ESTRO 36 Abstract Book

S93 ESTRO 36 _______________________________________________________________________________________________

in 8 (6%) and unknown in 3 (2,5%) patients. Late skin toxicity was registered in 29 (23,4%) patients, grade 1-2 in 28 (22,5%), grade 3 in 1 (0,8%). Late toxicity was significantly related to the skin administered doses (≤ 55% vs. > 55%, P < 0.05). Conclusion PBI delivered with 192 Ir HDR-BRT in selected breast cancer patients was associated to high local control and survival with excellent cosmetic outcomes. An appropriate patient selection and skin dose ≤ 55% provided optimal clinical outcomes. OC-0182 2nd breast conserving therapy with interstitial BT vs mastectomy for treatment of local recurrences V. Smanykó 1 , N. Mészáros 1 , M. Ujhelyi 2 , G. Stelczer 1 , T. Major 1 , Z. Mátrai 2 , C. Polgár 1 1 National Institute of Oncology, Center of Radiotherapy, Budapest, Hungary 2 National Institute of Oncology, Center of Surgery, Budapest, Hungary Purpose or Objective To compare the clinical outcomes of second breast conserving therapy (BCT) with perioperative high-dose- rate (HDR) interstitial brachytherapy (iBT) versus salvage mastectomy (sMT) for the treatment of ipsilateral breast tumor recurrences (IBTRs). Material and Methods Between 1999 and 2016, 92 patients who presented with an IBTR after previous BCT were salvaged either with reexcision and perioperative HDR multi-catheter iBT (n=35) or sMT (n=57). In the BCT + HDR iBT group a median of 7 (range: 4-23) catheters were implanted intraoperatively. A total dose of 22 Gy in 5 fractions of 4.4 Gy was delivered to the tumor bed with a margin of 1-2 cm perioperatively on 3 consecutive days. Similar proportion of patients received adjuvant chemotherapy in the two groups (17% after BCT + HDR iBT vs 21% after sMT) and/or hormonal treatments (71% vs 70%, respectively). Five-year oncologic outcomes (including ultimate local tumor control, regional tumor control, disease-free survival [DFS], cancer specific survival [CSS], and overall survival [OS]) were estimated by the Kaplan-Meier method. Survival curves were compared with the log-rank test. Results Mean follow up time was 63 months (range: 2-183) in the BCT + HDR iBT group vs 30 months (range: 4-164) in the sMT group. The mean diameter of IBTRs was 16.8 mm (range: 2-70) vs 24.5 mm (range: 2-60), respectively. There was no significant difference in any other patient (e.g. age, menopausal status) or IBTR related (e.g. grade, vascular invasion, margin status, receptor status) parameters between the two groups. Three out of 35 (8.6%) and 7 out of 57 (12.3%) second local recurrences occurred in the BCT + HDR iBT and the sMT group, respectively. The 5-year actuarial rate of second local recurrence was 7.4% after BCT + HDR iBT vs 17.5% after sMT (p=0.11). The respective 5-year rates of regional recurrence were 7.2% vs 5.3% (p=0.17). The 5-year probability of DFS, CSS, and OS were 69.7% vs 73.5% (p=0.79), 74.9% vs 80.5% (p=0.72), and 74.9% vs 69.6% (p=0.73), respectively. At the time of analysis data on cosmetic results were available for 31 patients (88.6%) in the BCT + HDR iBT group. Among these, 3 (9.7%), 16 (51.6%), 5 (16.1%), and 7 (22.6 %) patients had excellent, good, fair, and poor cosmetic results. Grade 2 and 3 late skin toxicity occurred in 2 (5.7%) and 1 (2.9%) patients, while grade 2 and 3 fibrosis developed in 9 (25.7%) and 1 (2.9%) patients. Asymptomatic fat necrosis was detected in 11 (31.4%) women. Conclusion Second BCT + HDR iBT is a safe and feasible option for the management of IBTRs resulting similar 5-year oncologic

outcomes compared to standard sMT. HDR iBT may decrease the risk of second IBTR with acceptable cosmetic results and low rate of late side effects.

Poster Viewing : Session 4: Brachytherapy miscellaneous

PV-0183 Microbrachytherapy: even more localised dose profiles? R. Brown 1,2 , X. Franceries 1,2 , M. Bardiès 1,2 1 INSERM, UMR1037 CRCT- F-31000, Toulouse, France 2 Université Paul Sabatier, UMR1037 CRCT- F-31000, Toulouse, France Purpose or Objective Owing to its intrinsic ability to deliver increased dose rates to tumours whilst respecting organ at risk (OAR) constraints, brachytherapy (BT) is being increasingly used for the treatment of radioresistant tumours. A new form of BT, microbrachytherapy (MBT), is proposed for small tumours. For this treatment, the grains used in BT are replaced by a solution containing β-emitters. More injections can be used with MBT than grains with BT, allowing for greater precision when targeting the tumour. As with all forms of radiotherapy, treatment planning is required. In this work, a method of generating optimal MBT treatment plans is proposed. Material and Methods The non-dominated sorting genetic algorithm II (NSGA2) [1] is used to generate treatment plans. This is a multi- objective algorithm, permitting the objective functions to be optimised independently. Two objective functions were used: the first to minimise the fraction of the tumour receiving less than the target absorbed dose (60 Gy) and the second to minimise the number of injections. The algorithm was validated on a spherical tumour of 20 mm radius. 20 mm was chosen because it represents the typical size of tumour that could be targeted with this new technique. Results The evolution of the Pareto front during the optimisation of the spherical tumour is shown in Figure 1. The optimisation finished after 200 iterations (generations), and so the final Pareto front represents the final results of the optimiser. Each point along the Pareto front represents a different treatment plan. The front can be seen as a set of compromises; it is impossible to decrease one objective function without increasing another. This enables the user to a posteriori decide relative objective importance and, hence, choose the ideal treatment plan for each patient.

As an example, the treatment plan using 30 injections was chosen. Its absorbed dose distribution through the central slice is shown in Figure 2. To highlight the steep absorbed dose gradient obtained with this treatment concentric spherical shells, surrounding the tumour were also included. Very satisfying treatment plans have been defined using this new method of MBC.