Backscatter factor measurements for kilovoltage X-ray beams using thermoluminescent dosimeters (TLDs)

Nelson, Vinod K.; Hill, Robin

doi:10.1016/j.radmeas.2011.08.019

Cited by 13 publications

(12 citation statements)

References 18 publications

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“…Multiple publications have demonstrated close agreement between backscatter factors from MC calculation, measurements with radiochromic films and TLDs, and published tabulated values from IPEMB and AAPM protocols (Hewson et al, 2018;Kim et al, 2010;Nelson and Hill, 2011). Our MC simulation also confirmed this agreement in Figure 4.…”

Section: Discussionsupporting

confidence: 83%

Erratum: Impact of backscatter material thickness on the depth dose of orthovoltage irradiators for radiobiology research (2019 Phys. Med. Biol. 64 055001)

et al. 2019

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The orthovoltage x-Ray energy frequently used in radiation research is prone to dosimetry errors due to insufficient backscatter conditions. In many radiobiology studies, especially for cell irradiations, precise dose calculation algorithms such as Convolution-Superposition or Monte Carlo are impractical and as such, less accurate hand calculation methods are used for dose estimation. These dose estimation methods typically assume full backscatter conditions. The purpose of this study is to demonstrate the magnitude of the dose error that results from insufficient backscatter, and to provide lookup tables to account this issue. The beam spectra of several widely used commercial systems (XRAD-225, XRAD-320, SARRP) were used in Monte Carlo (MC) simulations on a series of phantom setups to investigate the impact of varying backscatter conditions on dosimetry. The depth dose curves for different field sizes, water phantom thicknesses and beam qualities were generated. In addition, depth dependent backscatter factors for different field sizes and different beam qualities were calculated. It is demonstrated that as much as a 50% dose difference exists for different backscatter conditions at the beam qualities studied. The choice of cell dish size as well as other changes in the experiment setup can have more than 10% impact on the dose. The impact of backscatter is reduced with a decrease in field size. Further, the thickness needed to provide full backscatter can be approximated as being equal to the field size. It is imperative to ensure full backscatter conditions during system and dosimeter calibration, or to use the look-up table provided in this study.

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Section: Discussionsupporting

confidence: 83%

Erratum: Impact of backscatter material thickness on the depth dose of orthovoltage irradiators for radiobiology research (2019 Phys. Med. Biol. 64 055001)

et al. 2019

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“…Nelson and Hill (17) used two types of TLDs to measure BSFs and also performed Monte Carlo simulation of the specific beams used. They found moderate agreement, with measurements at all but one energy within 5% of AAPM and IPEM code of practice data and Monte Carlo results.…”

Section: Discussionmentioning

confidence: 99%

“…Several authors ( 3 , 6 , 17 ) have ascribed the differences between measured and code of practice values to differences in spectral distribution of local beams. However, in all of these cases, the differences are of the same order as the measurement uncertainties, so a more reasonable conclusion would be that the local factors agree with reference data within inherent uncertainties.…”

Section: Discussionmentioning

confidence: 99%

“…Local measurement of these factors is confounded by the finite size of many common detectors, leading to perturbation and partial volume effects, as well as the potential lack of water‐equivalence of detectors and solid phantom materials at kilovoltage energies. Recently, a number of novel detectors have been investigated to see if they can be used for local verification, including GAFCHROMIC film, ( 3 , 4 , 5 , 6 ) thermoluminescent dosimeters (TLDs), (17) and optically stimulated luminescent dosimeters (OSLDs) (6) . Results of these studies are discussed below, alongside data from this current work.…”

Section: Introductionmentioning

confidence: 99%

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Review of backscatter measurement in kilovoltage radiotherapy using novel detectors and reduction from lack of underlying scattering material

Eaton

Doolan

2013

J Applied Clin Med Phys

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Lack of underlying material can lead to dose reduction in kilovoltage radiotherapy treatments because of backscatter reduction. Conversely, the use of lead shielding can lead to large dose enhancement close to the lead interface. GAFCHROMIC film has been shown to be of use in verification of local backscatter factors compared to reference data in codes of practice, but careful handling and multiple readings are required to reduce systematic uncertainties to between 3% and 4%. Monte Carlo modeling of the specific treatment unit should be performed in cases which are found to differ from reference values before alternative values are adopted clinically, but these cases are expected to be few. GAFCHROMIC film may also be used to estimate backscatter reduction more readily than customized ionization chambers, for a range of beam qualities, applicator sizes and depth, with and without lead shielding. Differences were found between different studies, and it is not clear to what extent these are due to variation in equipment and/or technique. However, a layer of wax around lead shielding of 1 mm thickness should be sufficient to eliminate lead enhancement effects for all kilovoltage energies from 40 kV to 300 kVPACS numbers: 87.55.Qr, 87.56.jk

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“…Specifically, three LiF TLD100 per measurement were used with Harshaw 500 reader following the clinical in vivo dosimetry practice at the site. Literature indicates that the expected uncertainty of TLDs is within 3-5% [5,25]; therefore, the tolerance used in this study was 3%.…”

Section: E End To End Testingmentioning

confidence: 99%

The clinical impact of using a single set of radiotherapy planning data for two kilovoltage therapy units

Peters

Nelson

Deshpande

et al. 2023

Preprint

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Kilovoltage therapy units are used for superficial radiotherapy treatment delivery. Peer reviewed studies for MV linear accelerators describe tolerances to dosimetrically match multiple LINACS enabling patient treatment on any matched machine. There is an absence of literature on using a single planning data set for multiple kilovoltage units which have limited ability for beam adjustment. This study reviewed kilovoltage dosimetry and treatment planning scenarios to evaluate the suitability of ACPSEM annual QA tolerances to determine whether two units (of the same make and model) were dosimetrically matched. The dosimetric characteristics, such as measured half value layer (HVL), percentage depth dose (PDD), applicator factor and output variation with stand-off distance for each kV unit were compared to assess the agreement. Independent planning data based on the measured HVL for each beam energy from each kV unit was prepared. Monitor unit (MU) calculations were performed using both sets of planning data for approximately 200 clinical scenarios and compared with an overall agreement between units of < 2%. Additionally, a dosimetry measurement comparison was completed at each site for a subset of nine scenarios. All machine characterisation measurements were within the ACPSEM Annual QA tolerances, and dosimetric testing was within 2.5%. This work demonstrates that using a single set of planning data for two kilovoltage units is feasible, resulting in a clinical impact within published uncertainty.

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Backscatter factor measurements for kilovoltage X-ray beams using thermoluminescent dosimeters (TLDs)

Cited by 13 publications

References 18 publications

Erratum: Impact of backscatter material thickness on the depth dose of orthovoltage irradiators for radiobiology research (2019 Phys. Med. Biol. 64 055001)

Erratum: Impact of backscatter material thickness on the depth dose of orthovoltage irradiators for radiobiology research (2019 Phys. Med. Biol. 64 055001)

Review of backscatter measurement in kilovoltage radiotherapy using novel detectors and reduction from lack of underlying scattering material

The clinical impact of using a single set of radiotherapy planning data for two kilovoltage therapy units

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