Experimental determination of stereotactic cone size and detector specific output correction factor

Sharma, Dayananda Shamurailatpam; Chaudhary, Rahul; Sharma, Sunil Dutt; Pilakkal, Shaju; Rasal, Sachin K; Sawant, Mayur; Phurailatpam, Reena

doi:10.1259/bjr.20160918

Cited by 9 publications

(10 citation statements)

References 23 publications

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“…The daisy-chain method mitigates this effect by normalizing to an intermediate field size (e.g., 4 × 4 cm 2 ) using two different detectors (a diode and an ion chamber). Sharma et al reported up to −5% variation of OFs for the Edge detector when OFs measured using the daisy-chain method were compared with OFs directly normalized to a field size of 10 × 10 cm 2 for cones [22]. In our study, the OF difference between with and without the daisy-chain method for cones was less than 1% and OFs were underestimated without the daisy-chain method.…”

Section: Measurementscontrasting

confidence: 43%

Commissioning of the TrueBeam STx 6 MV FFF Beam in the RayStation Treatment Planning System for SRS and SBRT Treatments

Lee¹,

Kim²

2021

IJMPCERO

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Purpose: The purpose of this study is to provide technical information on commissioning the TrueBeam STx 6 MV flattening-filter free (FFF) beam in the RayStation treatment planning system (TPS) for stereotactic radiosurgery (SRS) and stereotactic body radiation therapy (SBRT) treatments. Methods: For beam modeling, percent depth dose curves, profiles and output factors for jaw-collimated fields and stereotactic cones as well as X-jaws transmission were measured. For multi-leaf collimator (MLC) modeling, MLC model parameters such as offset, gain, curvature, leaf tip width, tongue and groove and transmission were determined and output factors for MLC-collimated fields were measured. Absolute dose calibration was also performed. For beam model and MLC model validation, the American Association of Physicists in Medicine Task Group-119 plans, clinical SRS and SBRT plans and end-to-end testing were performed. Results: Beam characteristics of the 6 MV FFF beam agreed well with those in the literature. Validation results showed that our beam model and MLC model were acceptable for SRS and SBRT treatments. Conclusions: The technical information and dosimetric data provided in this study will be a useful reference for other clinics/institutions which will commission the same machine energy in the RayStation TPS.

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Section: Measurementscontrasting

confidence: 43%

Commissioning of the TrueBeam STx 6 MV FFF Beam in the RayStation Treatment Planning System for SRS and SBRT Treatments

Lee¹,

Kim²

2021

IJMPCERO

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“…In small fields, an additional opposing effect is due to the presence of silicon, which introduces an over-response in small fields due to a fluence perturbation that is not negligible. 146,147 A possible solution is to use the intermediate field method, sometimes referred to as the daisy chain technique [148][149][150] (cross calibration of diode against the chamber in an intermediate field to connect measurements in large fields to small fields) to measure field output factors normalized to a 10 cm 2 × 10 cm 2 field. Although this technique accounts for the energy dependence of large fields, it does not consider the electron fluence perturbation due to the high density of silicon in small fields.…”

Section: Solid-state Detectorsmentioning

confidence: 99%

“… For fields less than 1 cm × 1 cm, the interplay of source occlusion and detector choice demands precise positioning of the detector. The resolution of the scanning measurement should be smallest possible to the limit of device usually 0.1 mm. Dosimetric measurements should be performed with more than one detector system. Strategies to minimize variations in measurements among users should be tested, utilized, and shared The daisy chain approach 148‐150,322 can be used to determine output factors for the complete range of field sizes needed clinically. However, it should be remembered that this method normalizes the response increase in large fields, it does not account for the fluence perturbation effect that may require a correction.…”

Section: Key Recommendations and Summarymentioning

confidence: 99%

“…Strategies to minimize variations in measurements among users should be tested, utilized, and shared 5. The daisy chain approach [148][149][150]322 can be used to determine output factors for the complete range of field sizes needed clinically. However, it should be remembered that this method normalizes the response increase in large fields, it does not account for the fluence perturbation effect that may require a correction.…”

Section: Measurement Considerationsmentioning

confidence: 99%

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Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

