Experimental Validation of Small-field Dosimetry in Radiotherapy Using Ionization Chamber and Edge Detector

Introduction: Recently, modern radiotherapy techniques have been extensively developed to deliver doses only to therapeutic volume. The objective of the present study was to empirically evaluate the performance capability of the ionization chamber in comparison to the edge detector. Material and Methods: Firstly, the performance of the ionization chamber, compared to that of the edge diode detector, was validated at a 10×10 cm^2 field size. Then, the percentage depth dose (PDD), percentage surface dose, and transverse profile doses at the 2×2, 3×3, and 4×4 cm^2 field sizes were evaluated for both dosimeters. The empirical and statistical results in a water phantom were compared to those reported for the edge diode detector as the reference field dosimeter using the 6 MV Elekta linear accelerator. Results: The empirical and statistical results of the transverse profiles of the ionization chamber and edge detector are in agreement for the reference field of 10×10 cm^2. However, a small difference between the two dosimeters could be observed in small fields. A discrepancy of less than 1% was observed between the results of PDDs for two dosimeters in small fields. Conclusion: The dosimetric characteristics of the ionization chamber and edge detector illustrated some differences, especially in terms of transverse profiles at the small-field size. This discrepancy could be related to the volume effect of the chamber which affects the penumbra. Due to the importance of sensitive organs, it is recommended to utilize the ionization chamber for small radiotherapy fields.