Which of the following is a disadvantage of custom blocking compared to MLC blocking?

Custom blocking involves the manual design and fabrication of blocks to shape the radiation beam specifically for a patient's treatment. This process is generally more time-consuming and labor-intensive compared to the use of multileaf collimators (MLC), which allow for on-the-fly adjustments without the need for custom-shaped blocks.

The significant disadvantage of custom blocking is the time and effort required to fabricate these blocks, as it often involves multiple steps, such as designing the block plan, cutting materials, and finalizing shapes that accurately conform to the patient's anatomy. This increases treatment setup time and may contribute to inefficiencies in workflow, especially in busy treatment facilities.

In contrast, MLCs leverage technology that allows for quicker adjustments and localizing the radiation field through mechanical leaf movement. This automation dramatically reduces the fabrication time and enhances overall patient throughput in treatment centers. Therefore, the aspect of required time and effort in creating custom blocks stands out as a defining downside when compared to MLC blocking.