Correction factors for low perturbation <i>in vivo</i> diodes used in the determination of entrance doses in high energy photon beams

Roberts, R.J.; Philp, Amanda

doi:10.1118/1.2818729

Cited by 6 publications

(10 citation statements)

References 20 publications

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“…Accordingly, care should be taken when using the EDD5 at energies around 9 MV or higher. The results of the present study are in general agreement with a previous report which concluded that the EDD5 may be applied as a low‐perturbation diode at high energies (particularly for the lower megavoltage beam energies) and for angles of obliquity below

45 °

(24) . Our results suggest against the use of this diode in axial angles beyond

\pm 50 °

and exceeding the range

0 °

+ 50 °

tilt angle at 9 MV, because a small error in setup for such angles may cause large errors in the diode readings.…”

Section: Discussionsupporting

confidence: 92%

“…Therefore, a significant perturbation of the target dose may occur if it is used on most or all of the treatment fractions. Given the importance of performing in vivo dosimetry in most or all of complex treatment fractions, using thin buildup (low‐perturbation) diodes instead is gathering interest (24) . However, such diodes are strictly unsuitable for dosimetry of high‐energy megavoltage photons.…”

Section: Introductionmentioning

confidence: 99%

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A Monte Carlo and experimental investigation of the dosimetric behavior of low‐ and medium‐perturbation diodes used for entrance in vivo dosimetry in megavoltage photon beams

Mosleh-Shirazi

Karbasi

Shahbazi‐Gahrouei

et al. 2012

J Applied Clin Med Phys

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Full buildup diodes can cause significant dose perturbation if they are used on most or all of radiotherapy fractions. Given the importance of frequent in vivo measurements in complex treatments, using thin buildup (low‐perturbation) diodes instead is gathering interest. However, such diodes are strictly unsuitable for high‐energy photons; therefore, their use requires evaluation and careful measurement of correction factors (CFs). There is little published data on such factors for low‐perturbation diodes, and none on diode characterization for 9 MV X‐rays. We report on MCNP4c Monte Carlo models of low‐perturbation (EDD5) and medium‐perturbation (EDP10) diodes, and a comparison of source‐to‐surface distance, field size, temperature, and orientation CFs for cobalt‐60 and 9 MV beams. Most of the simulation results were within 4% of the measurements. The results suggest against the use of the EDD5 in axial angles beyond ±50° and exceeding the range 0° to +50° tilt angle at 9 MV. Outside these ranges, although the EDD5 can be used for accurate in vivo dosimetry at 9 MV, its CF variations were found to be 1.5–7.1 times larger than the EDP10 and, therefore, should be applied carefully. Finally, the MCNP diode models are sufficiently reliable tools for independent verification of potentially inaccurate measurements.PACS numbers: 87.10.Rt; 87.50.cm; 87.55.km; 87.56.Fc

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45 °

(24) . Our results suggest against the use of this diode in axial angles beyond

\pm 50 °

and exceeding the range

0 °

+ 50 °

tilt angle at 9 MV, because a small error in setup for such angles may cause large errors in the diode readings.…”

Section: Discussionsupporting

confidence: 92%

Section: Introductionmentioning

confidence: 99%

A Monte Carlo and experimental investigation of the dosimetric behavior of low‐ and medium‐perturbation diodes used for entrance in vivo dosimetry in megavoltage photon beams

Mosleh-Shirazi

Karbasi

Shahbazi‐Gahrouei

et al. 2012

J Applied Clin Med Phys

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“…8,9 Diodes are also designed to measure surface dose and dose from electron fields. 8,[10][11][12][13][14][15][16][17][18] This work is a study of diodes that are semiconductor detectors designed to measure surface dose. The surface-dose characteristic is accomplished with packaging that has an areal density of less than 0.1 g / cm 2 on the entrance side of the diode.…”

Section: Introductionmentioning

confidence: 99%

Angular dependence of dose sensitivity of surface diodes

Jursinic

2009

Medical Physics

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Commercially available surface diodes are found to have as great as +/-12% change in sensitivity with the angle of incidence of radiation. This work is a study of the cause of angular dependence in diode sensitivity and how it can be decreased. A number of different surface diodes were used in these measurements: A commercially available diode and four prototype diodes. A number of the diodes were constructed with the silicon chip, the die, mounted on a circuit board that had a plane of copper on its back side. These diodes had angular dependence of sensitivity as great as +/- 10%. It was hypothesized that the copper plane on the circuit board was the cause of the anisotropy in sensitivity of the diodes. To test this hypothesis, diodes with a new design [Patent No. 61/035,257 (pending)], without a copper back plane, were fabricated and characterized in this work. These diodes were found to have the following characteristics: A dependence on incident angle of radiation of +/- 3.6%; after 10 kGy of pre-irradiation, a 1.6% change in sensitivity for a 260-fold change in dose per pulse; an areal density of 0.08 g/cm2.

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“…19 The average percentage of CF angle effect 0?6% was found to have an relatively enhanced effect on cumulative diode reading. SSD correction factor, block correction factor have relatively reduced effect on diode response by 0?3%, 0?1%.…”

Section: Discussionmentioning

confidence: 87%

“…Geometric parameters, e.g. [16][17][18][19][20] If build up cap of diode is not thick enough then an overestimation of dose at short SSD can be observed because of the electronic contamination seen by diode not IC at maximum depth dose.…”

Section: Introductionmentioning

confidence: 99%

A study of dosimetric characteristics for in vivo dosimetry with cylindrical n-type Isorad diode

Islam

Haque²,

Muhammad³

et al. 2013

J Radiother Pract

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Background and purpose: The objective was to determine diode characteristics before actual dose verification on human phantom and patients. Materials and methods:The reliability and stability of equipment, signal stability, precision, dose response linearity, field flatness, perturbation of radiation dose, plastic to water conversion factor (K pl ), ionisation chambers (ICs) and diode calibration were determined. Correction factors for tray (CF tray ), wedge (CF wedge ), field size (CF FS ), SSD (CF SSD ), angle (CF angle ) and block (CF block ) were found. Patient dose monitor, Isorad diode (n-type) and IC (PTW Frieburg), Co-60 unit (Theratron), ATOM Adult male human phantom (Model 701-D, CIRS) were used.Results and conclusion: Good signal stability, precise data, and linear dose response, variation of 0?500% and 5?000% in field flatness and perturbation tests, respectively, were noted. K pl was 1?006 for IC PTW Frieburg TW30013, 0114. The diode calibration factor was 0?989. CF tray , CF FS , CF SSD , CF angle , CF block were 1?001, 1?001, 0?997, 1?006 and 0?990, respectively. CF wedge were 1?024, 1?030 and 1?038 for 308, 458 and 608 wedges, respectively. The verification of above correction factors (CFs) on Nasopharynx and lung of human phantom was also done.

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Correction factors for low perturbation in vivo diodes used in the determination of entrance doses in high energy photon beams

Cited by 6 publications

References 20 publications

A Monte Carlo and experimental investigation of the dosimetric behavior of low‐ and medium‐perturbation diodes used for entrance in vivo dosimetry in megavoltage photon beams

A Monte Carlo and experimental investigation of the dosimetric behavior of low‐ and medium‐perturbation diodes used for entrance in vivo dosimetry in megavoltage photon beams

Angular dependence of dose sensitivity of surface diodes

A study of dosimetric characteristics for in vivo dosimetry with cylindrical n-type Isorad diode

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