Two quality control procedures on radiotherapy beam calibration and treatment planning system implementation

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Modern radiotherapy utilizes advanced dosimetric techniques, including narrow x-ray beams and 3D treatment planning algorithms.
• Quality control (QC) is essential to ensure the accuracy and reliability of these new approaches.

Purpose of the Study:

• To report on two QC procedures for challenging dosimetric scenarios in radiotherapy.
• To evaluate the accuracy of silicon diodes for small x-ray beam dosimetry.
• To assess the accuracy of 3D treatment planning algorithms for breast cancer treatment.

Main Methods:

• Compared dose measurements from silicon diodes, diamond detectors, and radiochromic films for small, high-energy x-ray beams.
• Developed and applied a QC test to verify the dosimetry accuracy of 3D treatment planning algorithms, specifically addressing the "loss of scatter" phenomenon in breast treatments.

Main Results:

• Silicon diodes demonstrated an overestimation of output factors in phantom by up to 4% for high-energy x-ray beams, attributed to detector density and electron equilibrium restoration.
• The QC test for 3D algorithms showed good agreement (within 1.5%) between computed and experimental dosimetry data for breast treatment planning, even with "loss of scatter" conditions.

Conclusions:

• The findings highlight potential inaccuracies with silicon diodes in small field dosimetry, necessitating careful consideration and validation.
• The validated QC test confirms the reliability of 3D treatment planning algorithms for breast cancer dosimetry, ensuring accurate dose delivery.