Quality assurance and dosimetric evaluation for an endocavitary unit

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Endocavitary contact therapy is an effective treatment for selected rectal carcinomas.
• High dose rates and rapid dose fall-off present dosimetric and quality assurance challenges.
• Operating room environments pose radiation safety concerns due to variable conditions.

Purpose of the Study:

• To establish and assess a comprehensive quality assurance (QA) program for endocavitary contact therapy.
• To ensure accurate dosimetry and radiation safety during treatment.
• To validate the reliability of the treatment delivery system.

Main Methods:

• Utilized a 50 kVp X-ray unit with specific source-to-surface distance (SSD) and applicators.
• Implemented daily, monthly, and annual QA reviews.
• Employed parallel-plate ionization chambers, silver bromide film, electron diode systems, and ion chamber survey meters for dosimetry and radiation measurements.
• Conducted output checks, relative depth dose measurements, beam profile evaluations, and scatter/leakage assessments.

Main Results:

• Daily output checks confirmed stability across different operating rooms.
• Monthly ion chamber checks validated output trends.
• Percent depth dose measurements in liquid water and polystyrene agreed with published data.
• Radiation surveys indicated acceptable exposure levels.

Conclusions:

• A comprehensive QA program, including day-of-treatment output checks, enhances confidence in dose delivery.
• The established QA protocols effectively address dosimetric and radiation safety challenges.
• Endocavitary contact therapy, supported by rigorous QA, remains a viable treatment option for rectal cancer.