Megavoltage radiation field matching on uneven surface

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Accurate field matching in radiation therapy is essential to prevent overdosing at the junction of adjacent large radiation fields.
• Existing methods for determining optimal field separation assume a flat patient surface, which is often not the case in clinical practice.
• Patient thickness variations within large fields create uneven surfaces, complicating accurate dose delivery.

Purpose of the Study:

• To develop and validate an approach for calculating optimal field separation on uneven patient surfaces.
• To address the limitations of current field separation methods that do not account for surface inhomogeneity.
• To ensure precise dose delivery and avoid complications in radiation oncology.

Main Methods:

• Dose measurements were performed at the junction of two fields using 60Co and 4, 6, and 24 MV X-ray beams.
• The proposed approach for gap calculation was applied and verified using these measurements.
• Beam profiles were analyzed under simulated uneven surfaces to assess dose distribution.

Main Results:

• The 50 percent dose decrement line showed no significant shift towards the central axis despite variations in patient thickness.
• The study confirmed that careful geometric considerations are sufficient for achieving optimum field separation on uneven surfaces.
• The findings validate the proposed method for gap calculation in the presence of surface inhomogeneity.

Conclusions:

• The developed approach effectively calculates optimal field separation for uneven patient surfaces in radiation therapy.
• Ignoring surface inhomogeneity can lead to field overlap and potentially dangerous overdoses at the junction.
• This method enhances the safety and precision of radiation treatments involving large adjacent fields.