et al. 2021

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Abbreviations: %dd(10) x , The photon component of the percent depth dose at 10 cm depth in water for a 10 cm 2 × 10 cm 2 field; L∕ w air , Restricted mass collision stopping power ratio of water to air; en ∕ , Spectrum-averaged mass energy-absorption coefficient; AAPM, American Association of Physicists in Medicine; CPE, Charged Particle Equilibrium; DLG, Dosimetric leaf gap; D f msr w,Q msr , Absorbed dose to water at the reference depth z ref in water in the absence of the detector in a field specified by f msr and beam quality Q msr .; f clin , Clinical (clin) non-reference radiation field; f msr , Machine-specific reference (msr) field; f ref , Reference field (ref) specified in dosimetry protocols for which the calibration coefficient of an ionization chamber in terms of absorbed dose to water is provided by a standards laboratory; FWHM, Full-width at half-maximum; GUM, Guide to the expression of Uncertainty in Measurements.; IAEA, International Atomic Energy Agency; ICRU, International Commission on Radiation Units and Measurements; IMRT, Intensity-modulated radiation therapy; k Q,Q 0 , The beam-quality correction factor, which corrects for the differences between the response of an ionization chamber in the reference beam of quality Q o used for calibrating the chamber and the beam of quality Q (defined as k Q . in TG-51 4 ); k f ref Q,Q 0 , Correction factor that accounts for the differences between the response of a detector in field f ref in a beam of quality Q and reference beam quality Q 0 as defined in TRS-483. 1 and Palmans et al 2 ; k fclin,fmsr Qclin,Q msr , The detector-specific correction factor that accounts for the difference between the responses of the detector in fields f clin in a beam of quality Q clin and in fields f msr in beam of quality Q msr as defined by Alfonso et al. 3 ; LCPE, Lateral charged particle equilibrium; M fmsr Qmsr , Detector reading in field f msr and beam quality Q msr corrected for influence of changes in pressure and temperature, incomplete charge collection, polarity effect and electrometer correction factor (TRS-483 1 ); MU, Monitor unit; N D,w,Q 0 , This is N D,w in TG-51, 4 and defined as the calibration coefficient in terms of absorbed dose to water for an ionization chamber at a reference beam of quality,Q 0 and field size f ref ; N f ref D,w,Q 0

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“…In addition, the complex issues involving small field mentioned above could also lead to incorrect calculations of absorbed dose in treatment planning systems (TPS), 2 due to simplifications in the modeling of the lateral electron scattering or using extrapolated beam data for small fields, 3,4,[8][9][10] with the inaccuracies mostly prominent in highly heterogeneous cases such as in the thorax.…”

Section: Introductionmentioning

confidence: 99%

Small‐field measurement and Monte Carlo model validation of a novel image‐guided radiotherapy system

et al. 2021

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The RefleXion™ X1 is a novel radiotherapy system that is designed for image-guided radiotherapy, and eventually, biology-guided radiotherapy (BgRT). BgRT is a treatment paradigm that tracks tumor motion using real-time positron emission signals. This study reports the small-field measurement results and the validation of a Monte Carlo (MC) model of the first clinical RefleXion unit. Methods: The RefleXion linear accelerator (linac) produces a 6 MV flattening filter free (FFF) photon beam and consists of a binary multileaf collimator (MLC) system with 64 leaves and two pairs of y-jaws. The maximum clinical field size achievable is 400 × 20 mm 2 . The y-jaws provide either a 10 or 20 mm opening at source-to-axis distance (SAD) of 850 mm. The width of each MLC leaf at SAD is 6.25 mm. Percentage depth doses (PDDs) and relative beam profiles were acquired using an Edge diode detector in a water tank for field sizes from 12.5 × 10 to 100 × 20 mm 2 . Beam profiles were also measured using films. Output factors of fields ranging from 6.25 × 10 to 100 × 20 mm 2 were measured using W2 scintillator detector, Edge detector, and films. Output correction factors k of the Edge detector for RefleXion were calculated. An MC model of the linac including pre-MLC beam sources and detailed structures of MLC and lower yjaws was validated against the measurements. Simulation codes BEAMnrc and GATE were utilized. Results: The diode measured PDD at 10 cm depth (PDD10) increases from 53.6% to 56.9% as the field opens from 12.5 × 10 to 100 × 20 mm 2 . The W2-measured output factor increases from 0.706 to 1 as the field opens from 6.25 × 10 to 100 × 20 mm 2 (reference field size). The output factors acquired by diode and film differ from the W2 results by 1.65% (std = 1.49%) and 2.09% (std = 1.41%) on average, respectively. The profile penumbra and full-width halfmaximum (FWHM) measured by diode agree well with the film results with a deviation of 0.60 mm and 0.73% on average, respectively. The averaged beam profile consistency calculated between the diode-and film-measured profiles among different depths is within 1.72%. By taking the W2 measurements as the ground truth, the output correction factors k for Edge detector ranging from 0.958 to 1 were reported. For the MC model validation, the simulated PDD10 agreed within 0.6% to the diode measurement. The MC-simulated output factor differed from the W2 results by 2.3% on average (std = 3.7%), while the MC simulated beam penumbra differed from the diode results by 0.67 mm on average (std = 0.42 mm). The MC FWHM agreed with the diode results to within 1.40% on average. The averaged beam profile consistency calculated between the diode and MC profiles among different depths is less than 1.29%.

show abstract

Experimental determination of stereotactic cone size and detector specific output correction factor

Cited by 9 publications

References 23 publications

Commissioning of the TrueBeam STx 6 MV FFF Beam in the RayStation Treatment Planning System for SRS and SBRT Treatments

Commissioning of the TrueBeam STx 6 MV FFF Beam in the RayStation Treatment Planning System for SRS and SBRT Treatments

Report of AAPM Task Group 155: Megavoltage photon beam dosimetry in small fields and non‐equilibrium conditions

Small‐field measurement and Monte Carlo model validation of a novel image‐guided radiotherapy system

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