Bladder base dosage in patients undergoing intracavitary therapy

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Intracavitary therapy is a common treatment for gynecological cancers.
• Accurate dose delivery to the bladder is critical to minimize toxicity.
• Current methods for dose assessment may not fully capture the maximum bladder dose rate.

Purpose of the Study:

• To assess the maximum dose rate delivered to the bladder base during intracavitary therapy.
• To compare this measured dose rate with the International Commission on Radiation Units and Measurements (ICRU) reference point dose rate.
• To evaluate the impact of applicator positioning on bladder dose distribution.

Main Methods:

• Computed tomography (CT) scanning was used to assess dose rates in 20 patients during treatment.
• Dose rates were compared to ICRU bladder reference point dose rates calculated from post-insertion radiographs.
• Applicator positioning and packing were re-examined in a subset of patients.

Main Results:

• The ratio of maximum bladder base dose rate to ICRU reference dose rate ranged from 1.01 to 3.59.
• In 10 patients, the maximum bladder dose was not located in the midline.
• Changes in applicator positioning led to significant dose rate variations in 2 out of 5 re-examined patients.
• In 22/25 examinations, the dose rate on the vertical plane through vaginal ovoids was within +/- 25% of the maximum bladder base dose rate.

Conclusions:

• CAT scanning provides a more accurate assessment of maximum bladder dose rates than traditional methods.
• Applicator positioning significantly influences bladder dose distribution and requires careful attention.
• Current ICRU reference point may underestimate the actual maximum dose delivered to the bladder base, necessitating improved dosimetry for bladder dose optimization.