IMPLEMENTATION OF 3D-VIRTUAL BRACHYTHERAPY IN THE MANAGEMENT OF BREAST-CANCER - A DESCRIPTION OF A NEW METHOD OF INTERSTITIAL BRACHYTHERAPY

Purpose: We present the initial description of a new technique of inte rstitial breast brachytherapy in which a computer-generated image of a n implant template is applied virtually to serial-computed tomography (CT) scan images of a patient's breast. Optimal placement of the virtu al template around the CT images of the proposed target volume provide s the physician with a preplan for improved positioning of implant nee dles around the actual target volume intraoperatively. Methods and Mat erials: Since March of 1993, 110 patients with early-stage breast canc er were entered onto a protocol of low or high dose rate brachytherapy as the sole radiation modality for part of their breast-conserving th erapy. To improve the accuracy and reproducibility of target volume co verage in patients with a closed lumpectomy cavity, 11 of these implan ts were performed using the virtual brachytherapy technique. The virtu al implant procedure was performed by first placing radiopaque skin ma rkers on the breast surface for reference on the CT image and ultimate ly as intraoperative landmarks for the placement of implant needles. A CT scan of the breast was then performed and the target volume outlin ed on each CT scan slice by the physician. A virtual image of the brac hytherapy template was then positioned around the CT image of the targ et volume to achieve an idealized implant with optimal coverage. The p rojected entrance and exit points of all needles on the skin of the br east (from the idealized virtual implant) were then identified (by per spective rendering of multiple 3D views) and hard-copy images taken to the operating room. The implant was then constructed by referencing t he virtual implant images (needle entrance and exit points) to the rad iopaque skin markers on the breast. After the implant was completed, a CT scan of the breast with the template catheters or needles in posit ion was taken for comparison of the actual target volume coverage with the virtual implant generated preoperatively. Results: Intraoperative ultrasound was used to check the real-time position of the afterloadi ng needles in reference to the chest wall and posterior border of the target volume. No adjustment of needles was required in any of the 11 patients. Assessment of target volume coverage between the virtual imp lant and the actual CT image of the implant showed excellent agreement . In each case, all target volume boundaries specified by the physicia n mere adequately covered. The total number of implant planes, interte mplate separation, and template orientation were identical between the virtual and real implant. Conclusion: We conclude that 3D virtual bra chytherapy may offer an improved technique for accurately performing i nterstitial implants of the breast with a closed lumpectomy cavity in selected patients. Although preliminary results show excellent coverag e of the desired target volume, additional patients mill be required t o establish the reproducibility of this technique and its practical li mitations. (C) 1998 Elsevier Science Inc.