Purpose: To evaluate plan qualities with a modified TG43 dose calculation algorithm for the six channel non-magnetic tungsten-alloy direction modulation brachytherapy (DMBT) tandem applicator in image-guided cervical cancer brachytherapy.
Methods: The H-factor, that is the ratio of the 3D full Monte Carlo (FMC) dose calculation of the DMBT tandem combined with 192Ir source in tandem (off) centre over the 192Ir-TG43 dose at the same dwell position (DP), is used as part of brachytherapy inverse optimization planning to generate the optimal plans for 10 clinical cases from the EMBRACE patient dataset which were treated with conventional Tandem-and-ring (T&R) applicators. First, the DMBT tandem-and-ring (DMBT&R) plans utilizing cumulative superposition MC (SMC) dose calculations from multiplication of the Central H-factor and 192Ir-TG43 dose matrix (DMBT.CH&R) for all possible longitudinal tandem DPs were calculated. Then the DMBT&R plans corresponding to the multiplications of the FMC dose simulations for Exact (non-centre) H-factor equivalent to each individual DPs (DMBT.EH&R) where calculated. All scenario were compared with the clinical T&R plans.
Results: In general, the CTVHR D90, D98, and V100 differences were insignificant (p<0.02) between all plans, when T&R replaced with DMBT&R, and ring left untouched. The CTVHR D10 deviations were significant (P<0.02) between DMBT.CH&R and T&R plans. The D2cm3 OARs were significantly (p<0.05) improved between DMBT.CH&R (DMBT.EH&R) and T&R plans with average D2cm3 dose reductions of 6.02, 8.35, and 4.31% (5.92, 8.36, and 4.09%) for bladder, rectum, and sigmoid, respectively. While the corresponding values were insignificant (p<0.5) between DMBT.CH&R and DMBT.EH&R plans.
Conclusion: In this research, a new framework with single H-factor was introduced to the modified TG43 dose calculation formulism for DMBT tandem applicator. This inexpensive framework can be used as part of any standard TG43 planning system for accurate dose calculation of the shielded applicators.
Not Applicable / None Entered.