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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
Breast in vivo dosimetry by EPID
Andrea Fidanzio1, Francesca Greco, Alessandra Mameli
1U.O. di Fisica Sanitaria, Policlinico Gemelli UCSC, Roma, Italy. andrea.fidanzio@rm.unicatt.it
Journal of Applied Clinical Medical Physics
|November 18, 2010
Summary
This study introduces a new method using electronic portal imaging devices (EPID) for more accurate in vivo dosimetry during breast cancer radiotherapy. Accounting for patient setup variations significantly improves dose accuracy, ensuring better treatment delivery.
Area of Science:
- Medical Physics
- Radiation Oncology
- Radiotherapy Dosimetry
Background:
- Electronic Portal Imaging Devices (EPIDs) are valuable for real-time, two-dimensional in vivo dosimetry during patient treatment.
- Accurate patient setup is crucial for reliable dose delivery in radiotherapy.
- Existing EPID dosimetry methods may overestimate discrepancies if patient setup variations are not considered.
Purpose of the Study:
- To develop and validate a new procedure to enhance the accuracy of EPID in vivo dosimetry by incorporating patient setup variations.
- To reconstruct the dose at the breast midpoint (Dm) during tangential irradiation, accounting for patient positioning.
- To evaluate the impact of patient setup variations on the accuracy of transit dosimetry.
Main Methods:
- A novel procedure was developed to compare EPID images with digitally reconstructed radiographs (DRRs) to correct for patient setup variations.
- EPID transit signals were correlated with the geometrical projections of the breast midpoint for each therapy session.
- Dose ratios (R) between measured and treatment planning system (TPS) calculated doses at the breast midpoint were analyzed for 800 sessions across 20 patients.
Main Results:
- When patient setup variations were accounted for, 93% of the R values fell within ±5% tolerance levels.
- Without considering patient setup variations, only 72% of R values were within ±5%, indicating overestimation of dose discrepancies.
- Preliminary results show a ±3% accuracy for reconstructed dose profiles perpendicular to the central axis within the breast, with lung dose underestimation.
Conclusions:
- The proposed procedure significantly improves EPID in vivo dosimetry accuracy by accounting for patient setup variations.
- Failure to account for patient misalignment can lead to an overestimation of dose discrepancies, potentially limiting the detection of critical errors.
- The method shows promise for accurate dose profile reconstruction, though further refinement is needed for lung dose assessment.
