Characterizing Compromised Target Coverage With Hypofractionated Radiation Therapy for Pancreatic Cancer.

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Proximity of organs at risk (OAR) complicates radiation dose escalation for pancreatic cancer.
• Protracted-fractionation (PF) with moderate hypofractionation (MHF) is being explored to overcome OAR constraints.
• Underdosing and dose heterogeneity remain concerns, impacting tumor control in pancreatic cancer.

Purpose of the Study:

• To evaluate the initial planning experience with PF-MHF in pancreatic cancer.
• To assess dosimetric parameters and target volume coverage in PF-MHF plans.
• To explore strategies for improving tumor coverage in PF-MHF treatment planning.

Main Methods:

• Retrospective review of 26 PF-MHF radiation courses for pancreatic cancer (locally advanced or recurrent).
• Analysis of dosimetric parameters including PRV-GTV overlap, D99.9%, D0.1cc, Dmean, V75Gy, V60Gy, and gEUD.
• Reoptimization of plans to increase gEUD or relax maximum dose constraints.

Main Results:

• Median D0.1cc was 81.7 Gy, but median V75Gy (target coverage) was only 71%.
• Median gEUD values were 71 Gy (a = -5) and 62.8 Gy (a = -15), inversely correlated with PRV-GTV overlap.
• Reoptimization improved target coverage and gEUD, particularly with limited PRV-GTV overlap.

Conclusions:

• PF-MHF for pancreatic cancer faces challenges with low prescription dose coverage, especially with high PRV-GTV overlap.
• Relaxing maximum dose constraints can improve tumor coverage in specific scenarios (limited overlap).
• Further refinement of PF-MHF planning is necessary for optimal pancreatic cancer treatment.