Ehab Attalla - Physics Unit-Radiation Oncology, Children’s Cancer Hospital, Cairo, Egypt
Rasha Elawady - Physics Unit-Radiation Oncology, Children’s Cancer Hospital, Cairo, Egypt
Shimaa shoier - 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 (۶ MV & ۱۰MV) with ۸۲ 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 ۰.۱۲۵ cc simeflex ionization chamber. The small fields have different sizes ranging from ۱۲.۵۰ to ۴۰.۰۰ mm in diameter. Results: There were small observations of mean error ≤ ۱.۵۰ % for all collecting data related to depths and field sizes.  The Statistical Package of Social Science (SPSS) (version ۲۶) to generate results. Wilcoxon Signed Ranks Test was used to compare two groups; (p ≤ ۰.۰۵) 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 ۱.۰ cm x۱.۰ cm to ۱۰.۰ cm x۱۰.۰cm. 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.

Measured TMR, Calculated TMR, Small field dosimetry