Dosimetric comparison of ring and ovoid applicators

Area of Science:

• Medical Physics
• Radiation Oncology
• Brachytherapy

Background:

• Postoperative vaginal cuff irradiation is a crucial treatment modality for gynecological cancers.
• Accurate dosimetry is essential to maximize tumor control while minimizing toxicity to surrounding organs at risk, such as the rectum.

Purpose of the Study:

• To compare the dosimetric characteristics of different vaginal applicators (ovoids and rings) used in vaginal cuff brachytherapy.
• To evaluate the impact of applicator size and configuration on dose distribution to the vaginal cuff and rectum.

Main Methods:

• A dosimetric study using the Plato Treatment Planning System (TPS) was conducted.
• Standard ovoid and ring applicators of various sizes and angles were modeled.
• Dose calculations were performed for defined reference points, including the vaginal cuff (V(c)) and multiple rectal reference points (R(1)-R(5)).

Main Results:

• Ovoid applicators resulted in a significantly higher rectal reference dose (R(1)) compared to ring applicators (43.1% vs. 28.6%).
• Increasing applicator size led to an increase in rectal dose and the thickness of the reference isodose.
• The magnitude of the reference volume was independent of ring angle but decreased significantly with ring applicators compared to ovoids.

Conclusions:

• Ring applicators offer a dosimetric advantage by reducing the maximum rectal reference dose compared to ovoid applicators when used with recommended dwell positions.
• The reduction in rectal dose with ring applicators is associated with a significant decrease in the reference treatment volume.
• Careful selection of applicator size and type is necessary to optimize dose delivery and minimize toxicity in vaginal cuff brachytherapy.