Bin Sing Teh MD, Abstract Co-Author: Nothing to Disclose

Yuanhong Gao MD, PhD, Abstract Co-Author: Nothing to Disclose

Xiaozhen Wang MD, PhD, Presenter: Nothing to Disclose

Julie Zhu, Abstract Co-Author: Nothing to Disclose

Weiyuan Mai MD, Abstract Co-Author: Nothing to Disclose

Ying Huang MD, PhD, Abstract Co-Author: Nothing to Disclose

Arnold C. Dela Paulino MD, Abstract Co-Author: Nothing to Disclose

Michael Ittmann, Abstract Co-Author: Nothing to Disclose

Brian Butler, Abstract Co-Author: Nothing to Disclose

et al, Abstract Co-Author: Nothing to Disclose

Stereotactic body radiation therapy (SBRT) is an emerging radio-therapeutic paradigm that uses a very large dose per fraction treatment schedule for cancers. We investigated the use of this ablative hypofractionation radiotherapy in treating human prostate carcinoma in vitro and in vivo.

Human prostate cancer cell line CWR22RV1 was used. Clonogenic count assay, sulforhodamine B cytotoxity assay and cell density assay were used to evaluate the radiation anti-tumor efficacy in vitro. 5Gy and 15Gy per fraction were used. In vivo, nude mice were injected subcutaneously with CWR22RV1 human prostate carcinoma cells. Tumor-bearing animals were treated as follows: control (N=10), mid-dose hypofractionation (N=9, 5Gy/f in two fractions) and high dose hypofractionation groups (N=11, 15Gy/f in two fractions). The tumor growth delay assay and pathological examination were used to investigate the anti-tumor effect of irradiation.

Relative to the control group, the fraction of clonogenic formation was 5.06% for the 5Gy per fraction group and 0.06% for the 15Gy per fraction group (p<0.01). The marked difference in cell viability assay was noted among the control, mid-dosage and high-dosage hypofractionation groups (p<0.01). The cell density assay showed the lowest number of cells attached in high dosage group when compared to the mid-dosage and control groups (p<0.01). In vivo the tumor growth delay assay showed significant differences in anti-tumor effect of radiation with different fractionation dosages (p<0.01). The control animals demonstrated progressive tumor growth and were sacrificed because of tumor size. The rapid regression of the tumors was noted in high-dosage hypofractionation group. All the tumors achieved complete regression (CR). In the mid-dosage group, the tumor growth was noted to show slow progression during initial three weeks followed by rapid progression afterwards. Pathologic examination revealed no viable cancer cell and extensive necrosis in the high-dosage hypofractionation group.

Both in vitro and in vivo results demonstrate the efficacy of high-dosage hypofractionation irradiation resulting in a sustained anti-tumor control in human prostate cancer. These results are promising and exploratory work on the mechanism is in progress. Translating this finding into the clinic trial using ablative high-dose-per fraction radiation or SBRT for prostate cancer is planned.(Supported by a research grant from The Methodist Hospital)

Teh, B, Gao, Y, Wang, X, Zhu, J, Mai, W, Huang, Y, Paulino, A, Ittmann, M, Butler, B, et al, , In Vitro and in Vivo Efficacy of Ablative Hypofractionation Radiation/Stereotactic Body Radiation Therapy (SBRT) for Human Prostate Cancer.  Radiological Society of North America 2008 Scientific Assembly and Annual Meeting, February 18 - February 20, 2008 ,Chicago IL. http://archive.rsna.org/2008/7001195.html