Synchrotron radiation-based experimental determination of the optimal energy for cell radiotoxicity enhancement following photoelectric effect on stable iodinated compounds

This study was designed to experimentally evaluate the optimal X-ray energy for increasing the radiation energy absorbed in tumours loaded with iodinated compounds, using the photoelectric effect. SQ20B human cells were irradiated with synchrotron monochromatic beam tuned at 32.8, 33.5, 50 and 70 keV. Two cell treatments were compared to the control: cells suspended in 10 mg ml1 of iodine radiological contrast agent or cells pre-exposed with 10 mM of iodo-desoxyuridine (IUdR) for 48 h. Our radiobiological end point was clonogenic cell survival. Cells irradiated with both iodine compounds exhibited a radiation sensitisation enhancement. Moreover, it was energy dependent, with a maximum at 50 keV. At this energy, the sensitisation calculated at 10% survival was equal to 2.03 for cells suspended in iodinated contrast agent and 2.60 for IUdR. Cells pretreated with IUdR had higher sensitisation factors over the energy range than for those suspended in iodine contrast agent. Also, their survival curves presented no shoulder, suggesting complex lethal damages from Auger electrons. Our results confirm the existence of the 50 keV energy optimum for a binary therapeutic irradiation based on the presence of stable iodine in tumours and an external irradiation. Monochromatic synchrotron radiotherapy concept is hence proposed for increasing the differential effect between healthy and cancerous tissue irradiation

Clinical Implementation of Single Visit Palliative Adaptive Radiotherapy without Prior CT Simulation

Purpose/Objectives Standard workflows of radiotherapy for metastatic disease palliation often involve long waiting times or multiple clinic visits. Fast palliation completed during a single clinic visit can be achieved by omitting a planning CT scan and using available diagnostic imaging for treatment planning. The use of diagnostic CT can be challenging due to differences in patient positioning and location of target and organs at risk (OAR), but adaptive treatment platforms provide possible solutions. We integrated a fast palliative workflow using diagnostic imaging for pre-planning, with subsequent on couch contour and plan adaption based on a synthetic CT derived from the cone-beam CT imaging (CBCT), and report our clinical and dosimetric experiences. Material/methods An ethics-approved protocol for fast palliation (FAST-METS) was implemented in November 2021. Patients referred for palliative radiotherapy of painful bony metastatic disease of any primary site, available recent diagnostic imaging (Results Data of the first eight patients are presented. The treated metastases were located in the lumbar (2) or thoracic (3) spine and pelvis (3). In all patients, the on-couch re-optimized plan was used for treatment as clinical plan, with a PTVV95% coverage of ≥95%. In three patients, target and OAR volumes were adapted on-couch by the radiation oncologist. All patients completed their consult and treatment within 2 hours. Plan re-optimization time was Conclusion A fast workflow for a single visit palliative IMRT delivery without dedicated planning CT scan was implemented for patients with bone metastases. All patients completed consultation and treatment within 2 hours on average, and indicated satisfaction with the procedure