Clinical Experience and Evaluation of Patient Treatment Verification With a Transit Dosimeter

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• 作者：Kate Ricketts ; PhD^&lowast ; ; ^&dagger ; ; ^{k.ricketts@ucl.ac.uk" class="auth_mail" title="E-mail the corresponding author} ; Clara Navarro ; MSc^&dagger ; ; Katherine Lane ; MSc^&dagger ; ; Claire Blowfield ; MSc^&dagger ; ; Gary Cotten ; MSc^&dagger ; ; Dee Tomala ; MSc^&dagger ; ; Christine Lord ; MSc^&dagger ; ; Joanne Jones ; MSc^&dagger ; ; Abiodun Adeyemi ; PhD^&dagger ;
• 刊名：International Journal of Radiation Oncology*Biology*Physics
• 出版年：2016
• 出版时间：1 August 2016
• 年：2016
• 卷：95
• 期：5
• 页码：1513-1519
• 全文大小：658 K

文摘

To prospectively evaluate a protocol for transit dosimetry on a patient population undergoing intensity modulated radiation therapy (IMRT) and to assess the issues in clinical implementation of electronic portal imaging devices (EPIDs) for treatment verification.

Methods and Materials

Fifty-eight patients were enrolled in the study. Amorphous silicon EPIDs were calibrated for dose and used to acquire images of delivered fields. Measured EPID dose maps were back-projected using the planning computed tomographic (CT) images to calculate dose at prespecified points within the patient and compared with treatment planning system dose offline using point dose difference and point γ analysis. The deviation of the results was used to inform future action levels.

Results

Two hundred twenty-five transit images were analyzed, composed of breast, prostate, and head and neck IMRT fields. Patient measurements demonstrated the potential of the dose verification protocol to model dose well under complex conditions: 83.8% of all delivered beams achieved the initial set tolerance level of Δ_D of 0 ± 5 cGy or %Δ_D of 0% ± 5%. Importantly, the protocol was also sensitive to anatomic changes and spotted that 3 patients from 20 measured prostate patients had undergone anatomic change in comparison with the planning CT. Patient data suggested an EPID-reconstructed versus treatment planning system dose difference action level of 0% ± 7% for breast fields. Asymmetric action levels were more appropriate for inversed IMRT fields, using absolute dose difference (−2 ± 5 cGy) or summed field percentage dose difference (−6% ± 7%).

Conclusions

The in vivo dose verification method was easy to use and simple to implement, and it could detect patient anatomic changes that impacted dose delivery. The system required no extra dose to the patient or treatment time delay and so could be used throughout the course of treatment to identify and limit systematic and random errors in dose delivery for patient groups.