An adsorption chromatography assay to probe bulk particle transport through hydrogels

Biopolymer-based hydrogels such as mucus and the basal lamina play a key role in biology, where they control the exchange of material between different compartments. They also pose a barrier that needs to be overcome for successful drug delivery. Characterizing the permeability properties of such hydrogels is mandatory for the development of suitable drug delivery vectors and pharmaceutics. Here, we present an experimental method to measure bulk particle transport through hydrogels. We validate our assay by applying it to mucin hydrogels and show that the permeability properties of these mucin hydrogels can be modulated by polymer density and pH, in agreement with previous results obtained from single particle tracking. The method we present here is easy to handle, inexpensive, and high-throughput compatible. It is also a suitable platform for the design and screening of drugs that aim at modifying the barrier properties of hydrogels. This system can also aid in the characterization and development of synthetic gels for a range of biomedical applications.

Confidence limit variation for a single IMRT system following the TG119 protocol

PURPOSE

To evaluate the robustness of TG119-based quality assurance metrics for an IMRT system.

METHODS

Four planners constructed treatment plans for the five IMRT test cases described in TG119. All plans were delivered to a 30 cm x 30 cm x 15 cm solid water phantom in one treatment session in order to minimize session-dependent variation from phantom setup, film quality, machine performance, etc. Composite measurements utilized film and an ionization chamber. Per-field measurements were collected using a diode array device at an effective depth of 5 cm. All data collected were analyzed using the TG119 specifications to determine the confidence limit values for each planner separately and then compared.

RESULTS

The mean variance of ion chamber measurements for each planner was within 1.7% of the planned dose. The resulting confidence limits were 3.13%, 1.98%, 3.65%, and 4.39%. Confidence limit values determined by composite film analysis were 8.06%, 13.4%, 9.30%, and 16.5%. Confidence limits from per-field measurements were 1.55%, 0.00%, 0.00%, and 2.89%.

CONCLUSIONS

For a single IMRT system, the accuracy assessment provided by TG119-based quality assurance metrics showed significant variations in the confidence limits between planners across all composite and per-field evaluations. This observed variation is likely due to the different levels of modulation between each planner's set of plans. Performing the TG119 evaluation using plans produced by a single planner may not provide an adequate estimation of IMRT system accuracy.