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

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signal extent and regularity. The central portion of the torso containing lungs,
ribs, spine and heart is made of materials conveniently chosen for mim-
icking human tissue. Water equivalent inserts, simulating spherical tumors
and embedded into the phantom lungs, can host films in order to measure
dose distributions. Lungs can be easily customized to be adapted to dif-
ferent applications.
CT acquisitions of the phantom were performed and the constancy of lon-
gitudinal and vertical movements was assessed.
Results: ADAM CT acquisitions demonstrate realistic human tissues HU
values. Movement tests show a long and short-term amplitude repeatabil-
ity of about 1 mm along both vertical and horizontal axes.
Conclusions: ADAM demonstrates suitable performances to test instru-
ments and methods used to treat moving lesions.
A.165
COMMISSIONING OF VOLUMETRIC MODULATED ARC THERAPY AND
PATIENT QA WITH OCTAVIUS 2D ARRAY AND GAFCHROMIC EBT3 FILMS
M. Palombarini R. Romagnoli S. Magi S. Ricci G. Compagnone
P. Berardi a Servizio di Fisica Sanitaria, Ospedale Bellaria- AUSL Bologna,
Bologna, Italy; b Servizio di Fisica Sanitaria, Az.Ospedaliero-Universitaria
S.Orsola-Malpighi, Bologna, Italy
Purpose: To present tests and procedures we implemented for commis-
sioning VMAT on a linac SynergyS and patient QA dosimetry.
Materials and Methods: Beam flatness and symmetry were tested mea-
suring photon 6 MV beam profiles with an Octavius II 2D ion chamber array
in an octagonal shape phantom at the cardinal gantry angles, both in G-T
and A-B directions. Dose rates varied from approximately 600 MU/min down
to 40 MU/min.
The MLC leaves calibration was investigated by a stripe ‘garden-fence’ test
on a Gafchromic EBT3 film at same angles. A 1 cm × 16 cm field was de-
livered from A to B, at 1 cm intervals across the field. Films were digitized
by a flatbed professional scanner (Expression 10000XL/PRO, Epson). Global
rotational delivery accuracy during VMAT was tested by measuring the ab-
solute doses resulting from five ‘fully-dynamic’ prescriptions. Measures were
performed with a Farmer ion ch. in the Octavius phantom and compared
to TPS measurements.
21 VMAT prostate treatment plans were created (TPS Monaco, Elekta), then
verified with the 2D array in phantom and compared with the TPS in coronal
plane via local gamma analysis (3%,3-mm, Verisoft, PTW).
Five out of 21 plans were also verified with EBT3 films in Octavius phantom
to be compared both with the 2D array measurements and with the TPS
dose calculation (now in progress).
Results: Beam flatness and symmetry in G-T were respectively within ±5%
and ±2% at all d-r, while in A-B both were within ± 10% (d-r below
100 MU/min).
Stripe tests on MLC showed variations in dose profile of about ±3% at the
match lines.
Measurements of VMAT global rotational delivery accuracy were consis-
tent with TPS calculation within ±3%.
Finally, for QA dosimetry, measurements showed a very good agreement
with computed doses, with gamma passing-rate > 95% for all plans.
Conclusions: Preliminary tests showed that Octavius dosimetry system in
combination with EBT3 Gafchromic films proved to be a fast, complete and
reliable method for commissioning and QA of VMAT procedures.
A.166
CLINICAL AND DOSE PREDICTORS FOR THE INCIDENCE OF LATE URINARY
SYMPTOMS AFTER RADICAL RADIOTHERAPY FOR PROSTATE CANCER
F. Palorini T. Rancati A. Cicchetti I. Improta C. Cozzarini
V. Casanova Borca C. Degli Esposti P. Franco E. Garibald G. Girell
A. Maggio A. Bott M. Palombarini A. Pierelli E. Pignol N. Simon
V. Vavassor S. Vill R. Valdagni C. Fiorin a Ospedale San Raffaele IRCCS,
Milano, Italy; b Istituto Nazionale dei Tumori IRCCS, Milano, Italy; c Ospedale
ASL 9, Ivrea, Italy; d Ospedale Bellaria, Bologna, Italy; e Ospedale Regionale U.
