Measurements of dose distributions in small beams of 6 MV X-rays

Rice, R.; Hansen, J J; Svensson, Göran K.; Siddon, Robert L.

doi:10.1088/0031-9155/32/9/002

Cited by 166 publications

(101 citation statements)

References 6 publications

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“…[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] It is known that the main problems with the detectors are retraceable to their finite size compared to the small size of the beams and to the nonwater equivalence of the materials. Moreover, the dosimetry of small beams is complicated by the lack of lateral electronic equilibrium.…”

Section: Introductionmentioning

confidence: 99%

Total scatter factors of small beams: A multidetector and Monte Carlo study

2008

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The scope of this study was to estimate total scatter factors ͑s c,p ͒ of the three smallest collimators of the Cyberknife radiosurgery system ͑5-10 mm in diameter͒, combining experimental measurements and Monte Carlo simulation. Two microchambers, a diode, and a diamond detector were used to collect experimental data. The treatment head and the detectors were simulated by means of a Monte Carlo code in order to calculate correction factors for the detectors and to estimate total scatter factors by means of a consistency check between measurement and simulation. Results for the three collimators were: s c,p ͑5 mm͒ = 0.677± 0.004, s c,p ͑7.5 mm͒ = 0.820± 0.008, s c,p ͑10 mm͒ = 0.871± 0.008, all relative to the 60 mm collimator at 80 cm source-to-detector distance. The method also allows the full width at half maximum of the electron beam to be estimated; estimations made with different collimators and different detectors were in excellent agreement and gave a value of 2.1 mm. Correction factors to be applied to the detectors for the measurement of s c,p were consistent with a prevalence of volume effect for the microchambers and the diamond and a prevalence of scattering from high-Z material for the diode detector. The proposed method is more sensitive to small variations of the electron beam diameter with respect to the conventional method used to commission Monte Carlo codes, i.e., by comparison with measured percentage depth doses ͑PDD͒ and beam profiles. This is especially important for small fields ͑less than 10 mm diameter͒, for which measurements of PDD and profiles are strongly affected by the type of detector used. Moreover, this method should allow s c,p of Cyberknife systems different from the unit under investigation to be estimated without the need for further Monte Carlo calculation, provided that one of the microchambers or the diode detector of the type used in this study are employed. The results for the diamond are applicable only to the specific detector that was investigated due to excessive variability in manufacturing.

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Section: Introductionmentioning

confidence: 99%

Total scatter factors of small beams: A multidetector and Monte Carlo study

2008

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“…[1][2][3][4] The development of high-resolution small volume detectors, as microionization chambers and solid state detectors, was studied by several authors with the aim of determining new devices and methods for accurate dosimetry in high-energy narrow photon beams. [5][6][7][8] However, no device was found yet, matching all the features requested to an "ideal" detector for small field dosimetry.…”

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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“…Difference of 3.7% from the calculated value is somewhat better than 14% smaller value of the stereotactic device of Im et al 8) Because of thicker plates and heavy materials, the device of Im et al 8) showed larger decrease in absolute dose measured at the center of the device. Furthermore, the PTW Model 31006 Pinpoint Chamber (PTW, Germany) with sensitive volume of 0.015 cm 3 is too small to measure absolute dose because of its small charge accumulation volume 1,3,15) . On the other hand, this chamber is too big to measure the absolute dose of the 4 mm helmet of Gamma Knife as Im et al did in their measurements.…”

Section: Discussionmentioning

confidence: 99%