Room: AAPM ePoster Library
Multiple dwell (“multi-dwell”) positions can increase the viable treatment area of Leipzig-style applicators. Resultant dose distributions require model-based dose calculation algorithms (MBDCAs) to properly account for the tungsten and air features of the Leipzig-style applicator. The purpose of this work was to report the dwell times for our optimized multi-dwell plans and the associated increase in treatment area.
A commercial treatment planning system was used to model a Leipzig-style applicator and create three types of template plans based on the 90% isodose line (IDL) for a prescription of 6 Gy at 3 mm depth: template-1 uses the conventional single dwell at the center of the applicator, template-2 uses two dwells with one at the distal and another at the proximal end of the source channel, and template-3 uses a single-dwell positioned at the proximal end, followed by a 180° applicator rotation, and another single-dwell at the proximal end. To account for the non-water-equivalent geometry, an MBDCA was used to determine the dose distributions resulting from multiple dwell positions and/or applicator orientations. All dwell times were normalized to 10-Ci nominal activity.
Nominal 10-Ci activity dwell times were a single-dwell at 125.2 sec (template-1), two dwells at 76.6 sec each (template-2), or two dwells with different applicator orientations at 81.3 sec each (template-3). In-stem dimension of the 90% IDL increased from 9.4 mm in conventional single-dwell (template-1) to 16.6 mm (template-2) and 21.5 mm (template-3). Cross-plane coverage increased from 9.7 mm in conventional single-dwell (template-1) to 11.3 mm (template-2) and 12.0 mm (template-3).
The optimized template plans demonstrated significant increases in viable treatment area, with the prescription isodose line increasing up to 229% (124%) in-stem (cross-plane) compared against the conventional single-dwell technique. The template plans, after further validation, could eventually be considered by other clinics without a MBDCA.