ESTRO 2021 Abstract Book

S169

ESTRO 2021

SP-0261 Salvage surface-brachytherapy of thoracic wall - indications, technique, results A. Chicheł 1 1 Greater Poland Cancer Centre, Brachytherapy, Poznan, Poland

Abstract Text Purpose/Objective : Post-mastectomy irradiated patients are prone to a locoregional recurrence (LRR) as the first event depending on primary nodal clinical-stage pN 0 , pN 1-3 , and pN 4+ in 3, 3.8 to 13%, respectively. Historically, in a subgroup of primarily high-risk patients, LRR is as high as 17.3% (30% without prior RT, 5% after RT). Almost half of them (48.5%) were at the chest wall only. Further, another half of them would be assessed as inoperable or would have unsatisfactory surgery. Unfortunately, a 5-year distant metastasis event probability preceded by LCC is as high as 73%. Risk factors for chest wall-only recurrence were determined as increasing primary tumor size, ductal carcinoma, muscular fascia invasion, and ≥ four positive nodes. It is to search for proper indications to LRR management with surface-brachytherapy. Material/Methods : Existing guidelines and breast cancer treatment recommendations were searched. Also, available non-randomized, single-center, and retrospective analyses results published in the literature were analyzed. Results : Although there are some promising retrospective data available, their strength is too weak to be incorporated in official treatment recommendations, giving place external beam radiotherapy combined with hyperthermia, for which randomized data are accessible. However, in highly selected patients, s ingle or multiple-nodule superficial in-skin recurrences are a potential and an easy target for surface brachytherapy, which may be prescribed curatively or palliatively. Two patients groups are eligible: chest wall-only non- resectable nodules with thickness less than 1 cm; and macroscopically (R2) or microscopically (R1) resected disease. Possible non-invasive techniques considered helpful for external applications are standard flap techniques, individual molds of different materials, and emerging 3D printing techniques. Except for institutional shortages and experience, there are no other limitations to combine brachytherapy with superficial hyperthermia. Hyperthermia is proved to enhance the therapeutic ratio without increasing the risk of repeated irradiation. Published results on surface salvage brachytherapy efficacy prove its local efficacy. Depending on solitary or surgically preceded treatment, reported local complete remission is 71-86%; 5-year LCR 51-80%; 5-year survival rates range from 22 to 62%; acute Grade 2/3 toxicity occurs from 18 to 43%; late Grade 3/4 toxicity is observed 12 to 17%. All locally achieved successes are compromised by frequent distant metastases demanding simultaneous or sequential, most often systemic, treatment. The survival prognosis after chest wall-only failure was 3.8 years, and the significant independent parameters for survival after LRR were: tumor size, number of positive nodes, extracapsular extension, site of the recurrence (best prognosis for chest wall-only recurrences), and interval to the first LRR ≤ 2 years. Conclusions : Standardly recommended treatment is excisional or reconstructive surgery followed by reirradiation where necessary and possible. Unresectable LRRs are proposed reirradiation willingly combined with hyperthermia for the best results. Nevertheless, modern diagnostics and imaging enable a proper patient selection for a convenient, non-invasive, digitally optimized, highly locally curative, and healthy organs sparing salvage treatment with brachytherapy. The most optimal management should be planned in multidisciplinary tumor board meetings and explained to patients regarding their inhomogeneous groups. Abstract Text Following mastectomy, local recurrence usually occurs in the skin, subcutaneous tissue, or muscles of the chest wall. Local recurrence can be treated by radical surgery, however, in 70–93% the chest wall has been involved and this results mostly in incomplete margins. Treatment alternatives are limited in this situation; chemotherapy may be unsuccessful in resolving local recurrence. Second-course eradiotherapy can be a successful treatment. Interstitial high-dose-rate (HDR) implants for cases with deep infiltration combined with surgery is a very CT-based individual brachytherapy planning has been currently accepted for geometric optimization and realization of dose homogeneity for Brachytherapy. The feasibility of intensity-modulated Brachytherapy. The technique of interstitial and the clinical outcome and benefit for the group of patients with local recurrence after previous radiotherapy will be presented. In several cohort a local control rate of 62.5% for patients with subcutaneous dep sited recurrences had been observed. . It must therefore be assumed, that even patients with minor residual tumours after surgery will benefit from this interdisciplinary approach. Due to the fact that radiation therapy is effective in the treatment of local recurrence and the minimized reirradiation volumes result in reduced toxicity, brachytherpay is an alternative to deliver an additional effective dose in combination with surgery, resulting in a reduced risk of toxicity. Advanced intraoperative target definition and delineation as well as CT-based individual IMBT planning allow for a high coverage of the target volume with maximum sparing of organs at risk. In this palliative situation brachytherapy seems to offer the advantage of an effective treatment option with a short treatment time as well as a low acute toxicity. Particularly patients with residual tumours will benefit from this treatment modality. SP-0262 Interstitial Salvage -brachytherapy for recurrent breast cancer of thoracic wall P. Niehoff 1 1 Sana Klinikum Offenbach, Dep of Radiotherapy, Offenbach, Germany

Poster highlights: Poster highlights 9: Intra-fraction motion management

PH-0263 Pre-clinical vs. clinical 4D accumulated proton dose delivery for thoracic tumours with large motion C. O. Ribeiro 1 , E.W. Korevaar 1 , S. Visser 1 , A.C. Hengeveld 1 , G. G. Marmitt 1 , J.A. Langendijk 1 , R. Wijsman 1 , A. Knopf 1 , A. Meijers 1 , S. Both 1