S79Abstracts / Brachytherapy 13 (2014) S15eS126

POSTER DISCUSSION: BREAST

Saturday, April 5, 2014

9:30 AM - 10:30 AM

PD72

Targeted Brachytherapy Boost Using Innovative Targeting

Linda Ann Smith, MD1, Robert R. Kuske, MD2, Michael J. Cross, MD3.1Heights General Medical Center, Comprehensive Breast Care,

Albuquerque, NM; 2Arizona Center for Cancer Care, Arizona Breast

Cancer Specialists, Scottsdale, AZ; 3Breast Treatment Associates,

Fayetteville, AR.

Purpose: Surgical removal of a breast tumor can result in a large surgicaldefect, making radiation boost planning difficult and imprecise. Currentmethods for targeting the tumor bed include surgical clips, changes intissue contour and seroma formation, anatomic landmarks, or the surgicalincision. Each of these methods presents challenges in precise targeting ofthe surgical excision site for the radiation oncology team. Breastconservation surgery followed by closure of the surgical cavity withoncoplastic techniques can further complicate post-operative targeting forradiation treatment. Although some surgeons place surgical clips asfiducials, tissue rearrangement and post-operative healing with potentialclip migration may mis-represent the true target. In other cases, the patienthas received chemotherapy before presenting to the radiation oncologist,and this further complicates accurate localization of the tumor bed sincethe seroma has usually absorbed, and the clips may have migrated toerroneous positions.Materials and Methods: We have used a new type of marker tobetter delineate the surgical area following partial mastectomy. Itconsists of a semi-rigid bioabsorbable spiral with multiple clipsimbedded in a specific array along the spiral. This device issutured at the site of the tumor and provides an image that allowsprecision targeting of the surgical bed for post-operative radiationtreatment. We are reporting on 20 patients treated by two surgeonsand one radiation oncology team. The patients underwent standardbreast conservation surgery with sentinel node mapping and nodeharvesting. The fiducial spiral marker was inserted at the time ofsurgery and secured to the surrounding tumor bed. In this groupof patients, post-operative pathology supported whole breastirradiation plus a boost. When chemotherapy was indicated, it wasdelivered prior to radiation treatments, with a 3-5 month delay tostarting RT. Following surgical healing, patients were treated withboost interstitial brachytherapy, 12-18 Gy in divided doses of 3Gy per fraction, depending on margin width and tumoraggressiveness.Results: No patient required removal of the marker for positive margins,infection, or other reasons. All patients tolerated the boost with excellent

cosmesis and functional outcomes. There were no complications in thisgroup of patients. The radiation oncologist and his physics team notedsignificant improvement in target volume delineation.Conclusions: Precise boost targeting can be delivered with a very highdegree of accuracy when using this new multi-clip fiducial marker. It alsogives flexibility to the treatment schedule, with excellent cosmetic andfunctional outcomes. This targeted boost may decrease the integral doseof RT and make timing/sequencing less important. The addition of thisnew spiral fiducial marker provides a standardized method for markingthe surgical excision site following lumpectomy, and has the potential toimprove the quality of radiation delivery with resultant lowercomplication rates. Long-term followup is planned.

PD73

A Novel CT-based Permanent Breast Implant Technique Using

External Guiding Tools and Markers

Yen Pham, MSc1, Will Ansbacher, PhD1, Stephen Gray, Machinist1, Hosam

Kader, MD2. 1Medical Physics, BC Cancer Agency - Vancouver Island

Centre, Victoria, BC, Canada; 2Radiation Oncology, BC Cancer Agency -

Vancouver Island Centre, Victoria, BC, Canada.

Purpose: Recent single arm studies have suggested that partial breastirradiation, delivered in a relatively short overall treatment time, may bean effective alternative to adjuvant whole breast irradiation. Permanentbreast seed implant (PBSI) is a novel partial breast technique, which hasbeen piloted at the Odette Cancer Centre in Toronto, Canada usingultrasound to guide the implant. An alternative technique to ultrasoundguided permanent breast seed implants is presented.Materials and Methods: In the last two years we have been conducting aPBSI feasibility study and have developed a method to use externalreference guides for permanent breast seed implants. There are twovital components used in this approach - a back pointer bridge and aradio-opaque grid. The back pointer bridge was developed andfabricated in-house. It is an arch that holds the implant needletemplate on one end and a laser on the other. The laser projects backto the skin and marks the exit point of the reference needle path. Theradio-opaque grid was developed in collaboration with Webb MfgCorp by modifying their commercial product called Fast Find Grid. Itallows an identifiable dot pattern on each CT slice, which, whengenerated in the 3D rendering, recreates the grid with a dimension of8cm x 6cm and a 1.0cm spacing for precise needle placement. Thegrid consists of a PVC ink containing powdered lead, is printed onto aporous flexible sheet and conforms closely to the patient’s skin foraccurate imaging. Every patient undergoes a standard tangent CTplanning scan that serves as a first indication of suitability. Thelumpectomy bed size has to be less than 3.0cm equivalent spherediameter and able to accommodate a minimum 2-plane implant, basedon tumor location and breast size. This information is used to positionthe grids on the breast in suitable locations on the medial and lateralaspects of the breast at the pre-planning CT stage. Two corners oneach grid are tattooed on the breast and measurements to the nipple toall corners of both grids are recorded for reproducibility from planningto implant set up. MIM Symphony is used for planning. On theimplant day the grids are placed on the breast using the tattoomarkers. This ensures that the setup from the CT scan used forplanning is reproducible, despite the mobility of the breast. The exactlocations of the entry and exit points of the reference needle, asdetermined in planning, are then transcribed onto the skin. The grid isremoved and the markers are used to position the back pointer bridgewith the implant needle template guiding the needle. The referenceneedle is inserted and acts as an anchor for the breast. During theimplant procedure all measurements are relative to the reference needle.Results: To date, seven patients have been implanted using this technique.At the completion of this study a total of 15 patients will have been

