In-vivo portal dosimetry by an ionization chamber

Piermattei, Angelo; Grimaldi, Luca; D'Onofrio, Guido; Cilla, Savino; Viola, P.; Craus, M.; Fidanzio, A.; Azario, L.; Deodato, Francesco; Macchia, G.; Morganti, Alessio Giuseppe

doi:10.1016/s1120-1797(05)80003-1

Cited by 21 publications

(45 citation statements)

References 29 publications

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“…The accuracy of the in vivo dosimetry method here propose depends on, 1. the transit signal reproducibility equal to ±0.8% (2SD); 2. the uncertainty of the determination of the water equivalent thickness, w, of the phantom equal to ±1% (2SD); 3. the p value within 0.8% for 100 MU/min; 4. the uncertainty of the reconstruction factor for static beams C equal ±3% (2SD) as estimated in a previous paper [29].…”

Section: Resultssupporting

confidence: 56%

“…In a previous paper [29] measurements in water phantom with the presence of heterogeneous layers built with cork or plastic boneequivalent materials were carried out with the beam central axis orthogonal to the layer planes obtaining an agreement within ±3.0% (2SD) between the dose values measured in phantom and those reconstructed at the isocenter by equation …”

Section: Cine-loop Image Calibration For the In Vivo Dosimetrymentioning

confidence: 94%

“…The patient was irradiated with three coplanar arcs 30°, 40°and 50°. The square equivalent field size, L, [29,30] of the three conformal beams changed within ±0.5 cm during an arc. Therefore, in this study we assumed, for every arc, a mean value of the equivalent square field size.…”

Section: In Vivo Measurementsmentioning

confidence: 99%

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In patient dose reconstruction using a cine acquisition for dynamic arc radiation therapy

Piermattei

Fidanzio

Azario

et al. 2009

Med Biol Eng Comput

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An amorphous silicon (a-Si) electronic portal imaging device (EPID) was implemented to perform transit in vivo dosimetry for dynamic conformal arc therapy (DCAT). A set of images was acquired for each arc irradiation using the EPID cine acquisition mode, that supplies a frame acquisition rate of one image every 1.66 s, with a monitor unit rate equal to 100 UM/min. In these conditions good signal stability, +/-1% (2SD) evaluated during 3 months, signal reproducibility within +/-0.8% (2SD) and linearity with dose and dose rate within +/-1% (2SD) were obtained. The transit signal, S (t), due to the transmitted radiotherapy beam below a solid phantom, measured by the EPID cine acquisition mode was used to determine, (1) a set of correlation functions, F(w, L), defined as the ratio between S (t) and the dose at half thickness, D (m), measured in solid water phantoms of different thicknesses, w and with square fields of side L, (2) a set of factors, f(d, L), that take into account the different x-ray scatter contribution from the phantom to the S (t) signal as a function of the variation, d, of the air gap between the phantom and the EPID. The reconstruction of the isocenter dose, D (iso), for DCAT was obtained convolving the transit signal values, obtained at different gantry angles, with the respective reconstruction factors determined by a house-made software. The method was applied to a first patient and the results show that the reconstructed D (iso) values can be obtained with an accuracy within +/-5%. In conclusion, it was assessed that an a-Si EPID with the cine acquisition mode is suitable to perform transit in vivo dosimetry for the DCAT therapy.

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Section: Resultssupporting

confidence: 56%

Section: Cine-loop Image Calibration For the In Vivo Dosimetrymentioning

confidence: 94%

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In patient dose reconstruction using a cine acquisition for dynamic arc radiation therapy

Piermattei

Fidanzio

Azario

et al. 2009

Med Biol Eng Comput

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“…These last values were used to determine the empirical factors f(TPR,d,L)

f (TPR, d, L) = {normals}_{normalt} (TPR, w, L) / {normals}_{normalt} (TPR, w, L, d)

that took into account the variations of the scattered photon contributions on the EPID due to the different midplane phantom positions as respect to the SAD. In previous papers, ( 7 , 8 ) it was shown that, for distances, d, in the range of

\pm 7 cm

, the f(TPR,d,L) factors were independent of the thickness, w, within

\pm 0.5 %

. Hence, we can report the factors in Eq.…”

Section: Methodsmentioning

confidence: 79%

“…(3) was estimated equal to

\pm 4.5 %

also in inhomogeneous phantoms where w was obtained in terms of radiological thickness. ( 7 , 8 ) …”

