Current situation in Cuba March 28April 1 Havana Cuba 2016 Dr Fernando García Yip Dr Rodolfo Alfonso Laguardia Workshop on Physics and Applications of High Brightness Beams Round table on medical applications ID: 934529
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Updates in small field dosimetry Current situation in CubaMarch 28-April 1, Havana, Cuba, 2016Dr. Fernando García Yip *Dr. Rodolfo Alfonso Laguardia **
Workshop on Physics and Applications of High Brightness Beams Round table on medical applications
* Instituto Nacional de Oncología y Radiobiología, INOR** Instituto Superior de Ciencias y Tecnologías Aplicadas, INSTEC
Slide2INOR
Slide3Introduction - Why bother with small fields? -Advanced treatment devices (mini and micro MLC, Tomotherapy, Gammaknife, CyberKnife
...)Complex treatment techniques using non standard /composites fields (IMRT, VMAT, SBRT, SRS/SRT)
Slide4Beam related: - Lack of lateral charge particles equilibrium- Partial oclusion of primary source (collimation type)- Spectral changes => beam qualityDetector related - Size of the detector as compare to the size of the field (Volume averaging effects)
Issues with small fields- When a field is small ? -
IPEM
Report
103 (2010)
Slide5Clinical consequences/ impactReduction of the dose rate (output) of the fieldThe FWHM of the resulting field is wider than the collimator settings (!)The changes in beam quality (harder spectrum) carries the definition of beam quality (TPR20,10 or D10) index for the new small ref fieldSevere influences on treatment planning dataUncertainty in dose delivery (traceability)Risk of misadministration/accident
Slide6Small Beam Dosimetry Working GroupsIPEM– Report 103, UKAAPM TG 155 – Small field relative dosimetry, USAAAPM TG 178 – GammaKnife dosimetry , USAIAEA/AAPM - Small and non-standard fieldsICRU Report committee on “Prescribing, recording and reporting of stereotactic radiation therapy”DIN – Small field subcommittee, GermanyOther national efforts (France, Switzerland, …)
Slide7Joint IAEA/AAPM formalism Publication of the Code of Practice expected during 2016
Slide8Static small fields
Alfonso et al,
Med
Phys
35 (11),
Nov
2008
Slide9Small Static FieldsReference Calibration, ref field fmsr
is a factor which
corrects for the differences between the conditions of field size, geometry, phantom material and beam quality of the conventional reference field fref and the machine-specific reference field
f
msr
Bouchard H and Seuntjens J
Med. Phys.
31
(2004) 2454-2465
Capote R.,
Sánchez-
Doblado
F, Leal A, et al
Med. Phys.
31
(2004) 2416-2422
Sempau J, Andreo P, Aldana J, et al
Phys. Med. Biol.
49
(2004) 4427
Slide10Small Static Fields Relative dosimetry, clinical field fclin
Slide11The concept of output factor is “redefined”Is a dose ratio, a field factor (output factor) -- converts absorbed dose to water !
