Feasibility study of adapting national postal TLD dosimetry audits for tomotherapy units: the Polish experience

Abstract The continuous development of radiotherapy equipment and techniques requires existing dosimetry audits to adapt to these changes. One advanced form of radiotherapy is helical therapy, commonly referred to as tomotherapy. During helical therapy, a linear accelerator rotates around the patient, delivering radiation similar to a spiral CT scan. Simultaneously moving the treatment couch during irradiation allows large areas to be irradiated without combining fields. This is important for treating gynaecological, soft tissue and bone cancers, as well as for using special techniques such as total body irradiation (TBI), half-body irradiation (HBI) and total marrow irradiation (TMI). In 2022 and 2025, feasibility study of adapting TLD dosimetry audit of tomotherapy was conducted on the Accuray RADIXACT device at the Maria Sklodowska-Curie National Research Institute of Oncology in Warsaw. The study, performed using fifteen thermoluminescent (TL) detectors, yielded highly satisfactory results. The percentage deviation for individual detectors ( delta i ) ranged from − 1.2% to 0.8%, with a mean value of − 0.2% (SD = 0.6%). For the measurement sets, the mean deviation ( delta mean ) ranged from − 0.6% to 0.3%, with an overall average of − 0.1% (SD = 0.4%). All results were well within the required tolerance range of ± 3.5%. The positive outcome of this study performed using thermoluminescent (TL) detectors was one of the factors contributing to the approval of the helical technique for clinical use at our centre. The audit methodology for conventional accelerators has been modified because it was impossible to create the required conventional reference conditions (the source-axis distance of 100 cm and a field size of 10 cm × 10 cm) when using helical techniques. The study demonstrates the feasibility of adapting existing postal dosimetry protocols for unconventional radiotherapy devices.