Survey of 5 mm small‐field output factor measurements in Australia

Oliver, Christopher P.; Butler, Duncan; Takau, Viliami; Williams, Ian

doi:10.1002/acm2.12259

Cited by 8 publications

(4 citation statements)

References 22 publications

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“…The output factors measured here are compared to the Cheng et al (2016) reported output factors in table 5, which shows reasonable agreement. The largest difference is about 3% at the smallest cones, which is within the institutional variation of 3.6% seen by Oliver et al (2018). This difference is also expected as measurements at these small field sizes suffer from relatively high uncertainties in both setup accuracy and correction factors while Monte Carlo is generally accepted to be independent of small field issues.…”

Section: Discussionsupporting

confidence: 59%

“…If we specifically look at output factors, large variation exists across institutions using the same types of accelerators and equipment. The paper by Oliver et al (2018) showed that, even for measurements on the same accelerator, output factors between physicists from different institutions show a relatively large variation. While a large body of work exists on identifying the challenges in small fields, it is still difficult to implement these ideas in the clinic.…”

Section: Introductionmentioning

confidence: 99%

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Verification of representative data for output factors of SRS cones utilizing IAEA TRS 483 recommendations

et al. 2019

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Measurements of small fields continue to be a clinical challenge despite the recent work done to identify their characteristics. Due to this challenge, many physicists use representative data supplied by their vendors to verify their own measurements for small field output factors. However, with recent guidelines being released in IAEA TRS 483, the question remains if this representative data provides an accurate representation for small field dosimetry. A Sun Nuclear EDGE detector, PTW 60012 stereotactic diode, and GafChromic EBT3 films were used to measure the output factor for a set of Varian SRS cones (4 mm-17.5 mm diameters) on a TrueBeam linear accelerator. The measured output factors were then compared to the Varian provided SRS representative data. IAEA TRS 483 recommendations for measuring small field output factors were applied and the impact of those recommendations were examined. The EDGE detector showed good agreement with the representative data when correction factors were not applied (0.01%-1.64% difference) but the PTW 60012 diode showed larger deviation (0.61%-3.35% difference). The EBT3 film showed the largest difference with the representative data (0.66%-9.19%). After application of IAEA TRS 483 detector specific correction factors the output factors measured by the diodes showed good agreement with the EBT3 film for 6MV (<1.8% difference) but showed a large deviation with the representative data (up to 9% difference). The 6FFF energy output factors agreed between the EDGE, the PTW 60012, and EBT3 Film. This work shows that the use of uncorrected representative data on the Truebeam can lead to a significant over estimation of the SRS cone output factors.

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Section: Discussionsupporting

confidence: 59%

Section: Introductionmentioning

confidence: 99%

Verification of representative data for output factors of SRS cones utilizing IAEA TRS 483 recommendations

et al. 2019

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“…A detector‐reading ratio range of 7.8% is found in Oliver et al 2017 for 5 mm cones measured in Elekta Synergy using IBA SFD, Razor, EFD, and PTW T60017 and T60019 (microDiamond). This range decreased to 6.1% by applying appropriate output correction factors.…”

Section: Resultsmentioning

confidence: 84%

6‐MV small field output factors: intra‐/intermachine comparison and implementation of TRS‐483 using various detectors and several linear accelerators