Can be calculated directly as strict ratio of
Dw using Monte Carlo alone or measure with a ‘fair’ detector
or measured as a ratio of detector readings multiplied by a correction factor. Experimental values depend on the detector
Corrects over the conventional output factor (“field correction factor”). Tabulated as function of the detector and field size
Slide12for
6 MV linacs with FF,
collimated
with
MLC
or
SRS
cones
, as
function
of
equivalent
field
size
, (cm)
Sánchez-
Doblado
F, Leal A, et
al
Slide13Participating countriesAustriaGermanyItalyBangladesh Saudi Arabia Syria Thailand IndiaUSA (Pittsburgh, PA)CubaEgyptMexicoSouth Africa
IAEA project
officersKaren Christaki & Brendan Healy
IAEA Coordinated Research Project
Testing of the IAEA/AAPM Code of Practice for small field dosimetry ,
CRP E24061
Slide14Small Beam defining systems available in CubaCurrentElekta linacs (IMRT)Precise MLCi (1 cm)3dline mMLC (0.3 cm)Agility MLC (0.5 cm)SRS Cones set (5 – 15 mm)Purchased/Projectedm
icro MLC APEX (4)Icon LGK, (Gamma knife w/IGRT)
Slide15Dosimetry equipment available for the projectIonization chambers for absolute dosimetryDetectors for relative dosimetrySeveral electrometersWater and plastic phantoms Anthropomorphic phantomsOther ancillary devices for dosimetry
Slide16o Farmer type (0.6 cc)Four PTW 30013 (waterproof)One PTW 30004 (graphite/Al)One PTW 30002 (all graphite)o Semiflex
type (0.125 cc)Six PTW 31010
o Pinpoint typetwo PTW 310016
Ionization chambers available
for absolute dosimetry
Slide17Detectors available for relative dosimetryo Pinpoint chamberso Two Markus advanced 34045o Si diodes PTW 60016 (shielded) and 60017 (unshielded)o Two microdiamond PTW 60019o One liquid ion chamber PTW microlion 31018o Two
bidimensional chamber arrays model PTW Seven29o EBT2 and EBT3 gafchromic films & transmission scanner
o One RPL glass dosimetry system, model FGD-1000SE, with Glass Dosimeters GD-301 1.5 x 8.5mm
Slide18Water and plastic phantoms O 1D CNMC water phantomo Three PTW MP3 w/softwareo PMMA slab phantomso Solid water (RW3) slabs phantoms
Slide19Anthropomorphic phantoms availableo Thorax phantoms including holders for semiflex ion chamberCIRS 002LFC and CIRS 008Ao Alderson RANDO, including holders for films
o EasyCube for IMRTo Locally developed phantom for SRS (
Diaz&Pico)
Slide20Scientific Background in CubaAsencio Y. Procedure for preclinical commissioning of the radiosurgery system based on mMLC collimators (Jan 2013)González Y. Accuracy Assessment of an Extracraneal
Stereotactic System (Jan 2013)De la Fuente L. Improving
physical dosimetry in SRS with small beams
(Mar, 2013)
Valdes G. Monte Carlo
Monte Carlo calculations of corrections factors for 4 different detectors in non-standard radiation fields settings (Sep 2015)
Argota
R. Clinical testing of the new formalism for SBD (on going)
MSc
thesis conducted on the subject
of small beam dosimetry
Slide21National Introductory Course on Small Field Dosimetry6 - 7 November 2014 at INOR9 medical physicists attendedTheoretical and practical
Slide22Expected output / outcome of IAEA - CRPBased on the contribution of participating institutions and the results of tests, to release guidelines to Member States on the clinical implementation of the small field Code of PracticeFinalize a TECDOC report with recommendations on changes to the CoP and publish other papersThe ultimate benefit will be the reduction in the uncertainty to the dose delivered to the patients receiving radiotherapy that includes small static photon fields
Slide23Conclusions (i)Standard dosimetry methods do not apply to small and composite non-standard beams. Constrains are due both to machine and detector issuesDosimetry errors in SBD may be related to both reference and relative determinationsThe IAEA/AAPM new formalism (from TRS-398) keeps traceability to a broad beam calibrationThe new CoP will standardize recommendations for dosimetry procedures and detectors
Slide24Conclusions (ii)Due to the technology injection, there is and there will be an increased use of small beams for therapy in CubaContribution of local/external capacities is recommended since investigations on SBD are multidisciplinary Through the IAEA coordinated project (CRP) we can make a modest contribution to the clinical implementation of the CoP.
Slide25AcknowledgementThe clinical medical physicist colleagues at INOR and HHA, InsTec faculty and students who contributed to the SBD national efforts is very valuableIAEA/AAPM joint working group: R. Alfonso, P. Andreo, R. Capote, M. Saiful Huq, J. Izewska, J. Johansson, W. Kilby, T. R. Mackie, A. Meghzifene, H. Palmans, K. Kristaki, J. Seuntjens, W. UllrichThe support of IAEA through the research contract 19149/RB is recognized
Slide26Thank you to the Workshop organizers for including this medical applications round table in the program