ESTRO 2021 Abstract Book

S1198

ESTRO 2021

1 Apollo Proton Cancer Centre, Radiation Oncology, chennai, India; 2 Apollo Proton Cancer Centre, Radiation Oncology, Chennai, India; 3 Apollo Proton Cancer Centre, Medical Physics, Chennai, India

Purpose or Objective Pencil beam scanning proton beam therapy (PBS-PBT) dose distributions are extremely sensitive to tissue deformation. We conducted a retrospective audit of 190 consecutive patients treated with image guided PBS- PBT over a period of 1.5 years, to analyse the incidence, causes and trigger for adaptive re-planning. Materials and Methods Patients were treated with daily image guidance with either KV X-rays or Cone-beam CT scan (CBCT) or both. Patients underwent quality assurance imaging either with a CT (QA-CT) or MRI after every 5-10 fractions or earlier based on CBCT. The nominal plans were overlaid on the QA-CT and the doses were recalculated to assess dose perturbations and the need for adaptive re-planning. The thresholds for re-planning were based on the physician’s choice. The trigger for re-planning was also recorded and classified as elective QA-CT, QA-CT based on CBCT trigger, or based on clinical triggers. After the initial 6-9 months of the study, several measures were implemented with regards to simulation and planning such as skin rind evaluation for head neck patients, modified planning techniques, avoidance of certain beam angles, and changes to class solutions. Results At least 3 QA images were acquired for each patient. A total of 58 patients (30.52 %) required adaptive re- planning, of which 9 (15%) underwent re-planning more than once. Of the patients undergoing re-planning, 44.8%were of head neck, 15.5%brain, 10.3% pelvic, 5.2% skull base, 5.2% CSI, and 12.3% were of thoracic subsite. 68% of Head neck and 66% of thoracic patients underwent adaptive re-planning. The number of patients undergoing adaptive re-planning in week 1,2,3,4,5&6 were 11, 10, 18, 8, 7 and 4 respectively. The most common cause for adaptive planning was deformation of target (23.07%) and beam path changes (23.07%) followed by persistent setup errors (9.23%), OAR deformation (7.69%) and a combination of either of the factors in 26.15%. 59% of plans were adapted due to overdose in OARs, 29.7% were due to under-coverage of target while 10.8% had both. The average dose perturbation in the high dose target was higher than the intermediate dose target. Of the first 70 patients, 43% underwent plan adaptation while after implementation of measures to reduce the adaptive re-planning, in the next 120 patients only 23.3% required the same. Trigger for adaptive re-planning was elective QA-CT in 15%, CBCT trigger in 78%, and clinical triggers in 7% of patients. Conclusion Our retrospective audit showed that the need for adaptive re-planning for patients treated with PBS-PBT is significantly high especially for head neck and thoracic tumors. The most common causes for adaptive re- planning were target deformations and beam path changes which in a majority of cases are picked up by CBCT imaging. Innovative simulation and planning approaches could potentially reduce the need for adaptive re- planning. PO-1461 Impact of the COVID-19 pandemic on Radiation Oncology Departments in Brazil G.H. Yoshinari Jr 1 , H.F. Oliveira 2 , I.M. Veras 3 , W.J. Almeida Jr 4 , N.M. Freitas 5 , M.S. Castilho 6 , A.C.D.A. Pellizzon 7 , F. Erlich 8 , R.J. Affonso Jr. 9 , Í.T. De Carvalho 10 , A.C.C. Leite 11 , F.Q. Kuhnen 12 , R.M.X.F. Najas 13 , L.V. Magalhaes 14 , A.A. Rosa 15 1 oncominas; Faculdade De Medicina De Itajuba, Radiation Oncology, Itajuba, Brazil; 2 centro De Tratamento Em Radio-Oncologia (Ctr); Márcio Cunha Hospital – Fundação São Francisco Xavier, Radiation Oncology, Ribeirao Preto, Brazil; 3 regional Integrated Oncology Center, Radiation Oncology, Fortaleza, Brazil; 4 moinhos Dos Ventos Hospital, Radiation Oncology, Porto Alegre, Brazil; 5 araújo Jorge Hospital Of The Góias State Association Against Cancer, Radiation Oncology, Goiania, Brazil; 6 felicio Rocho Hospital, Radiation Oncology, Belo Horizonte, Brazil; 7 Ac Camargo Hospital, Radiation Oncology, Sao Paulo, Brazil; 8 José Alencar Gomes Da Silva National Cancer Institute (Inca), Radiation Oncology, Rio De Janeiro, Brazil; 9 barretos Cancer Hospital, Radiation Oncology, Barretos, Brazil; 10 albert Einstein Hospital, Radiation Oncology, Sao Paulo, Brazil; 11 dom Pedro De Alcantara Hospital, Radiation Oncology, Feira De Santana, Brazil; 12 charity Hospital Of Florianópolis, Radiation Oncology, Florianopolis, Brazil; 13 rio Grande Do Norte State League Against Cancer, Radiation Oncology, Natal, Brazil; 14 faculdade De Medicina De Itajuba, Medical School, Itajuba, Brazil; 15 santa Izabel Hospital And Português Da Bahia Hospital; Oncoclinicas Group, Radiation Oncology, Salvador, Brazil Purpose or Objective The COVID-19 pandemic brought several challenges to cancer practice, especially to ensure continuity of treatment during this period, minimizing the risks of transmission to a vulnerable population. For Radiation Oncology departments in Brazil, this contingency has become even more complex due to the significant impact observed in different sectors of society, the large number of cases and deaths by COVID-19. This study estimated the impact of the COVID-19 pandemic on Brazilian Radiation Oncology departments and the coping measures used in the country. Materials and Methods The Brazilian Radiotherapy Society (SBRT) developed a questionnaire with 14 questions, sent to all heads of Radiation Oncology departments in the country, between May and June 2020. These data were evaluated regarding cases confirmed and deaths by COVID-19 in epidemiological week 28, on July 11, 2020. Results One hundred twenty-six questionnaires from different regions were answered, representing 44% of the country’s services. A drop in the number of patients was observed in 61% of services. This drop was observed both in patients from the public and supplementary private health insurance systems. Regarding patients and employees with COVID-19, we observe that services that primarily treat SUS patients reported significantly fewer cases of the disease. About half of the services had collaborators and patients during radiotherapy with a positive diagnosis of COVID-19. Among the coping measures, the services used intensified hygiene and