ESTRO 37 Abstract book

S1026

ESTRO 37

AAA algorithm (Varian) on the Eclipse’s Treatment Planning System v13.6 and delivered on a Truebeam (Varian) v 2.5 MR2 in VMAT (6 MV, 600 UM/min). Several adjustable parameters with PO13 are tested on one patient: Normal Tissue Optimization (NTO) influence, calculation resolution during the optimization (1.25, 2.5, 5mm), one or more arcs, optimization volumes, PTV priority compared to OAR priority, PTV priority compared to NTO priority, use of the intermediate dose calculation. The methodology used is first to obtain the best PTV cover, changing one parameter at each optimization, and once parameters chosen and fixed, OAR constraints are introduced. These parameters will be tested with several patients (reproducibility). Plan evaluation is realised with DVH: - PTV: D95%, D98%, D2%, Dmin and Confomation Number (CN). - OAR: bladder and rectum V50Gy and femoral heads Dmax, Dmean/ The monitor units number (MU) per arc is also noted. The dosimetric benefit for the patient will be evaluated in comparison with the real treatment plan calculated with the PRO13 (Progressive Resolution Optimizer algorithm v13). Patient’s quality assurances were also performed using ionisation chamber and 2D gamma index. Results The protocol will be based on the plan presenting a sufficient coverage for the PTV with the best CN taking into account the DVH values on the OAR. The 1 st plan chosen is Plan_1 (table 1) with 2 arcs, PTV priority 200/NTO priority 500, calculation resolution 2.5mm, an intermediate dose calculation. Plan_2 with a single arc has D98% and D95% reduced by 1Gy compared to the other plans and Plan_4 has a CN too weak on the two PTV. Plan_3 with a calculation resolution of 1.25mm seems the same as Plan_1 but the optimization time is multiplied by 2, a resolution of 2.5mm is therefore preferred. The parameters are same for the 2 nd plan. With the use of this new protocol with PO13, we obtain a significant reduction of DVH values for rectum and bladder in comparison with PRO13 algorithm (table 2).

significant resource, particularly when a significant number of patients require adaptive planning during treatment. Therefore, developing automated or knowledge-based planning techniques for H&N cancer patients is important. The purpose of this study was to validate the initial RapidPlan (RP) H&N model at our institution. Material and Methods Varian Eclipse v13.7 was used for this study. An RP model was created using 81 randomly-selected H&N patients initially planned with 1-3 dose levels using IMRT or VMAT, and including both unilateral and bilateral tumours for a variety of diagnoses. Upper and lower objectives were added for targets, and line objectives for organs at risk (OARs). In both cases the default RP settings were used, allowing RP to automatically generate priorities. Local settings were used for the Normal Tissue Objective (NTO). Once the model had been created, it was tested for 11 previously planned patients, covering the same range of treatment techniques and diagnoses as were included in the model. MU constraints were used as they would be clinically but there was no additional user input for the optimizer when using RP. Plans were evaluated against local plan acceptance criteria. Results RP showed a statistically significant reduction in mean parotid doses. All plans met local criteria for PTV coverage and homogeneity, but RP showed statistically significant reduced homogeneity compared to the clinical plans (CP), as shown in Fig. 1. Spinal cord doses were similar between RP and CP and were within tolerance in all cases. Generally, Monitor Units (MU) of RP were higher than the CP, but they were all within the acceptable range. Further modifications were made to the RP model to improve target homogeneity and initial results indicate that it is possible to achieve this whilst still retaining much of the improved parotid sparing. Figure 1. The comparison of dose distribution of CP with RP for a patient, who has 3 different dose levels (PTV65, PTV60, PTV54). Conclusion An RP model using generated objectives was able to meet all clinical constraints and improve parotid sparing but at the expense of target homogeneity. Therefore, further work is required to modify the model in order to improve the PTVs homogeneity. EP-1893 Automated planning through explicit optimization of plan quality L. Engberg 1 , K. Eriksson 1 , A. Forsgren 2 1 Raysearch Laboratories AB, Research department, Stockholm, Sweden 2 KTH Royal Institute of Technology, Department of Mathematics, Stockholm, Sweden Purpose or Objective In this study, we address methodological shortcomings in the conventional penalty-based objective functions, and argue that resolving these issues has a similar potential as other automating methods to streamline the planning process. Our hypothesis is that any tractable formulation

Conclusion This study allowed us to simplify our practices with the use of the NTO as a replacement for all optimization volumes (rings). Treatment plans obtained with PO13 allow a better saving of OAR with an equal or a better coverage of PTV. EP-1892 Clinical validation of Rapid Plan Head & Neck Model S.C. Lee 1 , C.P. South 1 , E.J. Adams 1 1 St. Luke's Cancer Centre Royal Surrey County Hosp, Medical Physics, Guildford, United Kingdom Purpose or Objective Treatment planning for head & neck (H&N) intensity modulated radiotherapy (IMRT) or volumetric modulated arc therapy (VMAT) is time consuming and requires