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

A.195

THE USE OF A REDUNDANT INDEPENDENT CALCULATION SOFTWARE IN

THE EXTRA-CRANIAL STEREOTACTIC SMALL FIELD RADIOTHERAPY AS

PART OF QUALITY ASSURANCE PROGRAM

G. Rossi

* , a ,

A. Pentiricci

a , b ,

F. Chionne

b ,

M. Alessandro

c .

AUSL Umbria 1 –

Unità di Staff di Fisica Sanitaria, Città di Castello, PG, Italy;

AUSL Umbria 1

– Unità di Staff di Fisica Sanitaria, Perugia, Italy;

AUSL Umbria 1 – S.C. di

Radioterapia Oncologica, Città di Castello, PG, Italy

Introduction:

Quality assurance (QA) in the radiotherapy treatment plan-

ning process is essential to ensure accurate dose delivery to the patient and

to minimize the possibility of accidental exposure. A complete QA plan

should include the commissioning and the quality control of the radia-

tion treatment planning systems (TPS). We focused on the extra-cranial

stereotactic radiotherapy (SBRT): the correctness of each treatment plan

should be guaranteed by a pre-treatment redundant independent dosi-

metric calculation (RIDC) verifying monitor units (MU) calculated by TPS.

Materials and methods:

Treatment unit consisted of Elekta Precise linac

equipped with a body frame for SBRT treatments. The TPS was Philips Pin-

nacle 9.10, with Collapsed Cone Convolution Superposition algorithm for

the dose calculation, commissioned in October 2015. RIDC was per-

formed by PTW Diamond software, based on a modified Clarkson method

that manages both conventional and complex techniques, by importing treat-

ment plans from TPS through DICOM interface. The experimental beam data

for the stereotactic small fields have been acquired using PTWmicrodiamond

detector.

Results:

We first carried out a MU check for different treatment plans as

part of the TPS commissioning recommended tests; dose values calcu-

lated and measured with ion chambers in a slab phantom have been

compared at reference and off-axis points for square, rectangular, asym-

metric and wedge fields. The comparison between RIDC and both TPS and

experimental measurements showed good agreement with recent results

achieved for VMAT techniques.

Conclusions:

To avoid incorrect dose delivery to the patient, the MU to be

delivered by linac should be checked by a second independent verifica-

tion software before the start of treatment; PTW Diamond software has

been validated for the use in SBRT verifications and preliminary measure-

ments lead us to consider it as a fundamental tool in the QA program. Results

on patients undergoing SBRT are pending.

http://dx.doi.org/10.1016/j.ejmp.2016.01.199

A.196

FIRST CLINICAL SYSTEM FOR FULLY AUTOMATED PLANNING FOR NON-

COPLANAR CYBERKNIFE: COMPARISON WITH COPLANAR VMAT FOR

PROSTATE SBRT

L. Rossi

, a , b ,

S. Breedveld

a ,

S. Aluwin

i a ,

B. Heijme

n a .

Radiation Oncology,

Erasmus MC Cancer Institute, Rotterdam, Netherlands;

Medical Physics

Specialization School, Milan, Italy

Introduction

: With the robotic CyberKnife (CK), plan quality may be im-

proved due to the non-coplanar beam set-ups. Because of the tumor tracking,

CTV-PTV margins may be reduced, resulting in further sparing of organs

at risk. In previous work, we developed and validated our in-house opti-

mizer for fully automated, multi-criteria generation of VMAT plans (iCycle/

Monaco), which is now in routine clinical use. Recently, we have extended

the system for the CK (iCycle/Multiplan), including computerized beam angle

optimization. In this study, we have used fully automated plan genera-

tion for un-biased comparison of non-coplanar CK with coplanar VMAT for

prostate SBRT.

Material and methods:

For 10 patients, 3 clinically deliverable plans were

automatically generated: one for CK (iCycle/Multiplan) with 3 mm PTV

margin and two for VMAT (iCycle/Monaco) with 3 and 5 mm PTV margin,

respectively. For all plans, 38 Gy was delivered in 4 fractions.

Results

: With automated planning, high quality CK and VMAT plans were

generated without user dependency and trial-and-error approach. PTV cov-

erage was similar for all 3 approaches; however, with 5 mm margin,

coverage

95% was not always feasible. Mean values for rectum D1cc and

Dmean were 26.1, 28.5, 34.3 Gy, and 6.3, 7.1, 10.8 Gy for CK, VMAT-3 and

VMAT-5, respectively. The reductions in rectum D1cc for CK compared to

VMAT-3 and VMAT-5 were statistically significant (p

0.015 and p

0.007).

