The effect of an air gap on a 2D monolithic silicon detector for relative dosimetry

Utitsarn, Kananan; Alrowaili, Z.A.; Stansook, Nauljun; Biasi, Giordano; Carolan, Martin G; Lerch, Michael L. F; Rosenfeld, Anatoly B.

doi:10.1088/1748-0221/14/06/p06018

Cited by 7 publications

(3 citation statements)

References 29 publications

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“…1). A small air gap on top of the arrays minimizes, in small fields on CAX, the corrections required to relate its readings to dose 30 . The Duo was used in CIRS Plastic Water (CIRS, Norfolk, VA), and centered on CAX using a square field of side 0.5 cm, by maximizing the response of the central diode.…”

Section: Methodsmentioning

confidence: 99%

“…For off axis measurements, the central diode was used to determine the detector‐reading ratio, and not the maximum associated with the inherent asymmetry of the field, and the nominal square field of side 10 cm on CAX was used as the reference field. Supported by earlier investigations, 30–32,35 we did not apply any correction factors to detector‐reading ratios, hereafter referred to simply as OPF, which we reported with an associated accuracy given by the standard deviation of the mean (k = 3), and propagating the error. Lateral beam profiles were analyzed with MATLAB (MathWorks) using a shape‐preserving interpolant function.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Consistency of small‐field dosimetry, on and off axis, in beam‐matched linacs used for stereotactic radiosurgery

Muñoz

Kron

Petasecca

et al. 2021

J Applied Clin Med Phys

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Purpose Stereotactic radiosurgery (SRS) can be delivered with a standard linear accelerator (linac). At institutions having more than one linac, beam matching is common practice. In the literature, there are indications that machine central axis (CAX) matching for broad fields does not guarantee matching of small fields with side ≤2 cm. There is no indication on how matching for broad fields on axis translates to matching small fields off axis. These are of interest to multitarget single‐isocenter (MTSI) SRS planning and the present work addresses that gap in the literature. Methods We used 6 MV flattening filter free (FFF) beams from four Elekta VersaHD® linacs equipped with an Agility™ multileaf collimator (MLC). The linacs were strictly matched for broad fields on CAX. We compared output factors (OPFs) and effective field size, measured concurrently using a novel 2D solid‐state dosimeter “Duo” with a spatial resolution of 0.2 mm, in square and rectangular static fields with sides from 0.5 to 2 cm, either on axis or away from it by 5 to 15 cm. Results Among the four linacs, OPF for fields ≥1 × 1 cm2 ranged 1.3% on CAX, whereas off axis a maximum range of 1.9% was observed at 15 cm. A larger variability in OPF was noted for the 0.5 × 0.5 cm2 field, with a range of 5.9% on CAX, which improved to a maximum of 2.3% moving off axis. Two linacs showed greater consistency with a range of 1.4% on CAX and 2.2% at 15 cm off axis. Between linacs, the effective field size varied by <0.04 cm in most cases, both on and off axis. Tighter matching was observed for linacs with a similar focal spot position. Conclusions Verification of small‐field consistency for matched linacs used for SRS is an important task for dosimetric validation. A significant benefit of concurrent measurement of field size and OPF allowed for a comprehensive assessment using a novel diode array. Our study showed the four linacs, strictly matched for broad fields on CAX, were still matched down to a field size of 1 x 1 cm2 on and off axis.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Consistency of small‐field dosimetry, on and off axis, in beam‐matched linacs used for stereotactic radiosurgery

Muñoz

Kron

Petasecca

et al. 2021

J Applied Clin Med Phys

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“…In that case, the MP512 was sandwiched between two slabs of PMMA of thickness 5 mm; the top slab had a small recess (or air gap), centered on the axis of the MP512's active area, of thickness 0.5 mm. The air gap was necessary to minimize, in small radiation fields, the number and size of corrections required to relate the MP512's readings to dose …”

Section: Methodsmentioning

confidence: 99%

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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A Monte Carlo study to evaluate and optimise the angular dependence of the Octa – A 2D silicon array detector used for dosimetry in stereotactic radiotherapy

Filipev

Biasi

Poder

et al. 2023

Radiation Measurements

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The effect of an air gap on a 2D monolithic silicon detector for relative dosimetry

Abstract: The effect of an air gap on a 2D monolithic silicon detector for relative dosimetry The effect of an air gap on a 2D monolithic silicon detector for relative dosimetry

Cited by 7 publications

References 29 publications

Consistency of small‐field dosimetry, on and off axis, in beam‐matched linacs used for stereotactic radiosurgery

Consistency of small‐field dosimetry, on and off axis, in beam‐matched linacs used for stereotactic radiosurgery

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

A Monte Carlo study to evaluate and optimise the angular dependence of the Octa – A 2D silicon array detector used for dosimetry in stereotactic radiotherapy

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