Room: Exhibit Hall
Purpose: To compare plan quality achieved with the Yb169, Ir192, and Co60 HDR sources used in combination with conventional tandem-and-ring (Con.T&R)applicators for cervical cancer brachytherapy.
Methods: MCNP code was used to benchmark the Yb169, Ir192, and Co60 sources. Then, each source was placed inside the Con.T&R applicators and 3D dose matrix generated (1x1x1mm). The calculated 3D dose distributions were imported into an inverse optimization treatment planning algorithm to calculate optimal plans for 27 clinical cases treated with the Con.T&R-Ir192 source (ConT&R-Ir192). For re-plan optimizations, the Ir192 was replaced with the Yb169 and Co60 sources, individually. All plans with ConT&R-Yb169 or -Co60 were compared with the ConT&R-Ir192 plans as reference. All plans were normalized to receive the same HR-CTV D90. For HR-CTV, D98, D10, V100 and V200, and for OARs, bladder, rectum, and sigmoid D2cc were evaluated.
Results: In terms of HR-CTV coverage D90, D98, and V100 were nearly identical between all plans among the three sources. On average, D10 and V200 were lesser (5% and 2.5%) for Yb169 compared to Con.T&R-Ir-192 while these values were slightly greater (6% and 4.5%) for Co60. On average, Co60 generated less dose (2%) to OARs and Yb-169 source a little higher dose (1.4%) compared to the Ir-192 source. This is mostly because of the increase in scatter of the Yb169 source (93 keV) causing higher depth dose compared to Ir-192 (380 keV) and Co60 (1250 KeV). Specifically, the mean D2cc for bladder were 0.85% lower for Co60 and were 1.15% greater for Yb169. For rectum (Sigmoid), they were 2.3% (3%) lower for Co60 and were 1.3 (2.2%) higher for Yb169.
Conclusion: Best plans were generated with Co60, then Ir192, followed by Yb169, although the differences were minor (in D2cc) and all plans generally satisfied the ABS and GEC-ESTRO D2cc recommended limits.