ESTRO 2022 - Abstract Book

S1619

Abstract book

ESTRO 2022

B. Vanneste 1 , V. Skouteris 2 , L. Campos Pinheiro 3 , N. Stone 4

1 Maastro, Radiotherapy Oncology, Mastricht, The Netherlands; 2 Hygeia Hospital, Urology, Athens, Greece; 3 Hospital da Luz, Urology, Lisboa, Portugal; 4 The Icahn School of Medicine at Mount Sinai New York, Urology and Radiation Oncology, New York, USA Purpose or Objective To determine different approaches of focal brachytherapy with and without rectum spacer derived in an in-vitro prostate cancer simulation. Materials and Methods Two different focal strategies are examined: a lateralized approach (left-right) and the both posterior lobes strategy, which is the predominant position of a clinically significant prostate cancer. Two sets of implants were used in an in-vitro study using the Simulated Inanimate Models of prostate with a dominant lesion (Gross tumor volume, GTV)(SIM TM ): the loose Mick seeds in comparison with the linked stranded I 125 seeds. The prescribed dose to the clinical target Volume (CTV), and the GTV were at least 200 Gy. Furthermore a rectum spacer (barrigel®) was injected to decrease the dose to the rectum. Post- implant Computed Tomographies of the phantoms were performed with a post-implant dosimetry. The rectum D1cc and D2cc were compared with and without spacer implant. Results The focal volumes of the CTV varied from 5 to 15 cc (mean 8 cc, the percentages of ‘‘focal volume/whole prostate volume’’ varied between 17% and 38% with a mean of 26%). The focal volumes of GTV varied from 0.7 to 1 cc. The total number of needles necessary to implant the focal volume varied between 7 and 10 (mean, 9). The total number of seeds (activity 0.500 to 0.600 mCi) varied from 27 to 41 (mean, 33). The mean focal D90 of GTV and CTV were 273 Gy (range, 195 Gy – 434Gy) and 227 Gy (range, 168-277 Gy). The D90 for the entire prostate gland was 60.8 Gy (range, 32.6 - 111 Gy). No differences were observed between loose or stranded technique. On average, 12.5 mm separation was achieved between the prostate and the rectum (range, 11-14 mm). The mean doses to 1 cc of rectum (D1cc), and the mean doses to 2 cc of rectum (D2cc) without spacer vs. with spacer were 40.2% vs. 24.4%, 33.8% vs. 24.9% , and 48.9 Gy vs. 36.2 Gy, respectively.

Conclusion The prescription of doses above 200 Gy and the implantation of seeds in the clinical significant region for focal therapy in phantoms are feasible. All rectal dosimetric parameters improved for the spacer implants as compared with the non-spacer implants. Further clinical validation of this concept is warranted.

Poster (digital): Normal tissue radiobiology

PO-1820 A 3D-organoid drug screening method for the elimination of radiation-induced senescent cells

A. Soto Gamez 1 , Y. Wu 1 , X. Peng 1 , S. Pringle 2 , A. Vissink 3 , L. Barazzuol 1 , R.P. Coppes 1,4

1 University Medical Center Groningen, Dept. of Biomedical Sciences of Cells & Systems, Groningen, The Netherlands; 2 University Medical Center Groningen, Dept. of Rheumatology and Clinical Immunology, Groningen, The Netherlands; 3 University Medical Center Groningen, Dept. of Oral and Maxillofacial Surgery, Groningen, The Netherlands; 4 University Medical Center Groningen, Dept. of Radiation Oncology, Groningen, The Netherlands

Purpose or Objective