Implementation of Stereotactic Accelerated Partial Breast Irradiation Using Cyber-Knife – Technical Considerations and Early Experiences of a Phase II Clinical Study

Abstract

To report the implementation, dosimetric results of and early experiences with stereotactic accelerated partial breast irradiation (SAPBI) following breast conserving surgery (BCS) for postmenopausal low-risk St I-II invasive breast cancer (IBC) patients. Between November 2018 and August 2019, 27 patients were registered in our phase II prospective study. SAPBI was performed with Cyber-Knife (CK) M6 machine, in 4 daily fractions of 6.25 Gy to a total dose of 25 Gy. Respiratory movements were followed with implanted gold markers and Synchrony system. Corrections for patient displacement and respiratory movement during treatment were performed with the robotic arm. Early side effects, cosmetic results, and dosimetric parameters were assessed. The average volume of the surgical cavity, clinical target volume (CTV), and planning target volume (PTV_EVAL) were 8.1 cm 3 (range: 1.75-27.3 cm 3), 55.3 cm 3 (range: 26.2-103.5 cm 3), and 75.7 cm 3 (range: 40-135.4 cm 3), respectively. The mean value of the PTV_eval/whole breast volume ratio was 0.09 (range: 0.04-0.19). No grade 2 or worst acute side-effect was detected. Grade 1 (G1) erythema occurred in 6 (22.2%) patients, while G1 oedema was reported by 3 (11.1%) cases. G1 pain was observed in 1 (3.4%) patient. Cosmetic result were excellent in 17 (62.9%) and good in 10 (37.1%) patients. SAPBI with CK is a suitable and practicable technique for the delivery of APBI after BCS for low-risk, St. I-II. IBC. Our early findings are encouraging, CK-SAPBI performed with four daily fractions is convenient and perfectly tolerated by the patients.

Multicatheter interstitial brachytherapy versus stereotactic radiotherapy with CyberKnife for accelerated partial breast irradiation: a comparative treatment planning study with respect to dosimetry of organs at risk

“…The patients were treated with a CyberKnife M6 stereotactic system (Accuray, Sunnyvale, CA, USA) using InCise 2 TM multileaf collimators (MLC-s) with step-and-shoot IMRT technique. 40 The patient sel ection was the same as for MIBT. The mean monitor unit number was 2498.8 (range, 1578.7−4142.2), and the median segment number was 57 (range, 39−75).…”

Stereotactic partial breast irradiation in primary breast cancer: A comprehensive review of the current status and future directions

“…The Hungarian team ( 36 ) reported preliminary results on 27 patients with early BC treated in the context of a phase II trial (median fup less than 1 year): In this study, SPBI delivered a total dose of 25 Gy in four fractions and CK was used. No grade >2 acute toxicities were observed as well as no LRs or distant metastasis.…”

Robotic Stereotactic Body Radiation Therapy for the Adjuvant Treatment of Early-Stage Breast Cancer: Outcomes of a Large Single-Institution Study

“… 27 While the radiation dose, fractionation schedule, and use of robotic SAPBI is in keeping with our protocol, their prescription isodose line was higher (86% vs 78%) and median PTV was smaller (88.1 cm 3 vs 111.98 cm 3 ). As a part of a prospective study, Mészáros et al 28 used robotic SAPBI to deliver 25 Gy in 4 daily fractions to 27 patients with early-stage breast cancer. At a median follow-up of 12 months, no locoregional recurrence, distance metastasis, or grade 2 or worse side effects were observed, and the cosmetic outcome was excellent in 62.9% of patients.…”

“…At a median follow-up of 12 months, no locoregional recurrence, distance metastasis, or grade 2 or worse side effects were observed, and the cosmetic outcome was excellent in 62.9% of patients. 28 In a retrospective analysis, Obayomi-Davies et al 25 examined 10 patients with early-stage breast cancer treated with robotic SAPBI—30 Gy in 5 consecutive fractions—and found excellent/good cosmesis and no breast events at a median follow-up of 1.3 years. Taking it to its extreme, as part of a single-dose escalation trial, Rahimi et al 43 examined 30 patients aged 18 years or older with invasive or in situ disease treated with either 22.5, 26.5, or 30 Gy in 1 fraction.…”

“… 23 , 24 , 25 Thus far, the few studies examining toxicity and cosmetic outcomes among patients with early-stage breast cancer treated with stereotactic accelerated partial breast irradiation (SAPBI) delivered with a robotic radiosurgery system have reported no local recurrence, mild/minimal acute toxicity, and excellent or good cosmesis results. 23 , 25 , 26 , 27 , 28 …”