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Postmastectomy radiation therapy is technically difficult and can be considered one of the most complex techniques concerning patient setup reproducibility. Slight patient setup variations - particularly when high-conformal treatment techniques are used - can adversely affect the accuracy of the delivered dose and the patient outcome. This research aims to investigate the inter-fraction setup variations occurring in two different scenarios of clinical practice: at the reference and at the current patient setups, when an image-guided system is used or not used, respectively. The results were used with the secondary aim of assessing the robustness of the patient setup procedure in use. Forty eight patients treated with volumetric modulated arc and intensity modulated therapies were included in this study. EPID-based in vivo dosimetry (IVD) was performed at the reference setup concomitantly with the weekly cone beam computed tomography acquisition and during the daily current setup. Three indices were analyzed: the ratio R between the reconstructed and planned isocenter doses, γ % and the mean value of γ from a transit dosimetry based on a two-dimensional γ -analysis of the electronic portal images using 5% and 5 mm as dose difference and distance to agreement gamma criteria; they were considered in tolerance if R was within 5%, γ % > 90% and γ mean  < 0.4. One thousand and sixteen EPID-based IVD were analyzed and 6.3% resulted out of the tolerance level. Setup errors represented the main cause of this off tolerance with an occurrence rate of 72.2%. The percentage of results out of tolerance obtained at the current setup was three times greater (9.5% vs 3.1%) than the one obtained at the reference setup, indicating weaknesses in the setup procedure. This study highlights an EPID-based IVD system's utility in the radiotherapy routine as part of the patient's treatment quality controls and to optimize (or confirm) the performed setup procedures' accuracy., (© 2019 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

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 (γ mean ) using a 3%(global)/3 mm criteria. Alert criteria of ±5% for R ratio, γ %  < 90%, and γ mean  > 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 γ mean 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., (© 2019 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.)

Purpose: The aim of the in vivo dosimetry, during the fractionated radiation therapy, is the verification of the correct dose delivery to patient. Nowadays, in vivo dosimetry procedures for photon beams are based on the use of the electronic portal imaging device and dedicated software to elaborate electronic portal imaging device images., Methods: In total, 8474 in vivo dosimetry tests were carried out for 386 patients treated with 3-dimensional conformal radiotherapy, intensity-modulated radiotherapy, and volumetric modulated arc therapy techniques, using the SOFTDISO. SOFTDISO is a dedicated software that uses electronic portal imaging device images in order to (1) calculate the R index, that is, the ratio between daily reconstructed dose and the planned one at isocenter and (2) perform a γ-like analysis between the signals, S, of a reference electronic portal imaging device image and that obtained in a daily fraction. It supplies 2 indexes, the percentage γ% of points with γ < 1 and the mean γ value, γ mean . In γ-like analysis, the pass criteria for the signals agreement ΔS% and distance to agreement Δd have been selected based on the clinical experience and technology used. The adopted tolerance levels for the 3 indexes were fixed in 0.95 ≤ R ≤ 1.05, γ% ≥ 90%, and γ mean ≤ 0.5., Results: The results of R ratio, γ-like, and a visual inspection of these data reported on a monitor screen permitted to individuate 2 classes of errors (1) class 1 that included errors due to inadequate standard quality controls and (2) class 2, due to patient morphological changes. Depending on the technique and anatomical site, a maximum of 18% of tests had at least 1 index out of tolerance; once removed the causes of class-1 errors, almost all patients (except patients with 4 lung and 2 breast cancer treated with 3-dimensional conformal radiotherapy) presented mean indexes values ([Formula: see text], [Formula: see text]%, and [Formula: see text] ) within tolerance at the end of treatment course. Class-2 errors were found in some patients., Conclusions: The in vivo dosimetry procedure with SOFTDISO resulted easily implementable, able to individuate errors with a limited workload.

We evaluate the combined usage of two systems, the Integral Quality Monitor (IQM) transmission detector and SoftDiso software, for in vivo dose monitoring by simultaneous detection of delivery and patient setup errors in whole breast irradiation. An Alderson RANDO phantom was adapted with silicon breast prostheses to mimic the female anatomy. Plans with simulated delivery errors were created from a reference left breast plan, and patient setup errors were simulated by moving the phantom. Deviations from reference values recorded by both monitoring systems were measured for all plans and phantom positions. A 2D global gamma analysis was performed in SoftDiso for all phantom displacements. Both IQM signals and SoftDiso R-values are sensitive to small MU variations. However, only IQM is sensitive to jaw position variations. Conversely, IQM is unable to detect patient positioning errors, and the R-value has good sensitivity to phantom displacements. A gamma comparison analysis allows one to determine alert thresholds to detect phantom shifts or relatively large rotations. The combined use of the IQM and SoftDiso allows for fast identification of both delivery and setup errors and substantially reduces the impact of error identification and correction on the treatment workflow. [ABSTRACT FROM AUTHOR]

Abstract: The paper reports the results of a National project financed by the Istituto Nazionale di Fisica Nucleare (INFN) for the development of in vivo dosimetric procedures in radiotherapy. In particular, a generalized procedure for the in vivo reconstruction of the isocenter dose, D iso, has been developed for 3D conformal radiotherapy treatments with open and wedged X-ray beams supplied by linacs of different manufacturers and equipped with aSi Electronic Portal Imaging Devices (EPIDs). In this way, the commissioning procedure is very simplified and applicable to Elekta, Siemens and Varian linacs. The method here reported is based on measurements in solid-water phantoms of different thicknesses, w, irradiated by square field sizes, L. Generalized mid-plane doses, D 0, and transit signal by EPIDs, , obtained by 19 open and 38 wedged beams of 8 different linacs, were determined taking into account X-ray beam and EPID calibrations. Generalized ratios F 0 = /D 0 for open and wedged beams were fitted by surface equations and used by a dedicated software, for the D iso reconstruction. Moreover, for each beam the software supplied a set of transit signal profiles crossing the beam central axis to test the beam irradiation reproducibility. The tolerance level of the comparison between the D iso and the dose computed by the TPS, D iso,TPS, was estimated 5%. The generalized in vivo dosimetry procedure was adopted by 3 centers that used different linacs. The results of 480 tests showed that in absence of errors, the comparison between D iso and D iso,TPS resulted well-within the tolerance level. The presence of errors was detected in 10% of the tests and were due to essentially an incorrect set-up, presence of an attenuator on the beams and patient morphological changes. Moreover, the dedicated software used the information of the Record and Verify system of the centres and consequently the extra-time needed to obtain, for each beam, the D iso reconstruction after the dose delivery, was about 20s. [Copyright &y& Elsevier]

Abstract: Many 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 term stability, signal linearity with MU and dose per pulse and signal dependence 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) was within ±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, k lin, is independent of the beam quality, and the dose per pulse absorbed by the EPID. For 6, 10 and 15MV 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. [ABSTRACT FROM AUTHOR]

A method for the determination of the in vivo isocenter dose, Diso, has been applied to the dynamic conformal arc therapy (DCAT) for thoracic tumors. The method makes use of the transmitted signal, St,α, measured at different gantry angles, α, by a small ion chamber positioned on the electronic portal imaging device. The in vivo method is implemented by a set of correlation functions obtained by the ratios between the transmitted signal and the midplane dose in a solid phantom, irradiated by static fields. The in vivo dosimetry at the isocenter for the DCAT requires the convolution between the signals , St,α, and the dose reconstruction factors, Cα, that depend on the patient’s anatomy and on its tissue inhomogeneities along the beam central axis in the α direction. The Cα factors are obtained by processing the patient’s computed tomography scan. The method was tested by taking measurements in a cylindrical phantom and in a Rando Alderson phantom. The results show that the difference between the convolution calculations and the phantom measurements is within ±2%. The in vivo dosimetry of the stereotactic DCAT for six lung tumors, irradiated with three or four arcs, is reported. The isocenter dose up to 17 Gy per therapy fraction was delivered on alternating days for three fractions. The agreement obtained in this pilot study between the total in vivo dose Diso and the planned dose Diso,TPS at the isocenter is ±4%. The method has been applied on the DCAT obtaining a more extensive monitoring of possible systematic errors, the effect of which can invalidate the current therapy which uses a few high-dose fractions. [ABSTRACT FROM AUTHOR]

