Presentation on theme: "ASi-EPID for radiotherapy in vivo dosimetry A.Piermattei (Roma) 10 th International Conference on Radiation Effects on Semiconductor Materials, Detectors."— Presentation transcript:
aSi-EPID for radiotherapy in vivo dosimetry A.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 Parma Azienda Ospedaliera Universitaria Firenze Centro Oncologico Fiorentino Cagliari Presidio Oncologico Businco Viterbo Ospedale Belcolle Roma Campus Biomedico Roma Università Cattolica Campobasso Fondazione Giovanni Paolo II Rionero in Vulture Ospedale 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 damage and a simple procedure for the aSi EPID calibration was investigated. References in www.infndiso.altervista.org
DISO AIMS 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 Italy developed the version SOFTDISO-3DCRT
THE SOFTDISO-3DCRT SUPPLIES TWO TESTS : Diso Diso, TPS 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 R = Diso/ Diso, TPS 0.95 ≤ R ≤ 1.05 acceptance criteria: 0.95 ≤ R ≤ 1.05 3D CRT beam
2) The second test is a 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 P˃1 P˃1P˃1 P˃1 P <1 90% Our experience suggests a pass-rate with P <1 ≥ 90%
Causes of IVD discrepancies : 1.Patient Set-up 2.Occasional morphological changes 3.Systematic morphological changes 4.Attenuators on the beams (patient supports) 5.TPS implementation 6.CT number implementation 7.Laser misalignments 8.Output dose variations 9.Inaccurate MLC positions …generally due to inadequate quality controls.
R P <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
P <1 = 72.6% ….also the analysis shows the change of setup of about 1.5 cm grather than the tolerance (0.5 cm) and the P <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………..
P <1 = 25%....the presence of coch -attenuator off the beam central axis is well detected by the analysis that shows a P <1 = 25%. these underdosages areabout 10%.
P <1 = 54% due to Pelvic tumor : the -analysis supplied a P <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…….
P <1 = 76.8%,....the -analysis supplied a P <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 ….
Gantry 252° Gantry 293°Gantry 60° Microcitoma treated by 3 fields. After the first weak the R tests showed an increase and after the 6 th test all the R ratios were out of tolerance as the -analysis……
REI After one week At half treatment. 60° 229° 293° 81% 82% 70% 63% 76% 93% Summary of the -analysis on the 2D EPID images P <1
Gantry 252° Gantry 293° CT scan for adaptive The new CT scans confirmed 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
at the 2th P <1= 73% is due to the presence of a couch attenuator support on the beam suppling a underdosage of about 30% well IMRT STEP-SHOOT( Elekta) for pelvic tumor : 5 R tests at gantry 180°are within the tolerace lvels but at the 2th test P <1= 73% is due to the presence of a couch attenuator support on the beam suppling a underdosage of about 30% well estimated along the cranio-caudal profile 180
P <1 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 P <1 = 64 %, due to a shrinkage in the mandibular region and consequent change of patient setup
P <1 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 P <1 =18% were due to a partial delivery dose.
P <1 = 61 % VMAT (Elekta) for H-N tumor : R determinations for one arc (179°-181) in 6 days are within the tolerance levels but at the 3°test the -analysis in real time supplies a P <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)
Diso Conclusions: SOFTDISO-3DCRT and the successive SOFTDISO versions for IMRT and VMAT are able to supply in quasi real time the Diso test and the EPID images γ-analysis. Even if the γ-analysis between EPID images is not a true 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.
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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