[F-18] Fluorothymidine PET/CT Imaging for Pelvic Cancers

• Changes in FLT uptake as measured by PET/CT scanning [ Time Frame: baseline, weeks 1 and 2 of therapy, 1 month post radiation therapy, and 1 year post radiation therapy ] [ Designated as safety issue: No ]
  Standardized uptake values of the FLT tracer signal in pelvic bone marrow will be used to create patient-specific bone marrow spatial maps to reduce bone marrow dose during radiation therapy planning. Changes in uptake will be assessed in relation to the radiation therapy plan.
  
  

• Adverse event frequency [ Time Frame: weekly during radiation treatment treatment for up to 8 weeks; then at 1 month, 3 months and 1 year post-radiation ] [ Designated as safety issue: No ]
  Assess grade 2 and higher adverse events. Evaluate the relationship between radiation dose, the bone marrow spatial map, and the adverse event frequency and profile.
  
  
• Blood Cell Counts [ Time Frame: baseline, weekly during radiation treatment for up to 8 weeks, 30 days and 1 year after treatment ] [ Designated as safety issue: No ]
  Blood counts will be recorded to assess the effect of radiation dose on pelvic bone marrow activity.
  
  
• Chemotherapy compliance [ Time Frame: At 24 months ] [ Designated as safety issue: No ]
  The amount of chemotherapy administered will be compared to the amount of chemotherapy prescribed. A secondary comparison against the level of bone marrow suppression (as measured by both the blood cell counts and FLT PET/CT scans) may also be performed. This cannot be assessed until the participant has completed their entire prescribed course of chemotherapy, which will vary based on their tumor type.
  
  

Overall survival of pelvic cancer patients depends on control of systemic disease. If local radiation therapy depletes bone marrow function to such an extent that systemic therapies must be withheld, chances of metastatic failure increase significantly. This may be more significant for this group of patients because approximately one third of adult bone marrow is located in the pelvic region. Strategies to minimize toxicities would benefit a range of pelvic cancer patients including gynecologic, anal, rectal, and prostate. New chemoradiation combinations improve outcomes for these disease sites, but come at the cost of higher levels of toxicity. As many as 40% of cervical cancer patients miss at least one chemotherapy cycle due to hematologic toxicity and 36% of anal cancer patients experience grade 3 or 4 hematologic toxicity when undergoing chemoradiation therapy. A clinical trial of concurrent chemoradiation therapy for rectal cancer was terminated due to toxicity, including hematologic toxicities. Concurrent chemoradiation therapy shows promise for advanced stage prostate cancers, but it also increases grade 3 and 4 toxicities. To successfully limit hematologic toxicities for pelvic cancers, it is extremely advantageous to avoid irradiating the highly proliferative compartments of the pelvic bone marrow. However, the complex structure of the pelvis makes it difficult to assess the efficacy of radiation therapy (RT) planning strategies to avoid areas critical to hematopoiesis. Uptake of [18F]fluorothymidine imaged with positron emission tomography (FLT PET/CT) can be an accurate and sensitive tool for identifying and monitoring the effects of chemoradiation on proliferative pelvic bone marrow. Clinically validating the utility of FLT PET/CT imaging for identifying active bone marrow in the design of bone marrow sparing RT-plans and the important bone marrow assessment time points would provide a method to reduce acute and chronic hematologic toxicities for pelvic cancer patients.