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

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Materials and Methods: Investigated sample consisted of 51 patients, af-
fected by Graves’ diseases (47%) and nodular goiter (53%). In the pre-
treatment phase, a 131I sodium-iodide track activity was administered to
identify Umax and T1/2eff (SIE-AIMN-AIFM) and kt, kT and kB (EANM). The
uptake data at about 2, 6 (only for Graves’ disease), 24, 96 hours were fitted
through a bi-exponential curve. Therapeutic activity was calculated also
considering two and one late measurements as described by EANM. The
statistical analysis was performed by SPSS.20 software.
Results: Therapeutic activities due to SIE-AIMN-AIFM and EANM proce-
dures resulted always significantly different (p < 0.005), regardless of
pathology and number of pre-treatment measurements. For three or more
uptake assessments, EANM values were always greater than SIE-AIMN-
AIFM ones (Delta A%mean = 5.6 ± 2.7%). Moreover, EANM_3pts activities
resulted to be significantly different (p < 0.005) from EANM_2pts and
EANM_1pts ones (Delta A%mean = 2.1 ± 4.7% and Delta A%mean = −9.8 ± 15.8%
respectively).
Conclusion: The implementation of the EANM method increases the ac-
tivity necessary to achieve a specified clinical dose compared to the SIE-
AIMN-AIFM one. The different values of activity determined through the
three methods of EANM guidelines emphasize the importance of a com-
plete personalized treatment.
C.340
CHARACTERIZATION OF AN INTRAOPERATIVE GAMMA SYSTEM
M. Camarda *, P. D’Avenia, E. Di Nicola, L. Montani, G. Rossi, S. Fattori. Servizio
di Fisica Medica ASUR Marche AV3, Macerata, Italy
Introduction: A home made protocol was set up to characterize a CZT
gamma probe equipped with a new tool for spectral analysis. In addition
to the tests recommended by the Italian Quality Control protocol, spec-
tral analysis at various source activities and lateral scans of 2 point sources
at various separation distances were performed.
Materials and Methods: Conventional measurements were carried out as
suggested by the Italian protocol.
The count rate linearity test was performed with a 99mTc point source:
count rates (cps) in the 99mTc window, cps in the open energy window
and spectra were acquired at different times.
Lateral profiles of 2 point sources were performed at 1 cm PMMA depth
and at different source distances ranging from 17 mm to 40 mm to eval-
uate at which separation distance they can be detected separately.
Superficial scans of 1 and 2 sources at 1 cm PMMA depth have been ac-
quired, with 3 mm shift step.
Results: The count rate linearity test shows that the probe is linear within
10% until 25 kcps. Spectral analysis shows that average energy resolution
is 14.6% FWHM (13.5–15.6%) as long as the deviation from linearity is <2%
and the ratio between cps in the 99mTc window and open window is
62% ± 3%.
According to the profiles obtained with a single source at 1 cm PMMA depth,
the spatial resolution of the collimated probe is 15 mm FWHM. Profiles ob-
tained with 2 sources show a Peak-to-Valley ratio < 2 for separation
distance <25 mm.
Isoresponse curves were drawn from superficial scans and were of use in
aligning the probe with the point sources.
Conclusions: Through the home made protocol it is possible to survey the
spectral capability of the probe. As daily quality control, it is recom-
mended to calculate the ratio between cps in the 99mTc energy window
and cps in the open window.
Performing lateral profiles of 2 point sources with different separation dis-
tances it is possible to define the minimal distance at which two lymph
nodes can be detected separately.
C.341
RADIATION PROTECTION IMPACT OF RADIOIODINE THERAPY FOR
HYPERTHYROIDISM AFTER A PATIENT SPECIFIC DOSIMETRIC STUDY
C. Canzi *, V. Longari, M. Castellani, R. Lambertini, F. Zito, F. Voltini,
R. Benti. Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico, Milano,
Italy
In hyperthyroid pts treatment with 131I should rapidly obtain a
nonhyperthyroid status. There is a discussion about the method to deter-
mine the therapeutic activity: estimation (fixed activity) vs calculation (based
on radioiodine uptake measurements), however the optimization princi-
ple states that a pt should be given the minimum activity for the clinical
goal. In our Nucl Med Dept all hyperthyroid pts are submitted to a patient
specific pretreatment study to calculate the minimum activity to achieve
euthyroidism, for nodular autonomies, and hypothyroidism, for Graves
disease.
