Automated single-isocenter stereotactic body radiotherapy for multiple metastases from breast cancer: A case study

Oligometastatic breast cancer patients can today could benefit from a multimodal approach, combining systemic therapy with metastasis-directed treatment using stereotactic body radiotherapy (SBRT). However, the possibility to synchronously treat multiple lesions is still challenging, needing the ability to generate complex dose distributions with steep dose gradients outside the lesions and major sparing of surrounding organs at risk and accurately track and reproduce the patient's position before and during radiation therapy. We report the case of an oligometastatic patient from left breast cancer, which occurred after a full course of whole breast radiotherapy, treated using the potential of modern technology including single-isocenter setup, plan automation, breath-hold technique and surface guided tracking and reproducibility of patient's position before and during radiation therapy. A 44-year-old female patient with a history of left breast cancer, specifically a luminal-B-like invasive ductal carcinoma with Her2 overexpression, was admitted to our department. The patient previously underwent a left mastectomy (pT2N0M0), 4 cycles of adjuvant chemotherapy, adjuvant radiotherapy on the chest wall and lymph nodes drainage, and 5 years of hormonal therapy. A chest wall ultrasound and positron emission tomography revealed the presence of new lesions in the area of the surgical scar from the previous mastectomy, internal mammary, axillary and retropectoral levels. The 3 lesions were simultaneously treated with a mono-isocentric VMAT plan using SBRT technique with a total dose of 30 Gy delivered in 5 fractions. Due to the technical challenges, this treatment was supported by the use of planning automation, breath-hold technique and surface-guided radiation therapy to improve the accuracy of the dose delivery. Two different plans were generated and compared to pursue the best dosimetric result, including a summed plan obtained from 3 individual SBRT plans for each lesion with a separate isocenter placed in each of them (MIP), and a single-isocenter SBRT plan able to treat multiple lesions synchronously (SIP). Because of the advantages in terms of dosimetry and dose delivery efficiency, the patient was successfully treated with the SIP plan. The treatment time was reduced to about 4.5 minutes, allowing the comfortably use of breath-hold technique. After treatment, the condition of the patient was normal, and no toxicities have been observed in follow-up. SBRT with mono isocentric VMAT planning represents the recommended approach to simultaneously treat multiple lesions in close proximity in the thoracic district.