Optimization of Cervical Cancer Radiation Therapy through Functional Bone Marrow Sparing Philip J. Loury, Jakub Pritz, Yun Liang, Loren K. Mell

AbstractThe objective of this study is to improve cervical cancer treatment outcomes by minimizing the adverse effects of chemo-radiation therapy (CRT) on the immune system. Known as hematologic toxicities (HT), these effects weaken the body’s ability to fight off infections and often force a delay in life-prolonging treatment. Hematologic toxicities originate in pelvic bone marrow, where chemo-radiation suppresses the growth of bone marrow stem cells that produce the body’s white blood cells. MRI technology was used to pinpoint bone marrow regions low in fat fraction, and a cohort of patients were treated with intensity modulated radiation therapy (IMRT) to reduce radiation dosage to these sub-regions. The resulting analysis demonstrated that bone marrow fat fraction increased as radiation dosage increased, indicating that bone marrow fat fraction analysis may prove to be instrument to optimizing radiation treatment planning.

Materials and MethodsCell culture and stretch chamber preparation:• Bovine aortic endothelial cells (BAECs) cultured in growth media and

maintained at 37°C with 5% CO2

• 127 µm thick membrane affixed to 10 × 10 cm stretch chamber using rubber gasket

• 4 × 4 cm section on center of membrane coated with fibronectin for 18-24 hours

• Confluent BAECs seeded onto 4 × 4 cm square for 18-24 hours

Stretch and microscopy:• Cell-containing stretch chamber assembled onto movable plate above

stationary indenter• Plate moved in vertical direction with the indenter causing cells to stretch

(Figure 1)• Particle images acquired at rate of 5-7 frames/s for 3 min at 1-hr intervals for

24 hrs

Data analysis using Matlab:• Particle movement tracked at each 3 min time point• Realignment of axes using eigenvalues resulting in perpendicular soft and

stiff directions• MSD determined from particle movement in both soft and stiff directions• MSD of particles inversely proportional to stiffness of cell

Results

Results

ConclusionsIn response to uniaxial stretch, VECs become stiffer over the first seven hours. After 24 hours of exposure to stretch, VECs become softer again, past their original level. VECs gradually realign themselves perpendicular to the direction of stretch for the entire duration of the 24 hours.

IntroductionCervical cancer is the third most common cancer in women, with an estimate of 530,000 cases worldwide in 2008.1 Standard methods of radiation treatment are often constrained by the suppression of the patient’s immune system, known as hematologic toxicities. Pelvic bone marrow is known to be rich with stem cells that are responsible for the production of new white blood cells. Concurrent chemotherapy and radiation treatment has been shown to inhibit the bone marrow’s ability to produce new white blood cells, and as a result, patients are put at risk of developing infections or requiring hospitalization.2 The development of hematologic toxicities often prevents oncologists from intensifying chemotherapy regimens necessary to prevent the spread of a patient’s cancer. Pelvic bone marrow accounts for nearly 50 percent of the body’s total bone marrow, making pelvic cancers particularly problematic in confronting hematologic toxicities. Although current radiation techniques do their best to minimize radiation dosage to healthy tissues, basic CT imaging is unable to properly identify the critical non-cancerous tissues that are integral to a patient’s ability to withstand chemotherapy. Being able to significantly limit radiation exposure to critical areas of the bone marrow may limit the occurrence of hematologic toxicity and provide a breakthrough in a doctor’s ability to effectively use chemotherapy. The researchers at the Center for Advanced Radiotherapy Technologies at the UCSD Moores Cancer Center have developed Intensity Modulated Radiation Therapy (IMRT), a treatment method that hopes to provide less toxic treatments in cervical cancer patients. IMRT gives a radiation oncologist the ability to modulate radiation intensities in order to maximize the radiation to the tumor while minimizing dosage to healthy tissues.

References1. Del Alamo, et al. 2008. Anistropic rheology and directional mechanotransduction in vascular endothelial cells, Proc Natl Acad Sci U S A, Vol 105, 15211-15416.2. Sato, M., et al. 1996. Viscoelastic properties of cultured porcine aortic endothelial cells exposed to shear stress, J Biomech Vol 29, 461–467.

Figure 3. MSD over time in hours for stiff and soft directions. MSD in both directions decreases up until the 7 hour time point and then increase again. Colors represent 95% confidence interval of median.

Figure 2. Displacement of individual particles over time for static time point (left) and after seven hours (right). Colors closer to red represent less MSD over time, while colors closer to blue represent more MSD over time. MSD decreases over the first seven hours. Cells can also be seen realigning perpendicular to direction of stretch in the seven hour picture.

Figure 4. MSD over time in seconds. Colors represent hourly time points. For the first seven hours, mean square displacement decreases continuously, showed by the downward shift in the graph. The upward slope represents particles moving away from the origin over time with transparent colors representing two standard deviations.

Figure 5. MSD over time in seconds, with four additional time points imposed on original graph. Downward shifting trend no longer exists in last four time points, with last four lines shifting back towards starting position.

Materials and Methods

Figure 1. A: top view of stretch chamber. Rectangular shape of indenter causes membrane to stretch in one direction. B: Side view of chamber. Stage moves down, causing membrane to stretch. C: Stage returns to original position.

A B

C

StiffSoft

AcknowledgementsCalit2 program for funding, Phu Nguyen for technical support

Direction of stretch

Sponsored by:

Department of Radiation Oncology, Moores Cancer CenterUniversity of California, San Diego, La Jolla, CA