Technical Note: Dosimetry of Leipzig and Valencia applicators without the plastic cap

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• High dose rate (HDR) brachytherapy is common for skin lesions.
• Applicators often use a plastic cap to ensure electronic equilibrium and shield skin from secondary electrons.

Purpose of the Study:

• To investigate the dosimetric consequences of omitting the plastic cap during HDR brachytherapy fraction delivery.
• This impact has not been previously studied in the literature.

Main Methods:

• geant4 Monte Carlo simulations were used to model Leipzig and Valencia applicators.
• Simulations were performed with and without the plastic cap.
• Radiochromic film measurements validated the simulation results.

Main Results:

• Absence of the cap caused a 1500% dose increase within 1 mm of the skin for Leipzig applicators.
• A 180% dose increase was observed for Valencia applicators under the same conditions.
• Deeper than 1 mm, the dose increase diminished to approximately 10%.

Conclusions:

• Omitting the plastic cap leads to significant skin overdosage.
• Verification of cap placement before HDR skin treatments is crucial.
• Inclusion of cap verification in timeout checklists is recommended.