The influence of air cavities on interface doses for photon beams

Klein, Eric E.; Chin, Lee M.; Rice, R.; Mijnheer, Ben J.

doi:10.1016/0360-3016(93)90255-t

Cited by 77 publications

(59 citation statements)

References 15 publications

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“…MC algorithm was able to predict the dose distributions with a higher accuracy [3]. Many researchers have investigated the effect of air cavities on the dose distribution and dose reduction near air cavity, depending on geometry, beam energy, and field size using various MC codes in water equivalent phantoms [4][5][6][7].…”

Section: Introductionmentioning

confidence: 99%

Evaluation and Commissioning of Commercial Monte Carlo Dose Algorithm for Air Cavity

Miura¹,

Masai²,

Yamada³

et al. 2014

IJMPCERO

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The purpose of this study was to compare the Pencil Beam (PB) with Monte Carlo (MC) calculated dosimetric results using phantoms for air cavity region. Measurements in Tough water phantom with air gaps were used to verify the calculated dose. The plane-parallel ionization chamber was moved from 2 mm to 20 mm behind air gap. Calculations were performed for various air gaps (1.0, 2.0, 3.0 and 4.0 cm) and field sizes (4.2 × 4.2, 6.0 × 6.0 and 9.8 × 9.8 cm 2 ). The lateral missing tissue measurement was performed using the radiochromic RT-QA film. Dose difference between PB and chamber measurement near an air gap was greater for smaller field size, larger air gap thickness, and shallower depth behind air gap. As the distance from the phantom edge became shorter, the dose differences of the PB calculation and film measurement became larger. MC calculations were found within 3% agreement to the measured dose distributions. Our results demonstrate an excellent agreement between ionization chamber and radiochromic RT-QA film measurements and MC calculations.

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Section: Introductionmentioning

confidence: 99%

Evaluation and Commissioning of Commercial Monte Carlo Dose Algorithm for Air Cavity

Miura¹,

Masai²,

Yamada³

et al. 2014

IJMPCERO

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“…3 for the cavity of 1 Â 1 Â 2.8 cm 3 . However, it is evident from this figure that the effect on the dose maximum is not so strong as those observed for the previous energy.…”

Section: Resultsmentioning

confidence: 99%

“…These discrepancies between the PB and the MC become less significant as the thickness of the cavity decreases. For the cavity of 1 Â 1 Â 0.8 cm 3 , it was observed that the agreement between PB and MC PDD curves is within 2%/2 mm. These disagreements between both calculations may be attributed to the lack of electron scattering modeling of the PB algorithm, resulting therefore in a decrease of the scatter contribution to the central axis from the PMMA side adjacent to the cavity.…”

mentioning

confidence: 82%

“…The relative numbers of elemental compositions of PMMA, namely H ¼ 8; C ¼ 5 and O ¼ 2, and density of 1.19 g/cm 3 were considered by the PEGS4 data-preprocessing code [29] to create the data files containing information of material cross section and branching ratios. The low energy thresholds for the production of knock-on electrons were set to AE ¼ 0.521 MeV (total energy) and the threshold for bremsstrahlung events was set to AP ¼ 0.010 MeV.…”

Section: Monte Carlo Simulationsmentioning

confidence: 99%

“…Again, these discrepancies may be due to the nature of the measurement [34]. Figure 7 compares PB and MC calculated cross-plane dose profiles for the heterogeneous phantoms containing the cavity with the largest thickness (1 Â 1 Â 2.8 cm 3 ) and the largest area …”

Section: Off-axis Dose Variationmentioning

confidence: 99%

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Dosimetric effect by shallow air cavities in high energy electron beams

et al. 2014

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a b s t r a c tThis study evaluates the dosimetric impact caused by an air cavity located at 2 mm depth from the top surface in a PMMA phantom irradiated by electron beams produced by a Siemens Primus linear accelerator. A systematic evaluation of the effect related to the cavity area and thickness as well as to the electron beam energy was performed by using Monte Carlo simulations (EGSnrc code), Pencil Beam algorithm and Gafchromic EBT2 films. A home-PMMA phantom with the same geometry as the simulated one was specifically constructed for the measurements. Our results indicate that the presence of the cavity causes an increase (up to 70%) of the dose maximum value as well as a shift forward of the position of the depthedose curve, compared to the homogeneous one. Pronounced dose discontinuities in the regions close to the lateral cavity edges are observed. The shape and magnitude of these discontinuities change with the dimension of the cavity. It is also found that the cavity effect is more pronounced (6%) for the 12 MeV electron beam and the presence of cavities with large thickness and small area introduces more significant variations (up to 70%) on the depthedose curves.Overall, the Gafchromic EBT2 film measurements were found in agreement within 3% with Monte Carlo calculations and predict well the fine details of the dosimetric change near the cavity interface. The Pencil Beam calculations underestimate the dose up to 40% compared to Monte Carlo simulations; in particular for the largest cavity thickness (2.8 cm).

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