SU-E-J-209: A Simple Method to Minimize Uncertainty in ITV Delineation: Phantom Verification.

Area of Science:

• Radiotherapy
• Medical Imaging
• Radiation Oncology

Background:

• Irregular breathing introduces variability in internal target volume (ITV) delineation.
• Maximum intensity projection (MIP) based ITV may underestimate the true tumor range.
• Accurate ITV delineation is crucial for effective lung cancer treatment planning.

Purpose of the Study:

• To evaluate a novel method for ITV delineation by combining GTV from 3D-CT with ITV from MIP.
• To assess the accuracy of this combined method compared to MIP-alone ITV.
• To reduce errors in ITV delineation caused by respiratory motion during lung cancer treatment planning.

Main Methods:

• Utilized a dynamic thorax phantom with simulated irregular and regular breathing profiles.
• Acquired 3D-CT and 4D-CT scans for each breathing profile.
• Contoured GTV on 3D-CT and ITV on MIP images (ITVMIP); created a combined ITV (ITVCOMB) by merging GTV and ITVMIP.
• Compared ITVCOMB and ITVMIP against a ground truth ITV (ITVGT).

Main Results:

• For regular breathing, ITVMIP and ITVCOMB were comparable to ITVGT.
• For irregular breathing, ITVCOMB showed a significantly smaller mean absolute difference from ITVGT (6.3%) compared to ITVMIP (18.1%).
• The p-value for the difference was 0.0078, indicating statistical significance.

Conclusions:

• Combining GTV from 3D-CT with ITV from MIP (ITVCOMB) is a more accurate method for ITV delineation than using MIP alone.
• This combined approach offers a simple and effective strategy to mitigate breathing-induced errors in ITV delineation.
• The findings support the use of ITVCOMB for improved treatment planning in lung cancer patients with irregular breathing.