aSi-EPID for radiotherapy in vivo dosimetryA.Piermattei (Roma)

10 th International Conference on Radiation Effects on Semiconductor Materials,

Detectors and Device FIRENZE 8- 10 Oct . 2014

Following the EURATOM 97/43 recommendation, since 2000 is operative in

Italy the D.L.vo 187/00 about the radioprotection of the patients undergone at

medical radio exposition.In radiotherapy the number of Quality Controls

is increasing as function of the treatment complexity and the workload is responsible of their partial absence that increases errors . Moreover in this field severe incidents have

been recently reported by the media.

• Tumor Control

• Probability

Opinion of many physicists is that a dosimetric control during the treatment using a dedicated software for the in-vivo dosimetry (IVD) could

strongly reduce the presence of dosimetric errors. This mean a major presence of

physicists during the radiotherapy treatment execution, where actually there is a general

absence of this professional component.

Moreover the IVD is one of the best ways to gain experience to prevent errors when

introducing new radiotherapy techniques.

THE DISO PROGET, SUPPORTED BY “ISTITUTO NAZIONALE di FISICA NUCLEARE” INFN, AND UNIVERSITA CATTOLICA S.C. ROMA , INTEND TO DEVELOPE SOFTWARE FOR THE IN-VIVO DOSIMETRY CONTROL USING aSi-EPIDs

website: www.infndiso.altervista.org

ParmaAzienda Ospedaliera Universitaria

FirenzeCentro Oncologico Fiorentino

CagliariPresidio Oncologico Businco

ViterboOspedale Belcolle

RomaCampus Biomedico

RomaUniversità Cattolica

CampobassoFondazione Giovanni Paolo II

Rionero in VultureOspedale Oncologico Regionale CROB

EPID

LINAC

1024x1024 or 1024 x 768 pixel

aSi EPIDs dosimetric caracteristics have been studied for different x-ray beams of different linacs, in terms of : - reproducibility - linearity- ghosting effect- dose rate dependence- radiation damageand a simple procedure for the aSi EPID calibration was investigated.

References in www.infndiso.altervista.org

DISO AIMS

Easy implementation on linacs Varian, Elekta e Siemens

The tests can be obtained in quasi real time due to the interfacing with the R&V of the Center

In the recent years 20.000 IVD tests for 3DCRT

treatments have been obtained in 8 Italian

Centers participating at the DISO Project using a software prototype.

On the basis of these results recently the:

BEST Medical Italydeveloped the version

SOFTDISO-3DCRT

THE SOFTDISO-3DCRT SUPPLIES TWO TESTS:1) The first test is the ratio between the reconstructed

dose Diso at the isocenter point, and that planned Diso,TPS by TPS

R = Diso/ Diso,TPS

acceptance criteria: 0.95 ≤ R ≤ 1.05

3D CRT beam

2) The second test is a g analysis test between a reference EPID image (REI) acquired at the first fraction and the current obtained during the successive fractions. This is a suitable tool to find causes of incorrect beam delivery reproducibility.

reference current distribution image image of points in

disagreement

Pg˃1

Our experience suggests a pass-rate with Pg<1 ≥ 90%

Causes of IVD discrepancies:

1.Patient Set-up2.Occasional morphological changes3.Systematic morphological changes 4.Attenuators on the beams (patient supports)5.TPS implementation6.CT number implementation7.Laser misalignments8.Output dose variations 9.Inaccurate MLC positions

…generally due to inadequate quality controls.

0

250

500

750

1000

1250

1500

R ratio for single test (5603) 89% of tests within 5%

Mean R ratio for patient (281) 100% of tests within 5%

55 65 75 85 950

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Gamma analysis for 5241 test 87% of tests show Pg>90%

R Pg<1

Recent results of 281 patients tested by the version SOFTDISO-3DCRT

281 patients are here reported.

Some more frequent warnings

obtained by the

SOFTDISO-3DCRT

in the italian Centers using :

Varian,Elekta and Simens linacs

Brest irradiation, at the 3°test an incorrect setup, well evident by the shift of the green signal profile, the dose at the isocenter point increased R=1.062 and……….

R=1.062

….also the g analysis shows the change of setup of about 1.5 cm grather than the tolerance (0.5 cm) and the Pg<1 = 72.6% out of tolerance level.

