Irradiation insterstitielle partielle et accélérée du sein de haut débit de dose : résultats préliminaires cliniques et dosimétriques sur 61 patientes

Abstract

Purpose Among all the accelerated and partial breast irradiation (APBI) techniques, low then high dose rate, interstitial brachytherapy (HDIB) was the first to be used in this field. This study presents the preliminary clinical and dosimetric results of the APBI using HDIB, performed in Antoine Lacassagne Cancer Center of Nice. Patients and Methods From June 2004 to March 2008, 61 patients (37 primary tumors and 24 second conservative treatments after local recurrence) presenting with T1-2 pN0 non-lobular invasive breast carcinoma, underwent lumpectomy with sentinel lymph node dissection and intraoperative tube placement for HDIB. Dose distribution analysis, using dose–volume histograms, was achieved based on a postoperative CT scan. A comparative dosimetric study was performed between optimized (O) and non-optimized (NO) dose distribution. Then, based on conformal index calculation, a novel index was proposed taking into account not only the conformity but also the homogeneity of HDIB implant. An analysis of dose gradient impact on HDIB biological equivalence dose was also conducted. Statistical analysis used T test confirmed by Wilcoxon test for cohort including less than 30 patients. Results The comparative dosimetric analysis between O and NO dose distributions shown that conformity indexes (conformal index, conformal number, and D 90 %) were significantly increased after optimization. Improving conformity leads to increasing hyperdosage volumes ( V 150 % and V 200 %). A new index named conformity and homogeneity index (CHI) including V 150 % values, modified the conformal index. A total dose of 34 Gy, delivered through HDIB in 10 fractions over five days was biologically equivalent to 41.93 Gy assuming α/β = 4 Gy and 75.76 Gy if the dose gradient was considered in the calculation. Conclusions HDIB is considered as one of the best IPAS technique. HDIB allows dose distribution optimization, skin spearing and accurate clinical target volume definition. Furthermore, HDIB dose gradient could play a key role for breast cancer local control.