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

Introduction:

PET/CT imaging allows to obtain brain metabolic and func-

tional information that is fundamental for pre and post-therapy lesion

assessment. 11C-labeled methionine (MET) is the main radiotracer used

to study this kind of lesion. Therefore it becomes necessary to optimize

the clinical protocol for the use of this radiotracer. The purpose of this study

was to optimize the acquisition time.

Materials and Methods:

This study considered 15 patients who under-

went an MET-PET/CT examination performed on a Discovery 690 Scanner

(GE). The standard protocol is: acquisition time, 15′, and injected activity

550 MBq. Using the list mode function, the exams were reconstructed with

three different acquisition times: 5′, 7′30″ and 10′. The mean ROI counter

per pixel, placed in an internal lesion region (L) and also in a reference

normal region (N), and the Volume of each lesion were evaluated using home

made DICOM analysis software for all acquisition time. The data at 5′, 7′30″

and 10′ were compared with the standard one.

Results:

The assessment of L/N ratio of the three PET image reconstruc-

tions allows to identify the one that better matches the standard

reconstruction. The 10′ image reconstruction was the best to obtain

this result. In case of lesions with dimension smaller than 2 cm

, the

lesion volume measured in standard and 10′ reconstructions differed

about 6%. The 10′ reconstructions were evaluated by the nuclear physi-

cian team and no substantial differences with standard reconstruction were

noticed.

Conclusions:

Our study shows that, in our system, it is possible to reduce

the acquisition time for MET-PET/CT scan to investigate brain metabo-

lism, without affecting the clinical quality of images. This means that a

reduction of the dose to the patient can be carried out without interfer-

ing with the normal execution of the exam. In this way a better

radioprotection for the patient is achieved, with identical reliability of images

for diagnostic use.

http://dx.doi.org/10.1016/j.ejmp.2016.01.369

C.364

GAMMA TOMOSYNTHESIS FOR MOLECULAR IMAGING

M. Longo

* , a ,

R. Pellegrini

b , c ,

M.N. Cinti

b , c ,

V. Frantellizz

i d ,

G. De Vincentis

d ,

R. Pan

i c , e .

Post Graduate School of Medical Physics, Sapienza University of

Rome, Rome, Italy;

Department of Molecular Medicine, Sapienza University

of Rome, Rome, Italy;

INFN Roma I Section, Rome, Italy;

Department of

Radiological Sciences, Oncology and Anatomical Pathology, Sapienza University

of Rome, Rome, Italy;

Department of Sciences and Medical and Surgical

Biotechnologies, Sapienza University of Rome, Rome, Italy

Introduction:

It is well known that without the ability to detect small

lesions, indicative of early stage disease, molecular imaging technique has

limited clinical utility. Commonly available Anger cameras, which are large,

bulky and designed for general-purpose imaging, are not ideal for detect-

ing lesion smaller than 1 cm. To overcome these limitations, we propose

a gamma tomosynthesis method based on a slant collimation system that,

complemented to a conventional gamma camera, performs high resolu-

tion three-dimensional imaging.

Materials and Methods:

The slant hole collimation system dedicated to

gamma tomosynthesis is characterized by the capability of tilting its holes

according to variable angles. This system allows to acquire a set of planar

images at different angles, which are then reconstructed through the Shift

And Add (SAA) method to obtain the three-dimensional distribution of a

radioactive tracer. This technique was validated by experimental measure-

ments with dedicated phantoms, using our collimation system on the

gamma camera GE Millennium. A phantom is realized using a cylindrical

container with a background activity and two spheres filled with 99mTc,

with different uptakes, representing the hot spots. Moreover, the Mini Defrise

phantom was used to examine how well the tomosynthesis technique pre-

serves axial resolutions.

Results:

The system allows to reach sub-centimeters coronal and sagittal

spatial resolutions, while the spatial resolution becomes worst in the axial

direction. This latter sub-optimal response could be solved by perform-

ing the SAA reconstruction without small angle projections, even if this

implies a reduction of contrast and signal to noise ratio.

