SU‐DD‐A2‐01: The Utility of Depth Dose Modulation (DDM) for Electronic Brachytherapy

Abstract

Purpose: To illustrate the utility of Depth Dose Modulation (DDM) for Ir‐192, Electronic Brachytherapy (EB) and EBDDM. Method and Materials: A numerical model was created for a miniature x‐ray source equipped with an adjustable collimator that produces a fan‐beam distribution. A general‐purpose multi‐particle transport code was used to calculate the dose distribution for multiple collimator gaps. A software program superimposed the collimated dose images at intervals to build an overall dose distribution for a simulated micro‐stepping treatment. TG‐43 data were input to the Nucletron PLATO treatment planning system. Treatment plans were generated for breast, endometrial and lung cases; doses to target volumes and normal tissues were compared for each of the planning sources. Results: For the breast case, PTV coverage for Ir‐192, EB and EBDDM plans was 96, 100 and 94% with maximum skin doses of 100, 97 and 89% respectively. For the endometrial case, PTV coverage for the Ir‐192, EB and EBDDM plans was 99, 100 and 77% with maximum rectal doses of 140, 127 and 105% and bladder doses 115, 111 and 87% respectively. For equivalent prescription point doses in lung, with Ir‐192, EB and EBDDM, the maximum rib dose was 43, 30 and 34% while V50Lung was 11, 8 and 7% respectively. Conclusions: With intracavity breast cases, DDM is a useful tool, reducing Ir‐192 skin dose by up to 11% while maintaining adequate target coverage. For endometrial treatments, however, EBDDM target coverage is inadequate; because of collimated source anisotropy, there is little dose deposition superiorly. To achieve full target coverage while maintaining significant normal tissue sparing, a treatment would require a combination of EB and EBDDM. For lung, EBDDM allows a two‐fold reduction in V50Lung. Conflict of Interest: Partial financial support provided by Xoft, Inc.