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Effective Treatment Volume of the Small Size IORT Applicators

A Krechetov

A. S. Krechetov1,2*, D.A. Goer1* (1) , Intraop Medical Corp, Sunnyvale, CA (2), ASK Physics, Mountain View, CA


SU-E-T-611 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Mobile electron linear accelerators are gaining more attention recently, providing a lower cost and simpler way to perform intraoperative treatment. However, the simplicity of the treatment process does not eliminate the need for proper attention to the technical aspects of the treatment. One of the potential pitfalls is incorrect selection of the appropriate applicator size to adequately cover the tumor bed to the prescription dose.
When treating tumor beds in the pelvis, the largest applicator that fits into the pelvis is usually selected as there is concern about microscopic extension of the disease along the sidewalls of the pelvis. But when treating early stage breast tumors, there is a natural tendency to select an applicator as small as possible so as not to jeopardize cosmesis.


This investigation questions how much of the typical breast treatment volume gets adequate exposure and what is the correct strategy in selecting the proper applicator size. Actual data from isodose scans were analyzed

We found that typical treatment dose prescriptions can cover as much as 80% and as little as 20% of the nominal treatment volume depending on the applicator size and energy of the beam and whether the dose is prescribed to the 80 or 90% isodose level. Treatment volume is defined as a cylinder with diameter equal to applicator and height equal to the corresponding D80 or D90 depth.

If mobile linear accelerators are used, there can be significant amount of “cold volume” depending on the applicator size and this should be taken into account when selecting the applicator that is needed. Using too small of an applicator could result in significant under-dosing to the tissue at risk. Long-term clinical data demonstrates that selecting an adequate field size results in good ontological control as well as excellent cosmesis

Funding Support, Disclosures, and Conflict of Interest: Intraop Medical Corp was providing facilities and equipment for this research.

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