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Preliminary Study of the Comparison of Patient-Specific QAs Using the Diode and Ionization Chamber Based Dosimetry Systems

S Gupta*, X Zhang, E Han, X Liang, S Sharma, S Morrill, M Hardee, J Penagaricano, V Ratanatharathorn, University of Arkansas Medical Science, Little Rock, AR

SU-E-T-204 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Purpose:Patient QA comparison by using the ArcCHECK diode cylindrical and PTW 2D ionization chamber array based dosimetry systems for in-homogenous and small field size tumor.

Methods:Four head and neck (HN), 4 lung and 3 brain tumor patients were selected to study the behavior of in-homogeneity on QA and, 3 SRS and SRT patients were selected to investigate small field size effect. The detectors used for this study are the PTW Seven29 2D ion-chamber planar array (PTW, Freiburg, Germany) and the ArcCHECK cylindrical array (Sun-Nuclear, FL). All the patient QA plans were generated using the Eclipse (version-11) TPS; all the treatment plans were delivered on the TrueBeam-STX Accelerator and measured by both the systems. A gamma-index criterion of minimum 3% (3 mm) is used to evaluate the QA results. The Local-Dose and the Van-Dyk criteria are used to calculate the gamma, respectively.

Results:The QA results show that gamma-index scores are higher than 94% (3mm, 3%) for both the systems for the brain and lung patients; whereas for the HN patients, the gamma-index score is 86% and 98% for the PTW and ArcCHECK, respectively. For the small field size, the gamma-index scores (3%, 3 mm) are higher than 98% for the ArcCHECK; whereas the gamma-index score is lower for the PTW.

Conclusion:The tumor inhomgeneity does not affect the QA results since both systems give similar QA results for the brain and lung patients. However, ArcCHECK is better as compared to the PTW for the HN patients; this may be due to the relatively higher sensitivity of the diode and could pick up the lower signal for low dose area. For the SRS and SRT QAs, there will be volume averaging effect because of the large sensitive volume; hence, the PTW system may not be a good choice of detectors for these QAs.

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