Degree
Doctor of Philosophy (PhD)
Department
Physics and Astronomy
Document Type
Dissertation
Abstract
Purpose: To incorporate photon beam energy, optimization objective refinement, and non-coplanar beam geometry as additional degrees of freedom into the treatment planning process in order to produce dose distributions superior to those achieved with current inverse-planned photon IMRT or VMAT.
Methods: To extend the optimization to include additional beam energies, an Elekta Versa HD linac was modeled in BEAMnrc/EGSnrc to simulate 2 MV, 4 MV, and 6 MV photon beams, complemented with measured data for 10 MV and 18 MV. A custom MATLAB-based framework was utilized to perform simultaneous energy-fluence optimization, enabling individual beamlets to be assigned independent energy weights. Twelve single-, dual-, triple-, and quadruple-energy IMRT/VMAT configurations were generated for thirteen prostate cancer patients. Plans were evaluated using dose-volume histograms, homogeneity index, conformity index, and organ-at-risk (OAR) dose metrics. To refine the optimization process, an in-house exhaustive a priori multi-criteria optimization (MCO) framework, employing a parameter-refinement strategy and high-performance computing (HPC), was developed and retrospectively applied to twelve prostate cancer patients, with resulting plans compared with original clinical and Monaco-MCO plans. To maximize the angular degrees of freedom available during optimization, the MCO approach was integrated with non-coplanar beam angle optimization (NCBAO-MCO). A sequential forward-selection BAO algorithm searched collision-feasible coplanar and non-coplanar beam candidates using HPC, with the MCO-derived dose objectives from the a priori parameter-refinement framework serving as the optimization criteria. In twelve prostate patients, original coplanar VMAT, coplanar MCO-VMAT, non-coplanar MCO-VMAT, and NCBAO-MCO IMRT plans were compared.
Results: Multi-energy IMRT/VMAT maintained target coverage and improved OAR sparing relative to 6 MV and 10 MV single-energy plans, particularly for the bladder and rectum; triple-energy IMRT and 6&18 MV dual-energy VMAT provided the most consistent reductions in OAR dose. With the exhaustive MCO framework, target coverage remained comparable across plans, and deliverability was preserved with no significant differences in gamma passing rate; the new-MCO significantly reduced OAR mean doses versus original plans, including bladder, rectum, femoral heads, and penile bulb. Compared with Monaco-MCO, new-MCO further reduced bladder, femoral head, and penile bulb doses, while the rectum dose showed a nonsignificant reduction. Monitor units (MU) increased relative to original plans but decreased relative to Monaco-MCO. With the BAO-MCO framework, both non-coplanar approaches significantly reduced bladder, rectum, and femoral head doses relative to original plans while preserving target coverage; the additional benefit beyond coplanar MCO was modest and most consistent for the femoral heads. NCBAO-MCO IMRT and non-coplanar MCO-VMAT showed comparable OAR sparing, with IMRT requiring fewer segments and lower MU.
Conclusions: The frameworks developed in this work, namely multi-energy fluence optimization, exhaustive a priori MCO, and integrated NCBAO-MCO, together offer a deterministic and reproducible approach for improving OAR sparing in prostate VMAT and IMRT planning without compromising target coverage or deliverability. Their flexible structure supports future extension to other disease sites, advanced treatment techniques, and automated or cloud-based planning workflows.
Date
10-12-2026
Recommended Citation
Rohani, Aliasghar, "Exploration of Novel Degrees of Freedom for Optimization in Photon-Based IMRT and VMAT Treatment Planning" (2026). LSU Doctoral Dissertations. 7207.
https://repository.lsu.edu/gradschool_dissertations/7207
Committee Chair
Zhang, Rui
LSU Acknowledgement
1
LSU Accessibility Acknowledgment
1