ESTRO 2020 Abstract book

S705 ESTRO 2020

The median follow-up was 70 months. The average age of patients was 56 years. Women with Tr-neg variant turned out to be significantly younger (48.2 years). Lesion length, risk of pathological fracture, initial pain intensity were the same in various groups. The overall effectiveness of EBRT (сomplete and partial pain relief) was 97,8%, the complete response rate (CRR) - 62,5%. The relative pain reduction was 80%, the pain relapse rate - 8%. Significant differences between these indicators in various molecular subtypes of breast cancer could not be found. However, there was a trend to less complete pain relief in HER2-positive patients. The CRR in HER2+ group was 42,1% compared to 61,6% in RE/RP+ group and 66,7% in Tr-neg patients (p=0.09). The relative pain reduction was 72,2%, 79,4% and 80%, respectively (p=0.12). Dose escalation from 13 Gy to 19.5 Gy and 26 Gy in 2, 3, and 4 fractions of 6.5 Gy accompanied by a significant increase in the CRR from 41.4% to 50.3%, and 80.9%, correspondingly (p=0.012). Conclusion The dose escalation from 13 Gy to 26 Gy in 2-4 fractions of 6.5 Gy allows significantly increase the CRR with irradiation for bone metastases of breast cancer. It is most in demand at treatment of HER2-positive patients. PO-1250 Palliation of vertebral metastases and cord compressions: single field or VMAT? N. West 1 , R.A. Pearson 1 , A. Hashmi 1 , X. Jiang 1 , A. Ogilvie 1 , T. Simmons 1 1 Newcastle upon Tyne Hospitals Trust, Northern Centre for Cancer Care, Newcastle upon Tyne, United Kingdom Purpose or Objective In spite of advances in treatment planning and delivery, radiotherapy techniques for palliation of vertebral bone metastases or metastatic spinal cord compression have not evolved. Modern, more sophisticated VMAT approaches are often deemed unfeasible for this cohort of patients due to contouring and planning burdens. With more effective therapies, patients are living longer and the risk of retreatment is higher. We propose, and dosimetrically evaluate a pragmatic, semi-automated technique to treat vertebral metastases with VMAT. Material and Methods Fifteen cases (n=11 patients) who received radiotherapy to vertebral metastases for pain (n=11) or cord compression (n=4) between 2010 and 2018 were randomly selected for the study. Primary sites included lung (n=6), prostate (n=4) and breast (n=1). Target vertebra determined by patient’s history and CT/MRI imaging of the spine; with a single posterior field defined to encompass the target and a margin of one to two vertebral bodies above and below, prescribing dose at target depth as is convention (SCORAD III Clinical Trial). For the study, a new VMAT plan was generated for each case. Clinicians defined target vertebrae according to diagnostic information and original treatment intent using an automated technique with manual editing to generate a pseudo CTV, growing to a PTV (isotropic 1.5cm for the single field plan and 1.0cm for the VMAT plan). The previously delivered single field plan was recalculated and a VMAT plan generated. Treatment delivery times were calculated for both plans. Results Dosimetric differences between a single posterior field and a VMAT plan are displayed in Figure 1 and analysed in Table 1.

Data was prospectively collected at 3 months after treatment, then 6-monthly intervals thereafter. Results The median age of primary diagnosis and metastases detection was 65 and 69. Colorectal (27/91, 30%), Prostate (25/91, 27%) and rest of Gastrointestinal tract (11/91, 12%), were the most common primary malignancies in the cohort. Lymph node (32/91, 35%), Lung (17/91, 19%) and Liver (14/91, 15%) were the most common targets. There were three ≥Grade 3 late toxicities reported during this study period: benign ureteric stricture requiring stent placement and two patients with persistent fatigue. The median Biological equivalent dose (BED) prescribed assuming α/β = 10, was 60 Gy 10 . Most common dose/fractionation used was 30 Gy in 5 fractions with 48 Gy 10 BED (30%). Toxicity of ureteric stricture was observed in patient treated with 60 Gy 10 BED (30Gy in 3 fractions) for a prostate primary with single pelvic lymph node relapse, with planning target volume of 28.7cc the maximum point dose delivered to the ureter was 35 Gy, which was abutting the target . The other 2 patients with persistent fatigue were treated with 48Gy 10 BED (30 Gy in 5 fractions) for pelvic lymph node relapse due to colorectal primary and 115.5Gy 10 BED (55Gy in 5 fractions) for a liver metastasis due to Anal cancer. The median followup for the whole cohort was 24.83 months, with progression free survival (both local and distant progression) of 56.34% and 34.83% at 12 and 24 mths, respectively and Local control was 80% at 2 years for the whole cohort. The median OS was not reached for the cohort and OS at 12 and 24 mths was 89.8% and 77.5%, respectively. The multivariate analysis for OS was significant with respect to synchronous vs metachronous detection of metastases (HR 3.1, 95% CI 0.003 to 0.26), and local control (HR 2.5, 95% CI 1.26 to 5.05), favouring metachronous metastases and locally controlled disease group. Patients with prostate primary had 100% survival at 2 years, whereas colorectal primary had 88% survival at 2 years. Conclusion Although SABR to oligometastases has been proven to be relatively safe and feasible option of treatment with favourable outcomes in select group of patients, further data with respect to organs at risk (OAR) tolerance doses with hypofractionation is warranted, to safely deliver quality treatment. Our report suggests future studies to be directed towards defining OAR tolerances with common extreme hypofractionated, dose/fractionation regimens. PO-1249 Comparative efficacy of radiotherapy for breast cancer bone metastases. N. Bychkova 1 , E. Khmelevsky 1 1 Gertzen Moscow Research Oncological Institute, Radiotherapy department, Moscow, Russian Federation Purpose or Objective To study the effect of dose escalation during hypofractional radiotherapy for bone metastases of breast cancer in accordance with various molecular subtypes. Material and Methods Out of 768 cases of radiation therapy for bone metastases included in the long-term randomized trial breast cancer was diagnosed in 460 (60%). The molecular subtype of the tumor was defined in 114 patients. They were divided into 3 groups. 64% had hormone-receptor-positive/HER2- negative variant (RE/RP+), 17% - HER2-positive (HER2+) and 8% - triple-negative (Tr-neg) variant. Patient selection criteria for radiotherapy were non-stopping pain, the impossibility of surgical correction of pathological fracture/malignant spinal cord compression, increasing neurologic disfunction. Irradiation volume included one anatomical area of the skeleton with the affected area. The total dose was 13-26 Gy in 2-4 fractions of 6.5 Gy. Results