Comments on the <scp>TRS</scp>‐483 protocol on small field dosimetry

Das, Indra J.; Francescon, P.

doi:10.1002/mp.13236

Cited by 16 publications

(15 citation statements)

References 33 publications

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“…The PDD exhibits almost the same behavior for all detectors unless a little discrepancy is observed for ISD, especially in water depths larger than 15 mm. This effect can be strongly reduced by necessary corrections of the reference detector . Moreover, some discrepancies that appear in small fields and nearby water surfaces can be due to the proper centering of the reference dosimeter.…”

Section: Discussionmentioning

confidence: 99%

High spatial resolution inorganic scintillator detector for high‐energy X‐ray beam at small field irradiation

et al. 2020

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Purpose Small field dosimetry for radiotherapy is one of the major challenges due to the size of most dosimeters, for example, sufficient spatial resolution, accurate dose distribution and energy dependency of the detector. In this context, the purpose of this research is to develop a small size scintillating detector targeting small field dosimetry and compare its performance with other commercial detectors. Method An inorganic scintillator detector (ISD) of about 200 µm outer diameter was developed and tested through different small field dosimetric characterizations under high‐energy photons (6 and 15 MV) delivered by an Elekta Linear Accelerator (LINAC). Percentage depth dose (PDD) and beam profile measurements were compared using dosimeters from PTW namely, microdiamond and PinPoint three‐dimensional (PP3D) detector. A background fiber method has been considered to quantitate and eliminate the minimal Cerenkov effect from the total optical signal magnitude. Measurements were performed inside a water phantom under IAEA Technical Reports Series recommendations (IAEA TRS 381 and TRS 483). Results Small fields ranging from 3 × 3 cm2, down to 0.5 × 0.5 cm2 were sequentially measured using the ISD and commercial dosimeters, and a good agreement was obtained among all measurements. The result also shows that, scintillating detector has good repeatability and reproducibility of the output signal with maximum deviation of 0.26% and 0.5% respectively. The Full Width Half Maximum (FWHM) was measured 0.55 cm for the smallest available square size field of 0.5 × 0.5 cm2, where the discrepancy of 0.05 cm is due to the scattering effects inside the water and convolution effect between field and detector geometries. Percentage depth dose factor dependence variation with water depth exhibits nearly the same behavior for all tested detectors. The ISD allows to perform dose measurements at a very high accuracy from low (50 cGy/min) to high dose rates (800 cGy/min) and was found to be independent of dose rate variation. The detection system also showed an excellent linearity with dose; hence, calibration was easily achieved. Conclusions The developed detector can be used to accurately measure the delivered dose at small fields during the treatment of small volume tumors. The author's measurement shows that despite using a nonwater‐equivalent detector, the detector can be a powerful candidate for beam characterization and quality assurance in, for example, radiosurgery, Intensity‐Modulated Radiotherapy (IMRT), and brachytherapy. Our detector can provide real‐time dose measurement and good spatial resolution with immediate readout, simplicity, flexibility, and robustness.

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Section: Discussionmentioning

confidence: 99%

High spatial resolution inorganic scintillator detector for high‐energy X‐ray beam at small field irradiation

et al. 2020

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“…Melalui rentang keseimbangan partikel bermuatan pada bidang lateral, r LCPE (dalam mm) dapat ditentukan hubungan antara lapangan radiasi dan dimensi minimal detektor yang digunakan agar syarat rentang keseimbangan partikel bermuatan pada bidang lateral terhadap sumbu utama berkas radiasi foton dipenuhi yang bergantung pada energi berkas radiasi. Hubungan ini dinyatakan dengan Persamaan 1 atau Persamaan 2 (IAEA, 2017) (Das & Francescon, 2018).…”

Section: Kesetimbangan Partikel Bermuatan DI Lateral (Lateral Charge unclassified

Studi Awal Pengukuran Daisy Chaining Detektor Ionisasi pada Berkas Foton 6 MV Flattening Filter Free Lapangan Kecil

