The use of directional interstitial sources to improve dosimetry in breast brachytherapy
(a) Microscopic transverse plane cross section across the source axis. (b) MCNP4C3 generated longitudinal cross section across the gold shield and along the source axis of the first directional source. (c) Cross section across the source axis from (b). Legend for (b): gold shield (between the film and the nylon filament); nylon filament for carrying the radionuclide (inner cylinder); coating (outer cylinder); air space; thin film (behind the gold shield).
(a) Monte Carlo simulated isodose contours from 2 to 20 Gy per 2 Gy on the transverse plane across the source axis for the directional source. (b) The 5 Gy isodose surface of the simulated dose deposition for the directional source with strength of 0.43 mCi (0.546 U) through complete decay. The axis is parallel to the shield, the axis is perpendicular to the shield, and the axis corresponds to the long axis of the directional source.
(a) Isodose and ROI plots for the conventional HDR implant from the Nucletron HDR optimization (a) and the directional LDR implant from this work’s in-house MatLab program (b) on a CT image with target (thick lines in both (a) and (b)) and seroma contours (thin line in (a) only). Directional source orientations may be inferred from the isodose line at the grid positions. For example, the source is shielded toward the skin at location D10 but toward breast tissues at E9 and F8.
Dose volume histograms for the tumor target for: (a) the conventional HDR implant and (b) the directional LDR implant. The and doses are marked with arrows at 34 and 102 Gy for HDR and 45 and 135 Gy for LDR implants.
(a) Dose rate constant, (b) anisotropy function , and (c) radial dose function of the Best 2301 conventional source. In (d), is the directional source’s radial dose function at distance in the azimuthal angle , where , , and are in the unshielded, along the shield, and the shielded sides, respectively.
Corresponding doses of the LDR implant of 45 Gy in 108 h and HDR implant of 34 Gy delivered in ten fractions that have the same late reactions.
A comparison of skin area or dose volumes exposure for the directional LDR (45 Gy in 108 h) and the conventional HDR (34 Gy in ten fractions) plans relating the same percent physical (rows 1 and 2) or biological (rows 1 and 3) dose. is the absolute volume of the ipsilateral breast receiving at least percent of the prescribed dose, and is the absolute skin surface area receiving at least percent of the prescribed dose.
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