Room: Exhibit Hall | Forum 4
Purpose: DMBT tandem applicator has six symmetric peripheral grooves (1.4mm) made from non-magnetic tungsten alloy rod (18g/cc) (Figure1a-c), with an exceptional capability to modulate dose with directionality for the treatment of cervical cancer. In this research, the dose distributions of the DMBT tandem is calculated with the Oncentra Brachy Advanced Collapsed Cone Engine(ACE) treatment planning system(TPS) and validated against MC calculations.
Methods: The first ever 3D model of the DMBT applicator is built on the Oncentra Brachy TPS (Figure1a). Then, a two-level dosimetric validation was performed. First, the Ir-192 source(msHDR-v2) was placed inside a conventional tandem in an infinite water medium. Second, the Ir-192 source was placed inside the DMBT tandem in an infinite water medium. Dose calculations were performed by the ACE and MCNP MC code independently and compared.
Results: The overlapping isodose lines generated by the ACE and MCNP for the first scenario are shown in Figures1d-g. Dose distribution is normalized to the point at 10mm distance from the DMBT central axis. The agreement was excellent with deviations<1.5% for the high dose region (>10%), and <3% for the low dose region(<10%). The overlapping isodose lines generated by the ACE and MCNP for the second scenario are shown in Figures.1h-k. As can be seen, the visual agreement is excellent and reflected in the overall deviations<3.2%. At isodose lines<10%, the visual disagreement were more observable with having some â€œripple-effectâ€? shown by the ACE algorithm. This is attributed to the â€œray-effectâ€? of the collapsed cone approach generated from the multiple scatter kernels. In the high dose region, however, the deviations were<2%.
Conclusion: The ACE algorithm is capable of accurately and successfully calculating dose distributions of complex-shaped high-density metal-alloy applicators such as the DMBT tandem with agreements generally achieved within <2% for the high dose region and <5% for the low dose region.