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

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A.151
DOSIMETRIC AND PRECLINICAL RESULTS OF SMALL ANIMAL
IRRADIATION BY USING TOMOTHERAPY
A. Miranti A. D’ambrosi G. Cattar S. Bresciani M. Poli C. Cutai
P. Gabriele M. Stasi a Medical Physics, Candiolo Cancer Institute – FPO, IRCCS,
Candiolo, TO, Italy; b Laboratory of Cancer Stem Cell Research, Candiolo Cancer
Institute-FPO, IRCCS, Candiolo, TO, Italy; c Department of Oncology, University
of Torino, Torino, Italy; d Radiotherapy, Candiolo Cancer Institute – FPO, IRCCS,
Candiolo, TO, Italy
Introduction: Preclinical studies normally require dedicated instru-
ments, but the possibility of exploiting clinical devices for small animal
irradiation is of economical and scientific interest. The aim of this work is
to investigate the feasibility of small animal irradiation with Tomotherapy
by analysing dosimetric results, toxicity and tumour response in xeno-
graft models.
Materials and Methods: Xenograft models were established by injecting
human derived glioblastoma multiforme stem-like cells in
immunocompromised NOD-SCID mice. Mice (17 groups, on average 6 mice
per group) were anaesthetised and placed in a plexiglas cage pie to perform
CT scans. Target volumes and Organs At Risk (OARs, lung and gastro-
intestinal tract) were delineated. Three fractionation schedules were tested:
4 Gy in 1 and 2 fractions (Fr), respectively, and 6 Gy/3Fr. TomoDirect IMRT
technique was applied. 6 groups of xenografts were irradiated by cover-
ing the target volume with a bolus layer to reduce the build-up effect.
Irradiations originally performed without bolus were also simulated with
a virtual bolus. Mice were observed daily and sacrificed when they showed
signs of suffering or when tumour volume reached the established end-
point. Radiotoxicity (survival experiments) and tumour response were
evaluated, comparing irradiated mice as respect to their controls.
Results: The bolus layer significantly impact the maximum dose received
by both target volumes and OARs (t-test, p < 0.05). Irradiation with a dose
of 6 Gy/3 Fr in the presence of a bolus layer prolong mice survival (Sur-
vival analysis, Log-rank test, p < 0.02), showing to be the safest irradiation
protocol. Tumour volume response and mice survival were significantly dif-
ferent in irradiated xenografts as compared to their controls (t-test, p < 0.03;
Log-rank, p < 0.05) demonstrating the radiobiological potential of
Tomotherapy in inducing tumour growth stabilisation.
Conclusions: Tomotherapy systems may be a useful mean for small animal
irradiation.
A.152
INNOVATIVE SOLUTION FOR IORT BREAST TREATMENT: AN ON-LINE IN
VIVO DOSIMETER INTEGRATED IN THE RADIATION PROTECTION DISC
A. Montanari M. Iori N. Tosi E. Cagni A. Botti A. Ciccotelli
G. Felici a Istituto Nazionale di Fisica Nucleare – Sezione di Bologna, Bologna,
Italy; b Arcispedale S. Maria Nuova – Unità di Fisica Medica, Reggio Emilia, Italy;
c Università di Bologna, Dipartimento di Fisica e Astronomia, Bologna, Italy;
d S.I.T. - Sordina IORT Technologies S.p.a., R&D Dept., Aprilia, Italy
Introduction: IORT breast carcinoma treatment clinical practice has evi-
denced the need of real time monitoring the dose delivery on the target.
The commercially available in vivo dosimetry technologies allow either a
real time measurement in one point (MOSFET type detectors) or a non real
time measurement over a surface (radio chromic films). A cooperation
between ASMN Reggio Emilia, INFN and SIT has led to the conceptual design
of a new device capable of satisfying the above mentioned needs. Such
device has been patented (Italian Patent # TO2014A000943). The new do-
simeter consists in four leaf shaped plastic scintillators positioned between
the two parts of the radiation protection disc. Such device can measure in
real time the dose in the four sectors, providing both the integral dose and
a measurement of the field symmetry on the target.
Materials and Methods: The accelerator employed is LIAC S/N 010, a mobile
IORT dedicated electron accelerator capable of producing a 4, 6, 8 and
10 MeV electron beam, produced by SIT. Measurements have been per-
formed with a prototype based on a plastic scintillator tile placed in a PMMA
phantom; plastic scintillator data has been compared with the standard
dose measurements, performed by means of the PTW Roos ionization
chamber.
