Impact of a monolithic silicon detector operating in transmission mode on clinical photon beams

Utitsarn, Kananan; Alrowaili, Z.A.; Stansook, Nauljun; Petasecca, Marco; Carolan, Martin G; Perevertaylo, Vladimir; Lerch, Michael L. F; Rosenfeld, Anatoly B.

doi:10.1016/j.ejmp.2017.10.017

Cited by 5 publications

(6 citation statements)

References 28 publications

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“…Further experiments will be performed on different topologies of the grating structure, including much thinner gratings. It has been shown that the electron contamination reduces with distance from the linac head [25], [26], hence in the future we will include studies at different SSDs. The trench dimensions and overall thickness of the grating will be optimized to minimize the contribution from contamination electrons to the modulation total signal, allowing the photon signal to be extracted.…”

Section: Discussionmentioning

confidence: 99%

A Novel Approach to Contamination Suppression in Transmission Detectors for Radiotherapy

Beck

Velthuis

Page

et al. 2020

IEEE Trans. Radiat. Plasma Med. Sci.

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The current trend in X-ray radiotherapy is to treat cancers that are in difficult locations in the body using beams with a complex intensity profile. Intensity-modulated radiotherapy (IMRT) is a treatment which improves the dose distribution to the tumor whilst reducing the dose to healthy tissue. Such treatments administer a larger dose per treatment fraction and hence require more complex methods to verify the accuracy of the treatment delivery. Measuring beam intensity fluctuations is difficult as the beam is heavily distorted after leaving the patient and transmission detectors will attenuate the beam and change the energy spectrum of the beam. Monolithic active pixel sensors (MAPSs) are ideal solid-state detectors to measure the 2-D beam profile of a radiotherapy beam upstream of the patient. MAPS sensors can be made very thin (∼30 µm) with still very good signal-to-noise performance. This means that the beam would pass through the sensor virtually undisturbed (<1% attenuation). Pixel pitches of between 2 µm to 100 µm are commercially available. Large area devices (∼15×15 cm 2) have been produced. MAPS can be made radiation hard enough to be fully functional after a large number of fractions. All this makes MAPS a very realistic transmission detector candidate for beam monitoring upstream of the patient. A remaining challenge for thin, upstream sensors is that the detectors are sensitive to the signal of both therapeutic photons and electron contamination. Here, a method is presented to distinguish between the signal due to electrons and photons and thus provide real-time dosimetric information in very thin sensors that does not require Monte Carlo simulation of each linear accelerator treatment head. Index Terms-Clinical/preclinical evaluation/application studies, dosimetry for radiation-based medical applications, monolithic active pixel sensors (MAPSs), Monte Carlo simulations for imaging and therapy, radiation detectors for medical applications, radiotherapy verification.

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Section: Discussionmentioning

confidence: 99%

A Novel Approach to Contamination Suppression in Transmission Detectors for Radiotherapy

Beck

Velthuis

Page

et al. 2020

IEEE Trans. Radiat. Plasma Med. Sci.

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“…Note that, in the present study, the MP512 was not modeled into the TPS. Its transmission factor was reported to be in the range from 1.020 to 0.997 for SDDs from 0.3 to 24 cm . However, if clinical use will be considered, it is suggested that transmission factor has to be adequately incorporated into a TPS …”

Section: Discussionmentioning

confidence: 99%

“…In the literature, the MP512 has been characterized as a phantom‐based detector for quality assurance in modern radiotherapy; it was demonstrated to be an accurate dosimeter for the measurement of output factors, percentage depth dose distributions, and lateral‐dose profiles; furthermore, its angular dependence was investigated and corrected for, making it a suitable candidate for quality assurance in arc deliveries . The use of the MP512 as a transmission detector was also assessed . In that study, it was reported that the MP512 in TM increases the surface dose by <25% for a SDD in the range from 0.3 to 18 cm, and by <5% for SDD >18 cm .…”

Section: Methodsmentioning

confidence: 99%

“…The use of the MP512 as a transmission detector was also assessed . In that study, it was reported that the MP512 in TM increases the surface dose by <25% for a SDD in the range from 0.3 to 18 cm, and by <5% for SDD >18 cm . The transmission factor, at d max depth in Solid Water, 100 cm SSD, was in the range from 1.020 to 0.997 for SDDs from 0.3 to 24 cm …”

Section: Methodsmentioning

confidence: 99%

“…Commercially available options include the Device for Advanced Verification of IMRT Delivery (DAVID) system (PTW, Freiburg, Germany), a flat, multiwire transmission‐type ionization chamber; the Dolphin detector with the COMPASS software (IBA Dosimetry, Germany), which uses 1513 air‐vented plane parallel ionization chambers, the integral quality monitoring (IQM) system (iRT Systems GmbH, Koblenz, Germany), a large‐area wedge ionization chamber; the Delta 4 Discover (ScandiDos AB, Uppsala, Sweden), a 2D solid‐state array . Several prototypes have also been proposed in the literature, including optical attenuation‐based scintillating fibers; 2D solid‐state arrays, such as the MP121 and the MP512 …”

Section: Introductionmentioning

confidence: 99%

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Two‐dimensional solid‐state array detectors: A technique for in vivo dose verification in a variable effective area