Conclusion:

Different from currently used SPECT, a conventional gamma

camera equipped with this slant collimation system could be located

in a fixed position at the minimum distance from the patient, thus

improving detection, localization and characterization of sub-centimeter

lesions.

http://dx.doi.org/10.1016/j.ejmp.2016.01.370

C.365

MONTE CARLO AND CLINICAL STUDY OF THE IMPACT OF ATTENUATION

AND SCATTER CORRECTIONS ON PROSPECTIVE 3D DOSIMETRY FOR

RADIOEMBOLIZATION WITH 90Y MICROSPHERES

M. Pacilio

a ,

L. Lorenzon

* , b ,

M. Ferrari

c ,

C. Chies

a d ,

F. Botta

c ,

M. Mir

a e ,

D. Becci

b ,

L.A. Torres

f ,

M.C. Perez

f ,

C. Basile

a ,

M. Ljungberg

g ,

R. Pani

h ,

M. Cremones

i c .

Department of Medical Physics, Azienda Ospedaliera San

Camillo Forlanini, Rome, Italy;

Postgraduate School of Medical Physics, Sapienza

University of Rome, Rome, Italy;

Department of Medical Physics, Istituto

Europeo di Oncologia, Milan, Italy;

Department of Nuclear Medicine, Istituto

Nazionale Tumori IRCCS Foundation, Milan, Italy;

Post graduate Health Physics

School, University of Milan, Milan, Italy;

Department of Nuclear Medicine,

Clinical Research Division of the Center of Isotopes (DIC-CENTIS), Havana, Cuba;

Department of Medical Radiation Physics, University of Lund, Lund, Sweden;

Department of Molecular Medicine, Sapienza University of Rome, Rome, Italy

Introduction:

The aim of this study was to evaluate the impact of the

absence of attenuation or scatter corrections in 99mTc-MAA-SPECT images

in radioembolization treatment planning.

Materials and Methods:

Monte Carlo simulations were performed for three

anthropomorphic phantoms with different activity distributions in the liver.

Liver motion due to breathing was also simulated. 36 patients with hepa-

tocellular carcinoma or liver metastasis were considered. Images were

reconstructed by OSEM algorithm, switching on and off attenuation (AC)

and scatter (SC) correction. 3D dosimetry was performed with voxel S value

approach, using a relative calibration method. Cumulative dose–volume his-

tograms in Tumoral Liver (TL) and Healthy Parenchyma (HP) were compared,

assessing differences for D95%, D70% and D50%. For simulated cases, the

dose image derived from the input activity map was the Gold Standard (GS).

For clinical cases, the dose map obtained using AC and SC was the reference.

Results:

For simulated cases, differences vs. GS are severe. Modest com-

pensation derives from AC and SC. For TL, dosimetric indicators are

underestimated in most cases. For HP, differences are distributed around

zero and show a reduced spread considering the D50% parameter. Patient

breathing worsens the differences, in particular for TL. In the clinical cases,

the absence of AC (not available in all centers) affects lesion dosimetry more

importantly than SC (always feasible), but it is less critical for HP, which

is the main focus of the planning.

Conclusions:

All corrections would be needed to improve dosimetric ac-

curacy. For TL, more efforts are required to obtain an accurate dosimetry.

HP dosimetry seems to be less critical and D50% is a more reliable dosi-

metric indicator. Dosimetric planning without CT based AC, although

approximated, is preferable than adopting non dosimetric methods.

http://dx.doi.org/10.1016/j.ejmp.2016.01.371

C.366

ACCURATE MEASUREMENTS OF LOW ACTIVITY FOR CALIBRATION OF A

RIA GAMMA COUNTER USED IN RED MARROW DOSIMETRY

L. Lorenzon

* , a ,

S. Donatiello

b ,

V. Cannatà

b ,

M.C. Garganese

c ,

G. Giannon

e d ,

C. Orland

i b ,

M. Pacili

o e ,

E. Genoves

e b .

Postgraduate School of Medical Physics,

Sapienza University of Rome, Rome, Italy;

Enterprise Risk Manager/Medical

Physics, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy;

Department

of Nuclear Medicine, Bambino Gesù Children’s Hospital, IRCCS, Rome, Italy;

Department of Laboratories, Bambino Gesù Children’s Hospital, IRCCS, Rome,

Italy;

Department of Medical Physics, Azienda Ospedaliera San Camillo

Forlanini, Rome, Italy

Introduction:

In radionuclide therapy, a RIA gamma counter can be used

routinely to measure the activity concentration in the blood for red marrow

dosimetry, essential to control haematological toxicity. Calibration of a

gamma counter, due to its high sensitivity, has to be performed with sources

of low and known activity. The aim of this work was to perform the cali-

bration in terms of activity-counts of a RIA gamma counter, used for 131-I

blood sample measurements, by implementing the weighing method for

accurate measurements of low activity calibration sources.

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Abstracts/Physica Medica 32 (2016) e97–e115