A precise and simple isodose-volume-based verification method for HDR and LDR brachytherapy plans

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Planning

Background:

• The American Association of Physicists in Medicine (AAPM) recommends independent treatment time calculations for brachytherapy.
• Existing dose-volume-based methods for HDR and LDR brachytherapy require specific parameters for verification.

Purpose of the Study:

• To implement and validate an easy-to-use, isodose-based verification method for HDR and LDR brachytherapy plans.
• To provide a practical alternative for independent treatment time verification in brachytherapy.

Main Methods:

• Developed an isodose-based verification method for HDR (Ir-192) and LDR (I-125 prostate) brachytherapy.
• Validated the method using 55 clinical HDR and 243 clinical LDR plans.
• Compared estimated integral dwell times/activity with calculated values based on isodose volumes.

Main Results:

• For HDR brachytherapy, mean absolute differences in integral dwell time were 0.8% ± 1.0% (single source path) and 2.7% ± 1.1% (multiple source paths).
• For LDR brachytherapy, the mean absolute difference was 1.8% ± 2.0%.
• Good agreement was achieved using the 2 Gy isodose for HDR, while LDR verification parameters depended on seed distribution.

Conclusions:

• Isodose-based verification methods are precise and simple to implement in clinical practice.
• These methods do not require specialized tools, making them accessible.
• The study recommends using an isodose at the prescribed dose for prostate HDR therapy verification.