ESTRO 2021 Abstract Book

S958

ESTRO 2021

Talaya 1 , R. Rubiato 1 , M.T. Murillo 1 1 Hospital Universitario de La Princesa, Radiation Oncology, Madrid, Spain; 2 Hospital Universitario de La Princesa, Radiation physics, Madrid, Spain Purpose or Objective To determine the incidence and the clinical relevance of CW toxicity. To evaluate clinical and dosimetric features that predict CW toxicity after lung SBRT. To set a constraint for CW. To determine the need to use 5 fractions schemes instead of 3 in order to avoid unacceptable toxicities. Materials and Methods 48 patients were eligible as they received lung SBRT, 50Gy in 5 fractions from January 2018 to May 2020 for peripheral lesions (metastases or primary; <2 cm from CW). 4DCT images for radiotherapy simulation were obtained in Toshiba CT Acquilion 64LB (Canon Medical Systems, JP) with Real-time position management system simulation (VARIAN, FL). Clinical factors evaluated were: age at the time of the treatment, sex, diabetes, osteoporosis, body max index (BMI) and tumour histology. These clinical data were prospectively collected, and retrospectively reviewed in the digital medical chart. Dose parameters in CW, Dmax, V30, V40 and V50 have been evaluated. Volume of the overlapping region between planning target volume and CW were collected. The CW was contoured retrospectively on each treatment plan for consistency and similarity in contouring. The CW was delineated on the average scan, using a margin of 2.0 cm. The follow-up computed tomography scans were reviewed in order to detect rib fractures. Toxicity was scored according to the CTCAE v4.0 and was collected retrospectively by reviewing the digital medical chart with subsequent telephone confirmation by the patient to detect grade 1 pain. Results The median follow-up was 20 months. Frequency of any CW toxicity was low (14%), and in most cases it manifested in mild pain easily controlled with conventional analgesia. No case of acute CW toxicity was detected and the median onset of CW pain was 6 months. Only one patient developed a rib fracture and it was symptomatic (gr. 2). The clinical, histological, and dosimetric characteristics of the different groups based on CW toxicity are shown in Table 1.

Although there is a relationship with V30, in the direct analysis we couldn't find a significant relationship between any of the DVH metrics and CW toxicity. Interestingly, it was a clinical feature, diabetes, that was significantly related (p=0.01) with any grade of CW pain. The mechanism for CW pain in the absence of rib fracture, remains unclear. Some authors have suggested peripheral nerve damage as a primary mechanism. That's why it is speculated that diabetes is an important condition for peripheral neuropathy. Conclusion Adequate tumor coverage remains the primary objective when treating peripheral lung lesions with SBRT since there is no clear CW constraint and the clinical relevance on CW toxicity is mild. Clinical features such as diabetes are predictive factors to consider. Given the recommendations derived from the COVID-19 pandemic and the clinical relevance of CW toxicity, it is reasonable to consider 3-fraction schemes in selected patients with favorable clinical characteristics, even for peripheral lesions. PO-1153 Preliminary mono-institutional report of stereotactic body radiotherapy for lung oligometastases F. Cuccia 1 , R. Mazzola 2 , G. Attinà 2 , V. Figlia 2 , N. Giaj-Levra 2 , L. Nicosia 2 , F. Ricchetti 2 , M. Rigo 2 , E. Pastorello 2 , F. Alongi 2,3 1 Sacro Cuore Don Calabria Hospital , Advanced Radiation Oncology Department, Negrar di Valpolicella, Italy; 2 Sacro Cuore Don Calabria Hospital, Advanced Radiation Oncology Department, Negrar di Valpolicella, Italy; 3 University of Brescia, Radiation Oncology, Brescia, Italy