22 research outputs found
Rydberg-atom trajectories in a ponderomotive optical lattice
Using semiclassical simulations, we investigate the trajectories and the microwave spectra of Rydberg atoms excited in a ponderomotive optical lattice. We relate distinct features found in the microwave spectra to characteristic types of trajectory. Several methods are presented that are designed to greatly improve the trapping efficiency of the lattice and to generalize the trapping from one to three dimensions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/85435/1/njp10_11_113036.pd
The impact of a highâdefinition multileaf collimator for spine SBRT
PurposeAdvanced radiotherapy delivery systems designed for highâdose, highâprecision treatments often come equipped with highâdefinition multiâleaf collimators (HDâMLC) aimed at more finely shaping radiation dose to the target. In this work, we study the effect of a high definition MLC on spine stereotactic body radiation therapy (SBRT) treatment plan quality and plan deliverability.Methods and MaterialsSeventeen spine SBRT cases were planned with VMAT using a standard definition MLC (M120), HDâMLC, and HDâMLC with an added objective to reduce monitor units (MU). M120 plans were converted into plans deliverable on an HDâMLC using inâhouse software. Plan quality and plan deliverability as measured by portal dosimetry were compared among the three types of plans.ResultsOnly minor differences were noted in plan quality between the M120 and HDâMLC plans. Plans generated with the HDâMLC tended to have better spinal cord sparing (3% reduction in maximum cord dose). HDâMLC plans on average had 12% more MU and 55% greater modulation complexity as defined by an inâhouse metric. HDâMLC plans also had significantly degraded deliverability. Of the VMAT arcs measured, 94% had lower gamma passing metrics when using the HDâMLC.ConclusionModest improvements in plan quality were noted when switching from M120 to HDâMLC at the expense of significantly less accurate deliverability in some cases.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/139989/1/acm212197.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/139989/2/acm212197_am.pd
Impact of 90Y PET gradient-based tumor segmentation on voxel-level dosimetry in liver radioembolization
Abstract
Background
The purpose was to validate 90Y PET gradient-based tumor segmentation in phantoms and to evaluate the impact of the segmentation method on reported tumor absorbed dose (AD) and biological effective dose (BED) in 90Y microsphere radioembolization (RE) patients. A semi-automated gradient-based method was applied to phantoms and patient tumors on the 90Y PET with the initial bounding volume for gradient detection determined from a registered diagnostic CT or MR; this PET-based segmentation (PS) was compared with radiologist-defined morphologic segmentation (MS) on CT or MRI. AD and BED volume histogram metrics (D90, D70, mean) were calculated using both segmentations and concordance/correlations were investigated. Spatial concordance was assessed using Dice similarity coefficient (DSC) and mean distance to agreement (MDA). PS was repeated to assess intra-observer variability.
Results
In phantoms, PS demonstrated high accuracy in lesion volumes (within 15%), AD metrics (within 11%), high spatial concordance relative to morphologic segmentation (DSCâ>â0.86 and MDAââ0.99, MDAâ<â0.2 mm, AD/BED metrics within 2%). For patients (58 lesions), spatial concordance between PS and MS was degraded compared to in-phantom (average DSC = 0.54, average MDA = 4.8 mm); the average mean tumor AD was 226â±â153 and 197â±â138 Gy, respectively for PS and MS. For patient AD metrics, the best Pearson correlation (r) and concordance correlation coefficient (ccc) between segmentation methods was found for mean AD (râ=â0.94, cccâ=â0.92), but worsened as the metric approached the minimum dose (for D90, râ=â0.77, cccâ=â0.69); BED metrics exhibited a similar trend. Patient PS showed low intra-observer variability (average DSC = 0.81, average MDA = 2.2 mm, average AD/BED metrics within 3.0%).
Conclusions
90Y PET gradient-based segmentation led to accurate/robust results in phantoms, and showed high concordance with MS for reporting mean tumor AD/BED in patients. However, tumor coverage metrics such as D90 exhibited worse concordance between segmentation methods, highlighting the need to standardize segmentation methods when reporting AD/BED metrics from post-therapy 90Y PET. Estimated differences in reported AD/BED metrics due to segmentation method will be useful for interpreting RE dosimetry results in the literature including tumor response data.https://deepblue.lib.umich.edu/bitstream/2027.42/146544/1/40658_2018_Article_230.pd
SafetyNet: streamlining and automating QA in radiotherapy
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135420/1/acm20387-sup-0002.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135420/2/acm20387.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/135420/3/acm20387-sup-0003.pd
Improving treatment plan evaluation with automation
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135377/1/acm20016.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
Predicting deliverability of volumetricâmodulated arc therapy (VMAT) plans using aperture complexity analysis
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/135304/1/acm20124.pd