TH-AB-BRA-09: Radiation and Thermal Dosimetric Considerations of a Combination of Hyperthermia and Thermo-Brachytherapy Seeds

Authors


Abstract

Purpose:

A novel dual-modality thermo-brachytherapy (TB) seed invented by our group offers a potential means of adding hyperthermia to brachytherapy of prostate tumors, either simultaneously for dose enhancement or as a salvage therapy. To improve the minimum target temperature and temperature uniformity with this implant, we propose use of adjuvant hyperthermia-only (HT-only) seeds in unused spots within the needles used to implant the TB seeds. The impact on temperatures reached within the target, temperature uniformity, and the radiation interseed effect due to HT-only seeds were studied.

Methods:

Previous patient plans were reproduced in a Monte Carlo (MCNP5) model to generate dose distributions of TB seeds, with and without additional HT- only seeds. Temperature distributions for these simulated implants were obtained with the finite element analysis solver COMSOL Multiphysics. In-house software calculated dose-volume and temperature-volume histograms from these distributions.

Results:

Use of additional hyperthermia-only seeds substantially improves the temperature uniformity of the implant. The power generation required of the seeds for adequate temperature coverage (90% of the PTV heated to 42 °C) increases exponentially with the blood perfusion rate (BPR) of the implanted tissue, but decreases with an increase in the seeds’ Curie temperature. Large blood vessels within the target decrease the volume of the PTV reaching 42 °C by ≤7%. The temperature heterogeneity coefficient was found to vary linearly with the BPR. The interseed and scatter effect on radiation dose (beyond that of a standard LDR implant) due to non-radioactive HT-only seeds in the target was found to reduce D90 by <10% and D50 by <7%.

Conclusion:

Additional HT- only seeds are useful in improving the quality of hyperthermia delivered by TB seeds. For future application of these seeds in the clinic, addition of HT-only seeds is recommended, provided the planned D90 is adjusted to compensate for the incresed interseed effect.

This research is partially supported with NRC grant No. NRC-HQ-12-G-38-0042.

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