The effect of lead underlying water on the backscatter of X-rays of beam qualities 0.5 mm to 8 mm Al HVT

Lanzon, P; Sorell, Graham

doi:10.1088/0031-9155/38/8/012

Cited by 10 publications

(20 citation statements)

References 1 publication

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“…The acquisition of a new superficial treatment unit in our department, a Pantak SXT 150, prompted an independent measurement of dose reduction to confirm the clinical applicability of the previously published comprehensive data 1,2 . Differences between x-ray units in inherent filtration, x-ray tube design, treatment cone design, and peak potential mean that beams of the same nominal quality (i.e.…”

Section: Introductionmentioning

confidence: 80%

Dose reduction from loss of backscatter in superficial x-ray radiation therapy with the Pantak SXT 150 unit

Healy

Sylvander

Nitschke

2008

Australas. Phys. Eng. Sci. Med.

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Loss of backscatter has been measured for a Pantak Therapax SXT 150 superficial x-ray therapy unit. Ionisation chamber measurements at the surface were performed in solid water with and without underlying lead to confirm the applicability of previous published measurements. Measurements of loss of backscatter with and without lead allowed the effect of underlying lead to be separated from the effect of loss of backscatter. It was found that the difference between the effect of lead and that of air on surface dose is minimal for solid water phantom thickness exceeding 3 cm. Differences up to 3% in dose reduction at the surface were found between this work and previous published results with different x-ray units.

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Section: Introductionmentioning

confidence: 80%

Dose reduction from loss of backscatter in superficial x-ray radiation therapy with the Pantak SXT 150 unit

Healy

Sylvander

Nitschke

2008

Australas. Phys. Eng. Sci. Med.

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“…In their study they used x-ray beams with a HVL ranging from 0.5-8 mm Al and applicators with a treatment SSD of 10 cm. 7 They found that the surface dose decreased as the lead was positioned closer to the chamber.…”

Section: Introductionmentioning

confidence: 99%

An investigation of dose changes for therapeutic kilovoltage x‐ray beams with underlying lead shielding

et al. 2007

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Kilovoltage x-ray beams are used to treat cancer on or close to the skin surface. Many clinical cases use high atomic number materials as shielding to reduce dose to underlying healthy tissues. In this work, we have investigated the effect on both the surface dose and depth doses in a water phantom with lead shielding at depth in the phantom. The EGSnrc Monte Carlo code was used to simulate the water phantom and to calculate the surface doses and depth doses using primary x-ray beam spectra derived from an analytical model. The x-ray beams were in the energy range of 75-135 kVp with field sizes of 2, 5 and 8 cm diameter. The lead sheet was located beneath the water surface at depths ranging from 0.5-7.5 cm. The surface dose decreased as the lead was positioned closer to the water surface and as the field size was increased. The variation in surface dose as a function of x-ray beam energy was only small but the maximum reduction occurred for the 100 kVp x-ray beam. For the 8 cm diameter field with the lead at 1 cm depth and using the 100 kVp x-ray beam, the surface dose was reduced to 0.898 of the surface dose in the water phantom only. Measured surface dose changes, using a Farmer-type ionization chamber, agreed with the Monte Carlo calculated doses. Calculated depth doses in water with a lead sheet positioned below the surface showed that the dose fall-off increased as the lead was positioned closer to the water surface as compared to the depth dose in the water phantom only. Monte Carlo calculations of the total x-ray beam spectrum at the water surface showed that the total fluence decreased due to a reduction in backscatter from within the water and very little backscatter from the lead. The mean energy of the x-ray spectrum varied less than 1 keV, with the lead at 1 cm beneath the water phantom surface. As the Monte Carlo calculations showed good agreement with the measured results, this method can be used to verify surface dose changes in clinical situations where measurements are difficult. The clinical impact of the use of lead must be considered in the dose prescription for patients being treated with kilovoltage x-ray beams.

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“…In superficial radiotherapy, dose is prescribed to or near the skin surface and backscatter of radiation from underlying tissue contributes to that dose . Tissue backscatter is dominated by Compton interactions and the dependence of such backscatter on beam quality, SSD, and field size is well documented . Loss of backscatter radiation due to the presence of a lead, air or bone interface downstream from the surface has been investigated using experimental techniques that involve surface‐based ion chamber measurements as well as with a chamber at depth in a phantom .…”

Section: Introductionmentioning

confidence: 99%

“…Surface‐based ion chamber techniques measure backscatter reduction effects on surface dose. Such measurements have been restricted to a minimum surface‐interface separation ≈5 mm due to the chamber dimensions . This limitation is in part vindicated by the large number of clinical treatments that involve tissue with underlying lead or air at comparable or even greater depths.…”

Section: Introductionmentioning

confidence: 99%

“…Such measurements have been restricted to a minimum surfaceinterface separation %5 mm due to the chamber dimensions. 4,5 This limitation is in part vindicated by the large number of clinical treatments that involve tissue with underlying lead or air at comparable or even greater depths. However for the treatment of lesions on the face and scalp, for example, the proximity of bone to the tissue surface may be < 5 mm.…”

Section: Introductionmentioning

confidence: 99%

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Measured and Monte Carlo simulated surface dose reduction for superficial X‐rays incident on tissue with underlying air or bone

et al. 2017

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This work demonstrates the feasibility of using an Advanced Markus chamber with entrance window facing downstream to investigate surface dose reduction with underlying air or bone in tissue. As the field size decreases and beam quality increases surface dose with underlying bone tends to full backscatter values even though tissue thicknesses are below those normally associated with full backscatter. Conversely with underlying bone close to the surface dose will increasingly fall below full backscatter values as the beam energy is reduced and field size is increased.

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The effect of lead underlying water on the backscatter of X-rays of beam qualities 0.5 mm to 8 mm Al HVT

Cited by 10 publications

References 1 publication

Dose reduction from loss of backscatter in superficial x-ray radiation therapy with the Pantak SXT 150 unit

Dose reduction from loss of backscatter in superficial x-ray radiation therapy with the Pantak SXT 150 unit

An investigation of dose changes for therapeutic kilovoltage x‐ray beams with underlying lead shielding

Measured and Monte Carlo simulated surface dose reduction for superficial X‐rays incident on tissue with underlying air or bone

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