Influence of breast composition and interseed attenuation in dose calculations for post-implant assessment of permanent breast¹⁰³Pd seed implant

Abstract

The impact of tissue heterogeneity and interseed attenuation is studied in post-implant evaluation of five clinical permanent breast (103)Pd seed implants using the Monte Carlo (MC) dose calculation method. Dose metrics for the target (PTV) as well as an organ at risk (skin) are used to visualize the differences between a TG43-like MC method and more accurate MC methods capable of considering the breast tissue heterogeneity as well as the interseed attenuation. PTV dose is reduced when using a breast tissue model instead of water in MC calculations while the dose to the skin is increased. Furthermore, we investigate the effect of varying the glandular/adipose proportion of the breast tissue on dose distributions. The dose to the PTV (skin) decreases (increases) with the increasing adipose proportion inside the breast. In a complete geometry and compared to a TG43-like situation, the average PTV D(90) reduction varies from 3.9% in a glandular breast to 35.5% when the breast consists entirely of adipose. The skin D(10) increases by 28.2% in an entirely adipose breast. The results of this work show the importance of an accurate and patient-dependent breast tissue model to be used in the dosimetry for this kind of low energy implant.

The difference of scoring dose to water or tissues in Monte Carlo dose calculations for low energy brachytherapy photon sources

“…In addition, D w,w is also shown ͑obtained when all voxels are water͒. The decrease of D 90 when going from D w,w to D m,m is consistent with the literature, 3 which reports D m,m . Scoring D w,m reverses this trend and results in increased D 90 values.…”

Review of clinical brachytherapy uncertainties: Analysis guidelines of GEC-ESTRO and the AAPM

“…This is followed by uncertainty in the composition of adipose and mammary gland tissue, leading to a 10% variation in D 90 , and the use of breast density from CT data, resulting in a 4% increase in D 90 on average. In view of the above, the authors state that for breast cases tissue composition effects overshadow the ISA effect reported to correspond to a 3% decrease of D 90 [30].…”

Prospects for in vivo estimation of photon linear attenuation coefficients using postprocessing dual‐energy CT imaging on a commercial scanner: Comparison of analytic and polyenergetic statistical reconstruction algorithms

“…For example, neglecting tissue composition differences in low energy Pd-103 and I-125 permanent seed implants of the breast and prostate have been shown to lead to errors in dose-volume histogram (DVH) metrics used for prescription and plan assessment ranging from 8% to 40%. [3][4][5][6] Even higher energy brachytherapy sources, such as Ir-192 and Yb-169, have been shown to suffer from dose calculation errors on the order of 5%-30% when neglecting patient-specific tissue composition and geometry. 7,8 Recommended bulk tissue compositions 9 are derived from a handful of measurements that exhibit large sample-tosample variability.…”