CT image-based interstitial HDR brachytherapy boost in the conservative treatment of Stage I–II breast cancer – introducing the procedure

CT image-based interstitial HDR brachytherapy boost in the conservative treatment of Stage I–II breast cancer – introducing the procedure

Abstracts / Brachytherapy 7 (2008) 91e194 was prescribed to a total dose of 34 Gy delivered in ten fractions of 340 cGy per fraction. Immediate readou...

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Abstracts / Brachytherapy 7 (2008) 91e194 was prescribed to a total dose of 34 Gy delivered in ten fractions of 340 cGy per fraction. Immediate readouts of the accumulated doses were obtained following irradiation. Results: The thyroid dose measured by the MOSFET was 8.9 cGy per fraction. This was in close agreement to our treatment planning dose calculation of 7.6 cGy per fraction. The NSABP-39 partial breast protocol allows a maximum point dose to the thyroid of 3% of the prescribed dose. The cumulative dose to the thyroid in our study was approximately 89 cGy which is less than 2.6% of the maximum dose. Conclusions: Studies have shown that standard breast external beam radiation offers a total cumulative dose of 3e6 Gy to the thyroid. Our study shows a cumulative dose of 0.89 Gy to the thyroid with MammoSite treatment. Our case also represents a scenario where the MammoSite was located in the superior portion of the breast and did not exceed dose limits provided by NSABP-39 to the thyroid. MOSFETS demonstrate a reliable method of examining in-vivo dosimetry during MammoSite brachytherapy and we plan to continue monitoring patients to evaluate dose to surrounding tissues.

PO19 Dosimetric comparison of three methods of partial breast irradiation Cathryn Yashar, M.D., D. Scanderbeg, Ph.D., R. Rice, Ph.D., G. White, Arno Mundt, M.D. Radiation Oncology, University of California San Diego, La Jolla, CA. Purpose: Whole breast radiation has been the standard for breast conservation, despite data that remote failures do not exceed 1e5%. Recently, partial breast radiation has demonstrated excellent preliminary results. Methods include interstitial and MammoSiteÒ brachytherapy, and 3D conformal (3DCF) radiation. MammoSite is simple to perform and is widely accepted. However, some catheters are removed for poor tissue conformance, balloon asymmetry, or inadequate skin distance. In addition, up to 32% may develop persistent seromas. 3DCF therapy uses external radiation focused on the target but exposes more normal tissue. The Cianna Medical multi-catheter, single entry high-dose-rate applicator, SAVI, was designed to allow greater flexibility in treatment planning with fewer anatomic and cavity conformity and volume constraints. The applicator contains 6e10 peripheral struts for source dwell positions so dosing can be modulated and optimized for normal tissue conformance. Methods and Materials: To compare modalities, patients treated with SAVI were also evaluated for MammoSite and 3DCF partial breast radiation and a dosimetric comparison was made. For MammoSite evaluation, a single dwell position was selected in the center of the tumor bed and dose was prescribed at 3 cm, mimicking a 4 cm diameter balloon (~ 30 cc volume) prescribed to a 1 cm margin. For the 3DCF evaluation, the tumor bed was outlined on a CT scan and a 3DCF plan was generated per NSABP guidelines. Dosimetric comparisons were performed evaluating maximum skin, lung, chestwall/rib dose, V100, V150, V200 and dose homogeneity index (DHI). Results: The target volumes differed with SAVI having the least at 50 vs. 82 and 272 cc MammoSite and 3D CF, respectively. The V100, 150 and 200 (%) for the three modalities were 89, 41, 18 (SAVI) vs. 93, 34, 38 (MammoSite) vs. 86 (V100 3DCF). The DHI was 0.54 for SAVI and 0.64 for MammoSite. The average max lung dose (%) was 55, 87, and 98; rib 86, 150, and 105 and for skin 75, 103, and 99 (SAVI, MammoSite, and 3DCF). Conclusions: Comparing modalities, PTV coverage varied between 86e93%, with more breast tissue covered by 3DCF, as expected, given the differences between external beam and brachytherapy. The volume that received 150e200% of the prescription dose was similar between SAVI and MammoSite, while the DHI was considerably higher for MammoSite, as expected, considering the differing device geometries. However, it is unclear whether the DHI is related to SAVI efficacy. The average maximum lung, skin and rib doses were lowest for the SAVI, highlighting its ability to conform to exclude normal tissues. In offering partial breast radiation, the availability of a variety of techniques allows for maximal patient eligibility, and comparison of individual method pros and cons guide the most appropriate choice. I have spoken at one meeting for the company, Biolucent, in which they paid my travel expenses.

