Abstract
We evaluate the CyberKnife (Accuray Incorporated, Sunnyvale, CA, USA) for non-invasive delivery of accelerated partial breast irradiation (APBI) in early breast cancer patients. Between 6/2009 and 5/2011, nine patients were treated with CyberKnife APBI. Normal tissue constraints were imposed as outlined in the National Surgical Adjuvant Breast and Bowel Project B-39/Radiation Therapy Oncology Group 0413 (NSABP/RTOG) Protocol (Vicini and White, 2007). Patients received a total dose of 30 Gy in five fractions (group 1, n = 2) or 34 Gy in 10 fractions (group 2, n = 7) delivered to the planning treatment volume (PTV) defined as the clinical target volume (CTV) +2 mm. The CTV was defined as either the lumpectomy cavity plus 10 mm (n = 2) or 15 mm (n = 7). The cavity was defined by a T2-weighted non-contrast breast MRI fused to a planning non-contrast thoracic CT. The CyberKnife Synchrony system tracked gold fiducials sutured into the cavity wall during lumpectomy. Treatments started 4–5 weeks after lumpectomy. The mean PTV was 100 cm3 (range, 92–108 cm3) and 105 cm3 (range, 49–241 cm3) and the mean PTV isodose prescription line was 70% for groups 1 and 2, respectively. The mean percent of whole breast reference volume receiving 100 and 50% of the dose (V100 and V50) for group 1 was 11% (range, 8–13%) and 23% (range, 16–30%) and for group 2 was 11% (range, 7–14%) and 26% (range, 21–35.0%), respectively. At a median 7 months follow-up (range, 4–26 months), no acute toxicities were seen. Acute cosmetic outcomes were excellent or good in all patients; for those patients with more than 12 months follow-up the late cosmesis outcomes were excellent or good. In conclusion, the lack of observable acute side effects and current excellent/good cosmetic outcomes is promising. We believe this suggests the CyberKnife is a suitable non-invasive radiation platform for delivering APBI with achievable normal tissue constraints.
Highlights
The American Cancer Society estimated 192,370 new breast cancers were diagnosed in 2009 (Jemal et al, 2009)
This observation has led to an enormous interest in accelerated partial breast irradiation (APBI) for early breast cancer over the last decade
A recent presentation at the ASCO Breast Cancer Symposium reported that at a mean 36.7 months less than 14% of the 1,367 women enrolled in the 3D-CRT arm of the NSABP B-39/RTOG 0413 trial had Grade 2 or 3 fibrosis–cosmesis and fibrosis-deep connective tissue toxicities (Julian et al, 2010), other institutions on a smaller scale have not been able to duplicate the results and have published their concerns about poor cosmetic outcomes (Hepel et al, 2009; Jagsi et al, 2010)
Summary
The American Cancer Society estimated 192,370 new breast cancers were diagnosed in 2009 (Jemal et al, 2009). Following a lumpectomy with clear margins (≥2 mm), 90% of recurrences in women who present with early disease (stage 0, I, II) have been observed to occur within 10 mm of the resection cavity (Clark et al, 1992; Vicini et al, 2003, 2004) This observation has led to an enormous interest in accelerated partial breast irradiation (APBI) for early breast cancer over the last decade. Because of the invasiveness of these procedures, their steep learning curve and risks of infection, lumpectomy cavity coverage with three-dimensional conformal radiotherapy (3D-CRT), and intensity-modulated radiotherapy (IMRT) have grown in popularity These external beam techniques come with a price: to assure coverage of a moving target beneath the fixed beam of a linear accelerator, the planning target volumes (PTVs) are enlarged compared to brachytherapy volumes. A recent presentation at the ASCO Breast Cancer Symposium reported that at a mean 36.7 months less than 14% of the 1,367 women enrolled in the 3D-CRT arm of the NSABP B-39/RTOG 0413 trial had Grade 2 or 3 fibrosis–cosmesis and fibrosis-deep connective tissue toxicities (Julian et al, 2010), other institutions on a smaller scale have not been able to duplicate the results and have published their concerns about poor cosmetic outcomes (Hepel et al, 2009; Jagsi et al, 2010)
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