Controlled mold geometry for surgical deficit treatment planning

Area of Science:

• Oncology
• Medical Physics
• Surgical Technology

Background:

• Stereotactic frames enable precise brachytherapy in the brain due to fixed cranial geometry.
• Similar precision is challenging in other anatomical sites lacking fixed geometry.
• Rigid molds inserted into surgical defects offer a potential solution for localized brachytherapy.

Purpose of the Study:

• To develop and validate a technique for precise brachytherapy seed placement in surgical defects using a custom mold.
• To adapt stereotactic principles for non-cranial brachytherapy applications.
• To improve radiation delivery accuracy for recurrent cancers in challenging locations.

Main Methods:

• A custom acrylic mold is created for the surgical defect and embedded in a dental stone cast within an aluminum box.
• Three reference markers are created in the mold using a ball mill, with their precise locations determined via computed tomography (CT).
• Brachytherapy seed (125I) catheter positions are planned in CT coordinates and transformed to mill coordinates for accurate drilling into the mold.

Main Results:

• The technique allows for precise transformation of CT-based treatment plans to the physical mold coordinates.
• The method was successfully applied to treat recurrent maxillary cancer and recurrent orbital rhabdomyosarcoma.
• The described method enables accurate and reproducible placement of brachytherapy sources in non-cranial surgical defects.

Conclusions:

• This mold-based technique provides a viable method for precise brachytherapy in surgically created defects outside the brain.
• It overcomes the limitations of fixed geometry in non-cranial sites, enhancing treatment accuracy.
• The technique offers a valuable approach for delivering targeted internal radiation therapy in complex oncological cases.