ESTRO 2024 - Abstract Book

S5339

Radiobiology - Tumour biology

ESTRO 2024

These results demonstrate the usefulness of the Biodose Actor recently developed and the potential of the experimental set up for irradiating biological samples in a helium SOBP. While the theoretical depth of the SOBP was validated by the means of radio-chromic films, the observed heterogeneity remains to be further investigated. According to this preliminary data, while NanOx appears to predict well cell survival between 0 and 2 Gy, the discrepancy observed for higher doses requires further investigation.

Keywords: Monte Carlo simulation, helium-ion therapy

713

Digital Poster

Low incidence of high-grade lymphopenia following radiotherapy for oligometastatic prostate cancer

Samuel A Moffet 1 , Kelly Guardian 1 , Zach Lee 1 , Alan Zwart 1 , James Tetty 1 , Taylor Recher 1 , Malika Danner M.D. 1 , Marilyn Ayoob 1 , Thomas Yung 1 , Deepak Kumar Ph.D. 2 , Henghong Li 3 , Simeng Suy Ph.D. 1 , Michael Atkins M.D. 3 , Sean P Collins M.D. Ph.D. 1 1 Georgetown University Hospital, Department of Radiation Medicine, Washington, USA. 2 North Carolina Central University, Biotechnology Research Institute, Durham, USA. 3 Georgetown University Hospital, Department of Oncology, Washington, USA

Purpose/Objective:

Radiotherapy (RT) is a commonly used treatment for localized prostate cancer and subsequent oligometastatic recurrences. Common sites of recurrence include pelvic/abdominal nodes and bone metastases. Lymphocytes are radiation sensitive with variable recovery with prostate RT having a rapid return to baseline. Multiple courses of RT may cause high-grade lymphopenia which could impact cancer control and lead to secondary infections. The aim of this study is to evaluate the incidence of lymphopenia following RT and its severity depending on the target, treatment volumes, and number of treatment courses.

Material/Methods:

Institutional IRB approval was obtained (IRB#: 2012-1175). The absolute lymphocyte count was measured 1-2 hours prior to RT (27.5-35 Gy in 5 fractions) and at each follow-up (3, 6, 12, and 24 months). Lymphopenia was graded using the CTCAEv.4: Grade 1 (1.0-0.8 k/ul), Grade 2 (0.8-0.5 k/ul), Grade 3 (0.5-0.2 k/ul) and Grade 4 (<0.2 k/ul). Multivariant analysis was done comparing lymphopenia grade against prior prostate radiation, radiation dosage, course of treatment, and target volume. The target volume was grouped into regions of the pelvis, abdomen, pelvis and abdomen, and bone. The median course of treatment was 2.18 courses.

Results: