ESTRO 2021 Abstract Book

S1622

ESTRO 2021

Conclusion The script used for the automation of prostate planning in our institution is able to reduce clinical workload and the created plans have similar quality and similar characteristics as the manual created plans. If the created plan does not fulfil the desired criteria it is possible to do manual modifications to the plan at the end of the process. 1 SØREN M. B. et al. , QUANTITATIVE ANALYSES OF NORMAL TISSUE EFFECTS IN THE CLINIC (QUANTEC): AN INTRODUCTION TO THE SCIENTIFIC ISSUES, Int. J. Radiation Oncology Biol. Phys., Vol. 76, No. 3 2010 2 Masi L. et al., Impact of plan parameters on the dosimetric accuracy of volumetric modulated arc therapy, Med. Phys. 40(7) July 2013 PO-1901 A semi-automatic 3D printable bolus design workflow for use in electron radiotherapy of the skin R. van Leeuwen 1 , T. Lam 2 , P. van Herpen 1 , R. Monshouwer 1 1 Radboudumc, Radiotherapy, Nijmegen, The Netherlands; 2 Fontys University of Applied Science, Applied Physics, Eindhoven, The Netherlands Purpose or Objective In electron radiotherapy of skin lesions on or directly adjacent to the nose, custom boluses of water-equivalent material are placed on the skin to improve coverage of the clinical target volume (CTV). These boluses can be produced using 3D printing technology, using a design manually prepared in a treatment planning system (TPS). We developed a semi- automated procedure to design such boluses, decreasing the time required for treatment planning, and improving consistency between dosimetrists. Our procedure takes into account patient anatomy, CTV delineation, and dose calculation accuracy. In this study, we aim to evaluate the amount of manual intervention in this semi-automated procedure. Materials and Methods After delineation of the CTV and the skin in the Pinnacle TPS (v16.0.2, Philips, Eindhoven, The Netherlands), contours are sent using the DICOM standard to a custom python script for further processing. First, the optimal beam direction is determined using the dimensions of the CTV contour. Next, boluses of three different thicknesses (5, 7 and 10mm) are automatically generated by our algorithm, optimally meeting the following requirements: (1) fits the skin without air gaps (2) meets the required thickness and (3) yields an angle of incidence of the beam with respect to the outer surface of the bolus that is smaller than 30 degrees. The 3 bolus options and beam angle are sent to the TPS using DICOM after finishing the design. Next, the bolus with optimal CTV coverage is chosen by the dosimetrist, and further adapted manually if necessary. A retrospective analysis was conducted for twenty treatments in which the algorithm was used, comparing the automatically generated bolus with the final clinically used bolus by visual inspection. Both the beam angle and bolus thickness were considered, and manual adjustments were recorded and clarified if possible. Results In the majority of cases, only minor adjustments were made to the bolus shape suggested by the algorithm. Among the reasons for adjustment were: improvement of angle of incidence near the off-axis part of the CTV and adjustments for comfort in positioning. In most cases, the 7 mm bolus was chosen by the dosimetrist for further processing. The beam angle was slightly changed with respect to the suggested angle suggested in most cases. Conclusion We developed a procedure using python scripting to semi-automatically design boluses of water-equivalent material for treatment of skin lesions using 6 MeV electrons. This method drastically reduced the amount of steps required for a dosimetrist to design a bolus; only minor manual adjustments to the automatically-generated bolus were necessary to create a bolus optimally taking into account CTV coverage, patient comfort and dose calculation accuracy. PO-1902 Treating left-sided breast patients in breath hold using a real time surface tracking system Y. Zhao 1 , B. Tang 1 , J. Li 1 , P. Wang 1,1 , X. Liao 1 , X. Yao 1 , X. Xin 1 , L.C. Orlandini 1 1 Sichuan Cancer Hospital & Institute, School of Medicine University of Electronic Science and Technology of China, Radiation Oncology Department , Chengdu, China

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