REI

Head tumor. Attenuating support not included in the TPS computation, R<0.95

R=0.906

Attenuating support was in the TPS,computation R values within the tollerances

R=0.982

Pelvic tumor. The R ratios are within the tolerance level of 5% even if the beam at 180° intercept a couch support and………..

...the presence of coch -attenuator off the beam central axis is well detected by the g analysis that shows a Pg<1 = 25% . these underdosages areabout 10%.

Pelvic tumor : the g-analysis supplied a Pg<1 = 54% due to the Belly bord shifted of about 2 cm. The dose discrepancy is up to 20%.

22 cm

Pelvic tumor Presence of a distended rectum in the planning CT-scan. At the 1°and 3°tests the rectum is again distended by gas and R ratios are within the tolerance, but at the 2°test the pocket size decreased and R= 0.907 this means dose variations estimated in 10%.

R= 0.907

aa Pelvic tumor. Large gas pocket in the TC scan used for planning. The R ratios are within the tolerance but the profiles change, and…….

....the g-analysis supplied a Pg<1 = 76.8% , underdosages up to 15% can be estimated by the profiles ( these could be responsible of recurrences).

Some results obtained during

the DISO Project

in the field of adaptive planning

when major systematic anatomical

changes occur

Some IVD tests have supplied informations about lung tumor variations, successively confirmed by new CT scans.In some cases an adaptive plan (to reduce the lung toxicity and/or to supply tumor dose escalation) have been realized, as reported in Medical Physics of 2009 ….

2 CT

2 CT

2 CT

Gantry 252° Gantry 293° Gantry 60°

Microcitoma treated by 3 fields. After the first weak the R tests showed an increase and after the 6th test all the R ratios were out of tolerance as the g-analysis……

REI After one week

At half treatment.

60°

229°

293°

81%

82%

70%

63%

76%93%

Summary of the g-analysis on the 2D EPID images

P g<1 P g<1

Gantry 252° Gantry 293°CT scan for adaptive

The new CT scansconfirmed a tumor regression and a adattive plan was

used for the residual tumor.

The R ratios improved

Original

CT scan

RESULTS OBTAINED BY SOFTDISO VERSIONS DEVELOPED BY BEST MEDICAL ITALY FOR

-Intensity Modulated RT IMRT-Volumetric Modulated Arc T VMAT

BEAMS

IMRT STEP-SHOOT( Elekta) for pelvic tumor : 5 R tests at gantry 180°are within the tolerace lvels but at the 2th test Pg<1= 73% is due to the presence of a couch attenuator support on the beam suppling a underdosage of about 30% wellestimated along the cranio-caudal profile

180

IMRT SLIDING WINDOW (Varian) for Head-Neck tumor : the R determinations for the field at gantry at 103°in the first 3 days is within the tolerance levels. Successively R increases up to 1.13 and Pg<1 = 64 % , due to a shrinkage in the mandibular region and consequent change of patient setup

IMRT SLIDING WINDOW (Varian) for Head-Neck tumor : casual beam interruptions are frequent . In the present case, two linac-interruptions occored at the 3th

test,for the field at gantry 206°,both were restarted but the R= 0.155 and Pg<1 =18% were due to a partial delivery dose .

VMAT

VMAT (Elekta) for H-N tumor : R determinations for one arc (179°-181) in 6 daysare within the tolerance levels but at the 3°test the g-analysis in real time supplies a Pg<1 = 61 % due to a shift of the patient setup. New radiological immages were

required confirming ………….

179 - 181

…………..a shift of the patient setup about 1.5cm ( off tolerance level = 0.3cm)

Conclusions: SOFTDISO-3DCRT and the successive SOFTDISO versions for IMRT and VMAT are able to

supply in quasi real time the Diso testand the EPID images γ-analysis.

Even if the γ-analysis between EPID images is not atrue 2D dosimetric comparison, the IVD result

supplies a suitable option to intercept the causes of incorrect reproducibility of the dose delivery.

The tests in quasi real time are possible because

the SOFTDISO is interfaced with the Record and Verify system of the Center.

