Lexicographic ordering: intuitive multicriteria optimization for IMRT

Optimization problems in IMRT inverse planning are inherently multicriterial since they involve multiple planning goals for targets and their neighbouring critical tissue structures. Clinical decisions are generally required, based on tradeoffs among these goals. Since the tradeoffs cannot be quantitatively determined prior to optimization, the decision-making process is usually indirect and iterative, requiring many repetitive optimizations. This situation becomes even more challenging for cases with a large number of planning goals. To address this challenge, a multicriteria optimization strategy called lexicographic ordering (LO) has been implemented and evaluated for IMRT planning. The LO approach is a hierarchical method in which the planning goals are categorized into different priority levels and a sequence of sub-optimization problems is solved in order of priority. This prioritization concept is demonstrated using two clinical cases (a simple prostate case and a relatively complex head and neck case). In addition, a unique feature of LO in a decision support role is discussed. We demonstrate that a comprehensive list of planning goals (e.g., ∼23 for the head and neck case) can be optimized using only a few priority levels. Tradeoffs between different levels have been successfully prohibited using the LO method, making the large size problem representations simpler and more manageable. Optimization time needed for each level was practical, ranging from ∼26 s to ∼217 s. Using prioritization, the LO approach mimics the mental process often used by physicians as they make decisions handling the various conflicting planning goals. This method produces encouraging results for difficult IMRT planning cases in a highly intuitive manner.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58100/2/pmb7_7_006.pd

Source placement error for permanent implant of the prostate

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134896/1/mp8058.pd

Calibration and quality assurance for rounded leaf‐end MLC systems

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134970/1/mp3517.pd

Dose reconstruction in deforming lung anatomy: Dose grid size effects and clinical implications

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135133/1/mp9749.pd

How extensive of a 4D dataset is needed to estimate cumulative dose distribution plan evaluation metrics in conformal lung therapy?a)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134757/1/mp0624.pd

Monte Carlo-based lung cancer treatment planning incorporating PET-defined target volumes

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135172/1/acm20065.pd

Quantumâ inspired algorithm for radiotherapy planning optimization

Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/153600/1/mp13840.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/153600/2/mp13840_am.pd

The influence of beam model differences in the comparison of dose calculation algorithms for lung cancer treatment planning

In this study, we show that beam model differences play an important role in the comparison of dose calculated with various algorithms for lung cancer treatment planning. These differences may impact the accurate correlation of dose with clinical outcome. To accomplish this, we modified the beam model penumbral parameters in an equivalent path length (EPL) algorithm and subsequently compared the EPL doses with those generated with Monte Carlo (MC). A single AP beam was used for beam fitting. Two different beam models were generated for EPL calculations: (1) initial beam model (init_fit) and (2) optimized beam model (best_fit), with parameters optimized to produce the best agreement with MC calculated profiles at several depths in a water phantom. For the 6 MV, AP beam, EPL(init_fit) calculations were on average within 2%/2 mm (1.4 mm max.) agreement with MC; the agreement for EPL(best_fit) was 2%/0.5 mm (1.0 mm max.). For the 15 MV, AP beam, average agreements with MC were 5%/2 mm (7.4%/2.6 mm max.) for EPL(init_fit) and 2%/1.0 mm (1.3 mm max.) for EPL(best_fit). Treatment planning was performed using a realistic lung phantom using 6 and 15 MV photons. In all homogeneous phantom plans, EPL(best_fit) calculations were in better agreement with MC. In the heterogeneous 6 MV plan, differences between EPL(best_fit and init_fit) and MC were significant for the tumour. The EPL(init_fit), unlike the EPL(best_fit) calculation, showed large differences in the lung relative to MC. For the 15 MV heterogeneous plan, clinically important differences were found between EPL(best_fit or init_fit) and MC for tumour and lung, suggesting that the algorithmic difference in inhomogeneous tissues was most influential in this case. Finally, an example is presented for a 6 MV conformal clinical treatment plan. In both homogeneous and heterogeneous cases, differences between EPL(best_fit) and MC for lung tissues were smaller compared to those between EPL(init_fit) and MC. Although the extent to which beam model differences impact the dose comparisons will be dependent upon beam parameters (orientation, field size and energy), and the size and location of the tumour, this study shows that failing to correctly account for beam model differences will lead to biased comparisons between dose algorithms. This may ultimately hinder our ability to accurately correlate dose with clinical outcome.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/48983/2/pmb5_5_006.pd

Magnetic confinement of radiotherapy beam-dose profiles

We have used electron and photon beams from the 50 MV electron microtron at UM Hospital together with a large-bore 3.5T superconducting solenoid to demonstrate the magnetic confinement of HE electron and photon beam-dose profiles for typical radiotherapy beams. The HE electron beams in particular exhibit a large reduction in penumbra when entering a tissue-equivalent phantom and, in addition, confinement of the secondary electrons produced by the primary beam. Likewise photon beams show a similar confinement of the dose from secondary electrons. While the results resemble features predicted from Monte Carlo calculations, there are a number of anomalous details in the actual experimental data which serve to illustrate the problems associated with practical clinical implementations. However the data suggest that in certain cases HE electrons may provide a cost-effective alternate to proton or HI radiotherapy beams and, also, improve the dose profile for HE photon beams. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87615/2/44_1.pd