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Image Guided Radiotherapy Without the Clinical Target Volume: Leveraging the Abscopal Effect

S Yasmin-Karim*, R Mueller, N Bih, M Moreau, V Ainsworth, W Ngwa, harvard Medical School, Dane Farber cancer Institute, Brigham and Womens Hospital, Boston, MA

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: Recent studies have led to the hypothesis that priming the abscopal effect will make the time-consuming addition of clinical target volumes during treatment planning unnecessary. The purpose of this study is to investigate this hypothesis during image-guided radiotherapy (IGRT) for different cancer models.

Methods: Syngenic-murine tumor models were generated using cell lines for aggressive prostate, pancreas, and lung cancers. To demonstrate the abscopal effect, two contralateral tumors were implanted in each mouse where only one subcutaneous tumor was treated as the primary tumor and the other representing the metastasis was not treated. IGRT treatment was implemented with Small Animal Radiation Research Platform, which allows use of different field sizes: 1x1, or 3x3, 5x5 or 10x10 mm2. Instead of fiducial markers used for IGRT, smart-radiotherapy-biomaterials loaded with anti-CD40 (srbAntiCD40) were employed to help prime the abscopal effect as shown in previous studies. Following tumor growth, the animals were randomized into different groups. In one treatment group, only a partial/sub volume of the gross tumor (GTV/sub-volume) was irradiated. The unirradiated tumor portion was left to represent microscopic disease, typically accounted for by the clinical target volume (CTV). Tumor volume and immune cell population of both treated and untreated tumors and survival percent were analyzed. Results were compared with those of mice in a group where the whole tumor, representing the PTV/CTV, was irradiated.


Results: The results showed equal or significantly better outcomes in terms of survival for animals in the group were only a partial/sub tumor volume was irradiated compared to animals in groups where the PTV/CTV was irradiated. This was consistently observed in different studies for lung, prostate and pancreatic cancer (P value < 0.001).


Conclusion: The findings support the hypothesis that developing reliable approaches to prime the abscopal effect will make the time-consuming addition of CTVs unnecessary.

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Keywords

Targeted Radiotherapy, Small Fields, Radioimmunotherapy

Taxonomy

TH- Small Animal RT: Planning

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