A pelvic phantom for modeling internal organ motions

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Technology

Background:

• Prostate radiotherapy requires precise targeting to minimize dose to surrounding organs.
• Internal organ motion, particularly prostate motion and rectal volume changes, presents a significant challenge in delivering accurate radiation doses.
• Existing methods for simulating these motions in a controlled environment are crucial for developing and testing advanced radiotherapy techniques.

Purpose of the Study:

• To develop and validate a realistic pelvic phantom for simulating anterior-posterior internal organ motions during prostate radiotherapy.
• To assess the dosimetric accuracy of intensity-modulated radiation therapy (IMRT) and 3D conformal radiation therapy (3D-CRT) using the developed phantom.
• To evaluate the phantom's suitability for testing image-guided radiation therapy (IGRT) and adaptive radiation therapy (ART) applications.

Main Methods:

• A pelvic phantom was constructed, simulating the prostate, bladder, and rectum with adjustable volumes and motion capabilities.
• Computed tomography (CT) scans were performed for treatment planning, with structure sets adapted from patient data.
• Radiation plans (IMRT and 3D-CRT) were created, and delivered doses were measured using an ionization chamber under simulated prostate motion and rectal volume variations.
• Dose measurements were taken with various beam configurations, including anteroposterior (AP), posteroanterior (PA), and lateral (LAT) beams.

Main Results:

• The phantom successfully simulated prostate motion (±1 cm) and variable rectal volumes.
• Dose variations from calculated doses were minimal: <1% for IMRT, ~1% for 3D-CRT, <4.5% for AP beams, up to 9% for PA beams, and ~0.5% for LAT beams.
• The phantom's performance and measured dose variations align with findings from real-patient studies, indicating high fidelity.

Conclusions:

• The developed pelvic phantom is a realistic and valuable tool for testing and validating image-guided radiation therapy (IGRT) and adaptive radiation therapy (ART) protocols.
• The phantom allows for accurate simulation of internal organ motion, crucial for improving treatment planning and delivery in prostate radiotherapy.
• This model can be utilized to investigate the dosimetric impact of organ motion corrections in radiotherapy, enhancing the safety and efficacy of cancer treatments.