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Clonogenic Assay of Normal Cell Lines Treated by Pulsed Low-Dose-Rate Radiotherapy

J Xu1*, Y Zhang1,2 , C Ma1 , (1) Fox Chase Cancer Center, Philadelphia, PA, USA, (2) Tangdu Hospital, Air Force Military Medical University, Xi'an, Shaanxi, China


(Sunday, 7/29/2018) 3:00 PM - 6:00 PM

Room: Exhibit Hall

Purpose: To investigate the damage of normal cell lines induced by pulsed low-dose-rate (PLDR) and regular radiotherapy (RT).

Methods: CCD 841 cells (epithelial tissue cells of human colon) were examined in this in vitro clonogenic study. Cells were cultured in six-well plates with a plating density ~ 200 cells per well and maintained at 37°C under aseptic conditions. The plates were irradiated by Siemens Artiste 6-MV beams at a low dose rate of 100 MU/min. The radiation treatment was delivered using a pulse train of 0.2 Gy separated by 3-minute time intervals, with single fraction dose sampled at 0.2, 0.4, 0.8, 1, 2, and 4 Gy, respectively. The treated cells were incubated for 2 weeks for colony formation before fixation and staining with Giemsa. Regular RT treatment (at a dose rate of 300 MU/min) was also performed for comparison.

Results: Cell survival fractions for PLDR radiotherapy are 1, 0.83, 0.71, 0.55, 0.45, 0.18, and 0.06 in control, for 0.2 Gy, 0.4 Gy, 0.8 Gy, 1 Gy, 2 Gy, and 4 Gy, respectively, in comparison to 1, 0.76, 0.5, 0.27, 0.19, 0.09, and 0.02 for clinical treatment. Half survival (D50) is set as the threshold for damage extent classification, which are 0.8-1 Gy and 0.4 Gy for PLDR and regular RT, respectively. When single fraction dose is higher than 1 Gy, there is no clinical difference between PLDR and regular RT treatments in damage extent.

Conclusion: Compared to regular radiotherapy, PLDR treatment exhibits a low cell damage rate on normal cells, CCD 841, below 1 Gy. PLDR is a promising treatment method for normal tissue sparing in re-radiotherapy of patients with recurrent cancers.


Radiation Effects, Radiobiology


TH- Radiobiology(RBio)/Biology(Bio): RBio- Photons

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