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

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employed for dose of the day calculation in clinical strategies for adap-
tive tomotherapy of head and neck cancer.
A.18
CHARACTERIZATION AND COMPARISON OF TWO EPID-BASED SOFTWARE
SOLUTIONS FOR IN-VIVO DOSIMETRY OF VMAT TREATMENTS
S. Bresciani *, M. Poli, A. Miranti, A. Maggio, A. Di Dia, C. Bracco,
M. Stasi. Medical Physics, Candiolo Cancer Institute–FPO, IRCCS, Candiolo, TO,
Italy
Introduction: The aim of this paper is to evaluate sensitivity and speci-
ficity of two commercial EPID-based software solutions for in vivo dosimetry
of VMAT treatments to identify dosimetric and geometric errors and an-
atomical variations.
Materials and methods: Measurements were performed by using TrueBeam
STx accelerator equipped with EPID aSi1000 (Varian, Palo Alto, CA), Portal
Dosimetry (PD) (Varian, Palo Alto, CA) and PerFraction (PF) software (Sun
Nuclear Corporation, Melbourne, FL). Both PD and PF are commercial EPID-
based dosimetry software, which allows performing transit dosimetry to
provide an independent daily verification of the treatment. Their perfor-
mances on anthropomorphic phantom were studied, simulating 21
perturbations of the reference VMAT plan. Systematic variations in dose
values and dose-rate (1%–5% output variation, 100–600 MU/min), shifts (2.5–
11 mm in anterior direction), anatomical variations (adding bolus over
phantom), and MLC positioning were applied. The difference in local and
global gamma pass rate (%GP) between the no-error and error-simulated
measurements with 1%/1 mm, 2%/2 mm and 3%/3 mm tolerances was cal-
culated. The clinical impact of these errors was also analyzed through the
calculation of the difference between reference DVH and perturbed DVH
(%DE). A %GP value of 95% and a %DE equal to 3% were used to calculate
sensitivity (SE) and specificity (SP) of PD and PF, and compared them.
Results: Repeatability and reproducibility of no-error measurements were
excellent with %GP = 100% for all gamma methods and for both PD and PF.
SE of PF is slightly higher than SE of PD, reaching a maximum of 1 with
1%/1 mm and local normalization criteria. SP is comparable for the two
software.
Conclusions: PD and PF can be confidently used in the clinic to detect do-
simetric, geometrical and anatomical discrepancies and they could have
a very positive impact on improving daily patient QA.
A.19
STEREOTACTIC RADIOTHERAPY IN THE RETREATMENT OF RECURRENT
CERVICAL CANCERS
A. Brogna F. Midili C. Siragus V. Mongell A. Di Pasquale A. Micali
M.C. Angiocch I. Bonapart G. Fet A. Pontoriero G. Iat S. Pergolizz
I. Ielo a A.O.U. Policlinico G. Martino – U.O.C. di Fisica Sanitaria, Messina, Italy;
b Università degli Studi di Messina – Scuola di Specializzazione in Fisica Medica,
Messina, Italy; c A.O.U. Policlinico G. Martino – U.O.C. di Radioterapia Oncologica,
Messina, Italy
Introduction: Locally recurrent cervical cancer is treated with external beam
radiation therapy and concurrent chemotherapy followed by brachytherapy.
In patients submitted to previous irradiation, an option for retreatment could
be BT. However, some patients with gynecological cancer have clinical con-
ditions that do not allow to deliver BT. Cyberknife SBRT could be an
alternative because it permits to deliver high doses of external radiation
resembling BT dose distribution. Our study reports the use of endovaginal
device for tracking in an IGRT modality.
Material and methods: Five patients were enrolled. The vaginal applica-
tor, CT and MRI compatible, is a cylinder with 1 cm diameter and 10 cm
length. In the cylinder, embedded with wax, 3 gold landmarks for IGRT with
fiducial tracking system were placed. Contours were defined with MRI/CT
fusion. The SBRT treatment planning was obtained with inverse planning
algorithm using a nonisocentric technique. A heterogeneous dose distri-
bution was generated to emulate HDRBT.
