Percentage depth dose evaluation in heterogeneous media using thermoluminescent dosimetry

Abstract

The purpose of this study is to investigate the influence of lung heterogeneity inside a soft tissue phantom on percentage depth dose (PDD). PDD curves were obtained experimentally using LiF:Mg,Ti (TLD‐100) thermoluminescent detectors and applying Eclipse treatment planning system algorithms Batho, modified Batho (M‐Batho or BMod), equivalent TAR (E‐TAR or EQTAR), and anisotropic analytical algorithm (AAA) for a 15 MV photon beam and field sizes of 1×1,.2em2×2,.2em5×5, and 10×10.2emcm2. Monte Carlo simulations were performed using the DOSRZnrc user code of EGSnrc. The experimental results agree with Monte Carlo simulations for all irradiation field sizes. Comparisons with Monte Carlo calculations show that the AAA algorithm provides the best simulations of PDD curves for all field sizes investigated. However, even this algorithm cannot accurately predict PDD values in the lung for field sizes of 1×1 and 2×2.2emcm2. An overdosage in the lung of about 40% and 20% is calculated by the AAA algorithm close to the interface soft tissue/lung for 1×1 and 2×2.2emcm2 field sizes, respectively. It was demonstrated that differences of 100% between Monte Carlo results and the algorithms Batho, modified Batho, and equivalent TAR responses may exist inside the lung region for the 1×1.2emcm2 field.PACS number: 87.55.kd

A Monte Carlo approach to lung dose calculation in small fields used in intensity modulated radiation therapy and stereotactic body radiation therapy

“…[17] In a similar study by da Rosa et al, they compared the accuracy of different inhomogeneity correction methods in a lung phantom. [13] Analyzing their pertinent data on the MC and the curves without correction revealed that the dose reduction inside the lung at the depth 10 cm (the comparable depth with our results, 5 cm distance from interface) was 50% and 90% respectively for 2 cm × 2 cm and 1 cm × 1 cm field sizes respectively for 15 MV photon beam. Comparing to our results of 46% and 70% for the same field sizes, the differences were acceptable with consideration of differences in used MC code, geometries, and photon beams energies.…”

“…While, the other algorithms were not capable to predict the lung dose accurately in the conditions of electronic disequilibrium with high energy photons. [3,13,14] Otherwise, the presence of small sold lung tumor would make more difficult situation for TPSs to predict the dose inside the tumor. To address these issues we planned a MC study for depth dose variations in the lung with and without a small tumor resembling the situations occur in IMRT of lung tumors.…”

Dosimetric evaluation of Acuros XB Advanced Dose Calculation algorithm in heterogeneous media

“…by van Esch [4], Fogliata [2], daRosa [5]. Results showed that accuracy significantly depends on energy, field size, and density of the materials.…”

Impact of the calculation resolution of AAA for small fields and RapidArc treatment plans

“…The dosimetric accuracy of complex RapidArc plans which are associated with more small MLC segments was also investigated. As the accuracy of AAA is expected to decrease in low density media, 8,18 we also compared dose calculations for a typical RapidArc plan for lung stereotactic body radiotherapy (SBRT) with measurements in different heterogeneous phantoms, and evaluated the actual dosimetric implications.…”