Results: The behavior of the plastic scintillator has been tested with the
IORT accelerator electron beam and the system fully complies with the stan-
dards requirements.
Conclusions: The above described in vivo dosimeter significantly im-
proves the IORT clinical documentation, allowing the real time check of the
dose delivery over the whole PTV. Furthermore, since the device sensitiv-
ity is high enough to produce a precise dose map with an overall delivery
of less than 1 cGy, the correct positioning of the disc with respect to the
PTV and the applicator can be checked before delivering the treatment, al-
lowing the surgeon to correct it should the symmetry on the PTV be out
of tolerance levels.
A.153
BOLUS IN VMAT BREAST TREATMENT
A. Monti * M.G. Brambilla L. Sarno A. Torresin A. Maldera
M.B. Ferrar D. Zann C. Carbonini H.S. Mainardi V. Arient a Ospedale
Niguarda Ca’ Granda – Medical Physics, Milano, Italy; b Ospedale Niguarda Ca’
Granda – Radiotherapy, Milano, Italy
Introduction: Post mastectomy radiotherapy adds challenges in breast treat-
ment due to the target volume: complex, thinner than the whole breast
and adjacent to the lung, heart (if left), and opposite breast. It can also suffer
the build up effect of high energies. Photon fluence modulation can par-
tially compensate the underdosage at the chest surface, but a high dose
gradient is often generated inducing hot spots. In this work we associate
VMAT treatment and chest bolus to generate more uniform dose coverage.
Material and Methods: In our site more than 400 breasts per year are
treated, 5% of which are chest wall. Six patients (3 left-right) underwent
a CT scan with and without a 10 mm thick bolus. PTVs included the chest
wall (PTVc) and regional lymph nodes (PTVn). A 6MV VMAT treatment was
optimised for each patient with and without bolus using a TPS Monaco vn
5 (Elekta, SWE). The dose delivered was 50 Gy in 25 fractions. Plans were
compared on the basis of PTVs coverage (V47.5Gy, D98% and D2%), dose
homogeneity index (HI) and conformity index (CI); and dose to OARs, par-
ticularly to ipsilateral and contralateral lung, heart, contralateral breast and
the remaining volume (RVR).
Results: When the bolus is removed, PTVc parameters significantly change.
V47.5Gy, D98% and CI decrease respectively of 5.9, 4.1 and 11.5%, while D2%
and HI increase respectively of 1.4 and 5.9%. No reasonable changes af-
fected PTVn while all OARs are approximately the same with a small absolute
reduction in favour of the treatment without bolus. Acute skin toxicity was
G1 in all patients.
Conclusion: VMAT alone it is not enough to remove the underdosage af-
fecting PTVc. The use of a bolus covering the chest wall can improve the
PTV coverage at the surface reducing regions of high doses without in-
creasing skin toxicity. Being PTVn often deeper into the patient, there are
no differences between the two treatments. OARs show a not clinically sig-
nificant small reduction in values when the bolus is removed.
A.154
ANALYSIS OF SETUP UNCERTAINTIES AND CHOICE OF WIDTH OF GATING
WINDOW FOR LEFT-SIDED BREAST TREATMENT DURING DEEP
INSPIRATION BREATH-HOLD (DIBH)
L. Pozzi C. Mordacchini * D.P. Doino R. Novario P. Antognoni a S.C.
Fisica Sanitaria, Ospedale di Circolo e Fondazione Macchi, Varese, Italy; b S.C.
Radioterapia, Ospedale di Circolo e Fondazione Macchi, Varese, Italy;
c Dipartimento Biotecnologie e Scienze della Vita, Università degli Studi
dell’Insubria, Varese, Italy
Introduction: Since 2014 17 pts received radiotherapy of left-sided breast
in DIBH.
The aim of our study is to assess the suitability of the gating window by
analysis of setup images.
Material and Methods: Two CT series were obtained for each pt eligible
for treatment, in free breathing (FB) and DIBH, using Varian RPM system.
In DIBH the width of the gating window, i.e. the allowed chest wall motion,
e45 Abstracts/Physica Medica 32 (2016) e1–e70