For differences in rectum Dmean, these p-values were 0.08 and 0.008.

Bladder sparing was slightly better for VMAT-3, however, p

0.05. No rel-

evant differences were found for other OARs. With CK, the low-to-medium

dose bath was reduced; p

0.007 and 0.008 for CK compared to VMAT with

3 and 5 mm margin.

Conclusion

: The first system for automated generation of clinically deliv-

erable CK plans was built and used for unbiased plan comparison with VMAT.

Optimized non-coplanar CK plans showed better rectum sparing than VMAT

plans. This difference was especially large for VMAT with 5 mm margins.

http://dx.doi.org/10.1016/j.ejmp.2016.01.200

A.197

CLINICAL SUPPORT IN RADIATION THERAPY SCENARIOS: MR BRAIN

TUMOR SEGMENTATION USING AN UNSUPERVISED FUZZY C-MEANS

CLUSTERING TECHNIQUE

L. Rundo

* , a , b ,

C. Militello

a ,

S. Vitabil

e c ,

G. Russ

o a , d ,

P. Pisciott

a a , e ,

M.G. Sabin

i d ,

F. Marletta

d ,

M. Ippolito

d ,

C.D. Arrigo

d ,

M. Midiri

c ,

M.C. Gilardi

a .

Istituto

di Bioimmagini e Fisiologia Molecolare – Consiglio Nazionale delle Ricerche

(IBFM-CNR), Cefalù, Italy;

Dipartimento di Informatica, Sistemistica e

Comunicazione (DISCo), Università degli Studi di Milano-Bicocca, Milano, Italy;

Dipartimento di Biopatologia e Biotecnologie Mediche (DIBIMED), Università

degli Studi di Palermo, Palermo, Italy;

Azienda Ospedaliera per l’Emergenza

Cannizzaro, Catania, Italy;

Università degli Studi di Catania, Catania, Italy

Introduction:

Magnetic resonance imaging (MRI) is intensively used in ra-

diotherapy and neuro-radiosurgery, thanks to its greater ability to

discriminate healthy and diseased soft-tissues, by providing excellent image

contrast and high spatial resolution. Moreover, MRI is superior to com-

puted tomography (CT) in determining the extent of tumor infiltration,

although the literature shows that some histological evidence of malig-

nancy may extend beyond the margin of enhancement.

Currently, the target volume to be treated with radiation therapy is con-

toured with slice-by-slice manual segmentation on MR datasets. This

procedure is time-consuming and operator-dependent.

Materials and methods:

The repeatability of the lesion boundary delin-

eation may be ensured only by using automatic or semi-automatic methods,

supporting clinicians in the treatment planning phase as well as in the

patient follow-up (staging and assessing tumor response). A semi-

automatic segmentation method, based on the unsupervised Fuzzy C-Means

clustering technique, was developed. Our approach helps segment the target

and automatically calculate the lesion volume.

Results:

To assess the performance of the implemented segmentation

method, evaluation tests were done on 15 MRI datasets concerning pa-

tients, affected by brain tumors, who were treated with the Leksell Gamma

Knife® stereotactic radio-surgical device. Empirical discrepancy mea-

sures were used, requiring a reference segmentation (“gold-standard”)

defined by an experienced neurosurgeon. Both area-based and distance-

based evaluation metrics were calculated.

Conclusions:

The achieved experimental results, in terms of area-based

metrics and distance-based metrics, demonstrate the reliability and accu-

racy of the proposed segmentation method even when MRI datasets were

affected by acquisition noise or magnetic field inhomogeneties.

http://dx.doi.org/10.1016/j.ejmp.2016.01.201

A.198

DOSIMETRIC CHARACTERIZATION OF A COMMERCIAL 2-D SCINTILLATION

DETECTOR FOR QUALITY ASSURANCE TESTS IN SCANNED PROTON AND

CARBON ION BEAMS

S. Russo

* , a ,

A. Mirandol

a a ,

S. Molinelli

a ,

A. Mairan

i a ,

E. Mastella

a ,

G. Magr

o a ,

S. Giordanengo

b ,

M. Ciocca

a .

Fondazione CNAO, Pavia, Italy;

INFN, Torino,

Italy

Introduction:

Pencil beam scanning technique used at CNAO requires beam

characteristics to be carefully assessed and periodically checked to guar-

antee patient safety. Radiochromic films are widely used within daily QA

checks for pencil beam measurements and determination of dose homo-

geneity in scanned fields. This study aimed at characterizing the Lynx PT

system (IBA Dosimetry) and assessing its suitability for QA tests as com-

pared to EBT3 films, for proton and carbon ion beams.

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Abstracts/Physica Medica 32 (2016) e1–e70