PIN diodes for radiation therapy use: Their construction, characterization, and implementation.

Area of Science:

• Medical Physics
• Radiation Oncology
• Detector Technology

Background:

• Accurate patient surface dose measurement is crucial for radiotherapy verification.
• Comparing measured dose with treatment planning system (TPS) calculations ensures treatment accuracy.
• Development of simple, reliable dosimetry systems is essential for clinical implementation.

Purpose of the Study:

• To develop and implement a PIN diode measurement system for patient surface dose verification.
• To enable measurements for static and rotational photon and electron beams.
• To devise simple calibration procedures with minimal correction factors.

Main Methods:

• PIN photodiodes were fabricated into radiation detectors.
• Single or dual diodes on shielded cables were used for static and rotational measurements.
• Dose measurements were compared with calculations from a commercial TPS (Eclipse).

Main Results:

• PIN diode detectors exhibited intrinsic buildup characteristics (0.3-1.5 mm water equivalence).
• Correction factors for various parameters (dose-per-pulse, temperature, etc.) were determined.
• Diode measurements agreed within 1.0% with Eclipse TPS calculations.

Conclusions:

• PIN photodiodes can be fabricated into clinically usable dose detection devices.
• These devices can measure dose at the patient surface or under bolus.
• Specific diode types eliminate the need for correction factors in IMRT applications.