo, S.C. Medicina Nucleare, Monza, Italy;
d Dipartimento di Medicina e Chirurgia, Università degli Studi di Milano Bicocca,
Milano, Italy; e CERN, Ginevra, Switzerland; f LIP, Lisbona, Portugal; g VRIJE
Universiteit Brussels, Brussels, Belgium
Introduction: ClearPEM is a positron emission mammography (PEM) pro-
totype scanner developed within the framework of the Crystal Clear
Collaboration. It consists of two planar detector heads (16 × 18 cm2) mounted
on a dedicated gantry that can rotate to perform breast tomographic ac-
quisition; head distance can be adjusted to fit patient’s breast that hangs
out of a circular aperture in the scanner bed. Moreover, gantry can rotate
to 90° in order to perform planar axillary lymph node examinations. It is
equipped with 6144 LYSO:Ce crystal of 2 × 2 × 20 mm3; each side of a 32
crystal matrix is optically coupled to a 32-pixel Hamamatsu S8550 Ava-
lanche Photo-Diode array (APDs), allowing the estimation of the Depth of
Interaction information. A MLEM list-mode reconstruction algorithm is
implemented.
Material and Methods: The following guidelines are used to establish an
acceptance protocol: NEMA NU-1 for gamma camera, NEMA NU-2 for PET
and NEMA NU-4 for small animal PET. Measure of energy, time and spatial
resolution, count rate performance, sensibility, uniformity and image quality
are evaluated to characterize the scanner.
Results: Energy resolution at 511 keV is 14%, temporal resolution is 2.8 ns.
Scanner response is linear below an activity of 45 MBq, compatible with
its clinical use. Spatial resolution evaluated with an Na-22 point source is
about 2 mm; in an Ultra Micro Phantom (Data Spectrum) it is possible to
distinguish the 1.35 mm insert. Sensitivity with an Na-22 point source is
2.8 cps/kBq in the center of the FOV. Integral tomographic uniformity is
16% for ROI 95% and 12% for ROI 75%. Image quality is performed with the
Micro Hollow Sphere phantom (Data Spectrum) with a signal to back-
ground ratio of 10:1; contrast is 33%, 24%, 13% and 6% for sphere diameter
of 7.8, 6, 5 and 4 mm respectively.
Conclusion: Acceptance test protocol for a PEM scanner has been estab-
lished. ClearPEM shows a particularly good spatial resolution, whereas
uniformity and sensitivity have to be optimized.
e115 Abstracts/Physica Medica 32 (2016) e97–e115