ESTRO 2021 Abstract Book

S1603

ESTRO 2021

Conclusion There is b etter tumor conformity using HA and better homogeneity using RA. There was almost no difference in MU required in those two planning techniques. The normal brain showed much lower dose in HA, which means RA may be superior in protecting brain function.

PO-1883 Evaluation of an automated treatment planning system for head and neck treatment L. calmels 1 , D. Sjöström 2 , Z. Pohl 2 , P. Sibolt 3

1 Herlev & Gentofte hospital, Herlev, Denmark, Radiotherapy Research Unit, Department of Oncology, Herlev, Denmark; 2 Herlev & Gentofte Hospital, Herlev, Denmark, Radiotherapy Research Unit, Department of Oncology, Herlev, Denmark; 3 Radiotherapy Herlev & Gentofte Hospital, Herlev, Denmark, Research Unit, Department of Oncology, Herlev, Denmark Purpose or Objective Treatment planning system (TPS) has become more sophisticated over the past decade, enabling creation of complex radiotherapy plans securing target coverage while sparing organs at risk (OAR). Recent intelligent solution development for automated plan optimization has the potential to better support the planners. The aim of this study was to compare the dosimetric performance of automated intensity modulated radiation therapy (IMRT) plans and manually generated volumetric modulated arc therapy (VMAT) plans generated with an automated TPS (TPS-1) and a conventional TPS (TPS- 2) respectively for head and neck (H&N) treatment sites. Materials and Methods Clinical goals and dose constraints were used by TPS-1 to build the underlying optimization objective functions. These planning directives sets and the internal prioritization between goals and constraints were worked out using nine retrospectively selected H&N cases as input. The tuned planning directives were saved as templates and applied for systematic generation of three IMRT (7, 9 and 12 field) plans on the radiotherapy planning computed tomography (pCT) for the same set of patients. Nine VMAT plans were correspondingly optimized and calculated with TPS-2. The IMRT plans were transferred from TPS-1 to TPS-2. Dose-volumetric data for the planning target volume (PTV) and relevant OAR, the homogeneity index (HI), the conformity index (CI), the modulation factor (Monitor Units (MU) per Gy), and the dose to the normal tissue of both treatment approaches were all compared. The TPS-1 best IMRT plan was approved (reference plan) and used to simulate four treatment fractions (fraction 5, 10, 20 and 30) for each patient. At each simulation, the reference plan was recalculated on the pCT deformed to the fraction-specific cone-beam CT geometry and compare to the reference plan in terms of target coverage and OAR sparing. Results Both the PTV coverage and OAR sparing were comparable between the best IMRT plans and the corresponding VMAT plans. No statistically significant differences were observed for the CI or HI, and the dose to the normal tissue was comparable for all technique investigated (Figure 1). The PTV coverage and the OAR sparing were within the clinical constraint for all the fractions simulated. The median change in PTV size was within 6% (interquartile range 5%-9%), which in general resulted in no critical OAR DVH parameters significant changes. One patient had an 11% mean PTV volume decreased, resulting in less than 8% and 32% increase in the maximum dose to the spinal cord and mean dose to the left parotid, respectively.