ESTRO 2024 - Abstract Book

S3621

Physics - Dose prediction, optimisation and applications of photon and electron planning

ESTRO 2024

To ensure that accurate dose calculations could be performed on all available dCT images in our hospital uptake region, we evaluated 168 CatPhan scans acquired on 33 different CT scanners from four different vendors.

A workflow was then designed: A recent (< 4 weeks old) dCT is imported to RayStation (version 11B; RaySearch Laboratories AB, Stockholm, Sweden) for target delineation and standard palliative VMAT planning (referred to as a pre-plan). The pre-plan is prepared for treatment in Mosaiq (Elekta AB, Stockholm, Sweden), before the patient arrives for treatment on one of our Elekta C-arm linacs (Synergy, Infinity, Versa HD or Harmony Pro;Elekta AB, Stockholm, Sweden). At treatment, a pre-treatment CBCT image is acquired and transferred to RayStation. Here, deformable image registration to the dCT is performed, before a so-called corrected CBCT (cCBCT) suitable for dose calculation is created. Target and OAR delineations are transferred from the dCT to the cCBCT and corrected if required, before the treatment plan is transferred and reoptimised on the cCBCT image. When a satisfying plan has been approved, the oART plan is transferred to Mosaiq before a second CBCT image is acquired (with the cCBCT as reference) prior to treatment. Before treatment delivery of the adapted plan, standard plan QA procedures are enforced, including independent physicist check and independent dose calculation. QA of the 33 diagnostic CT-scanners in our uptake region showed that kVp in the range of 100-140 creates acceptable Hounsfield Unit (HU) levels for palliative treatment planning using our normal HU to density table. As an extra check of each dCT scan, plan recalculation using delineation-based bulk density override is performed once during the pre-planning step, to detect any major problems in the HU of the actual dCT image being used for planning. Our pilot patient had RT for bone metastasis in four sequential vertebrae (Th11-L2, Figure 1). The total treatment time was 53 minutes for the first fraction and the patient had to remain on the treatment couch for 50 minutes (see Table 1 for detailed information on process times). The patient was allowed to move both arms during the oART procedures between the first and second CBCT. The patient was satisfied with the treatment, and the time spend on the treatment couch was not considered as a problem. Results:

We believe that the treatment time for the first fraction can be reduced by 10 minutes simply by gaining more experience and streamlining the independent parts of the workflow (e.g. starting repositioning for final treatment while the oART plan is imported and checked in Mosaiq). Furthermore, advances in the TPS will likely reduce the oART time by up to 5 minutes, leading to a potential first fraction treatment time of 40 minutes or less. The entire hospital visit including consultation with the physician, treatment preparation and delivery of the first RT fraction will potentially be as short as two hours in total.