Purpose: A new rotatable tandem applicator for intensity modulated brachytherapy (IMBT) in intracavitary brachytherapy(ICR) was recently proposed. This work presents an integrated framework with rotatable tandem applicator and ovoid applicator by modifying dose deposition matrix and plan optimization algorithm.
Methods: The rotatable, single-channel tandem applicator enables for generating asymmetric dose distribution by rotating Ir-192 source in selected transverse direction. The previous work focused on plan optimization with tandem applicator only that constrains the number of source dwell points and activated rotational angles for enhancing delivery efficiency, while excluding ovoid applicator. To comprehend ovoid applicator in inverse planning, this work computed Monte-Carlo (MC) simulated dose distributions for 10 available dwell points belonging to ovoid applicator. Combining the dose information from tandem and ovoid applicators constructs dose deposition matrix for inverse planning. The optimization algorithm constrained the dwell points in tandem with group-wise in L2,1/2-norm and element-wise sparsity in approximated L0-norm to minimize number of activated angles and entire elements, while constraining the dwell points by element-wise sparsity only in ovoid applicator. The complete framework is validated by three clinical cases, compared against conventional ICR, and IMBT with tandem applicator.
Results: Integrated IMBT framework increased the number of dwell point by comprehending ovoid applicator, while it did not affect the number of dwell points and activated angles assigned to tandem applicator. Although IMBT with tandem enabling fluence-modulation spared critical organs relative to conventional ICR, insufficient geometric target coverage led to greater target volume exposed to high dose of radiation. IMBT with both tandem and ovoid applicators enhanced target volume homogeneity by optimizing dwell points in ovoid applicator, while maintaining enhanced dose sparing to critical organs.
Conclusion: IMBT with integrated framework was achieved by new dose deposition matrix and modified plan optimization algorithm, which yield superior dose sparing and target volume homogeneity simultaneously.