1,721,019 research outputs found
Preliminary results in solid state dosimetry of proton beams for ocular pathology treatment
No full textCalibration factors for ionization chambers used for reference air kerma rate determination.
No full text
Correlation functions for Elekta aSi-EPIDs used as transit dosimeter for open fields. S. Cilla, A. Fidanzio, F. Greco, L. Azario, A. Piermattei.
No full textCalibration of portal imaging devices for radiotherapy in-vivo dosimetry A. Piermattei, S.Cilla, A.Fidanzio, F.Greco, L.Azario.
No full textGeneralized EPID calibration for in vivo transit dosimetry
No full textMany researchers are studying new in vivo dosimetry methods based on the use of
Elelctronic portal imaging devices (EPIDs) that are simple and efficient in their daily use.
However the need of time consuming implementation measurements with solid water phantoms
for the in vivo dosimetry implementation can discourage someone in their use.
In this paper a procedure has been proposed to calibrate aSi EPIDs for in vivo transit dosimetry.
The dosimetric equivalence of three aSi Varian EPIDs has been investigated in terms of signal reproducibility
and long termstability, signal linearity withMUand dose per pulse and signaldependence
on the field dimensions. The signal reproducibility was within 0.5% (2SD), while the long term
signal stability has been maintained well within 2%. The signal linearity with the monitor units
(MU) waswithin 2% and within 0.5% for the EPIDs controlled by the IAS 2, and IAS 3 respectively.
In particular it was verified that the correction factor for the signal linearity with the monitor
units, klin, is independent of the beam quality, and the dose per pulse absorbed by the EPID.
For 6, 10 and 15 MV photon beams, a generalized set of correlation functions F(TPR,w,L) and
empirical factors f(TPR,d,L) as a function of the Tissue Phantom Ratio (TPR), the phantom thickness,
w, the square field side, L, and the distance, d, between the phantom mid-plane and the isocentre
were determined to reconstruct the isocenter dose.
The tolerance levels of the present in vivo dosimetry method ranged between 5% and 6% depending
on the tumor body location.
In conclusion, the procedure proposed, that use generalized correlation functions, reduces the
effort for the in vivo dosimetry method implementation for those photon beams with TPR within
0.3% as respect those here used
Routine EPID in-vivo dosimetry in a reference point for conformal radiotherapy treatments
No full textIn-vivo dosimetry (IVD) in external beam radiotherapy is used to detect major clinically relevant differences between planned a.d delivered dose. Moreover, a.detailed a.alysis of its results, when routinely reported a.d discussed by the radiotherapy staff, can limit the likelihood of error transmission to many treatments. A first experience of routine EPID-based IVD in a.reference point has been performed in our department for 3D-CRT treatments over a.three-year period. More than 14 000 images were a.quired a.d 1287 treatment plans were verified. The IVD checks were obtained three times in the first week a.d then weekly. Tolerance levels of ±5% for pelvic-abdomen, head-neck a.d breast irradiations a.d ±6% for lung treatments were a.opted for the in-vivo measured dose per fraction. A statistical a.alysis of the IVD results was performed grouping the data by: a.atomical regions, treatment units, open a.d wedged fields a.d gantry a.gles. About 10% of the checked doses per fraction showed dosimetric discrepancies out of the tolerance levels. The causes of the discrepancies were 70% delivery or planning errors, 20% morphological changes a.d 10% procedural limitations. 41 cases (3.2%) have required special investigations because their in-vivo doses per fraction, a.eraged over the first three sessions, were out of the tolerance levels a.d in 19 cases (1.5%) the deviations gave rise to a. intervention. Statistically significant differences of a.erage variations between planned a.d delivered doses were observed for: (i) 30° wedged 10 MV fields with respect to those of other wedged or open 10 MV fields delivered by two linacs, due to the incorrect TPS implementation of that wedge transmission factor; (ii) a.terior-posterior a.d posterior-anterior beams with respect to the other gantry orientations for one linac, due to the beam a.tenuation introduced by the treatment couch; (iii) lateral fields with respect to medial fields of breast irradiations for a.l linacs, due to small systematic set-up variations. The a.alysis of our data shows a.substantial homogeneity of the IVD results for a.l the considered body regions and treatment units. However, the observed discrepancies have supplied indications for taking further steps in the optimization process a.d in some cases to adopt an adaptive a.proac
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