Open Freehand Interstitial Catheter Insertion

Open freehand technique depends upon the skill of the brachytherapist to insert catheters or needles in an array that both covers the target volume, and provides a spacing that will insure a homogeneous dose distribution. It was the original method of breast brachytherapy, used by Geoffrey Keynes in England in the 1920s as the original breast conservation therapy (Keynes 1937), Samuel Hellman from the Joint Center for Radiotherapy in the late 1970s and early 1980s as a boost, and myself in the early 1990s as the first modern day APBI technique.

At the time of a lumpectomy or reexcision, the radiation oncologist goes to the operating room with the surgeon. With the skin incision open, the extent of the surgical excision can be determined by probing the cavity with an index finger. A sterile magic marker delineates the edges of the cavity onto the skin surface. A single, double, or rarely triple plane implant is then designed by marking the planned needle entry and exit sites on the skin (Figs. 9.3 and 9.4).

Fig. 9.3 Two-plane interstitial implant as performed on the RTOG 95-17 phase II trial. With the wound open, the edges of the lumpectomy cavity are marked on the skin. Deep and superficial planes are placed posterior and anterior to the cavity, extending 2 cm beyond the cavity in all dimensions. In the study, the end dwell positions of the radioactive source(s) were planned 1 cm from the skin surface on both sides, in contrast to modern 3D planning where the positions span the target volume only

Isodose Curve For Breast Cancer

A single-plane implant is indicated if the thickness of the tissue to be covered is 1.5 cm or less. This typically is the case for very medial lesions near the parasternal breast tissue or in very small breasts or in augmented breasts (Fig. 9.5). It is appropriate to design a single-plane implant for one side of the target volume, and broaden it out in a "Y" pattern where the breast becomes thicker, such as under the nipple. A double plane is

Fig. 9.4 Sagital cross-sectional view of a two-plane Fig. 9.5 Prebrachytherapy photograph of a para-implant with the cavity in purple and the catheters sternal medial tumor excision site in an augmented represented by black dots breast. Ultrasound-guided catheter insertion is preferred, and the thin breast tissue can usually be covered by either a single plane or Y-shaped single plane branching out to a second plane laterally towards the nipple

Fig. 9.4 Sagital cross-sectional view of a two-plane Fig. 9.5 Prebrachytherapy photograph of a para-implant with the cavity in purple and the catheters sternal medial tumor excision site in an augmented represented by black dots breast. Ultrasound-guided catheter insertion is preferred, and the thin breast tissue can usually be covered by either a single plane or Y-shaped single plane branching out to a second plane laterally towards the nipple necessary if the tissue thickness is greater than 1.5 cm but less than 3 cm. A third plane is added when the target tissue exceeds or equals 3 cm.

The spacing between needles within a plane varies with the size of the implant. Smaller volumes require closer spacing and larger volumes can be cover with wider spacing. For example, when using a single-plane implant, the needle spacing typically is 1.0-1.2 cm. For double-plane implants, the spacing is 1.5 cm. In high-risk areas such as directly under the lumpectomy scar, smoother dose distributions under the skin can be obtained by adding extra catheters in between the original marks at a superficial depth. By adding these extra catheters, called the "gauntlet under the skin," the dose under the skin can be feathered by varying the dwell times without overdosing the skin surface and running the late risk of telangiectasia.

General principles of freehand technique include:

1. When in doubt about coverage, add an extra catheter in the OR, because you can always pull it or not use it if the dose distribution is acceptable without it, but it is harder (but not impossible!) to add it later after the patient has awoken.

2. Catheter entry and exit locations should be selected at least 1 cm away from the target volume, or a source dwell will need to be in the skin, guaranteeing a telangiectatic spot.

3. Ideally, the needles are perfectly straight and parallel to each other.

4. At the ends of the implant, placing an extra catheter in between the two planes will prevent bowing in of the isodose curves.

5. Crossing needles in a perpendicular orientation near the catheter entry and exit sites can be helpful in contouring the dose at these ends of the target volume, so that you do not have to past-load dwell positions in each catheter to prevent a scalloping in of the dose at the ends of a line source (Fig. 9.6).

Fig. 9.6 An ultrasound-guided implant illustrating: (1) triangulation between the superficial and deep planes, where the superficial needles are in between pairs of deep needles, and (2) the use of crossing needles at right angles and between the two planes, at the periphery of the target volume, benefiting dosimetry in the z-plane of the implant and avoiding medial sources too close to the skin

Apbi Cross Catheter

Clearly, freehand techniques require skill and experience from the brachytherapist. For this reason, this technique is less commonly used than the other image-guided techniques discussed in this chapter. This technique is still frequently used with augmentation mammoplasty where seeing the silicone surface as you guide each needle across the target volume is helpful in avoiding augmentation implant puncture and subsequent rupture. For the target volume not visible within the cavity at the right and left sides, however, it is much safer to have intraoperative ultrasound in order to avoid puncture.

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