Utitsarn

Biasi

Stansook

et al. 2019

J Applied Clin Med Phys

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Purpose:We introduce a technique that employs a 2D detector in transmission mode (TM) to verify dose maps at a depth of d max in Solid Water. TM measurements, when taken at a different surface-to-detector distance (SDD), allow for the area at d max (in which the dose map is calculated) to be adjusted. Methods:We considered the detector prototype "MP512" (an array of 512 diodesensitive volumes, 2 mm spatial resolution). Measurements in transmission mode were taken at SDDs in the range from 0.3 to 24 cm. Dose mode (DM) measurements were made at d max in Solid Water. We considered radiation fields in the range from 2 × 2 cm 2 to 10 × 10 cm 2 , produced by 6 MV flattened photon beams;we derived a relationship between DM and TM measurements as a function of SDD and field size. The relationship was used to calculate, from TM measurements at 4 and 24 cm SDD, dose maps at d max in fields of 1 × 1 cm 2 and 4 × 4 cm 2 , and in IMRT fields. Calculations were cross-checked (gamma analysis) with the treatment planning system and with measurements (MP512, films, ionization chamber).Results: In the square fields, calculations agreed with measurements to within ±2.36%. In the IMRT fields, using acceptance criteria of 3%/3 mm, 2%/2 mm, 1%/ 1 mm, calculations had respective gamma passing rates greater than 96.89%, 90.50%, 62.20% (for a 4 cm SSD); and greater than 97.22%, 93.80%, 59.00% (for a 24 cm SSD). Lower rates (1%/1 mm criterion) can be explained by submillimeter misalignments, dose averaging in calculations, noise artifacts in film dosimetry.Conclusions: It is possible to perform TM measurements at the SSD which produces the best fit between the area at d max in which the dose map is calculated and the size of the monitored target. K E Y W O R D S2D solid-state array detector, MP512, transmission detector, in vivo QA

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Two-dimensional real-time quality assurance dosimetry system using μ-Al2O3:C,Mg radioluminescence films

Nascimento

Verellen

Goossens

et al. 2020

Physics and Imaging in Radiation Oncology

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Background and purpose: There is a continual need for more accurate and effective dosimetric systems for quality assurance (QA) as radiotherapy evolves in complexity. The purpose of this project was to introduce a new system that minimally perturbs the main beam, while assessing its real time 2D dose-rate and field shapes. The system combined reusability, linear dose-rate response, and high spatial and time resolution in a single radiation detection technology that can be applied to surface dose estimation and QA. Materials and methods: We developed a 2D prototype system consisting of a camera, focusing lenses and short pass filter, placed on the head of a linear accelerator, facing an Al 2 O 3 :C,Mg radioluminescent film. To check the appropriateness of multi-leaf collimator, stability/reproducibility QA tests were prepared using the treatment planning system: including the routinely used alternating leaves, chair and pyramid checks. Results: The Al 2 O 3 :C,Mg film did not perturb the dose vs. depth dose curves determined with a point detector (-0.5% difference). Our results showed a dose-rate linear film response (R 2 = 0.999), from 5 to 600 MU/min. Measured output factors agreed with reference data within ~1%, indicating a potential for small field dosimetry. Both chair and pyramid measured profiles were comparable with those obtained with the treatment planning system within 1%. The alternating leaves test showed an average discrepancy in the valleys of 14%. Conclusions: The prototype demonstrated promising results. It obviated the need for corrections regarding the relative position of the camera, confirming accurate dose-rate delivery and detection of radiation fields.

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Impact of a monolithic silicon detector operating in transmission mode on clinical photon beams

Abstract: The study demonstrated that positioning the MP512T in air between the Linac head and the phantom produced negligible perturbation of the surface dose for D >18 cm, and was completely transparent for 6 MV photon beams.

Cited by 5 publications

References 28 publications

A Novel Approach to Contamination Suppression in Transmission Detectors for Radiotherapy

A Novel Approach to Contamination Suppression in Transmission Detectors for Radiotherapy

Two‐dimensional solid‐state array detectors: A technique for in vivo dose verification in a variable effective area

Two-dimensional real-time quality assurance dosimetry system using μ-Al2O3:C,Mg radioluminescence films

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Impact of a monolithic silicon detector operating in transmission mode on clinical photon beams

Abstract: The study demonstrated that positioning the MP512T in air between the Linac head and the phantom produced negligible perturbation of the surface dose for D >18 cm, and was completely transparent for 6 MV photon beams.

Cited by 5 publications

References 28 publications

A Novel Approach to Contamination Suppression in Transmission Detectors for Radiotherapy

A Novel Approach to Contamination Suppression in Transmission Detectors for Radiotherapy

Two‐dimensional solid‐state array detectors: A technique for in vivo dose verification in a variable effective area

Two-dimensional real-time quality assurance dosimetry system using μ-Al2O3:C,Mg radioluminescence films

Contact Info

Product

Resources

About

Abstract: The study demonstrated that positioning the MP512T in air between the Linac head and the phantom produced negligible perturbation of the surface dose for D >18 cm, and was completely transparent for 6 MV photon beams.