A dosimetric comparison of AccuBoost® noninvasive partial breast brachytherapy to electron beam tumor bed boost and 3-D conformal accelerated partial breast irradiation

Oral Presentations / Brachytherapy 8 (2009) 105e180 Results: Dosimetry was outstanding with median V90, V150 and V200 of 96.2%, 25.7, and 12.9 cc. Thirty percent received antibiotics, and the infection rate was 5%. Keloid formation was seen in 1 patient. There were no symptomatic seromas and one report of asymptomatic fat necrosis seen on mammogram at 1 year. Fourteen patients (35.0%) were treated with a skin-cavity spacing of <7 mm. The median skin dose remained less than 100% in patients with skin bridges <7 mm. Even in patients with the device in close proximity to both skin and lung, dose to both structures remained less than 100%. There have been no local recurrences to date. Conclusions: Early clinical experience with the SAVI demonstrates the ease of placement of single entry brachytherapy devices combined with the increased dose modulation of interstitial brachytherapy. Dose to normal structures has remained exceedingly low. Almost half of evaluated patients were not candidates for other single entry brachytherapy devices because of skin spacing or breast size, demonstrating an expansion of candidates for single entry partial breast brachytherapy. OR26 Presentation Time: 10:15 AM A dosimetric comparison of AccuBoostÒ noninvasive partial breast brachytherapy to electron beam tumor bed boost and 3-D conformal accelerated partial breast irradiation Shirin Sioshansi, M.D.,1,3 Jessica R. Hiatt, M.S.,3 Mark J. Rivard, Ph.D.,1 Amanda A. Hurley, C.M.D.,3 Yoojin Lee, M.S., M.P.H.,2 Jaroslaw T. Hepel, M.D.,1,3 Gene A. Cardarelli, Ph.D., M.P.H.,3 Sean O’Leary, R.T.T.,1 David E. Wazer, M.D.1,3 1Radiation Oncology, Tufts Medical Center, Tufts University School of Medicine, Boston, MA; 2 Institute for Clinical Research and Health Policy Studies, Tufts Medical Center, Boston, MA; 3Radiation Oncology, Rhode Island Hospital, Brown Medical School, Providence, RI. Purpose: To perform 3D dose modeling and dose-volume analysis of the AccuBoostÒ system and compare it to electron boost and 3D-CRT APBI techniques. Methods and Materials: AccuBoostÒ is an image-guided non-invasive breast brachytherapy approach consisting of breast immobilization via moderate compression followed by 2D mammographic target localization. Tungsten applicators mounted on mammography paddles are centered on the target and direct HDR 192Ir emissions along orthogonal axes. Dosimetric characterization of single applicators has been performed. However, 3D dose modeling of all 4 applicator positions has not been examined due to limitations of conventional brachytherapy treatment planning systems to model the tungsten applicator collimation and variable tissue deformation as a consequence of breast compression in both axes. Consequently, within PinnacleÒ AccuBoost applicator dose distributions were modeled as single point-sources with appropriate simulated anisotropy using the 2D brachytherapy dosimetry formalism. This source data was applied to compressed breast CT data from 8 patients imaged in the prone position on a table such that the breast would fall forward and be compressed between parallel plates in the

Median AccuBoostÒ boost Median eboost p-value Median AccuboostÒ APBI Median 3DCRT APBI p-value

PTV Volume (cc)

PTV Dmax (Gy)

PTV Dmin (Gy)

PTV Dmean (Gy)

Chest Wall Max (cGy)

Skin Max (cGy)