Aim: To retrospectively evaluate the radioprotection impact of 131I thera-
pies for hyperthyroidism after patient specific dosimetric studies, with
respect to a standard administration of 600 MBq (max activity allowed by
Italian law).
Materials and Methods:532 pts were considered (207 Graves, 388 F, median
age = 65 y [17–89 y]). They all reached a nonhyperthyroid status within 1 y.
Results: Median 131I therapeutic administered activity = 398 MBq [66–
629 MBq]. Total administered activity was 228 GBq. If the standard activity
of 600 MBq had been administered to all pts total activity would have been
319 GBq, 40% greater than the really used one. This acts also on the patient
mean effective dose equivalent and on the mean absorbed dose to the
stomach wall (critical organ for 131I iodide-ICRP 53) that were 6 Sv instead
of 9 Sv and 0.20 Gy instead of 0.28 Gy respectively, with a maximum of dose
saving (8 times) for the patient who was given 66 MBq. The reduction of
131I administered activity also acts on the exposure of the nucl med staff
and of population: the mean dose rate at 1 m at the dismission time is
12 μSv/h instead of 20 μSv/h. This approach involves also the environ-
ment, as in the first 24 h 60% of administered activity is excreted.
Conclusion: The application of a patient specific pretreatment dosimet-
ric study can reduce to 40% the radioprotection impact of 131I treatments
of hyperthyroidism with clinical results guaranteed.
C.342
STUDY OF INTER-FRACTION VARIABILITY OF ABSORBED DOSE TO BONE
METASTASES AND FOLLOW-UP FOR A PATIENT WHO UNDERWENT
223RA-DICHLORIDE THERAPY
M. Pacilio B. Cassano * G. Ventroni P. Ialongo L. Lorenzon
E. Di Castr F. Recine C.N. Sternberg L. Mango a Department of Medical
Physics, Azienda Ospedaliera San Camillo Forlanini, Roma, Italy; b Postgraduate
School of Medical Physics, Sapienza University of Rome, Roma, Italy;
c Department of Nuclear Medicine, Azienda Ospedaliera San Camillo Forlanini,
Roma, Italy; d Department of Radiology, Azienda Ospedaliera San Camillo
Forlanini, Roma, Italy; e Department of Radiological, Oncological and Anatomo
Pathological Sciences, Sapienza University of Rome, Roma, Italy; f Department
of Medical Oncology, Azienda Ospedaliera San Camillo Forlanini, Roma, Italy
Introduction: A 70 year old man, affected by bone metastases from
castration-resistant prostate cancer, underwent 223Ra-dichloride therapy
(6 administrations of 50 kBq per kg of body weight). The inter-administration
variability of absorbed dose to lesions was evaluated, and the lesion uptake
was monitored with 99mTc-MDP imaging.
Materials and Methods: Biokinetic studies were performed for 4 lesions,
after the 1°, 3°, 5° and 6° injections, acquiring antero-posterior planar static
images at 1 h, 1 day, between 2 and 4 days and 7–9 days, using MEGP col-
limator and double-peak acquisition. Lesions were delineated on 99mTc-
MDP WB images acquired before the therapy, and the ROIs superimposed
on the 223Ra images after image coregistration and Wiener filtering. The
activity was quantified with background, attenuation, and scatter correc-
tion, and absorbed doses assessed with the MIRD approach, after delineation
of the lesions on the CT images. Uptake of 8 lesions (i.e., uptake ratio between
lesion and normal bone, TNT) was monitored 4 days before the 3° injec-
tion, 11 days before the 5° injection, and 16, 45 and 93 days after the 6°
injection.
e100 Abstracts/Physica Medica 32 (2016) e97–e115