S80 Abstracts / Brachytherapy 13 (2014) S15eS126

implanted. The average post-op (preliminary) results at day zero and daythirty for the lumpectomy bed plus 1.0 cm margin, for a prescription of90Gy, are as follows: D90 5 88.2Gy and 68.7Gy, V100 5 89.0% and83.2%, V150 5 62.3 and 49.2%, V200 5 38% and 30.9%, and skinsurface dose to a 1.0sq.cm area was 51% and 55.7% respectively.Conclusions: The results of the post-operative data of this technique arecomparable to those of ultrasound-guided implants conducted at theOdette Center. The benefit of the external-guided technique is that it is atool-guided method and thus does not depend on extensive ultrasound-guided implant experience.

PD74

Deformable Image Registration for Defining the Postoperative

Seroma in PBSI

Michelle Hilts, PhD, Deidre Batchelar, PhD, Jim N. Rose, MD, Juanita M.

Crook, MD. BC Cancer Agency - Southern Interior, Kelowna, BC,

Canada.

Purpose: To demonstrate the benefit of using pre-implant seroma contoursdeformed onto postoperative CT scans to define seromas for day 0 qualityassurance of permanent breast seed implants.Materials and Methods: Planning and day 0 CT scans from 8consecutive patients who received Pd-103 permanent breast seedimplants (PBSI) for low risk breast cancer at the BC Cancer Agency -Southern Interior were included. Clinically, seromas were contouredon the pre-implant CTs by an experienced radiation oncologist.Following implant, deformable registration (DR) (MIM Maestro) wasused to adapt and transfer pre-implant seroma contours to the post-implant scans. The resulting post-implant seroma contours wereevaluated for accuracy by the experienced radiation oncologist. The

accuracy of DR was assessed by measuring the spatial correspondenceof surgical clips between the pre and post-implant CT scans.Retrospectively, MIM Symphony was used to rigidly register (RR) preand post-implant CTs and the pre-implant seroma contours weretransferred to the post-op CT images. RR was performed both usingautomatic box-based registration and manually by 3 different observers(2 physicists and 1 radiation oncologist) yielding four independentobservers. Inter-observer variability was assessed using a conformityindex (CI 5 overlapping volume/encompassing delineated volume).The effect of variability in seroma location due to RR on thesubsequent assessment of implant quality was evaluated via DVHparameters for all seromas.Results: Mean time between planning and implant was 29 �9 days.Seroma visualization was good to excellent on all pre-implant CTs.Median seroma volume was 7.9 cc (range 4.2 - 20.2 cc). Due toartefacts from theseeds (79 � 25) seroma visualization on post-implantCTs was difficult and direct contouring of post-implant seromas wasunreliable. Following DR, the coordinates of surgical clips present inboth the pre and post-implant images had a mean agreement of 0.8 �0.9mm, lending confidence to this process. On adaption of the pre-implant seroma to the post-implant images, the change in seromavolume was minimal in 6 of the 8 cases (mean 11.0%). For one casebreast edema post-op was reflected in a significantly increased (81.8%)seroma volume post-implant. For a second case the seroma visiblychanged post-op appearing smaller and less distinct. This was reflectedin a 39.2% decrease in adapted seroma volume. These casesdemonstrate the ability of DR to reflect post-implant changes thatwould not be recognized by RR techniques. In all cases of DR, visualinspection by the experienced radiation oncologist confirmed that theadapted seroma coincided with the post-implant seroma and in nocases were contour alterations required. Inter-observer variability inRR of the pre-implant and post-implant CTs was poor and resulted inlow concordance of seroma location post-implant (median CI 526.5%, range 0 - 52.7%). Further, this variability in seroma locationtranslated into substantial variability in reported post-op dosimetrywith RR. For example, the mean spread in seroma V100 and V150was 14.8 � 5.5% and 15.6 �6.3% respectively. This variabilitypersists though PTV dosimetry and impacts the record of implant quality.Conclusions: Deformable image registration and adaptive contouring allowthe pre-implant seroma contour to be used for post-implant dosimetry in