This work reports a practical method for the determination of the in vivo breast middle dose value, Dm, on the beam central axis, using a signal St, obtained by a small thimble ion chamber positioned at the center of the electronic portal imaging device, and irradiated by the x-ray beam transmitted through the patient. The use of a stable ion chamber reduces many of the disadvantages associated with the use of diodes as their periodic recalibration and positioning is time consuming. The method makes use of a set of correlation functions obtained by the ratios St/Dm, determined by irradiating cylindrical water phantoms with different diameters. The method proposed here is based on the determination of the water-equivalent thickness of the patient, along the beam central axis, by the treatment planning system that makes use of the electron densities obtained by a computed tomography scanner. The method has been applied for the breast in vivo dosimetry of ten patients treated with a manual intensity modulation with four asymmetric beams. In particular, two tangential rectangular fields were first delivered, thereafter a fraction of the dose (typically less than 10%) was delivered with two multi leaf-shaped beams which included only the mammarian tissue. Only the two rectangular fields were tested and for every checked field five measurements were carried out. Applying a continuous quality assurance program based on the tests of patient setup, machine settings and dose planning, the proposed method is able to verify agreements between the computed dose Dm,TPS and the in vivo dose value Dm, within 4%. [ABSTRACT FROM AUTHOR]

Abstract: The accuracy and reproducibility of endometrial carcinoma treatment with intensity-modulated radiotherapy (IMRT) was assessed by means of in vivo dosimetry. Six patients who had previously undergone radical hysterectomy for endometrial carcinoma were treated with IMRT using a vaginal applicator with radio-opaque fiducial markers. An ion-chamber inserted into the applicator supplied an endocavitary in vivo dosimetry for quality assurance purposes. The ratio R = D/DTPS between the in vivo measured dose D and the predicted dose by the treatment planning system DTPS was determined for every fraction of the treatment. Results showed that 90% and 100% of the ratios resulted equal to 1 within 5% and 10%, respectively. The mean value of the ratios distribution for the 6 patients was R = 0.995 and the SD = 0.034. The ratio R* between the measured and predicted total doses for each patient was near to 1, within 2%. The dosimetric results suggest that the use of a vaginal applicator in an image-guided approach could make the interfractions target position stable and reproducible, allowing a safe use of the IMRT technique in the treatment of postoperative vaginal vault. In vivo dosimetry may supply useful information about the discrimination of random vs. systematic errors. The workload is minimum and this in vivo dosimetry can be applied also in the clinical routine. [Copyright &y& Elsevier]

Abstract: In this paper the cine acquisition mode of an electronic portal imaging device (EPID) has been calibrated and tested to determine the in vivo dose for dynamic conformal arc radiation therapy (DCAT). The EPID cine acquisition mode, that allows a frame acquisition rate of one image every 1.66s, was studied with a monitor unit rate equal to 100UM/min. In these conditions good signal stability, ±1% (2SD) evaluated during three 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 beam below the phantom) measured by the EPID cine acquisition mode was used to determine, (i) 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, (ii) 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 tested with cylindrical and anthropomorphic phantoms and the results show that the reconstructed D iso values can be obtained with an accuracy within ±2.5% in cylindrical phantom and within ±3.4% for anthropomorphic phantom. In conclusion, the transit dosimetry by EPID was assessed to be adequate to perform DCAT in vivo dosimetry, that is not realizable with the other traditional techniques. Moreover, the method proposed here could be implemented to supply in vivo dose values in real time. [Copyright &y& Elsevier]