ODP638 Towards the development of treatment planning for microwave thermal ablation of adrenal adenomas
Authors: Cappiello Grazia , Farnan Richard , Rahmani George , Newell Caoimhe , Senanyake Russell , Gurnell Mark , O’Halloran Martin , Dennedy Michael Conall 
Published: November 2022

Primary aldosteronism (PA) is the principal cause of secondary hypertension and accounts for 5-12% of all hypertension. PA is characterized by unregulated aldosterone secretion from unilateral or bilateral nodules on the adrenal glands. High levels of aldosterone are associated with an increased risk of cardiovascular and cerebrovascular complications.

Conventional therapy includes adrenalectomy and mineralocorticoid receptor antagonists. These carry the challenges of surgical complication and poor tolerability to medication side effects. Moreover, no definitive therapy exists for bilateral PA driven by nodular disease. Microwave thermal ablation (MTA) offers a percutaneous alternative to adrenalectomy for PA and with precision engineering of microwave antennae may also offer a definitive option for bilateral PA. MTA can be applied to select and localize therapy to aldosterone producing adenomas while preserving the surrounding functional adrenocortical tissue. Advance treatment planning is essential to optimize the following parameters (i) microwave power delivery, (ii) probe placement, (iii) heat-sink minimisation.

We present a novel and state-of-the-art simulated treatment planning approach to adrenal MTA through 3D anatomic reconstruction and dielectric electromagnetic modeling to predict therapeutic response. MTA consists of a microwave applicator antenna to transfer the electromagnetic (EM) energy and induce cytotoxic hyperthermia. The EM power distribution across tissue is calculated by solving the Maxwell's equations. The Finite-Difference Time-Domain (FDTD) method computes the SAR (Specific Absorption Rate) patterns and the Pennes’ bio heat equation models the bioheat transfer within the adrenal gland. Treatment planning combines CT abdomen and 11C-metomidate PET/CT images to generate a 3D patient specific model using a segmentation routine in iSeg (version 3.1, Speag, Zurich, Switzerland)) which is combined with the applicator model in Sim4Life (version 6.2, Speag, Zurich, Switzerland). Electrical and thermal properties of the organ are assigned and the microwave power is modelled to optimally and selectively heat the target tissue while minimizing damage to adjacent cortical tissue.

We present results from 3D computational modelling derived from patient imaging-scans employed to predict the thermal ablation zone in patients affected by PA. Using this system, anatomically, dielectrically and thermally accurate models of adrenal glands, nodules and adjacent sensitive structures were reconstructed and energy delivery strategies were evaluated. This method was used to assess the ability to inform appropriate power settings and probe placement for ablating adrenal gland nodules. Treatment planning not only represents an important tool to precisely deliver controlled doses of microwave thermal therapy in the context of adrenal ablation but also represents an important tool to inform future applicator probe design and appropriate imaging.

Presentation: Sunday, June 12, 2022 12:30 p.m. - 2:30 p.m.