Mammo Site Brachytherapy

The first and perhaps most critical factor to consider in assessing risk of normal tissue effects with MammoSite brachytherapy is that, from the perspective of both dosimetry and radiobiology, it is a distinctly different implant from interstitial brachytherapy. As such, one must be cautious in transferring the lessons learned from interstitial brachy-therapy APBI as they likely have limited relevance to this applicator system. As an example of these inherent differences, Shah et al. (2004) reported a series of interstitial and MammoSite implants and found significant differences in critical dosimetric parameters. MammoSite implants are associated with significantly less irradiated tissue and smaller volume "hotspots" as compared to interstitial brachytherapy (for example, V150 of 26 cm3 with MammoSite vs. 40 cm3 with interstitial technique, P<0.0001). In contrast, the global uniformity as reflected in the calculated DHI is superior with an interstitial implant (DHI of 0.83 with interstitial technique vs. 0.73 with MammoSite, P<0.0001). The relative importance of these variables in predicting normal tissue toxicity after MammoSite brachytherapy has yet to be fully elucidated.

In addition to the standard toxicity endpoints as described in the RTOG/EORTC rating scale, there are events that are, for the most part, specific to the MammoSite catheter that can result in implant failure. These include:

• Non-conformance of the applicator to the excision cavity (Fig. 17.5)

• Suboptimal balloon-to-skin spacing (Fig. 17.8)

• Inadequate tumor excision margin or nodal status (for intraoperative placement) The initial safety and performance multi-institutional trial of the MammoSite catheter was performed by Keisch et al. (2003). This study of 43 patients investigated acute toxicity encountered up to 4 weeks after treatment. The most common side effects of the procedure included mild erythema (57.4%), drainage (51.9%), pain (42.6%), ecchymosis (31.5%), seroma (11.1%), and an infection rate of 3.7% (Figs. 17.9 and 17.10). Post-procedure infections have been the focus of some controversy in the early experience with the MammoSite catheter (Harper et al. 2005). However, it does appear that with meticulous wound care during the 1-2 weeks required to complete irradiation, the infection rate can be kept acceptably low even when assessed amongst a broad base of users. In a report of the American Society of Breast Surgeons (ASBS) Breast Brachytherapy Registry trial, the device-related infection rate among 793 patients was only 5.9% (Vicini et al. 2005). Prophylactic antibiotic use is advocated by some (Harper et al. 2005), but its role in modifying the rate of device-related infections remains unclear.

The incidence of seroma after MammoSite APBI is another area of on-going study (Fig. 17.11). The acute incidence of 11% reported by Keisch et al. (2003) likely under-represents the frequency of persistent asymptomatic and symptomatic seroma seen

Fig. 17.5 An example of unacceptable non-con- Fig. 17.6 Intracavitary hemorrhage 24 hours after formance to target breast tissue of the fully inflated intraoperative placement of a MammoSite cath-MammoSite catheter eter
Mammosite Catheter

Fig. 17.7 Spontaneous rupture of a MammoSite Fig. 17.8 Suboptimal balloon-to-skin spacing catheter 48 hours after placement results in partial after intraoperative MammoSite placement neces-

filling of the lumpectomy cavity with dilute con- sitating catheter removal trast material

Fig. 17.7 Spontaneous rupture of a MammoSite Fig. 17.8 Suboptimal balloon-to-skin spacing catheter 48 hours after placement results in partial after intraoperative MammoSite placement neces-

filling of the lumpectomy cavity with dilute con- sitating catheter removal trast material

Breast Brachytherapy
Fig. 17.9 An example of the severity of acute skin affects that can be seen after MammoSite brachy-therapy APBI: grade 3 skin reaction 5 weeks after completion of treatment. The balloon-to-skin distance was >9 mm

Fig. 17.10 Infection in the operative bed 8 weeks after completion of MammoSite brachytherapy APBI

Fig. 17.11 Persistent and painful seroma (with associated mammogram) at the operative bed in the upper outer quadrant 9 months after completion of MammoSite brachytherapy APBI

Fig. 17.10 Infection in the operative bed 8 weeks after completion of MammoSite brachytherapy APBI

Mammosite Treatment

after several months of follow-up. The factors that contribute to the risk of persistent seroma as well as the most effective clinical management strategy have yet to be fully elucidated.

As the MammoSite catheter was approved for clinical use in May 2002 by the United States Food and Drug Administration, few data exist on the intermediate and late tissue effects. Keisch et al. (2004) have reported on a more extended evaluation of their original 43 patient cohort with a median follow-up of 29 months. These data show that cosmetic scores are clearly related to balloon-to-skin spacing such that suboptimal results are seen when the spacing is <6 mm. Further, these authors report asymptomatic fat necrosis in 4.9%, subcutaneous fibrosis in 29%, and telangiectasia in 27%. In light of the time-dependent evolution of late effects reported with interstitial brachytherapy APBI by the Beaumont Hospital group (Fig. 17.2), a reasonable expectation is that similar changes may be seen with further follow-up of the MammoSite experience.

Additional data regarding intermediate and late effects on normal tissue after Mam-moSite APBI are being actively collected through the ASBS Registry trial (Vicini et al. 2005). In a report of 702 patients, factors found to be significantly associated with favorable cosmetic outcome are balloon-to-skin spacing, both as a continuous variable and at a cut-off value of >7 mm, and larger bra size (C/D versus A/B) (Vicini et al. 2005). The use of chemotherapy or tamoxifen was not found to adversely affect cosmetic outcome.

How do MammoSite and interstitial brachytherapy compare with respect to normal tissue side effects? One might expect that, with the smaller volume of irradiated tissue seen with MammoSite, that MammoSite would be clearly superior in this regard. To address this question, Shah et al. (2004) used an expanded dataset from the Tufts/Brown/ VCU collaboration to perform a comparison of normal tissue toxicity encountered with interstitial brachytherapy (75 cases) versus MammoSite (28 cases). When all patients were included, the use of the MammoSite catheter was associated with a higher rate of grade 1 acute skin toxicity (42.9% vs. 17.3%, P= 0.01) whereas subcutaneous fibrosis was more commonly seen with interstitial brachytherapy (32% vs. 10.7%). However, when interstitial brachytherapy patients who received chemotherapy were excluded from the analysis (as none of the MammoSite patients received chemotherapy), the only significant difference that remained between the groups was a higher rate of grade 1 skin toxic-ity with MammoSite.

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  • Saara
    Is mammosite intracavitary or intersitial brachytherapy?
    8 years ago
  • Jodi
    Is mammosite interstitial or intracavitary?
    8 years ago

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