Cone beam computed tomography-based online adaptive radiotherapy as a crucial step in increasing the effectiveness of cancer treatment — first clinical experience

INTRODUCTION: Online adaptive radiotherapy (oART) is an innovative approach that allows a treatment plan tobe adjusted accurately and precisely on a daily basis according to changes in tumour and normal tissues duringtreatment courses. MATERIAL AND METHODS: The publication will focus on the presentation and subsequent stages of treatmentplanning, as well as their implementation, using the example of a patient with prostate cancer treated at ourinstitution. The patient underwent hypofractionated radiotherapy with a daily fraction dose of 7.25 Gy to a totaldose of 36.25 Gy. RESULTS: The median time required for the adaptation workflow (AT) was 29 min (SD 5 min). The mean bladdervolume measured in the cone beam computed tomography (CBCT) images done before treatment was 184 cm3and ranged from 146 cm3 to 203 cm3. For comparison, the blader volume at baseline computed tomography (CT)was 238 cm3. The mean rectal volume during treatment was 82 cm3 and ranged from 70cm3 to 100 cm3 and wasalso less than at baseline CT (122 cm3). The observed differences in patient geometry influenced changes in dosedistribution in the planning target volume (PTV) and clinical target volume (CTV). In an extreme case (the fourthfraction of treatment), the patient treated according to the scheduled treatment plan would receive 99% (7.18 Gy)and 98% (7.11 Gy) of the prescribed dose only in 49% of CTV and 48% of PTV, respectively. The adaptation processimproved dose distribution to cover 100% of the PTV and CTV to at least 98% and 99% respectively of the prescribeddose during each fraction of treatment. CONCLUSIONS: The example shown presented very high interfractional mobility. The use of oART allowed for adjustmentto those changes, ensuring proper coverage of the CTV and PTV with the therapeutic dose during eachtreatment fraction.