Two‐dimensional solid‐state array detectors: A technique for in vivo dose verification in a variable effective area. Issue 11 (14th October 2019)

• Record Type: Journal Article
• Authors: Utitsarn, Kananan; Biasi, Giordano; Stansook, Nauljun; Alrowaili, Ziyad A.; Petasecca, Marco; Carolan, Martin; Perevertaylo, Vladimir L.; Tomé, Wolfgang A.; Kron, Tomas; Lerch, Michael L. F.; Rosenfeld, Anatoly B.
• Is Part Of: Journal of applied clinical medical physics. Volume 20:Issue 11(2019)
• Page Start: 88
• Page End: 94
• Publication Date: 2019-10-14
• Subjects: 2D solid‐state array detector -- MP512 -- transmission detector -- in vivo QA; Medical physics -- Periodicals; Clinical medicine -- Periodicals; Health Physics; Clinical Medicine; Electronic journals; Periodicals; Periodicals; Fulltext; Internet Resources; 610.153
• DOI: 10.1002/acm2.12744
• Languages: English
• ISSNs: 1526-9914

Abstract

Abstract: Purpose: We introduce a technique that employs a 2D detector in transmission mode (TM) to verify dose maps at a depth of dmax in Solid Water. TM measurements, when taken at a different surface‐to‐detector distance (SDD), allow for the area at dmax (in which the dose map is calculated) to be adjusted. Methods: We considered the detector prototype "MP512" (an array of 512 diode‐sensitive 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 dmax 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 dmax 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 dmax in which the dose map is calculated and the size of the monitored target.