The Dosimetric Comparison between Measured Tissue Maximum Ratio Directly by Water Phantom and That Calculated from Percentage Depth Dose Measurments in Small Field and Determind the Differnces between Two Methods

Document Type : Original Paper


1 Physics Unit-Radiation Oncology, Children’s Cancer Hospital, Cairo, Egypt

2 Department of Radiotherapy & Nuclear Medicine, National Cancer Institute, Cairo University, Cairo, Egypt


Introduction: The aim is to observe that the measurement of tissue maximum ratio (TMR) by water phantom directly differs from the calculation of TMR from percentage depth dose (PDD) or not.
Material and Methods: The linear accelerator Siemens (6 MV & 10MV) with 82 leaves (MLC)-based stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT). The water phantom (PTW) was used for measuring the dosimetric parameter of TMR &%DD. This data was calculated using 0.125 cc simeflex ionization chamber. The small fields have different sizes ranging from 12.50 to 40.00 mm in diameter.
Results: There were small observations of mean error ≤ 1.50 % for all collecting data related to depths and field sizes.  The Statistical Package of Social Science (SPSS) (version 26) to generate results. Wilcoxon Signed Ranks Test was used to compare two groups; (p ≤ 0.05) was considered significant. There were no significant differences between TMR data. The measured TMR data calculated from %DD had a strong positive correlation for cone sizes from 1.0 cm x1.0 cm to 10.0 cm x10.0cm.
Conclusion: It has been shown that the calculation of TMR data from PDD agrees with the measuring values directly, and it is accepted for use in treatment.


Main Subjects

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Volume 18, Issue 6
November and December 2021
Pages 384-388
  • Receive Date: 18 April 2020
  • Revise Date: 24 October 2020
  • Accept Date: 10 November 2020