Purpose: To assess changes in SpaceOAR™ implants throughout the course of treatment and determine the significance of any changes.
Methods: The SpaceOAR Vue™ implant was contoured on weekly CBCT images acquired during the external beam treatment of 7 clinical prostate patients. To compensate for the reduced image quality and difficulties clearly distinguishing the extent of the SpaceOAR Vue™ in the CBCT images, consensus contours were constructed from contours generated by multiple physicists. Parameters including the apparent volume and radiographic density of the implant were measured throughout the course of each patient’s treatment and their variation was studied as a function of time.
Results: The radiographic density of the implants showed minimal variation throughout the course of treatment (5-7 weeks) in all cases although scans performed after seed implants for four of the patients showed a marked decrease in the density approximately 3 months post implant. One patient had a significant delay starting treatment and showed complete contrast agent absorption after ~150 days, although the SpaceOAR™ structure itself was still present. Several patients showed a trend to decreased implant volume at a rate of approximately 0.3% per day, although the extent of this change varied from patient to patient. One patient showed a marked increase in the rate of change of the implant volume at ~60 days post implant.
Conclusion: Changes in SpaceOAR Vue™ implants were examined via weekly CBCTs throughout the course of treatment for 7 patients. Except over long courses of treatment (>60 days post implant), changes in volume and density were small and gradual, confirming the expected behavior of the implants.