Abstract Book

S1022

ESTRO 37

EP-1887 Real-time

treatment

planning

on

Tab.1. Comparison of PTV and OARs doses for standard HT and StatRT.

Tomotherapy for patients with rectal cancer. U. Sobocka-Kurdyk 1 , M. Skórska 2 , A. Ryczkowski 2 , B. Pawałowski 2,3 , T. Piotrowski 2,4 1 Greater Poland Cancer Centre, Department of Medical Physics, Kalisz, Poland 2 Greater Poland Cancer Centre, Department of Medical Physics, Poznan, Poland 3 Poznan University of Technology, Department of Technical Physics, Poznan, Poland 4 Poznan University of Medical Sciences, Department of Electroradiology, Poznan, Poland 1. To create a model of optimization for fast treatment planning process in real time (StatRT scheme) on the Helical Tomotherapy (HT). 2.To find out whether prepared StatRT scheme is comparable to standard HT plans. Material and Methods Twenty patients with rectal cancer were planned by standard HT procedure (6MV, according to conditions set by the ICRU for the planning target volume (PTV)) and by StatRT scheme on the HT. StatRT is fast method of planning in Tomotherapy. It was implemented for performing online MVCT scanning, treatment planning and treatment delivery in one session. In this study StatRT treatment plans based on averages, standardized parameters optimization (criteria for dose-volume and importance of structures) obtained from a standard HT were created. These plans were performed for certain number of iterations (3, 6, 9 or 12). Fractionation scheme was 5x5Gy. A comparison of treatment plans between variant for StatRT and standard HT plans has been performed. Comparison based on qualitative analysis of DVH for PTV and OARs, and also on quantitative analysis dose – volume criteria. For the HT and StatRT scheme, total treatment time (imaging, planning, positioning and treating) was also considered. Results 1.The treatment plan created for 9 iterations was the most optimal scheme StatRT compared with plans for 3, 6 and 12 iterations. It was chosen because there were no statistically significant differences in comparison dose - volume parameters for PTV with the plan set up for 12 iterations, but the time of preparation was much shorter (Fig.1). Purpose or Objective The main aims of this study were:

left femo ral head

right femo ral head

blad der

PTV

V98%

V95%

V35%

V2% V10% V10% V50%

V15%

Stand ard HT StatRT (9 iterati ons)

23,5 8Gy

24,0 0Gy

25,6 2Gy

14,0 6Gy

14,5 7Gy

11,0 4Gy

14,7 1Gy

20,2 7Gy

22,8 5Gy

23,5 0Gy

25,7 2Gy

13,4 2Gy

13,8 5Gy

13,1 9Gy

15,6 9Gy

19,6 9Gy

Fig. 2. Averaged DVH comparison of PTV and OARs for standard HT and StatRT scheme. 3.Total treatment time for StatRT scheme: MV scanning on HT–5 minutes, planning–20 minutes, treating 5 minutes (unnecessary additional positioning of patient).Total treatment time for standard HT: CT scanning–5 minutes (several days before treatment), planning–2 hours, treating–20 minutes. Conclusion The difference between the standard HT procedure and StatRT scheme for 9 iterations for PTV and OAR doses was not statistically and clinically significant. In time sensitive cases standard HT may be replaced by StatRT scheme for patients with good prognosis. There were no statistically significant differences between the HT plan and StatRT plan for 9 iterations, moreover it provides significantly faster start of treatment. EP-1888 A retrospective comparison of the new commercial algorithm ACE and TG43 for brachytherapy treatments V. Ravaglia 1 , G. Mazzotti 1 , G. Feliciani 1 , E. Menghi 1 , A. Sarnelli 1 1 IRST - Istituto Tumori della Romagna, Medical Physicist, ForliMeldola FC, Italy Purpose or Objective To evaluate the dosimetric impact of the novel commercial algorithm ACE (Advanced Collapsed-cone Engine, Elekta) respect to the TG43 calculation. Material and Methods 20 patients and a total of 100 plans of cervical and lung brachytherapy treatments were retrospectively evaluated using the commercial algorithm ACE, using both water density and the TG186 heterogeneity corrections. The original TG43 calculated plans were recalculated using ACE algorithm with same dwell positions and times. We recalculated the plans using both standard (grid size 1 mm within 1 cm from the implant, 2 mm within 8 cm and 5 mm beyond) and high resolution mode (grid size 1 mm within 8 cm from the implant and 2 mm beyond). The difference between TG43 and TG186 with and without density correction were calculated in terms of

Fig. 1. Dose distribution in 98% volume of PTV – comparison StatRT scheme for 3, 6, 9 and 12 iterations. 2.In comparison of standard Helical Tomotherapy procedure with StatRT scheme for 9 iterations, no statistically significant differences between the dose distribution in PTV and OARs was observed (Tab.1 & Fig.2).