Comparison of dose measurements in CT using a photodiode and a small ion chamber

Paschoal, C. M. M.; Ferreira, Fernanda Carla Lima; Souza, Divanízia do Nascimento; Santos, Luiz A. P.

doi:10.1016/j.radmeas.2016.05.002

Cited by 7 publications

(9 citation statements)

References 10 publications

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“…As a result, the BPW34S PIN photodiode was selected as the candidate dosimeter due to its very low sensitivity degradation with the absorbed dose. This good performance has also been reported for this device under Co‐60 gamma rays and X‐rays for radiodiagnosis 24–28 . In fact, an average sensitivity can be calculated, obtaining S ADR = 13.8 ± 0.4 nC/cGy (coverage factor k = 1).…”

Section: Resultssupporting

confidence: 76%

“…As for phototransistors, most research for commercial PIN photodiodes has consisted in studying their response under X‐ray radiation for diagnostic radiology, reporting mostly stable response and suitable performance for dose rate and absorbed dose monitoring 23–27 . Commercial PIN photodiodes have also been analyzed under gamma ray beams of Co‐60 sources.…”

Section: Introductionmentioning

confidence: 99%

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Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy

et al. 2021

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Purpose The response to radiation typically used in radiotherapy treatments has been experimentally evaluated for three samples of two phototransistors (BPW85B and OP505A) and two PIN photodiodes types (VTB8440BH and BPW34S). Methods To that end, a staggered irradiation cycle has been applied which included dose rate values from 0.81 to 4.87 cGy/s, achieving a total absorbed dose of 21.4 Gy. The samples have been irradiated with a linear accelerator and the relations between the induced photocurrent and the average and instantaneous dose rates, and between the accumulated charge and the absorbed dose, have been determined. The radiation‐induced output currents were measured by means of an external interface of the devices to a previously designed readout unit. Results Experimental results of Si PIN photodiode BPW34S have shown a sensitivity of (13.9 ± 0.5) nC/cGy, slight sensitivity dependence on dose rate, and a high linearity of the current with the average and instantaneous dose rate, requiring only 10 V of reverse bias voltage. This device thermal drift has characterized and modeled for temperature effect compensation. Conclusions Silicon PIN photodiode BPW34S, previously tested for X‐rays and Co‐60 gamma ray source, can also be a reliable candidate for dose rate and absorbed skin dose determination in typical radiotherapy treatments irradiations. A low sensitivity loss below 2% up to 21.4 Gy has been measured, allowing its use as an affordable reusable skin dosimeter. Moreover, no significant difference has been observed between its response to dose‐per‐pulse and changing pulse repetition frequency in terms of sensitivity and dependence with dose‐rate value.

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Section: Resultssupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy

et al. 2021

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“…Only one other study comparing the IAEA method to phantom‐only measurements was found: Gancheva et al used a traditional (360° scan) CT unit having a 16‐cm beam width and found that CTDI W‐c was 11.3% higher than CTDI W‐I and CTDI W‐o was 41% lower than CTDI W‐I. It is initially surprising that CTDI W‐o was found to be higher than CTDI W‐I in the current study, as numerous studies have indicated that CTDI W‐o for a wide beam is expected to be artificially low when using a 100‐mm ion chamber and 150‐mm acrylic phantom . Rather than contradicting the existing literature, this is most likely an indication that the IAEA method is not ideal for use with 180° acquisitions.…”

Section: Resultsmentioning

confidence: 50%

“…The IAEA method is not recommended for this purpose if the system employs a rotation of less than 360°. Accurate measurements would likely require specialized equipment such as extended phantoms, longer pencil chambers, or small ion chambers, as recommended by other researchers …”

Section: Resultsmentioning

confidence: 99%

“…The traditional pencil chamber is insufficient to measure the entire beam in these scanners. Although alternate measurement techniques have been proposed to better measure wide beams, at this time, most clinical physicists do not have the equipment necessary to follow these recommendations. The International Atomic Energy Agency (IAEA) released a report in 2011 detailing a technique to calculate a CTDI for wide beam scanners using the standard 100‐mm pencil chamber and 32‐cm acrylic phantom, which was based on recommendations from the International Electrotechnical Commission and recommended for use by the wide‐beam CT dosimetry working party of the Institute of Physics and Engineering in Medicine .…”

Section: Introductionmentioning

confidence: 99%

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Assessment of volumetric absorbed dose for mobile fluoroscopic 3D image acquisition

Leon

2017

J Applied Clin Med Phys

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Mobile fluoroscopy (c‐arm) units offering 3D image reconstruction are becoming more common in surgical settings. Although these images are “CT‐like” and sometimes replace the postoperative CT, the acquisition is technically very different from a traditional CT acquisition. Dose assessment is complicated by a large beam width, automatic exposure rate control, and a rotation of less than 360°. The purpose of this work was to explore the impact of these factors on the volumetric dose calculation and to provide practical recommendations for clinical physicists assessing dose from these units using commonly available equipment. CTDIW was calculated using the IAEA method for dosimetry of wide beams and compared to scans of the 32‐cm CTDI phantom using the full beam width and a 20‐mm collimated beam width. The impact of the partial rotation on the CTDIW calculation was assessed by acquiring measurements at four and twelve positions on the phantom periphery. For the system tested, the CTDIW was calculated to be 16.1 mGy using the IAEA method with default clinical protocol. Results showed that measuring CTDIW with the full beam width or a collimated beam width alone resulted in CTDI values of 19.0 mGy and 19.5 mGy, respectively. Using four peripheral measurements instead of 12 resulted in a difference of 4% for a collimated beam and 6% for an open beam. Variations in positioning on the order of a few centimeters resulted in a variation of only 4% with an open beam. The excellent reproducibility of the measurements using the full beam width suggests that this simple method is adequate for year‐to‐year comparisons. In contrast, the IAEA method is difficult to employ, particularly with 180° acquisitions. Use of peripheral measurements in excess of the usual four is time‐consuming and not necessary for most applications obtained with the geometry specific to this system.

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Energy and air kerma dependence of response of a photodiode-based dosimetric system for radioprotection

Santos

Oliveira

Khoury

2019

Radiation Measurements

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Comparison of dose measurements in CT using a photodiode and a small ion chamber

Cited by 7 publications

References 10 publications

Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy

Commercial photodiodes and phototransistors as dosimeters of photon beams for radiotherapy

Assessment of volumetric absorbed dose for mobile fluoroscopic 3D image acquisition

Energy and air kerma dependence of response of a photodiode-based dosimetric system for radioprotection

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