What must be calculated for the entire rotation in rotation therapy?

In rotation therapy, particularly in techniques like rotational arc therapy, understanding the average Tissue Maximum Ratio (TMR) or Tissue Air Ratio (TAR) is crucial for accurate dosage calculation. TMR or TAR values provide essential information about how radiation interacts with different tissues at varying depths. These ratios help in determining how much radiation is delivered to a specific area of the body when it is irradiated from various angles during the treatment rotation.

Calculating the average TMR or TAR allows dosimetrists to account for changes in tissue density and variation in beam geometry that occur throughout the rotational delivery. This is significant because it ensures that the prescribed dose is consistently delivered across the entire treatment area, allowing for better targeting of the tumor while sparing surrounding healthy tissues.

In the context of the other options, while total dose delivered is important, it is a result of the calculations involving TMR or TAR. Field size requirements and skin thickness are relevant considerations in dosimetry but do not encompass the entire equation necessary for rotation therapy calculations the way TMR or TAR does. Thus, focusing on these ratios is fundamental to achieving precision in radiation treatment.