ABS 07 Abstract
Abstract Number: 150158
Presenting Author: Mark J Rivard Author for Correspondence: Mark J Rivard, PhD Department/Institution:
Radiation Oncology, Tufts-New England Medical Center Address: 750 Washington Street
City/State/Zip/Country: Boston, MA, 02111, United States Phone: 1+617.636.1680 Fax: 1+617.636.7621 E-
mail: mrivard@tufts-nemc.org
Abstract Categories: 2. Breast Presentation format: Paper (7 minute presentation) Financial Disclosure: Yes, I
have/had a financial interest, arrangement, or affiliation with a commercial organization that may have a direct or
indirect interest in the subject matter of my presentation, as described below.
The applicator was provided to Tufts-NEMC and RIH for free on a temporary basis to assess its dosimetric and
clinical potential. The rest of the disclosure can be viewed in the PDF version. Space here prevents full text from being posted.
Title: STEREOTACTIC BREAST BRACHYTHERAPY APPLIED PERIPHERALLY USING A COMPRESSION
APPLICATOR AND HDR 192Ir
Mark J Rivard, PhD1, Raymond J Bricault Jr., MSc2, Christopher S Melhus, MSc1, Jessica R Hiatt, MSc3, Piran
Sioshansi, PhD2 and David E Wazer, MD1,3. 1Radiation Oncology, Tufts-New England Medical Center, Boston,
MA, United States, 02111; 2Radiation Physics, Advanced Radiation Therapy, Billerica, MA, United States, 01821
and 3Radiation Oncology, Rhode Island Hospital, Providence, RI, United States, 02903.
Purpose: Breast brachytherapy has historically been applied via interstitial or intracavitary application. This
approach produces conformal dose distributions through an invasive surgical procedure. By using peripherally
positioned brachytherapy applicators to preferentially irradiate the lumpectomy cavity, breast brachytherapy may be
applied without surgery while minimizing dose to critical structures such as the skin and chest wall. A novel
applicator design applies teletherapy-like beam collimation with brachytherapy dose falloff. This study aims to
characterize dose rate distributions through application of this surface applicator, and compare these results to
current standard-of-care treatment techniques.
Materials and Methods: Treatment using the ART applicator positions the breast within two mammography
paddles under compression to mimic the diagnostic geometry and affix the skin:source separation. Applicator
diameters ranged from 5-7cm, and use a W-alloy collimator with a conventional HDR 192Ir source. Skin separations
ranged from 3-7cm. Dose rate distributions and skin dose relative to target dose were assessed using Monte Carlo
(MC) methods and experimental techniques (ionization chambers and radiographic film). Using the MCNPv5
geometry package, the breast was modeled as a 16 cm diameter right cylinder with thicknesses of 3-7 cm in 0.5 cm
increments. Dose rate was calculated in annular voxels 1 mm thick in 1 mm radial increments from 0.1 to 7.9 cm.
Measurements were performed in a rectilinear acrylic phantom using a parallel plate ionization chamber to minimize
dose gradient volume averaging in the depth direction. Radiographic film was positioned at various depths for
direct comparison with the MC dose profile, and to confirm cylindrical symmetry.
Results: There was good beam uniformity within the collimated region. Surface and midplane collimation provided
a factor of 8 and 5 attenuation, respectively. Ionization chamber measurements and MC-derived dose falloff agreed
within 2%. Film measurements and MC-derived relative dose profiles agreed within 6%. Ratios of skin/target dose
ranged from 0.5 to 1.1 over the wide range of applicator sizes and breast separations. For a typical 6 cm diameter
applicator and 5 cm separation, the skin/target dose ratio was 0.74 with V50 < 50% and CTV DHI=1.00. Teletherapy
and balloon APBI have DHIs of 0.95 and 0.70, respectively.
Conclusions: Compared to possibilities with other treatment modalities, the dose distributions, CTV DHIs, and
normal tissue sparing are superior with this non-surgical approach.