Results: The SBRT dose to the target was 5/20 Gy delivered in 3/4 frac-
tions, prescribed to the isodose [68–73]%. The median volume of the tumor
was 20 cm3, the median coverage of the target was 96.3%, the median
number of beams was 181, the median conformity index was 1.5, the median
homogeneity index was 1.39, and the median new conformity index was
1.56. The median number of total monitor unit was 25,436. Dmax was
1757 cGy at the bladder, 1747 cGy at the rectum, 868 cGy at the bowel, and
448 cGy and 469 cGy at the left and right femur head respectively. D2cc
was 3 Gy at the bladder, 8 Gy at the rectum and 4 Gy at the intestinal loop.
Conclusions: We describe an alternative curative approach using SBRT. We
can affirm that BT remains the standard of care to deliver higher radia-
tion doses in gynecological cancers; however, in patients with recurrent
cervical cancer previously submitted to irradiation and unable to receive
a BT procedure, SBRT is both safe and effective.
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THREE-ISOCENTER JAGGED-JUNCTION IMRT OF CRANIOSPINAL
IRRADIATION: TREATMENT PLANNING AND PRE-TREATMENT
VERIFICATIONS
A. Brogna C. Siragus V. Mongell F. Midili A. Di Pasqual A. Mical
M.C. Angiocch G. Feti I. Bonaparte G. Arena S. Pergolizzi I. Ielo
a A.O.U. Policlinico G. Martino – U.O.C. di Fisica Sanitaria, Messina, Italy;
b Università degli Studi di Messina – Scuola di Specializzazione in Fisica Medica,
Messina, Italy; cA.O.U. Policlinico G. Martino – U.O.C. di Radioterapia Oncologica,
Messina, Italy
Introduction: Craniospinal irradiation has become an important treat-
ment for tumors including medulloblastoma, high-risk germcell tumors,
and some radio-sensitive secondary malignant tumors of the meninges. CSI
involves complex anatomical structures and requires complex treatment
planning. An IMRT technique with three-isocenter jagged-junction was re-
produced. The goal is to simplify the implementation of the treatment plan
and ensure satisfactory CI and HI. Pre-treatment verification was per-
formed focusing on the overlap junction areas.
Material and methods: The patient was set in prone position. The three
isocenters were placed in the TIJJ plan. Field edges were staggered in [0.5–
1.5] cm steps. IsoA was set as the midpoint of the PTVbrain in the sagittal
plane. The length of the PTVcns was 70 cm, IsoB and IsoC were set to make
the three isocenters 25 cm apart from each other and were placed in the
spinal PTV. The collimator angle was set at 0° for all the field sets. The first
field set contained seven fields with gantry angles of 0°, 50°, 75°, 110°, 245°,
280° and 315°, respectively. The other field sets had five radiation fields,
with gantry angles of 295°, 325° 0°, 35° and 65° respectively. Pre-treatment
verifications were performed with the PTW 2DARRAY. QA plans were gen-
erated in Oncentra Masterplan TPS, and the dose distribution measurements
in the overlapping areas of field junctions were performed afterward.
Results: TIJJ reaches the goal of the 95% isodose curve covering at least 99%
of the PTV and OARs constraint were all respected. HI and CI obtained are
0.11 and 0.69 respectively. No cold or hot dosing spots were found in the
radiation beam overlapping regions between isocenters.
Conclusions: IMRT technology can offer better CI and HI than traditional
multi-field 3DCRT in complex target areas. The use of three isocenters and
beam overlap regions between the isocenters helps avoid typical CSI prob-
lems, such as over-long radiation fields and matching between the fields.
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IMRT PRE-TREATMENT VERIFICATION, 2D VS 4D: PROBLEMS ASSOCIATED
WITH THE COUCH ATTENUATION
A. Brogna A. Di Pasquale F. Midili V. Mongelli C. Siragusa
M.C. Angiocch I. Bonaparte G. Feti A. Mical G. Iati’ A. Pontorier
S. Pergolizzi I. Ielo a A.O.U. Policlinico G. Martino Messina – U.O.C. di Fisica
Sanitaria, Messina, Italy; b Università degli Studi di Messina – Scuola di
Specializzazione in Fisica Medica, Messina, Italy; c A.O.U. Policlinico G. Martino
Messina – U.O.C. di Radioterapia Oncologica, Messina, Italy
Introduction: Because of the complexity and the high dose gradients in
IMRT treatments, it is essential to test the prescribed and delivered dose
agreement through an adequate quality assurance program based on ac-
ceptance tests, periodic quality controls and pre-treatment verification.
e6 Abstracts/Physica Medica 32 (2016) e1–e70