Using a Monte Carlo model to predict dosimetric properties of small radiotherapy photon fields

Scott, A.; Nahum, Alan E.; Fenwick, John D.

doi:10.1118/1.2975223

Cited by 136 publications

(136 citation statements)

References 49 publications

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“…The higher output factor values of Edge and SFD detectors suggest an overresponse due to the use of diode detectors. It is known that the unshielded silicon diode detector has an over response to low‐energy secondary scattered photons due to the photoelectric effect 14 , 21 . There are a greater quantity of lower energy photons present in the flattening filter‐free energy spectrum when compared with a flattened energy spectrum.…”

Section: Discussionmentioning

confidence: 99%

“…Many recent studies have applied Monte Carlo simulations to examine the output factors of small field sizes used for radiosurgery such as CyberKnife, 6 , 7 Gamma Knife, 8 , 9 and Brainlab (10) . In addition, numerous studies have used Monte Carlo simulation to examine the accuracy of diode detectors measurements for small field dosimetry 11 , 12 , 13 , 14 …”

Section: Introductionmentioning

confidence: 99%

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Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter‐free stereotactic radiosurgery system

Cheng

Ning

Arora

et al. 2016

J Applied Clin Med Phys

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The dose measurements of the small field sizes, such as conical collimators used in stereotactic radiosurgery (SRS), are a significant challenge due to many factors including source occlusion, detector size limitation, and lack of lateral electronic equilibrium. One useful tool in dealing with the small field effect is Monte Carlo (MC) simulation. In this study, we report a comparison of Monte Carlo simulations and measurements of output factors for the Varian SRS system with conical collimators for energies of 6 MV flattening filter‐free (6 MV) and 10 MV flattening filter‐free (10 MV) on the TrueBeam accelerator. Monte Carlo simulations of Varian's SRS system for 6 MV and 10 MV photon energies with cones sizes of 17.5 mm, 15.0 mm, 12.5 mm, 10.0 mm, 7.5 mm, 5.0 mm, and 4.0 mm were performed using EGSnrc (release V4 2.4.0) codes. Varian's version‐2 phase‐space files for 6 MV and 10 MV of TrueBeam accelerator were utilized in the Monte Carlo simulations. Two small diode detectors Edge (Sun Nuclear) and Small Field Detector (SFD) (IBA Dosimetry) were applied to measure the output factors. Significant errors may result if detector correction factors are not applied to small field dosimetric measurements. Although it lacked the machine‐specific kQitalicclin,Qitalicmsrfitalicclin,fitalicmsr correction factors for diode detectors in this study, correction factors were applied utilizing published studies conducted under similar conditions. For cone diameters greater than or equal to 12.5 mm, the differences between output factors for the Edge detector, SFD detector, and MC simulations are within 3.0% for both energies. For cone diameters below 12.5 mm, output factors differences exhibit greater variations.PACS number(s): 87.55.k, 87.55.Qr

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter‐free stereotactic radiosurgery system

Cheng

Ning

Arora

et al. 2016

J Applied Clin Med Phys

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“…Discrepancies have been reported between doses predicted by treatment planning systems and those measured in patients or phantoms, [5][6][7][8] and sophisticated Monte Carlo codes have been used to calculate the dose properties of small fields in lieu of direct measurements, which may be too difficult to perform with typical detectors. [8][9][10][11] Moreover, the rapid advance of small-field radiotherapy technology has precipitated a decrease in the relevance of well-established standards of practice with respect to reference dosimetry. For example, the methods proposed in documents such as the American Association of Medical Physicists Task Group 51 ͑AAPM TG-51͒ ͑Ref.…”

