Purpose: Vital to all cancer therapy modalities, is an effective relationship between treatment and effect. This work evaluated this relationship for intratumoral infusions of liposome‐encapsulated, 186Re for the treatment of human head and neck squamous cell carcinoma xenografts in nude rats. Methods: Rats were separated into three treatment groups receiving intratumoral infusions of, 186Re‐liposomes (5mCi/cm3 tumor; infused volume = 45% tumor volume): one group received a single infusion location, one group received multiple (3) infusion locations, and one group received multiple (3) infusion locations following two systemically injected bevacizumab treatments (1mg/rat). Planar gamma camera imaging was used to obtain tumor clearance kinetics. SPECT/CT images were used to obtain intratumoral activity distributions. Tumor sizes were periodically measured up to 43 days post‐treatment. Intratumoral dose calculations were performed using a dose‐point‐kernel convolution technique with co‐registered SPECT/CT images. Average dose and EUD values were calculated for individual tumors in attempt to correlate values with relative tumor shrinkage by comparing day 43 tumor volumes with day 0.Results: Intratumoral dose calculations showed significant intratumoral dose heterogeneity. The use of three separate tumor infusion locations improved dose homogeneity compared to a single infusion location as a result of a more uniform radioactivity distribution. An excellent dose‐response correlation was seen with EUD calculations (R, 2 = 0.84) compared with average tumor doses (R, 2 = 0.22). Varying radiobiological parameters over commonly used values showed little effect on relative EUD calculations among rats and suggests individualized parameter use is of little significance as long as the intratumoral dose heterogeneity is taken into consideration in the dose‐response relationship. Conclusions: This work showed a much improved treatment‐effect relationship for intratumoral delivery of, 186Re‐liposomes when using tumor EUD calculations. This is useful for treatment planning and evaluation with this radiation delivery technique.
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging