Measurement of the influence of titanium hip prosthesis on therapeutic electron beam dose distributions in a novel pelvic phantom

The impact of metal implants on the dose and clinical outcome of radiotherapy (Review)

Radiotherapy (RT) is one of the most widely used and effective cancer treatments. With the increasing need for organ reconstruction and advancements in material technology, an increasing number of patients with cancer have metallic implants. These implants can affect RT dosage and clinical outcomes, warranting careful consideration by oncologists. The present review discussed the mechanisms by which different types of metallic implants impact various stages of the RT process, examined methods to mitigate these effects during treatment, and discussed the clinical implications of metallic implants on RT outcomes. In summary, when metallic implants are present within the RT field, oncologists should carefully assess their impact on the treatment.

Dosimetric evaluation of phantoms including metal objects with high atomic number for use in intensity modulated radiation therapy

The dosimetric effect of artefacts caused by metal hip prostheses in computed tomography imaging is most commonly encountered in the planning of prostate cancer treatment. In this study, a phantom, containing a metal with high atomic number, was prepared for intensity-modulated radiotherapy (IMRT) treatment plans to be used in quality assurance (QA) procedures. Two sets of image files, one without metal artefact correction (ORG) and another with MAR correction (MAR+), were sent to the treatment planning system. In this study, 12 IMRT treatment plans with different fields and segment numbers were calculated. The normal tissue complication probability (NTCP) values of imaginary organs at risk (OARs), such as the rectum and bladder, were investigated, as was the difference in dose maps for ORG and MAR+ derived by calculating gamma passing rates (GPRs). The MatriXX was used for the gamma evaluation of patient-specific IMRT QA measurements. The gamma evaluation was repeated, based on the measurements using an EBT³ gafchromic film, for the plan showing the lowest GPR. The mean relative difference in NTCP values between the two sets of image files was found to be 2.5, 2.1 and 1.4 for the rectum; and 5.33, 6.80 and 9.82 for the bladder, for the investigated 5-, 7- and 9-field beam arrangements, respectively. The relative differences and the standard deviations in GPRs for the standard and metal-containing phantoms were calculated for the MAR+ and ORG sets. The maximum difference found was 7.69% ± 0.88 for the 9-field beam arrangement calculated without metal artefact correction. In the IMRT QA procedures for prostate patients with hip prostheses, the application of a metal-containing phantom that is both easy and inexpensive to prepare, is considered to be a useful method for examining any dose changes involved in introducing a hip prosthesis. Therefore, it is recommended for use in clinics that do not have MAR correction algorithms.

Characterization of Nylon-12 as a water-equivalent solid phantom material for dosimetric measurements in therapeutic photon and electron beams

The tissue- or water-equivalence of dosimetry phantoms used as substitutes for water is essential for absorbed dose measurements in radiotherapy. At our institution, a heterogeneous pelvic phantom that consists of stacked Nylon-12 layers has recently been manufactured for Gafchromic film dosimetry. However, data on the use of Nylon as tissue-mimicking media for dosimetric applications are scarce. This study characterizes the water-equivalence of Nylon-12 for dosimetric measurements in therapeutic photon and electron beams. Employing an Elekta Synergy and SL25 linear accelerator (Linac), photon beam transmission measurements for 6 MV and 15 MV, acquired in narrow beam geometry with a 0.6 cm³ Farmer-type ion chamber showed that the mass attenuation coefficient μ_m of Nylon-12 agrees with the values of water, water-equivalent RW3 and Perspex phantom materials within 3%. For 6 MV, the μ_m values were 0.0477 ± 0.002 cm²/g, 0.0490 ± 0.003 cm²/g, 0.0482 ± 0.001 cm²/g and 0.0479 ± 0.002cm²/g for Nylon-12, water, RW3, and Perspex, respectively. Differences within 2% were attained between depth dose data measured in Nylon-12 slabs with Gafchromic EBT3 films and in water with a Roos ion chamber for 10 × 10 cm² 6, 12 and 20 MeV electron beams produced by the Elekta Synergy and SL25 Linacs. Also, a good agreement within 2% was obtained between percent depth doses computed by DOSXYZnrc Monte Carlo simulations in water, Nylon-12 and RW3 materials for photon spectra between 250 kV and 15 MV. The discrepancies between the ratios of average, restricted stopping powers of Nylon to air and water to air for photon spectra ranging from 2 to 45 MV are typically within 1% signifying that Nylon and water have equivalent stopping power characteristics. This study highlights that Nylon-12 can be used as a tissue-mimicking phantom material for dosimetric measurements in clinical megavoltage photon and electron beams as it exhibits good water-equivalence.