Estimation of the effects of normal tissue sparing using equivalent uniform dose-based optimization

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Intensity modulated radiotherapy (IMRT) is a standard technique for precise radiation delivery.
• Optimizing treatment plans involves balancing target coverage with organ at risk (OAR) sparing.
• Equivalent Uniform Dose (EUD) is a method to assess dose distributions.

Purpose of the Study:

• To compare normal tissue sparing in IMRT plans with and without a dose volume (DV)-based physical cost function.
• To evaluate the impact of dose inhomogeneity within the planning target volume (PTV) on OAR doses and complication probabilities.

Main Methods:

• Two sets of IMRT plans were generated for 20 prostate cancer patients: one with a DV-based cost function (EUDWith DV) and one without (EUDWithout DV).
• Both plan types aimed for a 72 Gy prescription dose to the PTV.
• Dosimetric parameters for OARs and normal tissue complication probabilities were analyzed.

Main Results:

• Plans allowing inhomogeneity (EUDWithout DV) resulted in higher mean PTV doses (80.42 Gy) compared to homogenous plans (EUDWith DV, 73.67 Gy).
• A significant portion (28%) of the PTV received >115% of the prescription dose in EUDWithout DV plans, versus negligible amounts in EUDWith DV plans.
• Contrary to expectations, EUDWith DV plans showed higher doses to OARs than EUDWithout DV plans, indicating better normal tissue sparing with inhomogeneity.

Conclusions:

• Allowing dose inhomogeneity within the target volume (EUDWithout DV) improves normal tissue sparing compared to homogenous dose distributions (EUDWith DV).
• Inhomogeneous dose distributions can be strategically used to escalate dose to high-risk subvolumes for enhanced local tumor control.
• EUD-optimized IMRT plans provide benefits of reduced OAR dose and selective dose escalation to the gross tumor volume.