Parini – AUSL Valle d’Aosta, Aosta, Italy; f Istituto di Candiolo – Fondazione del
Piemonte per l’Oncologia IRCCS, Candiolo, Italy; g Arcispedale S. M. Nuova IRCCS,
Reggio Emilia, Italy; h Cliniche Gavazzeni – Humanitas, Bergamo, Italy
Introduction: To assess clinical and dose factors affecting the incidence of
urinary symptoms between 6 and 24 months after therapy completion in
patients treated with radical RT for prostate cancer.
Materials and methods: Patients treated with conventional (74–80 Gy at
1.8–2 Gy/fraction) or moderately hypofractionated RT (65–75.2 Gy at 2.2–
2.7 Gy/fraction) in 5 fractions/week were enrolled in the DUE01 multicentre
prospective study.
Clinical factors were collected for each patient: comorbidities, drugs,
hormone therapies, previous surgeries, smoking, alcohol, age, and body mass
index. Bladder DVHs were corrected with alpha/beta = 3 Gy. Urinary symp-
toms were evaluated through the IPSS (International Prostate Symptom
Score) questionnaire filled in by the patients at the start/end of RT and every
6 months until 5 years of follow up. The endpoint for urinary toxicity was
IPSS > =15 at least once between 6 and 24 months after RT.
The best predictors were identified through backward feature selections
on 1000 bootstrap resamplings (the ranking of the leading variables was
summarized by the NArea); then multivariate logistic regressions on 1000
bootstrap resamplingswere employed to compute the odds ratio distributions.
Results: Dose parameters and toxicity data at baseline and between 6 and
24 months were available for 195 patients: 158/195 (81%) did not show
toxicity at baseline (IPSS ≤ 12) while, at 6–24 months, the incidence of
IPSS ≥ 15 was 42/158 (27%).
A 5-variable model (AUC = 0.84) was considered: basal IPSS (NArea = 0.72,
OR = 1.51) and the change of IPSS at RT end (NArea = 0.74, OR = 1.15) were
the leading risk factors. V62Gy was also a risk factor (NArea = 0.36, OR = 1.03),
while the analogues in hormone therapies were found protective
(NArea = 0.34, OR = 0.42).
Conclusions: The analysis shows an important correlation of late urinary
toxicities with the patient urinary condition at baseline and with the acute
worsening of symptoms, too.
Interestingly, hormone therapies with analogues were found protective
factors.
A.167
DOSE UNCERTAINTIES DUE TO INTER-FRACTIONAL ANATOMICAL
CHANGES FOR CARBON ION THERAPY IN THE ABDOMINAL REGION
D. Panizza S. Molinell A. Mirandola G. Magr S. Russ E. Mastella
A. Mairani P. Fossat F. Valv R. Orecchi M. Ciocc a Fondazione CNAO
– Centro Nazionale di Adroterapia Oncologia, Pavia, Italy; b Università degli
Studi di Pavia, Pavia, Italy; c Istituto Europeo di Oncologia, Milano, Italy
Introduction: This study was planned to investigate the impact of inter-
fraction anatomical variations in pancreatic patients when using carbon
ion therapy through a retrospective adaptive approach.
Materials and methods: We collected daily MVCT scans for 5 selected pa-
tients, previously treated for abdominal tumors. On the first MVCT, taken
as reference, a dummy target volume was contoured, based on clinical ex-
perience, and OAR original contours were imported from the planning CT
scan and modified according to anatomical variations. The HU to water
equivalent path length (WEPL) calibration curve was experimentally de-
termined and implemented in our TPS. According to prescription dose and
OARs dose limits of our clinical protocols, a plan was then optimized on
the first MVCT. For each patient, a number of MVCTs equal to the treat-
ment sessions planned according to our fractionation scheme were fused
on the reference one and structures were registered and manually cor-
rected. The reference plan was recalculated on each MVCT scan to simulate
a real treatment fraction. The cumulative dose was calculated by adding
the contribution of each different fraction and then registered on the ref-
erence MVCT. This dose distribution was compared against the reference
one in terms of target dose coverage and dose to OARs.
Results: A clinically relevant loss in target coverage is found: PTV D95%
decreases, on average, by 7%, with a maximum daily variation of −23%. Target
dose becomes less homogeneous, as shown by an average increase in the
PTV HI of 0.08. No clinically significant difference is found in the OAR DVHs.
Local deviations up to 30% with respect to the planned dose can be found
in the daily 3D dose distributions.
e49 Abstracts/Physica Medica 32 (2016) e1–e70