Principles and requirements of external beam dosimetry

Chen, Zhe; D’Errico, Francesco; Nath, Ravinder

doi:10.1016/j.radmeas.2007.01.010

Cited by 13 publications

(8 citation statements)

References 25 publications

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“…The advancement of such techniques requires reliable and precise treatment validation prior to, and during the course of the radiation therapy. 1 Although pretreatment quality assurance (QA) plays a vital role to ensure the accuracy of safe delivery, it is not adequate to ensure the precision of the whole treatment process. [2][3][4][5][6] In addition to pretreatment QA, real-time dosimetry verification can act as a powerful method to verify the safe delivery of complex radiotherapy treatments and to reduce mistreatments.…”

Section: Introductionmentioning

confidence: 99%

Modeling the temporal–spatial nature of the readout of an electronic portal imaging device (EPID)

et al. 2020

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In real-time electronic portal imaging device (EPID) dosimetry applications where on-treatment measured transmission images are compared to an ideal predicted image, ideally a tight tolerance should be set on the quantitative image comparison in order to detect a wide variety of possible delivery errors. However, this is currently not possible due to the appearance of banding artifacts in individual frames of the measured EPID image sequences. The purpose of this work was to investigate simulating banding artifacts in our cine-EPID predicted image sequences to improve matching of individual image frames to the acquired image sequence. Increased sensitivity of this method to potential treatment delivery errors would represent an improvement in patient safety and treatment accuracy. Methods: A circuit board was designed and built to capture the target current (TARG-I) and forward power signals produced by the linac to help model the discrete beam-formation process of the linac. To simulate the temporal-spatial nature of the EPID readout, a moving read out mask was applied with the timing of the application of the readout mask synchronized to the TARG-I pulses. Since identifying the timing of the first TARG-I pulse affected the location of the banding artifacts throughout the image sequence, and furthermore the first several TARG-I pulses at the beginning of "beam on" are not at full height yet (i.e., dose rate is ramping up), the forward-power signal was also used to assist in reliable detection of the first radiation pulse of the beam delivery. The predicted EPID cineimage sequence obtained using a comprehensive physics-based model was modified to incorporate the discrete nature of the EPID frame readout. This modified banding predicted EPID (MBP-EPID) image sequence was then compared to its corresponding measured EPID cine-image sequence on a frame-by-frame basis. The EPID was mounted on a Clinac 2100ix linac (Varian Medical Systems, Palo Alto, CA). The field size was set to 21.4 Â 28.6 cm 2 with no MLC modulation, beam energy of 6 MV, dose rate of 600 MU/min, and 700 MU were delivered for each clockwise (CW) and counterclockwise (CCW) arc. No phantoms were placed in the beam. Results: The dose rate ramp up effect was observed at the beginning irradiations, and the identification and timing of the radiation pulses, even during the dose rate ramp up, were able to be quantified using the TARG-I and forward power signals. The approach of capturing individual dose pulses and synchronizing with the mask image applied to the original predicted EPID image sequence was demonstrated to model the actual EPID readout. The MBP-EPID image sequences closely reproduced the location and magnitude of the banding features observed in the acquired (i.e., measured) image sequence, for all test irradiations examined here. Conclusions: The banding artifacts observed in the measured EPID cine-frame sequences were reproduced in the predicted EPID cine-frames by simulating the discrete temporal-spatial nature of the EPID read out. The MB...

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Section: Introductionmentioning

confidence: 99%

Modeling the temporal–spatial nature of the readout of an electronic portal imaging device (EPID)

et al. 2020

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“…The dose delivered to a given point in the medium is determined by measuring the amount of charge produced in the small air cavity placed in the medium. [2][3][4] The dose delivered to the medium can be calculated from the total charge or saturation charge produced in the air cavity according to Spencer-Attix theory. 5 The design and specification of the thimble chamber used for dose measurements in radiotherapy are described in various protocols.…”

Section: Introductionmentioning

confidence: 99%

Dosimetric Performance of Newly Developed Farmer-Type Ionization Chamber in Radiotherapy Practice

Sathiyan

Godson

Ponmalar

et al. 2016

Technol Cancer Res Treat

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Dose measurement with ionization chamber is essential to deliver accurate dose to the tumor in radiotherapy. The cylindrical Farmer-type ionization chamber is recommended by various dosimetry protocols for dose measurement of radiotherapy beams. The air-equivalent graphite wall Farmer-type ionization chamber (FAR 65 GB) of active volume 0.65 cm 3 with aluminum as the central electrode material was fabricated. Various dosimetric parameters were studied for the newly developed ionization chamber in cobalt-60, 6 and 18 MV photon beams. The preirradiation and postirradiation leakage of the chamber was within 0.08%. The long-term stability and the stem effect of the chamber were within 0.07% and 0.3%, respectively. The sensitivity of the ionization chamber was found to be 22.15 nC/Gy. The chamber shows linear response with dose for cobalt-60, 6 and 18 MV photon beams. The ion recombination correction factor increases with increase in bias voltage. For all energies and field sizes, the polarity correction factor is almost closer to unity. The ion recombination and polarity correction measurements show that the polarizing potential and polarity recommended during the calibration of ionization chamber should be used for routine measurement to avoid the uncertainty. The chamber response is independent of dose rate and energy. The chamber is cost-effective and shows precise and reproducible response. The study carried out confirms that the newly fabricated ion chamber can be used in the measurement of absolute dose for high-energy photon beams.

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“…Therefore, MOSFETs could be suitable for in-vivo assessment of radiosurgery microbeams [7,6,8]. In the literature their use has been described extensively for such in vivo procedures as: in vivo dosimetry for external radiotherapy [9,10,11], dose verification in intensity modulated radiotherapy (IMRT) [12,13,14], measurements in head and neck Tomotherapy [15], skin dose measurement [16], entry dosimetry [17], implantable detectors for in-situ testing during radiation therapy treatment [18], dose verification of permanent low-dose-rate implants [19] and as a dosimeter for imaging in radiological procedures [20]. Additional studies have reported excellent linearity, dosimetric accuracy in the build-up region and directional independence [9,21].…”

Section: Introductionmentioning

confidence: 99%

In-vivo dosimetry for conformal arc therapy using several MOSFET in stereotactic radiosurgery computed by an inverse model

et al. 2016

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Principles and requirements of external beam dosimetry

Cited by 13 publications

References 25 publications

Modeling the temporal–spatial nature of the readout of an electronic portal imaging device (EPID)

Modeling the temporal–spatial nature of the readout of an electronic portal imaging device (EPID)

Dosimetric Performance of Newly Developed Farmer-Type Ionization Chamber in Radiotherapy Practice

In-vivo dosimetry for conformal arc therapy using several MOSFET in stereotactic radiosurgery computed by an inverse model

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