Section: Introductionmentioning

confidence: 99%

Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors

et al. 2010

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Purpose: As the practice of using high-energy photon beams to create therapeutic radiation fields of subcentimeter dimensions ͑as in intensity-modulated radiotherapy or stereotactic radiosurgery͒ grows, so too does the need for accurate verification of beam output at these small fields in which standard practices of dose verification break down. This study investigates small-field output factors measured using a small plastic scintillation detector ͑PSD͒, as well as a 0.01 cm 3 ionization chamber. Specifically, output factors were measured with both detectors using small fields that were defined by either the X-Y collimator jaws or the multileaf collimator ͑MLC͒. Methods: A PSD of 0.5 mm diameter and 2 mm length was irradiated with 6 and 18 MV linac beams. The PSD was positioned vertically at a source-to-axis distance of 100 cm, at 10 cm depth in a water phantom, and irradiated with fields ranging in size from 0.5ϫ 0.5 to 10ϫ 10 cm 2 . The field sizes were defined either by the collimator jaws alone or by a MLC alone. The MLC fields were constructed in two ways: with the closed leaves ͑i.e., those leaves that were not opened to define the square field͒ meeting at either the field center line or at a 4 cm offset from the center line. Scintillation light was recorded using a CCD camera and an estimation of error in the medianfiltered signals was made using the bootstrapping technique. Measurements were made using a CC01 ionization chamber under conditions identical to those used for the PSD. Results: Output factors measured by the PSD showed close agreement with those measured using the ionization chamber for field sizes of 2.0ϫ 2.0 cm 2 and above. At smaller field sizes, the PSD obtained output factors as much as 15% higher than those found using the ionization chamber by 0.6ϫ 0.6 cm 2 jaw-defined fields. Output factors measured with no offset of the closed MLC leaves were as much as 20% higher than those measured using a 4 cm leaf offset. Conclusions:The authors' results suggest that PSDs provide a useful and possibly superior alternative to existing dosimetry systems for small fields, as they are inherently less susceptible to volume-averaging and perturbation effects than larger, air-filled ionization chambers. Therefore, PSDs may provide more accurate small-field output factor determination, regardless of the collimation mechanism.

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“…Volume averaging effects due to the finite dimension of the device sensitive area, radiation induced leakage currents, and polarity effects are the main causes of under-response to smaller fields and over-response to the larger ones. 9,10,12 Better dosimetric performance was obtained from solid-state detectors 6,[13][14][15] and liquid filled ion chambers 16,17 in terms of spatial resolution in narrow beam penumbra analysis and accurate output factor measurements.…”

Section: Introductionmentioning

confidence: 99%

Dosimetric characterization of a synthetic single crystal diamond detector in clinical radiation therapy small photon beams

Ciancaglioni¹,

Marinelli²,

Milani³

et al. 2012

Med. Phys.

115

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Purpose:To determine the potentialities of synthetic single crystal diamond Schottky diodes for accurate dose measurements in radiation therapy small photon beams. Methods: The dosimetric properties of a diamond-based detector were assessed by comparison with a reference microionization chamber. The diamond device was operated at zero bias voltage under irradiation with high-energy radiotherapic photon beams. The stability of the detector response and its dose and dose rate dependence were measured. Different square field sizes ranging from 1 × 1 cm 2 to 10 × 10 cm 2 were used during comparative dose distribution measurements by means of percentage depth dose curves (PDDs), lateral beam profiles, and output factors. The angular and temperature dependence of the diamond detector response were also studied.Results: The detector response shows a deviation from linearity of less than ±0.5% in the 0.01-7 Gy range and dose rate dependence below ±0.5% in the 1-6 Gy/min range. PDDs and output factors are in good agreement with those measured by the reference ionization chamber within 1%. No angular dependence is observed by rotating the detector along its axis, while ∼3.5% maximum difference is measured by varying the radiation incidence angle in the polar direction. The temperature dependence was investigated as well and a ±0.2% variation of the detector response is found in the 18-40• C range. Conclusions:The obtained results indicate the investigated synthetic diamond-based detector as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques.

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Using a Monte Carlo model to predict dosimetric properties of small radiotherapy photon fields

Cited by 136 publications

References 49 publications

Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter‐free stereotactic radiosurgery system

Output factor comparison of Monte Carlo and measurement for Varian TrueBeam 6 MV and 10 MV flattening filter‐free stereotactic radiosurgery system

Measuring output factors of small fields formed by collimator jaws and multileaf collimator using plastic scintillation detectors

Dosimetric characterization of a synthetic single crystal diamond detector in clinical radiation therapy small photon beams

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