What is a disadvantage of using an MLC compared to custom blocking in radiation therapy?

The concept of using a multileaf collimator (MLC) in radiation therapy does provide significant benefits, such as improved efficiency in treatment delivery and the ability to create complex radiation fields. However, one of the notable disadvantages compared to custom blocking is related to field shaping accuracy.

Custom blocking involves creating physical blocks that are tailored to specific treatment plans and the patient's anatomy. These blocks can provide precise field shaping around the tumor while minimizing exposure to surrounding healthy tissues. In some cases, the construction and placement of these blocks can achieve optimal conformance to the intended target volume better than the mechanical leaves of an MLC, particularly in challenging geometric situations or when dealing with irregular tumor shapes.

MLCs might have limitations in achieving the exact conformity in certain geometries, especially at the edges of the radiation field. This is because the leaves of the MLC may not be able to mimic the precise contours of the tumor as effectively as custom blocks can. Consequently, while MLCs offer flexibility and efficiency, there may be scenarios where the accuracy of the field shaping does not match that of custom blocking.

This aspect of field shaping accuracy highlights why choosing the right method for radiation therapy is critical, as the specific anatomical and clinical context can significantly influence treatment efficacy and