Matching intraoperative electron-beam fields: dosimetric and clinical considerations

Area of Science:

• Radiation Oncology
• Medical Physics
• Dosimetry

Background:

• Intraoperative electron fields are used for large or irregular tumors.
• Matching these fields poses dosimetric challenges due to diverging isodose curves.
• Improper matching can lead to suboptimal tumor coverage or normal tissue damage.

Purpose of the Study:

• To investigate the dosimetry of gapped, adjacent, and overlapped intraoperative electron fields.
• To present optimal methods for matching rectangular intraoperative electron fields.
• To minimize dosimetric discrepancies in intraoperative radiation therapy.

Main Methods:

• Utilized film densitometry to analyze dosimetry.
• Examined 8 x 9 cm2 rectangular fields for 9 to 18 MeV electrons.
• Evaluated gapped, adjacent, and overlapped field configurations.

Main Results:

• Identified dosimetric problems associated with field matching at depth and surface.
• Diverging isodose curves create critical low- and high-dose regions.
• Determined specific techniques for ideal field matching.

Conclusions:

• A 2-mm gap with surface bolus is recommended for adjacent fields.
• A tenth-value layer shaped lead cutout is proposed for overlapped fields.
• These methods aim to enhance local tumor control and minimize normal tissue toxicity.