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

Purpose:

The standardization of small field dosimetry is fundamental to

ensure that different institutions deliver comparable and consistent radi-

ation doses. The current study presents a multicenter evaluation of MLC-

defined small field Tissue Phantom Ratio (TPR), dose profiles FWHM and

penumbra and output factors (OF), for the two major linear accelerator

manufacturers.

Materials and Methods:

The project initially enrolled 31 Italian centers,

15 equipped with Elekta Linacs and 16 equipped with Varian Linacs. Each

center performed TPR measurement, in-plane and cross-plane dose profile

of 0.8

0.8 cm

field and OFs measurements for field sizes ranging from

0.6

0.6 to 10

10 cm

defined by both secondary jaws and MLC. Set-up

conditions were 10 cm depth in water phantom at SSD 90 cm. Measure-

ments were performed using the new Exradin W1 plastic scintillator

detector. To take into account for the Cerenkov effect, a correction factor

for each detector was measured and then applied before any measure-

ment session.

Results:

The analysis of the measurements performed by 13 Varian and

13 Elekta centers was performed; 7 centers were excluded due to mea-

surements inaccuracy, probably due to detector’s instability. TPR

measurements showed standard deviations within 0.6%; penumbra values

of dose profiles showed standard deviations within 0.5 mm, while FWHM

measurements showed a greater variability. OF measurements showed stan-

dard deviations within 1.5% for field size greater than 2

2 cm

; for field

size less than 2

2 cm

measurements’ variability increases with decreas-

ing field size. OF values show no dependence from the effective field size.

Conclusions:

Results show that there is a relatively high degree of con-

sistency regarding TPR and penumbra values. FWHM and OF instead show

greater variability, also for Linac with the same model of the head. Mea-

surements confirmW1 PSD as a candidate for small field clinical radiation

dosimetry in advanced radiation therapy techniques.

http://dx.doi.org/10.1016/j.ejmp.2016.01.138

A.135

STUDY ON THE DOSIMETRY OF LASER ACCELERATED BEAMS FOR FUTURE

CLINICAL APPLICATIONS

R. Manna

* , a ,

G.A.P. Cirrone

a ,

G. Cuttone

a ,

F. Romano

a ,

V. Scuderi

a , b ,

A.G. Amico

a , c ,

G. Candiano

a ,

G. Larosa

a ,

R. Leanza

a , c ,

V. Marchese

a ,

G. Milluzzo

a , c ,

G. Petringa

a , c ,

J. Pipek

a ,

F. Schillaci

a ,

N. Amato

a ,

G. Gallo

a ,

L. Allegra

a .

Laboratori Nazionali del Sud, Istituto Nazionale di Fisica Nucleare,

Catania, Italy;

Department of Experimental Program at ELI-Beamlines, Institute

of Physics of the ASCR, Prague, Czech Republic;

Dipartimento di Fisica e

Astronomia, Università degli studi di Catania, Catania, Italy

Introduction:

Charged particle acceleration, based on the interaction of

ultra-intense and ultra-short laser with a solid target, can represent a future

alternative to conventional techniques, in many applications, from Nuclear

Physics to Radiobiology.

In this context, The ELIMED (MEDical and multidisciplinary applications

at ELI-Beamlines) project aims to realise transport, diagnostics and dosi-

metric elements able to make suitable laser-driven ion beams for

multidisciplinary applications, with particular interest in hadrontherapy.

Materials and Methods:

The detectors dedicated to dosimetry of laser-

accelerated beams must offer a response independent of dose rate and they

must be suitable to operate with a highly intense beam pulse and strong

electromagnetic noise (EMP), in order to obtain a precise knowledge of the

absolute dose delivered, which is mandatory for clinical applications.

For the absolute dosimetry system, an innovative Faraday Cup, optimised

for highly pulsed ion beams, has been developed within the ELIMED

collaboration.

The designed FC has a peculiar geometry, which has been inspired to similar

detectors already developed for ion beam dosimetry; it contains a second

bevelled electrode coaxial and internal to a traditional one that deter-

mines a special-shaped electric field.

Results:

Dosimetric tests, performed with conventional proton beam at

CATANA facility (INFN-LNS), show that the innovative design of FC optimises

the charge collection efficiency and reduces the uncertainties related to the

charge collection in agreement with simulations performed using SIMION

software.

Furthermore, preliminary tests have been performed during experimen-

tal campaigns at laser facility; the preliminary results will be presented.

