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Entrance dose measurement: a simple and reliable technique
D P Banjade1, T Aloysius Raj, B S Ng
1School of Physics, Universiti Sains Malaysia, Penang, Malaysia.
Summary
This study validates using thermoluminescent dosimeters (TLDs) to measure entrance dose in radiotherapy, ensuring accurate tumor dose delivery. The method shows high agreement with treatment planning systems, enhancing radiation oncology quality assurance.
Area of Science:
- Medical Physics
- Radiation Oncology
- Dosimetry
Background:
- Accurate tumor dose verification is crucial in radiation oncology quality assurance.
- In vivo entrance dose measurement is a reliable method for verifying delivered tumor dose.
- Thermoluminescent dosimeters (TLDs) offer a practical means for in vivo dosimetry.
Purpose of the Study:
- To evaluate the accuracy of LiF:Mg;Ti and LiF:Mg;Cu;P thermoluminescent dosimeters (TLDs) for in vivo entrance dose measurements in external beam radiotherapy.
- To compare TLD-measured entrance doses with doses calculated by treatment planning systems (TPS) for photon and electron beams.
- To assess the reliability of TLD-based entrance dose measurements for patient treatment verification.
Main Methods:
- TLDs (LiF:Mg;Ti and LiF:Mg;Cu;P) were calibrated using a water-equivalent phantom and an ionization chamber for 6-MV, 10-MV photon, and 9-MeV electron beams.
- Calibrated TLDs were used to measure entrance doses in a phantom and directly on actual patients during radiotherapy treatments.
- System stability was monitored through simultaneous phantom measurements.
Main Results:
- For photon beams, TLD measurements in a phantom showed a maximum discrepancy of 4.1% (mean 1.3%) compared to TPS calculations.
- In actual patients receiving photon therapy, measured entrance doses had a maximum discrepancy of 5.7% (mean 2.2%) versus TPS.
- For electron beams, discrepancies were within 3.2% (mean 2.0%) in phantoms and 4.8% (mean 2.3%) in patients.
Conclusions:
- The TLD-based in vivo entrance dose measurement technique is accurate and reliable for verifying radiotherapy tumor doses.
- This method provides confidence in treatment planning system algorithms or highlights the need for parameter re-evaluation.
- Accurate entrance dose verification using TLDs contributes significantly to patient safety and quality assurance in radiation oncology.