Single Fraction IORT Delivered In Situ to the Tumor

The IORT technique of Veronesi et al.²³ presents significant technical challenges for the radiation oncologist including the accuracy of tumor bed definition when tissues are re-approximated and the variable margin of normal tissue irradiated in the reopposed tissues. In order to address these issues, the authors modified the Veronesi IORT technique. Instead of delivering the IORT after the tumor is excised by quadrantectomy and the tissues re-approximated, the authors elected to treat the tumor and surrounding tissues with IORT prior to excision.This allowed them to clearly define the target tumor, and normal tissue margin in conventional terms, using ultrasound.

The author’s technique has previously been described in detail.²⁴ Briefly, their modified technique is as follows. Patients aged 55 or older diagnosed by core biopsy with clinically node-negative infiltrating ductal carcinoma less than 3cm in greatest diameter and visible by preoperative breast ultrasound were eligible. Preoperatively, each patient underwent breast ultrasound and ultrasound-guided needle localization of the cancer by a radiologist trained in breast imaging. After the tumor is identified, the optimal angle of approach is determined to minimize the distance to tumor while maximizing distance to lung.At this angle, the width of the tumor, depth from skin to posterior–anterior (PA) and posterior edges of the tumor and from skin to the pleural surface is measured. Dosimetric pre-planning is performed using these parameters to determine the cone size necessary to cover the tumor width plus 1.5–2cm margin and the electron energy necessary to cover a depth of 1cm deep to the posterior edge of the tumor with the 90% isodose line, while delivering at least 1,500cGy to the tumor isocenter.

In the OR each patient underwent lymphatic mapping (LM) and sentinel lymphadenectomy (SL) with a combined isosulfan blue dye and technetium 99m (99mTc)-labeled sulfur colloid technique.25 After completion of LM/SL, a curvilinear incision is made in the standard fashion over the appropriate quadrant of the breast.The incision is long enough (approximately 6–7cm) to ensure adequate exposure of the breast tissue and to allow for placement of the appropriate size radiation cone, as determined pre-operatively by the ultrasound measurements and dosimetric planning. Subcutaneous skin flaps are raised circumferential from the incision for approximately 2–3cm. The skin edges are protected with moist gauze sponges and retracted from the radiation field using a circular retractor with metal hooks. The radiation cone is then locked into position so that the edge is just abutting the breast tissue, at the angle of approach pre-determined by ultrasound guidance, with the tumor as localized by the needle and pre-operative ultrasound in the center of the radiation field. After the surgeon and radiation oncologist have placed and secured the cone, the patient is brought to the position underneath the mobile, self-shielded, linear accelerator for docking. Once docked, the entire team exits the room.The preplanned dose is delivered at a dose rate of 1,000 monitor units per minute. It typically takes approximately one to two minutes for the actual radiation delivery. The entire procedure adds 20–30 minutes to the case. Once the radiation phase of the procedure is complete, partial mastectomy is performed in the standard fashion.

Twenty-three patients have been enrolled with a median age of 63 and a range of 55 to 82 years. The median follow-up is six months, with a range of one to 22 months. The median clinical tumor size as defined by ultrasound was 1.1cm, with a range of 0.5–2.1cm. Five patients did not receive IORT. In one patient, IORT was not delivered due to a machine fault. In two patients, the tumor could not be conclusively located by ultrasound after initial biopsy; therefore, dosimetric planning could not be accomplished with confidence. In two additional patients the tumor was adjacent to the chest wall so that the radiation dose constraints to the lung could not be satisfied. Five of the first 18 patients received WBRT, and three received mastectomy. Only 10 in 18 patients were therefore treated with IORT partial-breast RT. The reasons for receiving WBRT were extensive intraductal component, invasive lobular carcinoma, and involved lymph nodes (LNs). Reasons for mastectomy included an inability to achieve negative margins with re-excision, and patient request in lieu of WBRT recommended for extensive intraductal component.

Discussion

Since the vast majority of in-breast recurrences occur in the lumpectomy bed, several approaches to accelerated partial breast irradiation (APBI) have emerged to treat only the portion of the breast harboring the index lesion.^19–21 The rationale for this approach is that with smaller treatment volumes the treatment can be delivered over a significantly shorter period by using a larger dose per fraction, without excess normal tissue toxicity. Options for APBI include interstitial catheterbased brachytherapy, endocavitary, brachytherapy, and conformal 3-D RT. All of these approaches still require the patient to travel numerous times to the radiation facility following surgery to complete their PBRT. Only IORT affords the patient the opportunity of having the area at highest risk, the tumor bed, managed in a single visit by both the surgery and radiation oncology team.