Dose comparison between Gafchromic film, XiO, and Monaco treatment planning systems in a novel pelvic phantom that contains a titanium hip prosthesis

Abstract

The presence of metallic prostheses during external beam radiotherapy of malignancies in the pelvic region has the potential to strongly influence the dose distribution to the target and to tissue surrounded by the prostheses. This study systematically investigates the perturbation effects of unilateral titanium prosthesis on 6 and 15 MV photon beam dose distributions using Gafchromic EBT2 film measurements in a novel pelvic phantom made out of a stack of nylon slices. Comparisons were also made between the film data and dose calculations made on XiO and Monaco treatment planning systems. The collapsed cone algorithm was chosen for the XiO and the Monte Carlo algorithm used on Monaco is XVMC. Transmission measurements were taken using a narrow‐beam geometry to determine the mass attenuation coefficient of nylon = 0.0458 cm2/g and for a water‐equivalent RW3 phantom, it was 0.0465 cm2/g. The perturbation effects of the prosthesis on dose distributions were investigated by measuring and comparing dose maps and profiles. The magnitude of dose perturbations was quantified by calculating dose enhancement and reduction factors using field sizes of 3 × 3, 5 × 5, 10 × 10, and 15 × 15 cm2. For the studied beams and field sizes, dose enhancements between 21 and 30% and dose reductions between 15 and 21% were observed at the nylon‐prosthesis interface on the proximal and distal sides of the prosthesis for film measurements. The dose escalation increases with beam energy, and the dose reduction due to attenuation decreases with increasing beam energy when compared to unattenuated beam data. A comparison of film and XiO depth doses for the studied fields gave relative errors between 1.1 and 23.2% at the proximal and distal interfaces of the Ti prosthesis. Also, relative errors < 4.0% were obtained between film and Monaco dose data outside the prosthesis for 6 and 15 MV lateral opposing fields.

Dose shadowing and prosthesis involvement for megavoltage photon In vivo diode dosimetry

“…The enhanced dose then tends to counteract the dose shadow underneath the diode; (3) Figure 4a and b also show that the backscatter dose at the proximal nylon-prosthesis interface in reduced when using a diode in the photon fields compared to the case without a diode. This could be attributed to the attenuation effect of the diode which reduces the primary photon radiation reaching the interface before being backscattered, as it was observed in our previous study that the backscatter dose increased with increase in photon energy;[22] (4) the attenuation effect of the in vivo diode and prosthesis involvement shows a small dependence on field size where the dose shadow increases with decreasing field size except for the 6 MV beam for non-prosthetic fields where the dose attenuation increases from a 10 cm × 10 cm field to a 5 cm × 5 cm field, and then decreases again for a 2 cm × 2 cm field.…”

“…Due to the relatively weak energy dependence of Gafchromic EBT3 films over a broad range of beam qualities and modalities used clinically in the megavoltage photon and electron energy range, film calibrations were performed in a 10 MV beam in a similar procedure as reported by Ade and du Plessis. [22] A rational function of the type:…”

Gel and thermoluminescence dosimetry for dose verifications of a real anatomy simulated prostate conformal radiation treatment in the presence of metallic femoral prosthesis

“… 6 , 25 Third, miscalculations of the dose calculation algorithm version. 5 Using a newer TPS algorithm would reduce the dose miscalculations. However, the other uncertainties would still be present in the study.…”

“…A considerable number of patients requiring radiotherapy for prostate cancer have one or two hip prostheses, 1 , 2 , 3 , 4 , 5 which distorts the prostate region dose distribution due to the increased beam attenuation. It also increases the dose at the bone–metal interface due to scattered electrons.…”

VMAT Optimization and Dose Calculation in the Presence of Metallic Hip Prostheses

“…However, when planning in regions near metal hip prostheses, the CCCS algorithm fails to accurately calculate dose. Ade and du Plessis 9 showed errors of up to 23.2% when using the CCCS algorithm in the XiO Treatment Planning System (ELEKTA, Stockholm, Sweden). The Pinnacle Treatment Planning System (Philips, Fitchburg, Wisconsin) also utilizes CCCS for its dose calculation methods.…”