Accelerated Partial Breast Irradiation Techniques and Clinical Implementation - part 10 doc

 David E Wazer cised tissue, tumor diameter, and a history of diabetes or hypertension were not found to be significantly associated with either cosmetic score or normal tissue toxicity In contrast, several implant-associated variables could be identified as having significant influence on the risk of an adverse cosmetic outcome or increased risk of late skin toxicity, late subcutaneous toxicity, and clinically evident fat necrosis (Table 17.3) (Wazer et al 2006) In general, the volume of the implant, the volume of dose “hotspots” as defined by the V150 and V200, and the global dose homogeneity of the implant as described by the DHI were strongly correlated with adverse outcome This study was the first to provide some specific dosimetric parameters to guide clinicians in defining, at least with respect to late tissue effects, what constitutes an optimal interstitial HDR implant 17.3.3 Is there an Adverse Interaction between Interstitial Brachytherapy and Chemotherapy? The answer is “possibly” The first evidence presented in this regard was reported by Kuske et al (2002) from the RTOG 95-17 trial In their study, grade toxicity was significantly increased with the use of chemotherapy This was true for both HDR and LDR techniques, but particularly so for LDR implants Similarly, Arthur et al (2003) found that APBI with an LDR interstitial technique was associated with a significant decrement in cosmetic outcome when patients also received Adriamycin-based chemotherapy In the combined Tufts/Brown/VCU series (Wazer et al 2006) of HDR interstitial brachytherapy, the use of Adriamycin-based chemotherapy was associated with an increased risk of clinically evident fat necrosis, grade 1/2 skin toxicity, and suboptimal cosmetic scores In contrast, no adverse interactive effect has yet been found between the use of chemotherapy and the MammoSite catheter (Vicini et al 2005) 17.3.4 Toxicity Avoidance Guidelines As clinical data continue to accumulate, toxicity avoidance guidelines can, at best, be considered preliminary and subject to future revision The guidelines that will be put forward are, by and large, limited to the use of HDR interstitial brachytherapy To date, the amount and dosimetric specificity of data regarding LDR implants is simply too sparse to make even limited recommendations With these caveats, current data suggest the following: • Volume probably matters; that is, keep it as low as practically achievable within the constraints imposed by adequate coverage of the PTV Ideally, less than 60% of the normal whole breast reference volume should receive greater than or equal to 50% of the prescribed dose • Minimize hot spots The dosimetric parameter that appears to be particularly sensitive in this regard is the V150 Most certainly, this value needs to be ≤70 cm3 though it appears preferable to strive for 0.75, even better >0.85 This is achievable with all of the common currently employed interstitial catheter placement techniques but does require attention to the detail of catheter position 17 Normal Tissue Toxicity after Accelerated Partial Breast Irradiation • •  The dose/volume limits to the skin and chest wall are as yet not defined In general, the dose delivered to these structures should be less than the prescribed dose Delineate the PTV such that it is at least mm from the skin Proceed with caution if chemotherapy is to be used after interstitial brachytherapy APBI 17.4 MammoSite 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 brachytherapy 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