Reliance on Max IP in Tumor Motion Management: A Flawed Approach

Few things are more challenging for Radiation Therapy treatment planners than tumors that move. In lung cancer cases and other scenarios involving respiratory movement, accurately and efficiently contouring the internal target volume (ITV) is the key challenge to overcome.

An accurate ITV is critical to ensuring that tumors are not underdosed and critical organs are not overdosed. When you can achieve the most precise ITV possible, you have the confidence to treat your patient’s cancer as aggressively as possible.

Recent studies show that contouring directly on the phases of a 4D CT is the most accurate method for ITV delineation.^1,2 The same studies show that contouring on a maximum-intensity projection (MIP) underestimates or overestimates the actual tumor size. Yet, contouring on the MIP is still widely practiced.

Why Are MIPs Still Used for ITV Contouring?

Although contouring the target on every phase of the 4D CT results in a more accurate ITV, traditional systems limit many physicians’ ability to use this method.

Limitations in traditional systems include:

• Unreliable image registrations and limited display options — It’s difficult and time-consuming to register diagnostic images and 4D images accurately. And you often can’t display diagnostic images, 4D images, and registrations at once in a useful layout. As a result, it’s not always possible to create the registrations and layouts needed to accurately contour the target on the 4D CT phases.
  
  
• A time-consuming, manual contouring process — Even if your system allows you to manually create the registrations and display layouts needed, contouring the target on every phase of the 4D CT is typically not feasible due to the painstaking, manual contouring work required.

In short, physicians often continue relying on MIPs because they don’t think it’s possible to efficiently contour the ITV directly on the phases of the 4D CT.

A Better Way: Efficiently Contouring on 4D CT Phases

You shouldn’t have to choose between accuracy and efficiency when creating your ITV. What’s needed is an efficient way to contour the ITV directly on the phases of a 4D CT, because it’s the most precise method, and precision matters.

Miriam Weiser, a medical physicist at Kaiser Permanente Northwest, sums up her team’s experience efficiently contouring ITVs on 4D CT phases and managing tumor motion.

See how Miriam Weiser's team simplifies tumor motion management.

¹Wang, Yu et al, “Comparison of internal target volumes defined by three-dimensional, four-dimensional, and cone-beam computed tomography images of a motion phantom,” Annals of translational medicine vol. 8,22 (2020): 1488. doi:10.21037/atm-20-6246.

²Turner, K et al, “SU-E-J-209: A Simple Method to Minimize Uncertainty in ITV Delineation: Phantom Verification,” Medical physics vol. 39,6Part9 (2012): 3700-3701. doi:10.1118/1.4735049.