Immunogenicity after two and three doses of mRNA vaccine in patients with cancer treated with exclusive radiotherapy.

BACKGROUND AND PURPOSE: Data on immunoresponse after SARS-CoV-2 vaccines for patients treated with exclusive radiotherapy (RT) are scarce. Since RT may affect the immune system, we conducted the MORA trial (Antibody response and cell-mediated immunity of MOderna mRNA-1273 vaccine in patients treated with RAdiotherapy). MATERIALS AND METHODS: Data regarding humoral and cellular immune response of patients treated with RT were prospectively collected after the second and third dose of mRNA vaccines. RESULTS: Ninety-two patients were enrolled. With a median of 147 days after the second dose, the median SARS-CoV-2 IgG titer was 300 BAU/mL: six patients were seronegative (Spike IgG titer ≤ 40 BAU/mL), whereas 24, 46 and 16 were poor responders (Spike IgG titer:41-200 BAU/mL), responders (Spike IgG titer:201-800 BAU/mL) and ultraresponders (Spike IgG titer > 800 BAU/mL), respectively. Among seronegative patients, two patients were negative also for cell mediated response, as tested with IFN-γ release Assay (IGRA) test. With a median of 85 days after the third dose, the median SARS-CoV-2 IgG titer was 1632 BAU/mL in 81 patients: only two patients were seronegative, whereas 16 and 63 patients were responders and ultraresponders, respectively. Among the 2 persistently seronegative patients, IGRA test was negative in one who had previously received anti-CD20 therapy. Documented paucisymptomatic (n = 3) or asymptomatic (n = 4) infection occurred after the third dose, during the Omicron wave. CONCLUSION: In patients treated with exclusive RT, even during the Omicron breakthrough, robust humoral response and clinical protection from severe SARS-CoV-2 disease were achievable with three doses of mRNA vaccine.

Clinical implementation of 3D in vivo dosimetry for abdominal and pelvic stereotactic treatments.

PURPOSE: To analyze results from three years of in vivo transit EPID dosimetry of abdominal and pelvic stereotactic radiotherapy and to establish tolerance levels for routine clinical use. MATERIAL: 80 stereotactic VMAT treatments (152 fractions) targeting the abdomen or pelvis were analyzed. In vivo 3D doses were reconstructed with an EPID commercial algorithm. Gamma Agreement Index (GAI) and DVH differences in Planning Target Volume (PTV) and Clinical Target Volume (CTV) were evaluated. Initial tolerance level was set to GAI > 85% in PTV. Fractions Over Tolerance Level (OTL) were deemed to be due to set-up errors, incorrect use of immobilization devices, 4D errors, transit EPID algorithm errors and unknown/unidentified errors. Statistical Process Control (SPC) was applied to determine local tolerance levels. RESULTS: Average GAI were (82.7 ± 20.9) % in PTV and (72.9 ± 29.7) % in CTV. 37.8% of fractions resulted OTL and were classified as: set-up errors (3.3%), incorrect use of immobilization devices (2.1%), 4D errors (2.1%), EPID transit algorithm errors (17.1%). OTL causes for the remaining 13.2% of fractions were not identified. The differences between PTV and CTV measured in vivo and calculated mean dose (average difference ± standard deviation) were (-3.3% ± 3.2%) and (-2.3% ± 3.0%). When tolerance levels based on SPC to PTV mean dose differences were applied, the percentage of OTL decreased to 7% and no EPID algorithm error occurred. One error was not identified. CONCLUSIONS: The application of local tolerance levels to EPID in vivo dosimetry proved to be useful for detecting extra-lung SBRT treatment errors.