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

Abstract

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

A Novel Approach to Contamination Suppression in Transmission Detectors for Radiotherapy

“…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.…”

Semiconductor dosimetry in modern external-beam radiation therapy

“…Different layouts were explored (Stansook et The Magic Plate, the Duo and the Octa were used for dosimetry in FFF beams (Biasi et al 2018c), for dosimetry in a CyberKnife ® (Accuray) (Biasi et al 2018b), and in transmission mode to verify dose maps at a depth of maximum dose (d max ) in Solid Water (Utitsarn et al 2019b). They were also used in combination with a movable platform, using a patient-specific 3D (x, y, time) lung-motion pattern and the electromagnetic beacon motion tracking system (Petasecca et al 2015b), and to measure dose maps during In synchrotron-based MRT (Bartzsch et al 2020), the FWHM of the micro-beams is one of the parameters used to assess the quality of the radiation field.…”