Abstract
Background: The CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ formalism proposed by Watson et al. allows users of the INTRABEAM (Carl Zeiss Medical AG, Jena, Germany) electronic brachytherapy system to accurately determine the absorbed dose to water, in the absence of a primary dosimetry standard. However, all published CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ values are for PTW 34013 ionization chambers calibrated in a TW30 reference beam, traceable to PTB (Germany). For North American users, it would be advantageous to have CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ data for chambers calibrated in a kV reference beam maintained by the National Institute of Standards and Technology (NIST).
Purpose: In this work, we determine CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ for a PTW 34013 chamber calibrated in three NIST-traceable reference beams: M30, L40, and L50.
Methods: Using available photon spectra data for M30, L40, and L50 reference beam qualities, Monte Carlo simulations using EGSnrc were performed to calculate the ratio of the absorbed dose to the PTW 34013 chamber air cavity to air-kerma ( Dgas/Ka $D_{\textrm {gas}}/K_a$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">Dgas/KaDgas/Ka ) for these beams. From this ratio, CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ as a function of depth in water was determined. The effect of the use of a buildup foil was also investigated. An uncertainty analysis considering both the Type A and Type B uncertainties in the calculation of CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ was performed.
Results: The largest difference in CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ was found between L50 and TW30, with a relative decrease of 1.4% (no buildup) to 1.6% (buildup). For M30 and L40, the differences were minimal compared with measurement uncertainties.
Conclusions: We report CQ $C_Q$" role="presentation" style="box-sizing: inherit; display: inline-block; line-height: 0; font-size: 18.08px; font-size-adjust: none; overflow-wrap: normal; word-spacing: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; margin: 0px; padding: 1px 0px; position: relative;">CQCQ values for three NIST-traceable kV reference beams. This study reinforces the feasibility of adapting the Watson et al. methodology using different kV reference beams, facilitating the use of INTRABEAM in North America and ensuring the continuity and accuracy of dosimetry standards in intraoperative radiation therapy.
Publication Date
11-1-2024
Content Type
Article
PubMed ID:
Citation
Watson, P. G. F., Davis, S., & Culberson, W. S. (2024). Technical note: Determination of CQ$C_{Q}$ for a miniature x-ray source using a soft x-ray ionization chamber calibrated in NIST reference beam qualities. Medical physics, 51(11), 8597–8601. https://doi.org/10.1002/mp.17345
Comments
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