ESTRO 2023 - Abstract Book

S361

Sunday 14 May 2023

ESTRO 2023

Figure 1. Representative samples of the dose distribution; a: transversal, b: sagittal; c: coronal; d: three-dimensional reconstruction. Green: clinical target volume; yellow: rips; orange: heart; red: reference isodose-line Results Fifty-four patients were identified with 57 treated lesions. The median age was 50 years (range: 34 – 79). All patients had received EBRT. The mean dose of EBRT was 52.4 Gy (± 6.4). In 71,5% of the patients, mastectomy was performed as the primary surgical treatment for breast cancer. While in 28.5% of the patients, mastectomy was a salvage treatment after local recurrence. The mean dose of the HDR-IRT was 30.2 Gy (± 3.1), delivered in 2 daily fractions. The mean volume of the clinical target volume (CTV) as defined on CT images was 65.4cc (±9.3). The median number of the catheter was 6 (range 3 – 12). The mean CTV D90 was 98.4% (±4.1). Local recurrence occurred in 11 patients (20.4%). The mean time for local recurrence was 12.2 months (± 6.2). Treatment- related toxicities were grade 1-2 in the form of skin toxicity or fibrosis. No grade 3 or 4 late toxicities were encountered. Conclusion HDR-IRT combined with surgical intervention seems to be an effective reirradiation treatment modality with acceptable toxicity for breast cancer patients suffering from chest wall local recurrences after mastectomy and previous external irradiation. OC-0456 Dosimetric evaluation of accelerated partial breast irradiation using SAVI & TRIUMPH-T trial regimen U. Abraham 1 , R. Tolakanahalli 2 , M. Morcos 3 , T. Romaguera 3 , M.A. Rodrigues 3 , J. Ramirez 4 , F. Perk 3 , A. Gutierrez 3 , V. Chaswal 3 1 Miami Cancer Institute , Radiation Oncology, Miami, USA; 2 Miami Cancer Institute , Radiation Oncology, MIAMI, USA; 3 Miami Cancer Institute, Radiation Oncology, MIAMI, USA; 4 Florida International University, Herbert Wertheim College of Medicine, MIAMI, USA Purpose or Objective Dosimetric evaluation of APBI treatment plans using the HDR SAVI applicator and TRIUMPH-T Trial dosing and planning criteria. Materials and Methods Ten (n=10) patients treated with the 6-1 regular Strut Adjusted Volume implant (SAVI) applicator (Cianna Medicals, Aliso Viejo CA) were selected for this study. Treatment planning was done in Oncentra Brachy (Elekta Brachy, Veenendaal, The Netherlands) using the TRIUMPH-T trial dosing (22.5 Gy in 3 fractions) and dosimetric criteria. The target (PTV-Eval) and organs at risk (OARs) were delineated following NSABP B-39 guidelines with the exception of skin, which was contoured as a 3 mm rind from the external contour, and chest wall (CW) which included ribs and pectoralis muscle, as per institutional preference. Ribs were contoured separately for DVH analysis as recommended in TRIUMPH-T trial. All plans were optimized to achieve treatment planning goals of PTV-Eval coverage of V90% ≥ 90% while limiting Dmax (maximum dose to D0.03cc) to skin and CW less than 100% and 120% of prescription dose, respectively. V150% and V200% of the PTV-Eval were constrained to below 40 cc and 17 cc, respectively. The ribs Dmax was recorded for documentation. Additionally, a metric, PTV-ratio was defined as a ratio of PTV-Eval to PTV1cm (defined as the volume of breast tissue encompassing 1 cm expansion around the cavity) to study its correlation to achieved planning metrics, where the PTV-ratio, decreases with increasing overlap with OARs. Results Result: Cavity+1cm volume averaged at 85.2 ± 3.8 cc which is directly relatable to the of the 6-1 SAVI applicator. PTV-Eval volume measured an average of 58.2 ± 5.1 cc. All plans included in this study met all the clinical treatment planning goals. V90 of PTV-Eval averaged at 96.9+3.2%. The mean V150% and V200% were 24 ± 2.9 cc and 12.0 ± 1.5 cc respectively. Dmax to skin, CW and ribs were 93.4 ± 4.5 % and 103.0 ± 17 % and 71.4 ± 17.6 %, respectively. Plans with a smaller PTV-ratio volume (indicating closer proximity and overlap with OARs) met constraints marginally. The correlation coefficient between PTV-ratio and PTV-Eval V90, max dose to skin, CW and ribs were 0.87, -0.50, -0.70 and -0.45, respectively.