Rectal Gas-Induced Dose Changes in Carbon Ion Radiation Therapy for Prostate Cancer: An In Silico Study

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Rectal gas can alter radiation dose distribution in carbon ion radiation therapy (CIRT).
• Understanding the dosimetric impact of rectal gas is crucial for optimizing prostate cancer treatment planning.

Purpose of the Study:

• To determine the dosimetric influence of rectal gas in CIRT for prostate cancer.
• To establish a procedure for managing rectal gas in clinical scenarios.

Main Methods:

• Dose distributions were recalculated on CT scans with rectal gas.
• Simulations accounted for residual rectal gas across multiple fractions.
• Dosimetric parameters for the clinical target volume, rectum, and rectal wall were assessed.
• Indicators of dose changes were investigated using digital reconstruction radiograph (DRR) images.

Main Results:

• Clinical target volume doses (Dmin, D99.5%) showed no significant changes.
• Significant dose changes exceeding 1 cm³ were observed in the rectum and rectal wall with increasing fractions of rectal gas.
• Changes in rectal and rectal wall dose parameters correlated highly with the extent of rectal gas assessed on DRR images.

Conclusions:

• Rectal gas removal may not be necessary for up to 4 fractions of CIRT.
• Dose changes due to rectal gas can be estimated from kV-x-ray images (DRR).
• Gas effect evaluation can be integrated into CIRT irradiation protocols.