Comparison of methods for calculating rectal dose after (125)I prostate brachytherapy implants

Area of Science:

• Radiation Oncology
• Medical Physics
• Brachytherapy Dosimetry

Background:

• Accurate rectal dose assessment is crucial in prostate brachytherapy to minimize radiation-induced toxicity.
• Traditional methods may not fully capture the complex dose distribution to the rectal surface area.

Purpose of the Study:

• To compare various rectal dose calculation methods against rectal dose surface area (SA) measurements.
• To evaluate the accuracy and practicality of these methods for routine clinical use in prostate brachytherapy.

Main Methods:

• 55 prostate brachytherapy patients treated with Iodine-125 seeds were analyzed.
• Rectal dose was calculated using dose-volume (whole/anterior rectum) and point dose metrics.
• A 1-mm anterior rectal wall contour served as the reference standard for dose-surface histogram (DSH) surrogate measurements.

Main Results:

• Dose-volume measurements of the whole or anterior half rectum showed the highest correlation (R=0.949) with SA(144 Gy) measurements.
• Rectal length receiving > or =144 Gy also correlated well (R > or =0.898).
• Point dose measures demonstrated poor correlation (R < or =0.649) with SA(144 Gy). Dose-volume calculations were most practical (6 min/patient).

Conclusions:

• Dose-volume measurements for the whole or anterior half rectum are recommended as a standard method for reporting rectal dose.
• These methods are practical and accurately represent DSH measurements when DSH calculation is not feasible.
• Average or maximal anterior rectal doses are unreliable indicators of rectal surface area dosimetry.