A needed modification to vendor supplied oversized 45 degree wedges

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Equipment

Background:

• A modification in linear accelerator source-to-blocking tray distance impacts the simultaneous use of oversized wedges and custom blocks.
• This incompatibility affects radiotherapy treatment planning and delivery.

Purpose of the Study:

• To evaluate methods for enabling simultaneous use of 45-degree wedges and 7.5 cm or higher custom cerrobend blocks with new linear accelerators.
• To assess the dosimetric impact of modifying the vendor-supplied steel wedge and substituting it with a lead wedge.

Main Methods:

• Measurements of central axis depth dose, transverse dose profile, wedge transmission factor, and surface dose were performed.
• Dosimetric data were collected for 6 through 18 MV x-rays for both the truncated steel wedge and the lead substitute wedge.
• Comparison of dosimetric data between modified and original wedges.

Main Results:

• Truncating the steel wedge allows simultaneous use of wedges and blocks without significant dosimetric changes.
• Substituting with a lead wedge also enables simultaneous use but results in substantial dosimetric differences requiring remeasurement.
• The dosimetric data for the truncated steel wedge closely matches the untruncated original wedge.

Conclusions:

• Modifying the vendor-supplied steel wedge by truncating its heel is a viable solution for simultaneous wedge and block use in radiotherapy.
• The lead substitute wedge presents significant dosimetric deviations, necessitating thorough recalibration and validation before clinical implementation.
• These findings offer practical solutions for overcoming equipment limitations in radiation oncology.