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

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Conclusions: The reported results demonstrate that DIAPIX is a suitable
detector for dosimetric applications. Future plans foresee a new detector
covering a larger area of 2.5 × 7.5 cm2 and a new prototype to be em-
ployed as a transmission detector, mounted on the LINAC gantry.
This work has been supported by the experiments INFN CSN5 DIAPIX and
IRPT/MIUR.
A.222
MULTICENTRE STUDY OF RELATIVE DOSIMETRY MEASUREMENTS USING
RAZOR NEW SILICON DIODE
C. Talamonti * M.D. Falco L. Barone E. Di Castro , C. Iervolino
S. Luxard G. Pastor M.C. Pressell A. Vaian P. Mancosu a Università
degli studi di Firenze, Azienda Ospedaliera Universitaria Careggi, Firenze, Italy;
b Ospedale SS. Annunziata, Università di Chieti, Chieti, Italy; c A.R.N.A.S. Garibaldi,
Catania, Italy; d Policlinico Umberto I, Roma, Italy; e A.O.S. G. Moscati, Avellino,
Italy; f Ospedale Asl 1 Massa e Carrara, Carrara, Italy; g A.S.L., Lecce, Italy; h AO
San Camillo Forlanini, Roma, Italy; i A.S.L 3, Pistoia, Italy; j Humanitas Milano,
Milano, Italy
Introduction: In this study an Italian multicentre evaluation of small field
output factors (OFs) and field penumbras of different linear accelerator
manufacturers using a silicon diode of new generation is presented. The
main goal is to provide indications, for each linac model, on small field do-
simetry measurements that could be used by those centers which intend
to implement new and performing treatment techniques.
Materials and methods: Among 34 radiotherapy centres which took part
in the project, different LINACs were available: 2 Siemens, 13 Elekta Synergy
Agility and BM, 12 Varian CLINAC and 7 Varian True Beam. The same pro-
tocol was used by each centre. A flat ionization chamber was fixed on the
gantry as reference and the IBA unshielded silicon diode RAZOR was used.
The diode was positioned at the isocentre (d = 10 cm SSD 90 cm) in water
phantom. In-cross line beam profiles were used to calculate the effective
field size (FS_E), defined as (A*B)^0.5.OFs as a function of FS_E, and nominal
field size (FS), ranging from 0.6 to 5 cm, was calculated and normalized to
the 3 cm FS.
Results: Penumbra measurements were in agreement with each other for
each FS and accelerator model. The mean values of OFs of all LINACs were
found to be in good agreement within a few per mille up to 1 cm FS. In
the smallest fields, the agreement was within few per cent and for
FS = 0.6 cm was about 10%. For FS below 1 cm, a different trend is evident
depending on different accelerator manufacturer and different models from
the same vendor. Considering the FS_E, the agreement increased especial-
ly for Varian where a st.dev of 8% was found for FS = 0.6 cm. This was mainly
due to FS which differed from FS_E up to 15%.
Conclusions: The good agreement among data from different accelera-
tors indicate that RAZOR can be used with good accuracy to perform
measurements in small fields, and that our reported data can be used by
other centres as indicative values, especially when suitable detectors are
not available.
A.223
BEAM DELIVERY CHECK AND IN-VIVO DOSIMETRY DURING BREAST
RADIOTHERAPY TREATMENT
C. Talamonti L. Marrazzo C. Arilli C. Galeott M. Casati S. Calusi
C. Domizi A. Fidanzio I. Meattini S. Scoccianti P. Bonomo
A. Piermattei S. Pallotta a Università degli Studi di Firenze, Azienda
Ospedaliera Universitaria Careggi, Firenze, Italy; b Azienda Ospedaliera
Universitaria Careggi, Firenze, Italy; c Università Cattolica del Sacro Cuore, Roma,
Italy
Introduction: The goal of this study is to verify the delivery of the pre-
scribed dose during radiotherapy treatment using the integral quality
monitoring (IQM) device (iRT Systems GmbH, Koblenz, Germany) and the
portal imaging together with the software SoftDiso (Best Medical Italy Srl)
for in-vivo measurements. Furthermore the ability in detecting positional
and delivery errors intentionally introduced in breast treatments was studied.
Materials and methods: IQM consists of a large area ionization chamber,
with a gradient in the electrode plate separation, to be mounted on the
accelerator gantry. It is an independent on-line beam monitoring system
able to verify the accuracy and consistency of beam delivery during each
treatment session. The software SoftDiso permits to evaluate the dose at
the isocenter on the basis of portal images acquired during the delivery
and it allows to compare dose distributions at the isocenter plane of dif-
ferent acquisitions.
3DCRT and IMRT plans were calculated on a phantom and small delivery
errors were induced to simulate deviation on the treatment plans due to
delivery problems and/or to a wrong positioning of the phantom. The
phantom used was the Anderson Rando modified to mimic a female torso
by adding two silicone gel breast implants.
Results: IQM can detect, with a precision of per mille, errors due to small
changes in MU and field dimensions, while SoftDiso detects discrepancy
on dose reconstructed with a precision of 5%. The combined use of the two
systems allows to identify the source of error (phantom misalignment or
changes in the beam).
Conclusions:The concurrent use of the two tested systems allow for a check
of the correct functioning of all components in the radiotherapy chain, in-
cluding the treatment planning, the delivery system and the patient
positioning and thus play an important role in meeting the needs of modern
and upcoming radiotherapy QA.
A.224
QUALITY ASSURANCE TOOLS FOR RISK MANAGEMENT
S. Tomatis *, V. Palumbo, G. Maggi, A. Gaudino, G. Reggiori, F. Lobefalo,
A. Stravato, F. Zucconi, L. Paganini, G.R. D’Agostino, P. Navarria, P. Mancosu,
M. Scorsetti. Humanitas Research Hospital, Rozzano, Italy
Purpose: To develop proper quality indices to increase the control of the
workflow in radiotherapy by a quantitative analysis of data extracted from
the R&V system database of our radiotherapy department.
Materials and methods: Several parameters related to delivery modality,
use of flattened (FF) or unflattened (FFF) beams, pretreatment imaging and
other planning details were extracted for each patient by proper SQL que-
rying of the database. These features were analyzed to derive indicators
for radiotherapy treatment quality and workflow monitoring. Impact of
hypofractionation was quantified by considering the incidence of fraction
doses up to 3 Gy against higher doses. The application of IGRT was mea-
sured to quantify the quality of patient positioning. For a specific
hypofractionated protocol of breast treatment (48 Gy/15 fr), an indicator
was developed to verify that the total number of effective fractions does
not exceed the number of the planned ones.
Results: Data show an increasing trend in the number of new patients per
year (2500 in 2014). The fraction of VMAT treatments increased from 26.2%
in 2010 to about 85% in 2014. Since 2010, median treatment beam on time
(BOT) for fraction doses above 12 Gy decreased down to less than 2 minutes
in 2014 as for every treatment. In the last 5 years, use of hypofractionation
has grown from 19.2% to about 48.3% of treatments. In 2014 IGRT was
applied to more than 80% of all treatments and always performed in the
first fraction for all patients. Evaluation of excess time involved in the
hypofractionated breast protocol was found to be always below 5 days.
Conclusion: The introduction of new protocols coupled to a growing com-
plexity of treatments led to higher doses per fraction delivered in acceptable
times for a better patient overall comfort. The evaluation of IGRT frequen-
cy and excess therapy time using our indicators was found to be suitable
to obtain high quality standards in essential parts of the radiotherapy work-
flow in our center.
e66 Abstracts/Physica Medica 32 (2016) e1–e70