Physics aspects of the Papillon technique-Five decades later

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• The Papillon technique, utilizing 50-kVp soft X-rays for rectal adenocarcinoma, was developed in the 1960s.
• Recent advancements include new 50-kVp systems, prompting re-evaluation of the technique's dosimetry and clinical implementation.
• The introduction of a plastic lid for rectal applicators is investigated for its impact on dose delivery accuracy and reproducibility.

Purpose of the Study:

• To evaluate the dosimetric impact of a plastic lid on a 50-kVp electronic brachytherapy system for rectal adenocarcinoma treatment.
• To compare beam characteristics (HVLs, output, PDDs, profiles) of the Xoft eBT rectal applicator with and without a plastic lid.
• To address and clarify misconceptions regarding radiochromic film dosimetry for low-energy photon beams.

Main Methods:

• Utilized parallel-plate chamber and radiochromic film dosimeters for measurements.
• Characterized beam properties including half-value layers (HVLs), output, percent depth doses (PDDs), and beam profiles.
• Compared dosimetry data between the Xoft Electronic Brachytherapy rectal applicator system with and without the plastic lid.

Main Results:

• The applicator with the plastic lid produced a slightly harder beam quality (1.4 vs. 1.3 mm Al HVL).
• A reduction in output by 33% was observed with the plastic lid.
• The beam profile remained acceptably flat (≤3%) and symmetric (≤2%) with the lid.

Conclusions:

• The plastic lid modifies beam properties, offering a harder beam but reduced output.
• Accurate dosimetry is crucial for reproducible dose delivery in Papillon technique applications.
• Clarification of radiochromic film use in low-energy photon dosimetry is provided.