ESTRO 2024 - Abstract Book

S5400

Radiobiology - Tumour biology

ESTRO 2024

A retrospective study on the cohort of 30 patients treated for prostate carcinoma with high risk was conducted during the period from January 2,2022 to may 31,2022 using volumetric modulated arc therapy. The dose prescription was defined on these different volumes: 71.3 Gy 62 Gy and 52.3 Gy in 31 fractions for PTV1(prostate only), PTV2(prostate +seminal vesicles) and PTV3 (prostate+seminal vesicles+pelvis) respectively. The dose constraints were to give to PTV1, PTV2 and PTV3 a dose > 95% of prescribed dose and D2%< 110% of prescribed dose. The dose constraints on the organs at risk were defined for rectum (69.7 Gy to 1 cc, V32.6 Gy< 70 %, V46.5Gy< 50 %, V60.5 Gy< 30%,V65.1 Gy< 25 %) and bladder (Dmax 71.3 to, 1 cc V42 Gy< 39 %, V55.8Gy< 50 %,V65.1 Gy< 25 %).

Results:

The results obtained on D mean for PTV1 was 71.22 Gy and 70.98 Gy for helical Tomotherapy (HT) versus conformal therapy (3D-CRT). In case of organs at risk, the calculated mean dose are 66.5 Gy versus 38.76 Gy for bladder and 63.48 Gy versus 40.92 Gy for rectum in case of HT and 3D-CRT treatment. For the toxicity, we noticed an increase on the value of EUD for bladder in case of 3D-RTC compared to HT. EUD(bladder) = 60.81 Gy 34.15 Gy and the NTCP(bladder)=1.67% versus 2.8E-10 %. Concerning the risk of induced second cancer the results are similar for the two treatment modalities: EAR= 0.218 for 3D-CRT and 0.211 for HT. In case of rectum, a decrease on the value of EUD was obtained for HT compared to 3D-CRT where EUD = 63.48 Gy versus 40.92 Gy respectively. An decrease on the value of NTCP from 22.46% for 3D-CRT to 5.18% for HT and the associated risk of induced second cancer was similar EAR =1.60 per 10000P-Y and 1.71 per 10000P-Y respectively.

Conclusion:

Tomotherapy assure better protection of organs at risk with a minimum of toxicity but the risk is similar for the two modalities.

Keywords: prostate cancer,, TCP/NTCP, second cancer, EAR

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Aline P Becker 1 , Valesio Becker 1 , Ebin Sebastian 2 , S. Jaharul Haque 1 , Joseph McElroy 3 , Amy Webb 4 , Jessica Fleming 1 , Karnika Singh 1 , Chunhua Han 1 , Matthew K Summers 1 , Monica Venere 1 , Arnab Chakravarti 1 1 The Ohio State University, Radiation Oncology, Columbus, OH, USA. 2 Corewell Health William Beaumont University Hospital, Radiation Oncology, Royal Oak, MI, USA. 3 The Ohio State University, Center for Biostatistics, Columbus, OH, USA. 4 The Ohio State University, Biomedical informatics, Columbus, OH, USA