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Updated: May 11, 2026
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Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition
Published on: March 11, 2021
Determination of transit dose profile for a (192)Ir HDR source
G P Fonseca1, R A Rubo, R A Minamisawa
1Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN∕SP, São Paulo 05508-000, Brazil.
Medical Physics
|May 3, 2013
Summary
Accurate high dose rate (HDR) brachytherapy requires precise transit dose calculations. Using instantaneous source speed, not average, significantly improves dose accuracy near dwell positions, crucial for effective cancer treatment.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Current high dose rate (HDR) brachytherapy planning systems often use average source speed for transit dose correction, leading to inaccuracies.
- Realistic speed profiles of the moving radiation source are essential for precise dose determination.
Purpose of the Study:
- To quantify the transit dose component in HDR brachytherapy using instantaneous source speed measurements.
- To improve the accuracy of dose calculations in HDR brachytherapy planning systems.
Main Methods:
- Characterized the Nucletron microSelectron-HDR Ir-192 source per TG-43U1 specifications.
- Employed MCNP5 Monte Carlo code for dose distribution calculations at each source position.
- Measured instantaneous source speed using optical fibers, photomultiplier, and oscilloscope.
- Validated calculated dose profiles against experimental data from radiochromic films.
Main Results:
- Monte Carlo simulations showed agreement with literature values (<1% difference).
- Dose profiles corrected with instantaneous source speed differed up to 800% from average speed corrections near dwell positions.
- Instantaneous speed corrections showed excellent agreement with experimental data (≤3% discrepancy).
- Transit dose accounted for ~22% of dwell dose near a dwell position (1s dwell time).
Conclusions:
- Transit dose correction based on average source speed is inaccurate for HDR brachytherapy.
- Accurate dose calculations necessitate considering the instantaneous source speed profile.
- The impact of transit dose is significant and requires careful consideration in complex treatment scenarios.