Conclusion:

New technologies and innovative dosimeters must be devel-

oped and realised in order to achieve an accurate evaluation of the dose

delivered for the future use of these non-conventional beams in medical

applications.

http://dx.doi.org/10.1016/j.ejmp.2016.01.139

A.136

EVALUATION OF SCATTERED RADIATION FROM ELECTRON APPLICATORS

IN PATIENT WITH IMPLANTED ELECTRONIC DEVICES

L. Mantovani

, M. Lamborizio, G. Daprati, R. Di Liberto.

IRCCS Fondazione

Policlinico San Matteo, Pavia, Italy

Introduction:

In this study, the out-of-field scattered dose from electron

beams was measured in patient with implanted defibrillator Medtronic.

Manufacturing company indicates 5 Gy as maximum dose to prevent damage

or malfunction, but threshold dose may vary depending on the model.

Materials and Methods:

The PTV was the left parotid region irradiated with

9 MeV electron beam. The prescribed dose was 60 Gy (2 Gy per fraction),

using 10

10cm

applicator and 0.5 cm bolus. The inferior margin of PTV

valuated with CT scan was about 8 cm from defibrillator in longitudinal di-

rection; the depth of measurements was 1 mm simulating subcutaneous

region. The total dose to defibrillator was considered as amount of scat-

tered dose in body from direct beam and scattered dose in air from electron

applicator. The Monte Carlo algorithm, with CT scan and water-equivalent

slab phantom with a Markus chamber, were used to measure and evalu-

ate the scattered dose in tissue and in air respectively. Two P-type silicon

diode detectors have been used to monitor the dose delivered to defibril-

lator during treatment sessions.

Results:

The dose amount is mainly due to primary beam scattered from

electron applicator. In the experimental setup (ionization chamber posi-

tioned at the side of applicator edge) the total measured dose for the

complete treatment was 1.6 Gy. Dose typically increases with decreasing

distance from the source and falls with depth. Dose measured in-vivo with

semiconductor detectors confirms the expected results (0.05 Gy for single

fraction) and drastic dose reduction is obtained applying a 2 cmwater equiv-

alent bolus on the top of defibrillator.

Conclusions:

The results show that it is very important to evaluate ap-

propriate shielding for patient with electronic device to prevent

malfunctions. The dose measured can be significant when the applicator

is close to the electronic implanted device. The use of water equivalent bolus

is a practical solution to reduce peripheral dose.

http://dx.doi.org/10.1016/j.ejmp.2016.01.140

A.137

PROTOCOL IMPLEMENTATION OF TOTAL MARROW IRRADIATION (TMI)

PLUS TOTAL LYMPHOID IRRADIATION (TLI) USING HELICAL

TOMOTHERAPY (HT)

M. Marcantonini

, a ,

V. Lancellotta

b ,

G. Montesi

b ,

L. Falcinelli

a ,

C. Aristei

b ,

R. Tarducci

a .

Perugia General Hspital, Perugia, Italy;

University of Perugia

and Perugia General Hospital, Perugia, Italy

Introduction:

TBI plays an important role in patients undergoing stem-

cell-transplant for a wide variety of hematological malignancies, but is

associated with significant toxicities. TMI plus TLI delivered with HT may

overcome this problem. The protocol implemented in our department is

here described.

Materials and Methods:

Head and shoulders of patient are immobilized

by means a thermoplastic mask, with arms along the sides. Buns, legs and

feet are positioned in a vacuum cushion. Two CT scans 1 cm slice thick-

ness are collected, with head first (part I) and with feet first (part II) supine

orientation. The PTV (expansions 3–7 mm) consisted of whole body skel-

etal bone, spleen and major lymph node areas. The main OARs are lungs,

heart, liver, kidneys, small intestine, eyes. The plan is prescribed to ensure

90% PTV dose coverage with the 90% of 13.5 Gy prescribed dose (1.5 Gy BID)

and D50%

13.5 Gy. Dose limit for lungs, heart, liver, kidneys, small intes-

tine, eyes are maxD50%

7.5 Gy, 8 Gy, 7.5 Gy, 7.5 Gy, 9 Gy, 6 Gy respectively.

For each CT a treatment plan is elaborated, FW

5.0 cm, Pitch

0.430 and

0.287, MF

2 and 2.5 for parts I and II. The junction region is divided into

3 parts A, B, C with D50%

7.0 Gy, 3.5 Gy, 1.0 Gy in part I and D50%

6.5 Gy,

e40

Abstracts/Physica Medica 32 (2016) e1–e70