Room: Exhibit Hall | Forum 5
Purpose: Accurate tumor volume determination is essential to the assessment of treatment effects of different therapies in animal experiments. In this work we investigate tumor growth delay after radiation therapy (RT), high-intensity focused ultrasound (HIFU), and radiodynamic therapy (RDT) using CT/PET and MRI.
Methods: Nude mice were implanted with 106 cancer cells (LNCaP orthotopic implantation, PC3 subcutaneous implantation). Weekly imaging was performed using a GE 1.5T MR scanner and a Sofie-Biosciences G8 small animal CT/PET scanner (18F-FDG). When tumors grew to the size of 5-8 mm, mice with LNCaP tumors were treated with MR-guided HIFU on an InSightec ExAblate 2000 unit (n=18) or RT on a Varian IX linac with 6MV photons (n=20) while mice with PC3 tumors were treated with RT alone on a Top Grade LA45 RaceTrack Microtron using 45MV photons (n=20) or RT with photosensitizers (5ALA)(n=43). Tumors on different images were contoured and volumes were calculated using a home-grown algorithm.
Results: MRI has high soft-tissue contrast compared to CT and is useful for tumor delineation. Non-thermal HIFU produced a 20% (5W-60sec) to 40% (25W-60sec) tumor growth delay for LNCaP cells at weeks 1&2 post-treatment, as shown on MRI. The latter damage was similar to that of a 2Gy treatment as observed 3 weeks post-RT. Tumor suppression was observed one week after RDT for PC3 tumors, which grew aggressively and developed necrotic cores at weeks 2&3 post-RDT, thus leading to uncertainties in volume evaluation. PET was useful in identifying hypoxic portions of the tumor and sub-tumor volumes that were deactivated by RDT.
Conclusion: MRI is useful in tumor volume delineation while PET is necessary to identify sub-tumor volumes that were either hypoxic or deactivated by treatments. The combined use of both imaging modalities could help improve the treatment assessment for therapies of different mechanisms of action.