Measurement of the sensitometric curves of Kodak EDR2 and X-Omat V films using Enhanced Dynamic Wedges and Dynamic Multileaf Collimators

Abstract

Background

Modern linear accelerators, used in oncological radiotherapy, are often equipped with a dynamic wedge option and dynamic multileaf collimators. For linacs having these options, measurements of absorbed dose distribution require complete movement of the jaw, or of the dynamic multileaf collimator, for each measurement point. In conformal radiotherapy, three or more beams, modified by dynamic accessories, are combined to produce a summarized dose distribution.

Aim

This study is an investigation of the use of film as a detector of dose distribution produced by a single beam, or by a pair of beams modified by dynamic accessories, in phantoms.

Materials/Methods

Measurements of the sensitometric curve of the recently introduced EDR2 (extended dose range) and extensively used X-Omat V radiographic films were performed. Films were irradiated using a Clinac 2300 C/D Varian™ accelerator, equipped with dMLC (dynamic multileaf collimator) and EDW (enhanced dynamic wedge) options. The recorded wedge dose distribution created by the EDW and by programmed dMLC movement were used to obtain response curves of the films. Solid Water™ 457 blocks, manufactured by Gammex RMI, were used as phantoms, in which the films were irradiated.

Results

Measurement and verification of dose distributions created by beams modified by dynamic accessories can be performed using both EDR2 and X-Omat V radiographic films. The EDR2 low sensitivity films are suitable for measurements of total dose distribution, as created by a number of dynamically modulated beams. High sensitivity X-Omat V films are more suited to verification of energy flow, or of the dose distribution generated by single fields, modified by dynamic accessories.

Conclusions

The presented methods for the measurement of sensitometric curves may be applied in the routine calibration of film dosimetry chains for IMRT plan verification.