Ocean Gateways and Glaciation: Planktic Foraminiferal Records from the Southern Ocean, Equatorial Pacific, and Caribbean

Ocean gateway changes, once the best mechanism for driving abrupt climatic change, have fallen from favor. They have been largely replaced within the literature by changes in CO2 concentration and orbital forcing. This dissertation looks at three intervals of relative stability (Oligocene), prolonged change (Plio-Pleistocene), or transient events (Oligocene/Miocene boundary) in order to better understand the oceanographic circumstances which govern ‘events’ in the paleoceanographic record. Chapter 1 discusses the chronostratigraphy of Integrated Ocean Drilling Program (IODP) Site U1396 (Expedition 340) in the Caribbean Sea. A combination of paleomagnetostratigraphy, biostratigraphy, astrochronology, and correlation to Marine Isotope Stages (MIS) allows a high-resolution age model to be constructed. Sedimentation rates are calculated for the paleomagnetic and MIS age models, and with and without volcanic sediments. The findings agree with shipboard determination of slowing sedimentation toward the present, and suggest either increased winnowing due to bottom-water flow or changes in productivity altering the biotic flux at the site. Chapter 2 reexamines the Oligocene at Ocean Drilling Project (ODP) Sites 803 and 628 with revised taxonomic concepts. There are disagreements between the global compilations of macroevolutionary rates and the rates calculated at Site 803, though several hypotheses are discussed to explain the findings. A series of illustrations are presented to aid in taxonomic identification through this difficult interval. Chapter 3 focuses on the Mi-1 event, discussing several new records: Deep Sea Drilling Program Site 78, ODP Site 803 (both equatorial Pacific Ocean), and ODP Site 744 (southern Kerguelen Plateau). After reviewing the leading hypotheses for Mi-1, the three new sites are used to test the paleoproductivity hypothesis, and use those records to investigate the importance of different orbital parameters. Lastly, the foram fragmentation index is employed to examine changes in the lysocline at the sites, demonstrating that there are dramatic global changes in the lysocline throughout the leadup to Mi-1. While carbonate sequestering carbon through the lysocline changes (or infact deepening Calcite Compensation Depth) cannot explain abrupt cooling events on their own (e.g., Coxall et al., 2005), a narrative discussion of the leadup to Mi-1 puts the lysocline changes in context with findings at other sites

Summary and recommendations of a National Cancer Institute workshop on issues limiting the clinical use of Monte Carlo dose calculation algorithms for megavoltage external beam radiation therapy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135029/1/mp6990.pd

A dose‐gradient analysis tool for IMRT QA

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135372/1/acm20062.pd

Comment on “Dosimetric evaluations of the interplay effect in respiratory‐gated intensity‐modulated radiation therapy” [Med. Phys. 36, 893–903 (2009)]

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134968/1/mp2483.pd

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

Inverse plan optimization accounting for random geometric uncertainties with a multiple instance geometry approximation (MIGA)

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135142/1/mp1016.pd

Long-Term Results of Conservative Surgery and Radiotherapy for Ductal Carcinoma In Situ Using Lung Density Correction: The University of Michigan Experience

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72520/1/j.1524-4741.2007.00447.x.pd

Penalization of aperture complexity in inversely planned volumetric modulated arc therapy

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/134774/1/mp2566.pd

Dosimetric comparison of extended dose range film with ionization measurements in water and lung equivalent heterogeneous media exposed to megavoltage photons

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135483/1/acm20025.pd