Section: Methodsmentioning

confidence: 99%

Correlation functions for Elekta aSi EPIDs used as transit dosimeter for open fields

Cilla

Fidanzio

Greco

et al. 2010

J Applied Clin Med Phys

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In‐vivo dosimetry techniques are currently being applied only by a few Centers because they require time‐consuming implementation measurements, and workload for detector positioning and data analysis. The transit in‐vivo dosimetry performed by the electronic portal imaging device (EPID) avoids the problem of solid‐state detector positioning on the patient. Moreover, the dosimetric characterization of the recent Elekta aSi EPIDs in terms of signal stability and linearity make these detectors useful for the transit in‐vivo dosimetry with 6, 10 and 15 MV photon beams. However, the implementation of the EPID transit dosimetry requires several measurements. Recently, the present authors have developed an in‐vivo dosimetry method for 3D CRT based on correlation functions defined by the ratios between the transit signal, normalsnormalt(w,L), by the EPID and the phantom midplane dose, normalDnormalm(w,L), at the source to axis distance (SAD) as a function of the phantom thickness, w, and the square field dimensions, L. When the phantom midplane was positioned at distance, d, from the SAD, the ratios normalsnormalt(w,L)/snormalt'(d,w,L) were used to take into account the variation of the scattered photon contributions on the EPID as a function of d and L.The aim of this paper is the implementation of a procedure that uses generalized correlation functions obtained by nine Elekta Precise linac beams. The procedure can be used by other Elekta Precise linacs equipped with the same aSi EPIDs, assuming the stabilities of the beam output factors and the EPID signals. The procedure here reported avoids measurements in solid water equivalent phantoms needed to implement the in‐vivo dosimetry method in the radiotherapy department. A tolerance level ranging between ±5% and ±6% (depending on the type of tumor) was estimated for the comparison between the reconstructed isocenter dose, Diso, and the computed dose, Diso,TPS, by the treatment planning system (TPS).PACS number: 87.55.Qr; 87.56.Fc

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Epid‐based in vivo dose verification for lung stereotactic treatments delivered with multiple breath‐hold segmented volumetric modulated arc therapy

Cilla

Ianiro

Craus

et al. 2019

J Applied Clin Med Phys

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We evaluated an EPID‐based in‐vivo dosimetry (IVD) method for the dose verification and the treatment reproducibility of lung SBRT‐VMAT treatments in clinical routine. Ten patients with lung metastases treated with Elekta VMAT technique were enrolled. All patients were irradiated in five consecutive fractions, with total doses of 50 Gy. Set‐up was carried out with the Elekta stereotactic body frame. Eight patients were simulated and treated using the Active Breath Control (ABC) system, a spirometer enabling patients to maintain a breath‐hold at a predetermined lung volume. Two patients were simulated and treated in free‐breathing using an abdominal compressor. IVD was performed using the SOFTDISO software. IVD tests were evaluated by means of (a) ratio R between daily in‐vivo isocenter dose and planned dose and (b) γ‐analysis between EPID integral portal images in terms of percentage of points with γ‐value smaller than one (γ%) and mean γ‐values (γmean) using a 3%(global)/3 mm criteria. Alert criteria of ±5% for R ratio, γ% < 90%, and γmean > 0.67 were chosen. 50 transit EPID images were acquired. For the patients treated with ABC spirometer, the results reported a high level of accuracy in dose delivery with 100% of tests within ±5%. The γ‐analysis showed a mean value of γmean equal to 0.21 (range: 0.04–0.56) and a mean γ% equal to 96.9 (range: 78–100). Relevant discrepancies were observed only for the two patients treated without ABC, mainly due to a blurring dose effect due to residual respiratory motion. Our method provided a fast and accurate procedure in clinical routine for verifying delivered dose as well as for detecting errors.

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In-vivo portal dosimetry by an ionization chamber

Cited by 21 publications

References 29 publications

In patient dose reconstruction using a cine acquisition for dynamic arc radiation therapy

In patient dose reconstruction using a cine acquisition for dynamic arc radiation therapy

Correlation functions for Elekta aSi EPIDs used as transit dosimeter for open fields

Epid‐based in vivo dose verification for lung stereotactic treatments delivered with multiple breath‐hold segmented volumetric modulated arc therapy

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