Abstract Text
Partial breast irradiation (PBI) represents a standard treatment option for selected patients with low-risk early stage breast cancer (BC). Advantages of PBI included shorter treatment time (if accelerated, APBI), potentially improved safety profile and cost-effectiveness, as compared to whole breast irradiation (WBI). The available PBI techniques include single-entry balloon catheter, multi-field external-beam, interstitial/intracavitary brachytherapy, intra-operative electron- and low-energy photon beams. The role of PBI has been investigated in large-scale prospective randomized phase 3 clinical trials, demonstrating the non-inferiority (only external beam radiation therapy and brachytherapy testing trials) of PBI versus WBI for local recurrence (LR) risks and overall similar/lower long-term toxicity, the latter depending on the adopted technique and fractionation. Comprehensive patient reported outcome measures (PROMs) in the IMPORT LOW trial showed that the average number of adverse events (AEs) per person was lower in PBI versus WBI group and decreased over time in all groups. The RAPID trial showed that accelerated APBI was not inferior to WBI in preventing LR and was associated with less acute toxicity but showed increased late toxicity and adverse cosmesis, probably related to the dose/fractionation with a twice-daily regimen and the treated-volume issues (in agreement with preliminary results from IRMA trial). The NSABP B-39/RTOG 0413 trial - at a median follow up of 10.2 years – showed low breast events and a 10-year IBTR difference (0.7%) small and clinically not relevant, thus considering APBI an acceptable alternative to WBI for a consistent proportion of women undergoing breast conserving surgery (BCS).
Surgical techniques for contemporary breast conservation can be sophisticated, depending on aesthetic considerations. In most cases of straightforward small volume excisions, the breast parenchyma is carefully closed (simple excision or up to level 1 oncoplastic procedures). However, even in these cases the skin incision is often placed remote from the tumour in a cosmetically optimal location. In more challenging cases, where resection volumes are larger or more extensive breast reshaping is required using a variety of dermo glandular pedicles, the primary tumour bed margins may be substantially repositioned within the breast volume with margins often separated both from each other and from the surgical scars (≥level 2 oncoplastic procedures). Identifying the tumour bed, which does generally not equate with the lumpectomy cavity, is a very challenging process: reliance on the skin scar and seroma cavity has been shown to be inaccurate even in the case of standard BCS, resulting in poor localization of the target volume in over half of cases. Accurately positioned surgical clips in the lumpectomy cavity improve surgical bed identification on the planning CT scan, which contributes to more accurate delineation of the primary tumour bed both in volume and in location. This should lead to a better cosmetic outcome. Hence, the success of more localised RT strategies, such as APBI, may be jeopardised by a lack of communication between surgeons, radiologists, pathologists and radiation oncologists who all need to work closely together to ensure that the tumour bed and the margins around it to the CTV can be reliably identified. At present, only few studies evaluated the efficacy and effectiveness of preoperative PBI. Among the benefits of preoperative PBI are improved visibility of the primary tumour, resulting in smaller target volumes, higher accuracy, and minimized risk of geographical error. In addition, surgery is performed after preoperative PBI and can therefore remove the area of the breast that received the highest RT dose, possibly leading to limited fibrosis and a good cosmetic result. Even though preoperative APBI appears to be a feasible and widely available technique with promising results for low risk breast cancer patients, uncertainties remain with regard to tumour delineation, adequate planning target margins, optimal fractionation and timing of surgery. Concerning the optimal treatment schedule for APBI, the long-term results of the UK FAST trial show that postoperative whole-breast RT is equivalent to 50 Gy/25 fractions in terms of late cosmesis, and the UK FAST-Forward Trial (26 Gy in 5 fractions) tested - as the Florence phase 3 trial (30 Gy in 5 fractions) - a 5-fraction schedule with excellent results (both local control and safety). Similarly, postoperative fractionated multi-catheter brachytherapy appears to have less late skin toxicity than 50 Gy/25 fractions WBI. The existing level-1 evidence supporting the use of PBI derives from schedules based on 5 or more fractions.