Margins added to account for setup and motion are included in which volume?

• A. GTV
• B. CTV
• C. PTV
• D. Internal Target Volume

Answer: (C)

In radiation therapy planning, the planning target volume is created by expanding the clinically defined target to cover uncertainties. The clinical target volume includes the gross tumor and areas at risk for microscopic disease, but day-to-day variations in patient setup and small movements of the patient or target during treatment can cause the delivered dose to miss the intended area. Adding margins for these setup and motion uncertainties yields the planning target volume, which ensures the prescribed dose consistently covers the target across all treatment fractions. The Internal Target Volume, by contrast, specifically accounts for internal motion over time (like breathing) and is often incorporated into how margins are applied, but the margins addressing setup and motion uncertainties are what define the planning target volume. This is why the correct choice is the planning target volume.