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The rapid evolution of the Covid-19 pandemic demanded an equally rapid response in the form of vaccine development. When SARS-CoV-2 vaccination became available for vulnerable population groups such as oncologic patients in January 2021, little was known about the effects of vaccination during antineoplastic therapies. To meet related concerns and to be able to give advice on individual protective measurements, we offered patients to monitor SARS-CoV-2 binding antibodies and side effects during the course of their radiotherapy (RT) after the first and/or second vaccination. This dataset was analysed retrospectively after approval by the local ethics committee.

Patients attending the department of Radiation Oncology, Ordensklinikum Linz who were scheduled to receive a SARS-CoV-2 vaccination during (first and/or second dose) or within 6 weeks after RT were offered serial antibody measurements (Elecsys Anti-SARS-CoV-2 S Assay (Roche Diagnostics)) before and after vaccination (7 day intervals until end of radiotherapy, at least on day 35 after the first vaccination).  Intervals of measurement are according to the pivotal clinical trial of Walsh et al. (2020). Data on vaccination reactions/side effects were monitored. For longitudinal antibody titre evaluation the Wilcoxon rank sum test was applied (days 14, 21, 28, and 35 vs. pre-vaccination values). An alpha error of < 0.05 was considered significant.

74 patients could be analysed, 36% women, 64% men, median age 72 years. Distribution of tumor entities: prostate 30%, breast 16%, lung 16%, brain 15%, oesophagus 4%, head & neck cancer 4%, others 15%. Irradiated regions: pelvis 34%, thorax 22%, brain 16%, breast 16%, abdomen 5%, other 3%. Pure RT: 95%, concomitant RT and chemotherapy (ChT): 5%. In 51% of the cases RT was initiated before the first dose in 42% after the first and before the second dose and in 7% vaccination started within 6 weeks after RT. 3 patients had prior SARS-CoV-2 infection. Vaccine product: Comirnaty /Biontech/Pfizer 80 %, Vaxzevria/AstraZeneca 14% and Spikevax/Moderna 7%. Median antibody titres increased from 0 U/ml prior to vaccination to 0.9 U/ml on day 14 (p=0.001), 19 U/ml on day 21 (p=0.001), 126 U/ml on day 28 (p=0.001) and 367 U/ml on day 35 (p<0.000). 6 patients did not develop antibody titres by day 35 after the first dose and another 6 patients did not receive their second dose by day 35. Vaccine reactions: none 60%, injection site pain 19%, fatigue 11%, fever 6% and local reddening 6%.

In this patient collective undergoing localized RT, antibody response after SARS-CoV-2 vaccination was observed in 92% of the cases. Median antibody titres increased above baseline as soon as 14 days after the first dose. Vaccination was well tolerated. The data supports the use of SARS-CoV-2 vaccination in patients undergoing localized radiotherapy alone. For concomitant RT and ChT more data are needed.