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Rajagukguk

et al. 2020

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Salah satu alternatif untuk melakukan kalibrasi detektor ionisasi kecil pada lapangan radiasi kecil adalah dengan melakukan pengukuran daisy chaining. Makalah ini menguraikan pengukuran daisy chaining detektor ionisasi kecil pada berkas foton 6 MV flattening filter free lapangan radiasi kecil. Langkah pertama pengukuran daisy chaining adalah melakukan kalibrasi detektor ionisasi medium 0,13 cm3 terhadap detektor ionisasi standar 0,6 cm3 pada lapangan radiasi 10 cm × 10 cm. Setelah mendapatkan faktor kalibrasi dosis serap air (ND,W) dari detektor ionisasi medium, langkah berikutnya adalah menggunakan ND,W tersebut untuk mengalibrasi silang detektor ionisasi mikro 0,016 cm3 pada lapangan 5 cm × 5 cm. ND,W hasil kalibrasi tersebut dapat digunakan untuk pengukuran di lapangan radiasi kurang dari 5 cm × 5 cm. Penentuan laju dosis serap air dilakukan di lapangan 3 cm × 3 cm dan 2 cm × 2 cm. Verifikasi dilakukan dengan membandingkan hasil penentuan laju dosis serap air menggunakan ND,W hasil pengukuran daisy chaining, pengukuran langsung menggunakan ND,W detektor ionisasi tanpa pengukuran daisy chaining dan hasil perhitungan dari treatment planning system (TPS). Hasil yang diperoleh menunjukkan adanya perbedaan antara pengukuran daisy chaining, pengukuran langsung, dan hasil perhitungan TPS. Perbedaan masih dalam rentang kurang dari 3%.

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“…Later TRS‐483 10 provided the code of practice for small field dosimetry along with methods and correction factors to determine field output factors (FOF) for various detectors and square field sizes. When field sizes are reduced below around 15 or 20 mm, the uncertainty in FOF data increases as the curve is very steep 10,11 . The uncertainty of measurement is highly dependent on the definition of the field size that could potentially increase the uncertainty in the small field dosimetry due to the sensitivity to measurement errors.…”

Section: Introductionmentioning

confidence: 99%

Validity of equivalent square field concept in small field dosimetry

et al. 2022

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Purpose The equivalent square (ES) concept has been used for traditional radiation fields defined by the machine collimating system. For small fields, the concept Sclin was introduced based on measuring dosimetric field width (full‐width half maximum, FWHM) of the cardinal axis of the beam profiles. The pros and cons of this concept are evaluated in small fields and compared with the traditional ES using area and perimeter (4A/P) method based on geometric field size settings, for example, light field settings. Methods One hundred thirty‐seven square and rectangular fields from 5–50 mm with every possible permutation (keeping one jaw fixed and varying other jaw from 5 to 50 mm) were utilized to measure FWHM for the validation of Sclin. Using a microSilicon detector and a scanning water tank, measurements were performed on an Elekta (Versa) machine with Agility head and a Varian TrueBeam with different MLC/Jaw design to evaluate the Sclin concept and to understand the effect of exchange factor in small fields. Field output factors were also measured for all 137 fields. Results The data fitting for fields ranging from 5–50 mm between the traditional 4A/P method and Sclin shows differences and indicates a linear relationship with distinct separation of slope for Elekta and Varian machines. For Elekta Agility machine ES based on 4A/P < Sclin and for the VarianTrueBeam 4A/P > Sclin for square fields. Our measured data show that both methods are equally valid but does vary by the machine design. The field output factor is dependent on the elongation factor as well as machine design. For fields with sides ≥10 mm, the exchange factor is nearly identical in both machines with magnitude up to 4%, which is close to measurement uncertainty (±3%), but for small fields (< 10 mm), the Elekta machine has higher exchange factors compared to the Varian machine. Conclusion The results demonstrate that the two concepts for defining equivalent field (Sclin and 4A/P) are equivalent and can be directly related through an empirical equation. This study confirms that 4A/P is still valid for small fields except for very small fields (≤10 mm) where source occlusion is a dominating factor. The Sclin method is potentially sensitive to measurement uncertainty due to measurement of FWHM which is machine‐, detector‐ and user‐dependent, while the 4A/P method relies mainly on geometry of the machine and has less dependency on type of machine, detector, and user. The exchange factors are comparable for both types of machines. The conclusion is based on data from an Elekta with Agility head and a Varian TrueBeam machine that may have potential for bias due to light field/collimator set up and alignment. Care should be taken in extrapolating these data to any other machine.

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Comments on the TRS‐483 protocol on small field dosimetry

Cited by 16 publications

References 33 publications

High spatial resolution inorganic scintillator detector for high‐energy X‐ray beam at small field irradiation

High spatial resolution inorganic scintillator detector for high‐energy X‐ray beam at small field irradiation

Studi Awal Pengukuran Daisy Chaining Detektor Ionisasi pada Berkas Foton 6 MV Flattening Filter Free Lapangan Kecil

Validity of equivalent square field concept in small field dosimetry

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