44.2

2.31

1.77

2.07

30.8

91.2

68.8

2.27

1.11

2.14

214.2

229.3

0.023 77.9

NS 45.5

0.016 33.9

0.008 39.5

0.008 32.4

0.008 94.8

221.6

40.0

31.4

38.6

99.9

104

0.008

0.055

NS

NS

0.008

0.039

117

cranial-caudal and medial-lateral axes. Patient dose distributions were calculated using a 1 mm3 grid. PTV coverage and max dose to skin, lung, and chest wall were assessed and compared to conventional electron boost (using CT-based cavity + 0.5 cm, 2 Gy to 90% isodose line) and 3DCRT APBI (per NSABP B-39 protocol). Results: AccuBoostÒ target volumes are 35% and 65% smaller than the respective eboost and 3DCRT APBI volumes (p 5 0.023 for boost; p 5 0.008 for APBI). AccuBoostÒ max skin dose is 60% lower than eboost and 10% lower than 3DCRT. Compared to eboost and 3DCRT APBI, AccuBoostÒ delivers 70-90% less dose to the chest wall and lung. There is NSS difference between eboost and AccuBoostÒ boost for the PTV V110, V90, V80, V50, V20, Dmax, or D100. Eboost plans have a lower Dmin than AccuBoostÒ boost (1.11 Gy vs. 1.77 Gy, p 5 0.016), but higher V100, D90, and D50. With regards to PTV coverage, the only SS differences between the APBI techniques are: slightly higher D90 and V90 with 3DCRT and higher Dmax with AccuBoostÒ (45.5 Gy vs. 40 Gy p 5 0.055). Conclusions: By virtue of image-guidance and immobilization decreasing the need for extensive margin expansions, the AccuBoostÒ boost and APBI target volumes are substantially smaller than the respective eboost and 3DCRT volumes sparing more normal tissue. Max dose to skin, chest wall, and lung are also significantly lower with the AccuBoostÒ technique while PTV coverage remains comparable. Further efforts to model the tissue deformation as a result of serial compression are underway.

OR28 Presentation Time: 10:25 AM Initial dosimetric experience: ConturaÔ Multilumen Balloon Registry Trial Douglas W. Arthur, M.D.,1 Dorin Todor, Ph.D.,1 Frank A. Vicini, M.D.,2 Thomas B. Julian, M.D.3 1Radiation Oncology, Virginia Commonwealth University, Richmond, VA; 2Radiation Oncology, William Beaumont Hospital, Royal Oak, MI; 3Human Oncology, Allegheny General Hospital, Pittsburgh, PA. Purpose: The ConturaÔ Multilumen Balloon (MLB) registry trial is a multiple site accelerated partial breast irradiation (APBI), prospective, non-randomized study designed to compare the dosimetric efficacy of the ConturaÔ MLB with a single central lumen balloon device and to quantify the dosimetric improvement of multi-lumen use over single lumen use. The initial dosimetric comparison is presented. Methods and Materials: All patients are enrolled prior to ConturaÔ MLB placement. Eligibility criteria include early stage breast carcinoma confirmed to be <3 cm, unifocal, invasive or non-invasive histology that is estrogen receptor positive. Tumors must be resected with a negative pathologic margin, axillary nodes must be negative and the patient >50 years old. After successful post lumpectomy placement of the ConturaÔ MLB is confirmed by CT scan, three dosimetric plans are generated; multilumen (ML), centrallumen/multi-dwell (CL-M.D.) and central-lumen/single-dwell (CL-SD). All three plans are created with the goal of satisfying all five of the following dose criteria: >95% of the prescribed dose received by >95% of the target volume (with a 5% relaxation allowed on this parameter), max skin dose <125% (42.5 Gy), max rib dose <145% (50 Gy), V150 <50 cc and V100 <10 cc. All patients received 34 Gy delivered to the treatment target as 3.4 Gy bid over 5 days and continue with close followup. Secondary endpoints for this registry trial include disease control (local ipsilateral, contralateral, regional, and distant recurrences), cosmetic results and toxicity rates. Total accrual will be 342 patients. Results: Since opening in March 2008, the trial has accrued 52 patients. Twenty-five patients have completed data sets available for review. Seventy three percent of patients are >60 yo and overall 19% presented with disease stage Tis, 73.1% with T1 and 7.7% with T2. Median tumor size was 15 mm. When comparing the three dosimetric plans for each patient it was found that the ML approach succeeded in meeting all dosimetric criteria in 80% of the cases whereas the CL-M.D. and CL-SD plans only succeeded in 61.5% and 40%, respectively. There were 5 patients where CL-M.D. plans (20%) and 9 patients where CL-SD plans (36%) were unsuccessful in meeting all 5 dosimetric criteria but, with the use of the ML catheter, all criteria were successfully met. The ML plan delivered a max skin dose of <125% in 92% of cases as compared to 73.1% and 60% for the CL-M.D. and CL-SD plans generated for the same patients, respectively. When the balloon-skin