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PO20 CT image-based interstitial HDR brachytherapy boost in the conservative treatment of Stage IeII breast cancer e introducing the procedure Magda Kubaszewska, M.D.1 Magdalena Dymnicka, M.S.2 Janusz Skowronek1 Adam Chichel, M.D.1 Marek Kanikowski, M.D.1 1 Brachytherapy, Greatpoland Cancer Center, Poznan, Poland; 2Medical Physics, Greatpoland Cancer Center, Poznan, Poland. Purpose: Breast-conserving surgery (BCS) followed by radiotherapy (RT) is a standard treatment for the majority of early breast cancers. Postoperative whole-breast irradiation (WBRT) in patients remaining at high risk for local failure should be followed by additional boost to the tumor bed with proper safe margin and adequate technique. We present the preliminary findings of our protocol treating the tumor bed as a boost after BCT in selected patients with early-stage breast cancer using HDR brachytherapy (BT) based on CT image procedure. Methods and Materials: Between Jan 2006 and Aug 2007, 58 female patients with stage I-II breast cancer underwent BCT. This therapeutic procedure consist of a BCS, WBRT and a interstitial HDR BT boost to the tumor bed. Single, double and triple plan implant were used in 6, 42 and 10 cases, respectively. The boost dose was 10 Gy in all patients and they were treated with an afterloader using Ir-192 isotope with initial activity of 370 GBq (10Ci). Two sets (pre- and post-implant) of CT scans were required to improve the implant quality. The treatment planning was based on the CT-guided 3-D reconstruction of the surgical clips, implant tubes and critical structures. Results: The accuracy of tumor bed localization, the conformity of PTVand treated volume were analyzed. 3 methods of dose optimization were applied: manual, on dose point and geometrical in 23, 29 and 6 patients, respectively. The evaluations of implant parameters involved the use of: dose volume histogram (DVH), the volume of 100% reference isodose (V100%), the high dose volume calculation (V150%, V200%, V300%), the dose nonuniformity ratio (DNR), the conformity index (COIN). The mean PTV volume, the mean high dose volume (V150%; V200%; V300%), the DNR and COIN mean value were estimated at 57,38; 42,98; 21,38; 7,90; 0,52; 0,83; respectively. Conclusions: The use of surgical clips and CT together seems to be the best method to determine the target volume. Two sets (pre- and post-implant) of CT scans are required to improve the implant quality. CT-based BT boost treatment planning is useful tool to avoid geographical miss. The irregular 3-D shape of the target volume and the normal tissue structures can only be localized correctly on the basis of visual information obtained from cross-sectional CT-imaging. The advantages of HDR BT include: outpatient treatment, control of patient positioning to assure accuracy of treatment delivery, ability to optimize dose distribution, improvement in radiation protection for staff, possibility of treatment time shortening in comparison to electron boost technique.

PO21 A new shielding method for 192Ir MammoSite brachytherapy for using the microSelectron HDR Victor A. Lopez, M.S., Brent Murphy, M.S., James Wheeler, M.D., Ph.D. 1 Radiation Oncology, Center for Cancer Care, Goshen, IN; 2Medical Physics, Purdue University, West Lafayette, IN. Purpose: The high-dose-rate (HDR) brachytherapy MammoSiteÒ Radiation Therapy System is commonly used to deliver partial breast radiation therapy to women with early-stage breast cancer. The system is designed to treat the tissue immediately surrounding the lumpectomy site via an inserted balloon catheter. Patients with lumpectomy sites near the skin (!7 mm) are commonly excluded from MammoSiteÒ therapy. Placement of a shield between the source & the breast tissue allows for patients with a lesser skin distance to become eligible for MammoSiteÒ brachytherapy. Methods and Materials: Monte Carlo N-Particle version 5 (MCNP5) photon transport calculations using the new shielding method were completed and tabulated for an 192Ir source centered within 30 cm of water using a 50, 60, & 70 cc MammoSiteÒ catheter (4e5 cm). The 10