ESTRO 2020 Abstract Book

S1044 ESTRO 2020

Five left sided breast cancer patients with Aeroform AirXpanders were retrospectively identified. Two planning target volumes (PTV) were marked for each patient using the ESTRO guidelines for post mastectomy radiotherapy target volume delineation for both subpectoral and prepectoral positioned AirXpanders 3 . The supraclavicular fossa, level 3 axilla and internal mammary nodes were also included in both PTV delineations. OARs were contoured on the Pinnacle workstation according to the ESTRO guidelines 4 . t-IMRT and VMAT plans were generated to a prescribed dose of 50.4Gy in 28 fractions with 1.0cm bolus for dosimetric analysis. Results There was no significant difference between VMAT and t- IMRT plans with respect to PTV coverage. The use of t-IMRT resulted in improved PTV5040 D95%<95% compared to VMAT (average coverage 1.05 higher in t-IMRT, p=0.045). VMAT significantly reduced dose to the ipsilateral lung (mean, V20Gy), chest wall (min dose) and heart (mean) (all p-values <0.001); whilst significantly increasing dose to the contralateral lung (V5<10%) (p<0.001) and contralateral breast (mean) (p=0.008). In addition, the use of VMAT in patients with a subpectoral positioned AirXpander resulted in better PTV coverage with significantly less hotspots (PTV cc) within the PTV compared t-IMRT (p<0.001). Conclusion VMAT should be considered for patients treated with an Aeroform AirXpanders due to a significant reduction in heart, ipsilateral lung and chest wall doses. The use of VMAT in patients with a subpectoral positioned AirXpander significantly improved PTV coverage with less hotspots compared to t-IMRT, with a small increase in dose to contralateral breast and lung. Therefore the use of VMAT is recommended in this cohort of patients. PO-1873 SIDCA in patients with ≥ 10 brain mets: evaluation of neurological toxicity and treatment accuracy. L. Capone 1 , B. Nardiello 1 , R. El Gawhary 2 , G. Raza 2 , C. Scaringi 1 , F. Bianciardi 2 , B. Tolu 1 , F. Rea 1 , P. Gentile 2 , S. Paolini 3 , G. Minniti 1 1 UPMC San Pietro FBF, Radiotherapy, Rome, Italy ; 2 Ospedale San Pietro FBF, Radiotherapy, Rome, Italy ; 3 IRCCS Neuromed, Radiation Oncology Unit, Pozzilli, Italy Purpose or Objective To assess the clinical outcomes and treatment accuracy of frameless linear accelerator (LINAC) single-isocenter (SIMT) dynamic conformal arc (DCA) stereotactic radiosurgery (SRS) for multiple targets in patients with more than 10 brain metastases Material and Methods Thirty-five consecutive adult patients with ten or more brain metastases who received single isocenter multitarget SRS at UPMC Hillman Cancer Center San Pietro Hospital, Rome, were evaluated. All plans were created using the Brainlab Elements Multiple Brain Mets SRS software, version 1.5. Time-to-event analyses were estimated using the Kaplan-Meier method from the date of SRS. Neurocognitive function using the Hopkins Verbal Learning Test-revised (HVLT-R), and Activity of Daily Living Scale (ADLS) were completed at baseline and at 2-, 4-, and 6-month follow-up. Toxicity was assessed by the National Cancer Institute Common Toxicity Criteria for Adverse Events (version 5.0). In addition, the positioning accuracy of all treated targets was evaluated. Results For all patients, the median dose was 22 Gy prescribed at 80%; median gross total volume (GTV) and planning target volume (PTV) were 0.30 and 0.48 cm 3 , respectively. Median V95 (the volume of the PTV covered by 95% of the prescription dose) was 98.5%. With a median follow-up of 11 months, 1-year survival and local control rates were 66% and 87%. The treatment was safe, with Grade 2 or 3

toxicity occurring in five patients. Neurocognitive function remained relatively stable after SRS. A significant decline of neurocognitive functioning (assessed by HVLT-R) occurred in 11% and 6% of patients after 6 and 12 months, respectively. All but two patients were independent at 12- month follow-up. A significant variation of V95 (>5% or resulting in a V95<95%) in at least one lesion was observed in 27% of patients, although GTV coverage was maintained for all treated lesions using a 1 mm GTV-to-PTV margin. Conclusion SIMT DCA SRS represents an effective and safe approach for patients with 10 or more brain metastases able to maintain the pretreatment neurocognitive function in the majority of patients. A 1 mm GTV-to-PTV expansion is recommended to ensure dose coverage of all treated lesions. PO-1874 Improving Treatment Accuracy of Cranial Boost Radiotherapy (RT) with Total Body Irradiation (TBI) I.Z. TAN 1 , J. Francis 2 , G. Smyth 2 , H. Burland 2 , S. Eagle 2 , H. Mandeville 1 1 The Royal Marsden, Pediatrics/ TYA/ Hemato-Oncology, Sutton, United Kingdom ; 2 The Royal Marsden, Radiotherapy, Sutton, United Kingdom Purpose or Objective Patients with relapsed acute lymphoblasticleukaemia (ALL) with central nervous system (CNS) involvement receive additional cranial boost radiotherapy prior to TBI as part of their conditioning regimen for haematopoetic stem cell transplant (HSCT). RTT-led virtual simulation and treatment with lateral opposed fields has traditionally been used. We decided to evaluate whether a physician- led contouring of the whole brain as the clinical target volume (CTV) improves coverage of critical areas such as the cribriform plate (CP) and optic nerves (ON), compared to 2D virtual simulation using bony landmarks. Material and Methods Planning CT brain (1mm slices) were performed with the patient supine in a 3 point thermoplastic head mask. For the physician-led contoured whole brain CTV (including the CP and ON) were manually contoured; a 3 mm geometric margin applied from CTV to PTV. A further 6 mm geometric margin PTV to field edge to account for penumbra was done using multileaf collimator shaping for lateral opposed fields. For the bony landmarks referenced field, the outer canthus of the eyes, the CP and C2/3 cervical vertebral junction were used. The 95% isodose coverage of the PTV at the CP and ON were visually assessed for both. Results Retrospective data collection from Jan 2015 - Oct 2018 yielded 15 patients who received cranial boost RT in addition to TBI. Of these only 9 patients plans were available for this planning study. For the physician-led contoured PTV, the 95% isodose coverage of both the ON and CP was improved in 6 patients (67%) and CP or ON coverage alone was better in 2 patients (22%). In 8 out of 9 patients (89%) evaluated, physician-led contoured PTV fields (right) resulted in an improvement in one or both CP and ON coverage compared to bony landmarks referenced fields (left).