ESTRO 37 Abstract book

S1023

ESTRO 37

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).

Results C-VMAT reduced max dose to the heart (p<0.03) compared to 3DC and NC-VMAT, while MHD remained unchanged (p=0.5). No significant differences were found for trachea (p=0.7). NC-VMAT was superior to 3DC for max IMB dose (p<0.01) and offered best sparing to spinal cord, esophagus and CMB (all p<0.01), which were all outside the high dose area (more details in Table 2). The PTV included or abutted the heart in 6 patients and IMB in 7 patients. PTV min, n-min, max and n-max doses did not differ significantly between the plans (p>0.08). Mean GTV and PTV doses were reduced with both VMAT plans (p<0.05), resulting in less steep dose gradient within the PTV. The steepness of the dose gradient close to the PTV edge in 3DC was also expressed in substantial median differences between the max and n-max doses to the heart ( 2.5 Gy ) and IMB (6.8 Gy ), and min and n-min GTV dose (4 Gy).

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

Conclusion C-VMAT reduced max heart dose compared with 3DC; NC- VMAT was not superior to C-VMAT for heart parameters. EP-1887 Real-time treatment planning on 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

left femo ral head

right femo ral head

blad der

PTV

V35%

V98%

V95%

V15%

V2% V10% V10% V50%

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

Purpose or Objective The main aims of this study were:

22,8 5Gy

23,5 0Gy

25,7 2Gy

13,4 2Gy

13,8 5Gy

13,1 9Gy

15,6 9Gy

19,6 9Gy

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.