Robust Beam Selection Based on Water Equivalent Thickness Analysis in Passive Scattering Carbon-Ion Radiotherapy for...

Area of Science:

• Radiation Oncology
• Medical Physics
• Oncology

Background:

• Carbon-ion radiotherapy (CIRT) is a highly effective treatment modality.
• Passive CIRT requires robust beam configurations (BC) to account for variations like water equivalent thickness (WET).

Purpose of the Study:

• To select robust BCs for passive CIRT in pancreatic cancer using WET analysis.
• To evaluate the impact of robust BCs on dose distribution and accuracy.

Main Methods:

• Analysis of 110 CT images and 600 dose distributions from eight pancreatic cancer patients.
• Evaluation of robustness using planning and daily CT images, comparing bone matching (BM) and tumor matching (TM).
• Selection of two robust BCs (rotating gantry and fixed port) based on WET analysis.

Main Results:

• Posterior oblique (120-240°) and anteroposterior (0°, 180°) beams demonstrated the highest robustness to WET changes.
• Tumor matching (TM) with robust BCs resulted in mean CTV V95% reductions of -3.8% (gantry) and -5.2% (fixed port).
• Slight increases in OAR doses were observed with WET-based BCs but remained within constraints.

Conclusions:

• Robust BCs, identified through WET analysis, enhance the reliability of passive CIRT for pancreatic cancer.
• Tumor matching combined with robust BCs improves the accuracy of passive CIRT delivery.
• WET-robust BCs are crucial for optimizing dose distribution in pancreatic cancer CIRT.