What device is required for measuring surface or build-up region doses?

The extrapolation chamber is specifically designed for measuring surface or build-up region doses in radiation therapy. This device operates based on the principle of measuring the ionization produced by radiation in a gas-filled chamber. Its unique design allows it to perform measurements at very shallow depths, providing valuable data for understanding dose distributions in the build-up region where electron scattering occurs.

This capability is particularly important in radiation therapy because doses to surface tissues and close to the skin can have significant clinical implications. The extrapolation chamber can provide a precise measurement of the radiation dose in this critical region, which is often affected by factors such as beam energy, field size, and patient setup.

Other devices listed may not be capable of accurately measuring in the surface or build-up region for various reasons. For example, while a diode detector can measure dose rates and is useful in some clinical scenarios, it may not be as effective as an extrapolation chamber for very shallow depth measurements due to its physical design and the potential for inaccuracies in low-energy environments. A water phantom can provide a controlled environment for dosimetry measurements, but it typically requires the use of a detector to actually measure dose, making it less direct for surface dose measurements. TLDs (thermoluminescent dos