et al. 2019

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Purpose: To investigate the applicability of output correction factors reported in TRS-483 on 6-MV small-field detector-reading ratios using four solid-state detectors. Also, to investigate variations in 6-MV small-field output factors (OF) among nominally matched linear accelerators (linacs). Methods: The TRS-483 Code of Practice (CoP) introduced and provided output correction factors to be applied to measured detector-reading ratios to obtain OFs for several small-field detectors. Detector readings for 0.5 cm 9 0.5 cm to 8 cm 9 8 cm fields were measured and normalized to that of 10 cm 9 10 cm field giving the detector-reading ratios. Three silicon diodes, IBA PFD, IBA EFD (IBA, Schwarzenbruck, Germany), PTW T60017, and one microdiamond, PTW T60019 (PTW, Freiburg, Germany), were used. Output correction factors from the CoP were applied to measured detector-reading ratios. Measurements were performed on six Clinac and six TrueBeam linacs (Varian Medical Systems, Palo Alto, USA). An investigation of the relationship between the size of small fields and corresponding detector-reading ratio among the linacs was performed by measuring lateral dose profiles for 0.5 cm 9 0.5 cm fields to determine the full width half maximum (FWHM). The relationship between the linacs' focal spot size and the small-field detector-reading ratio was investigated by measuring 10 cm 9 10 cm lateral dose profiles and determining the penumbra width reflecting the focal spot size. Measurement geometry was as follows: gantry angle = 0°, collimator angle = 0°, source-to surface distance (SSD) = 90 cm, and depth in water = 10 cm. Results: For a given linac and 0.5 cm 9 0.5 cm field, the deviations in detector-reading ratios among the detectors were 9%-15% for the Clinacs and 4%-5% for the TrueBeams. Use of output correction factors reduced these deviations to 6%-12% and 3%-4%, respectively. For field sizes equal to or larger than 0.8 cm 9 0.8 cm, the deviations were corrected to 1% using output correction factors for both Clinacs and TrueBeams. For a given detector and 0.5 cm 9 0.5 cm field, the deviations in detector-reading ratios among the linacs were 11%-17% for the Clinacs and 5-6% for the TrueBeams. For 1 cm 9 1 cm the deviations were 1%-2% for Clinacs and 1% for TrueBeams. For field sizes larger than 1 cm 9 1 cm the deviations were within 1% for both Clinacs and TrueBeams. No relationship between FWHMs and detector-reading ratios for 0.5 cm 9 0.5 cm was observed. For Clinacs, larger 10 cm 9 10 cm penumbra width yielded lower 0.5 cm 9 0.5 cm detector-reading ratio indicating an effect of the focal spot size. For TrueBeams, the spread of penumbra widths was lower compared to Clinacs and no similar relationship was observed. Conclusions: Output correction factors from the TRS-483 CoP are not sufficient for accurate determination of OF for 0.5 cm 9 0.5 cm fields but are applicable for 0.8 cm 9 0.8 cm to 8 cm 9 8 cm fields. Nominally matched Clinacs and TrueBeams show large differences in detectorreading ratios for fields smaller than 1 cm 9 1...

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“…The measurements involved several different detector types, correction factors, setup variations, and analysis methods, highlighting the importance of completing accurate measurements with suitable detectors as well as obtaining or deriving appropriate correction factors [5].…”

Section: Resultsmentioning

confidence: 99%

Varian Eclipse Stereotactic Cone Data Commissioning

Firth

Fogg

Christiansen

2022

Preprint

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Conical collimators are effective and readily available accessories for the field shaping of small stereotactic fields, however the measurements required to accurately characterise the smallest radiation fields are difficult and prone to large errors. Furthermore, there is little published commissioning data to compare measurements against. The aim of this investigation was to commission the cone dose calculation algorithm of a Varian Eclipse treatment planning system for a Varian 5mm conical collimator attached to a Varian TrueBeam linear accelerator that had been beam-matched to the Varian Golden Beam Data (GBD). Tissue maximum ratios (TMRs), off-axis ratios (OARs), and the output factor (OF) were measured using a PTW 60019 microDiamond and a PTW 60018 SRS Diode detector. Results were compared to the GBD for this collimator, radiochromic film measurements, and an output factor measured during an independent audit by the Australian Clinical Dosimetry Service. Film dosimetry was used to evaluate Eclipse dose calculations in a solid water phantom and end-to-end accuracy with an anthropomorphic head phantom. A PTW BEAMSCAN water phantom was used to collect the data, and output correction factors were derived from IAEA TRS-483. Gamma analysis was used to compare measured TMRs and profiles, and to compare Eclipse dose planes with film dosimetry results. Good agreement was obtained between the measurements with the two detectors, and with the various comparisons carried out to confirm both measurement accuracy and planning system configuration. It was decided to configure Eclipse with the microDiamond OF and the SRS Diode measured TMR and OAR data.

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Survey of 5 mm small‐field output factor measurements in Australia

Cited by 8 publications

References 22 publications

Verification of representative data for output factors of SRS cones utilizing IAEA TRS 483 recommendations

Verification of representative data for output factors of SRS cones utilizing IAEA TRS 483 recommendations

6‐MV small field output factors: intra‐/intermachine comparison and implementation of TRS‐483 using various detectors and several linear accelerators

Varian Eclipse Stereotactic Cone Data Commissioning

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