Session Item

Transit in vivo dosimetry (IVD) has been used in our radiotherapy (RT) department since 2018 to evaluate patient treatments. The general analysis of these transit IVD results show a gradual improvement over the years. With this study we want to investigate if these improved results could be a result of adaptations to the clinical workflow that were introduced in our department over the last years.

A retrospective study was conducted, taking into account 63636 transit IVD measurements (PerFRACTION^TM, Sun Nuclear Corporation) of 10652 patients treated between Sept 2018 and Aug 2021, divided into 3 yearly periods. The investigated adaptations to the clinical workflow after the 1^st year include introduction of extra imaging for the boost in breast cancer, education of radiation therapists for positioning of patients’ shoulders in head & neck cancer (H&N) and patient education from dietitians for rectum-, stomach- and esophageal cancer patients. In the 2^nd year, ultrahypofractionated breast RT in 5 fractions with daily online pre-treatment imaging was introduced replacing a 15 fraction scheme. In the 3^rd year immobilization with calculated couch parameters and a surface Image Guided Radiotherapy (IGRT) solution (C-RAD) was introduced.

The number of failed measurements (FM) gradually decreased from 15,7% in the 1^st year to 13,5% in the 2^nd year and 10,5% in the 3^rd year. Excluding all causes of technical nature, the number of failed measurements decreased from 9,5% in the 1^st year to 6,6% in the 2^nd year and 6,1% in the 3^rd year. These FM have been divided per pathology and into 4 categories of causes of failure to assess the influence of adaptations to the clinical workflow: technical, planning and positioning problems, and anatomic changes. Analysis of the results from the 2^nd year showed that FM caused by positioning problems in breast cancer patients receiving a boost dropped from 10.0% to 4.9% compared to the 1^st year, FM related to anatomic changes in rectum patients have been reduced from 10.3% to 4.0% and FM attributed to positioning problems in H&N patients dropped from 9.1% to 3.9%. We observed no difference for stomach and esophageal cancer patients. For ultrahypofractioned breast RT, FM related to positioning problems dropped from 5.9% to 2.6% and FM linked to anatomical changes from 1.9% to 0.2%. There is still limited data on the effect of the immobilization with calculated couch parameters and the surface IGRT solution, but preliminary data shows that FM due to patient positioning are around 2% in the last months, compared to 4.9%, 3.0% and 2.4% in the 1^st, 2^nd and 3^rd years respectively. Data is still too limited to conclude this decrease is caused by the introduction of surface IGRT since there has been a consistent decrease in positioning problems over the years.

This data suggests that transit IVD can be a powerful tool to evaluate and assess possible impact of adaptations to the clinical workflow.