1) In vivo dosimetry by an aSi-based EPIDMedical Physics 33 (11) November, (2006)

2) Portal dose measurements by a Physica  Medica 23, 67-72, (200

3) Large discrepancies between planned and actually delivered dose in IMRT oh head and neck cancer. A case reportTumori, A juornal of Experimental and Clinical Oncology, 93, 319-322, (2007)

4) Breast in vivo dosimetry by a portal ionization chamberMedical Physics 34(2), February, (2007)

5) Application of a practical method for the isocenter point in vivo dosimetry by a transit signalPhysics in Medicine and Biology 52, 5101-5117, (2007)

6) EPID cine acquisition mode for in-vivo dosimetry in dynamic arc radiation therapyNuclear Instruments and Methods in Physics Research B, 266 (4), 658-666 (2008).

7) Dynamic conformal arc therapy: Transmitted signal in vivo dosimetryMedical Physics, 35 (5), 1830-39 (2008).

8) A method to determine the planar dose distributions in patient undergone radiotherapyNuclear Instruments and Methods in Physics Research B, 266 (11), 2643-2650 (2008).

9) Real time transit dosimetry for the breath-hold radiotherapy technique: an initial experienceActa Oncologica, 47, 1414-21 (2008).

10) In patient dose reconstruction using a cine acquisition for dynamic arc radiation therapyMedical & Biological Engineering & Computing, 47, 425-33 (2009).

11) Integration between in vivo dosimetry and image guided radiotherapy for lung tumorsMedical Physics, 36 (6), 2206-2214  (2009).

References

12) Dose-guide radiotherapy for lung tumorsMedical & Biological Engineering & Computing.  48: 79-86,  (2010).13) Calibration of portal imaging devices for radiotherapy in-vivo dosimetryNuclear Instruments and Methods in Physics Research A . n. 623, 829-831, (2010).14) Breast in-vivo dosimetry by EPIDJournal of applied clinical medical physics. 11(4) 249-262 , (2010).15) Generalized EPID calibration for in-vivo transit dosimetryA. Fidanzio,  S. Cilla, F. Greco, L. Grimaldi, L. Azario, D. Sabatino, G. D’Onofrio, A. PiermatteiEJMP, Phys.Med. 27(1) 30-38, (2011).16) A generalized calibration procedure for a in vivo transit dosimetry using Siemens   electronic portal imaging devices Medical of Biological Eng. & Computing 49;  373-383, (2011).17) Correlation functions for Elekta aSi-EPIDs used as transit dosimeter for open fieldsJournal of Applied Clinical Medical Physics, 12,1,218-233, (2011).18) Calibration of Elekta aSi EPIDs used as transit dosimeter Technology in Cancer Research & Treatments. 10. 39-48 , (2011).19) Real time dose reconstruction for wedged photon beams: a generalized procedureJournal of Applied Clinical Medical Physics, vol. 12,124-138, (2011).20) A National Project for  in-vivo dosimetry procedures in radiotherapy: first resultsNuclear Instruments and Methods in Physics Research B 274, 42-50,  (2012).21) ASi-EPID transit signal calibration for dynamic beams: a needeful step for the IMRT in vivo dosimetry. Medical of Biological Eng. & Computing, 51:1137-1145, (2013).22) An in-vivo dosimetry procedure for Elekta step and shoot IMRT S. Cilla, L. Azario, F. Greco, A. Physica Medica 30(4) 419-26, (2014)  23) Quasi real time in vivo dosimetry for VMAT A. Fidanzio, A. Porcelli, L. Azario, F. Greco, S. Cilla, M. Grusio, M. Balducci, V. Valentini, A. Piermattei, Med.Phis. 41(6) 2014

3° frazione

4° frazione

IIMRT sliding window beam at 206° splitted in two step. Two deliveries are presented 3° and 4° fractions

All the current IVD supply estimations of the real delivered doses in patient .

Indeed even the more complex clinical IVD procedures (3D) based on EPIDs, use initial reference CT scans ( for the planning) to reconstruct the x-ray fluence to use in a second step for the recomputation of the dose in the same reference CT scans.

Then if the patient’s shape or setup are changed, the reconstructed fluence is not accurate and so the reconstructed doses.

Only a wide-spread use of image guided radiation therapy (CBCT)could assure more accurate daily dose distributions, but also higher doses at normal tissues and time consuming.

For these reasons the IVD tests must supply in real time useful warnings to activate quality controls to remove

the causes of errors.

Staff of physicists Associated at INFN for the DISO Project

website: www.infndiso.altervista.org omme