arXiv subjects

Christian Velten

Publications and source records attributed to Christian Velten.

3 recordsLinked to original sources

arXiv2025

A primer on treatment planning aspects for temporally modulated pulsed radiation therapy

Temporally modulated pulsed radiotherapy (TMPRT) delivers conventional fraction doses of radiation using temporally separated pulses of low doses (<30 cGy) yielding fraction-effective dose rates of around 6.7 cGy/min with the goal to exploit tumor radiation hypersensitivity, which was observed in both, preclinical models and in human clinical trials. To facilitate TMPRT, volumetric modulated arc therapy (VMAT) and 3D-CRT planning techniques were developed following the guidelines of the proposed NRG CC-017 trial. Plans were evaluated with respect to homogeneity, conformality, and adherence to dose constraints. Deliverability of plans was assessed using in-phantom measurements for absorbed dose accuracy at low dose rates and using EPID for isodose verification. For VMAT only single arc plans were found to be acceptable due to otherwise unacceptably heterogeneous field doses, while for dynamic conformal arcs machine limtations on the number of monitor units per degree require the use of partial arcs for each pulse. Delivery of plans at low dose rates (< 100 MU/min) was accurate with high Gamma pass rates on modern LINACs and moderate pass rates on legacy LINACs, in line with their general performance. Generally, VMAT is preferred to achieve optimal homogeneity, conformality, and organ-at-risk sparing, while the use of 3D-CRT can increase the availability of TMPRT for more patients and clinics.

physics.med-ph↗

arXiv2023

Multi-compartmental modeling for Gd-EOB-DTPA using sparse human DCE-MRI data

Purpose: To derive kinetic equations for multi-compartmental contrast agent distribution from first principles and apply it to two and three compartments for Gd-EOB-DTPA using low time resolution human liver DCE-MRI data. Methods: The continuity and diffusion equation were combined and used to derive a general form for differential equations governing multi-compartmental particle exchange. They were applied to two (equivalent to the Tofts model) and three compartments. Both models were fit to human DCE-MRI data with low temporal resolution and three compartment model's parameters' implications are discussed. Results: The model derived for two compartments is shown to be equivalent with the Tofts model. Using reasonable biological and physical assumptions an analytical solution for the three compartment model is obtained. The three compartment model was able to fit all Gd-EOB-DTPA DCE-MRI data whereas the Tofts model did not. Differences were increased for cases with large as well as rapid uptake of contrast. Conclusion: We demonstrated the ability to fit sparse Gd-EOB-DTPA DCE-MRI data using a three compartment model derived from first principles whose parameters can be used to help quantify overall and regional liver function.

physics.med-ph↗

arXiv2023

Radiosensitization beyond DNA damage: Monte Carlo simulations of realistic nanomaterial biodistributions

We investigated cellular distribution of a tumor-specific gadolinium chelate in 4T1 and U87 cancer cells with the goal to generate more realistic geometries for Monte Carlo simulations of radiation interaction with nanoparticles in cells. Cells were exposed to the agent in-vitro for 30 minutes to 72 hours before being fixed and imaged using transmission electron microscopy. Initially, electron-dense areas consistent with gadolinium were observable throughout the cytoplasm. At six hours those areas were restricted to endosomes and at 24 hours or longer electron dense areas were only found in lysosomes. Lysosomes were on average larger in 4T1 cells, which were exposed to 1 mM concentration compared to U87 cells, exposed to 1 uM. Based on this information we built an extended cell model for Monte Carlo simulations that includes lysosomes with discrete nanoparticle enclaves in addition to mitochondria and the nucleus.

physics.med-ph↗