Day's integration of scatter dose with an analytical expression

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Dosimetry

Background:

• Accurate calculation of scatter dose is crucial for effective radiotherapy.
• Existing methods for scatter dose calculation may have limitations in accuracy or applicability.
• The need for precise dosimetric data across various radiation energies and field sizes is paramount.

Purpose of the Study:

• To develop and validate analytical formulae for predicting scatter dose on the central axis.
• To describe scatter dose as a function of depth, field size, and radiation quality (60Co gamma, 4/8 MV x-rays).
• To compare the accuracy of the developed formulae against established methods like Day's method.

Main Methods:

• Development of analytical formulae relating scatter-to-primary dose ratio to the area-to-perimeter ratio (A/P).
• Inclusion of depth and energy-dependent parameters within the formulae.
• Comparison of calculated total doses (on and off central axis) with those from Day's method using tabulated values.

Main Results:

• Analytical formulae were successfully developed for 60Co gamma and 4/8 MV x-ray beams.
• The core relationship is based on the area-to-perimeter ratio, incorporating depth and energy dependencies.
• Calculated doses using the new formulae showed discrepancies of less than 1% compared to Day's method on the central axis.

Conclusions:

• The developed analytical formulae provide a highly accurate method for calculating scatter dose in rectangular fields.
• These formulae offer a reliable alternative to tabulated data for radiotherapy dose calculations.
• The findings contribute to improved precision in radiation therapy planning and delivery.