Dosimetric and biological comparison of treatment plans between LINAC and robot systems in stereotactic body radiation therapy for localized prostate cancer

The aim of this study was to make a comparison of plan quality between MLC-based EDGE and the cone-based CyberKnife systems in SBRT of localized prostate cancer.

Ten patients with target volumes from 34.65 to 82.16 cc were included. Treatment plans were created for both systems using the same constraints. Dosimetric indices including target coverage, conformity index (CI), homogeneity index (HI), gradient index (GI) were applied for target, while the sparing of critical organs was evaluated with special dose-volume metrics and integral dose. Meanwhile, the delivery time and monitor units (MUs) were also estimated. The radiobiological indices such as equivalent uniform dose (EUD), tumor control probability (TCP) and normal tissue complication probability (NTCP) were also analyzed.

Both plans produced similar target coverage, HI and GI. For EDGE, more conformal dose distribution as well as reduced exposure of critical organs were obtained together with reduction of 91% delivery time and 72% MUs. EDGE plans also got lower EUD for bladder, rectum, urethra and penile bulk, which associated with reduction of NTCPs. However, higher values of EUD and TCP for tumor were obtained with CK plans.  

It indicated that both systems were capable of producing almost equivalent plan quality and can meet clinical requirements. CyberKnife has higher target dose while EDGE system has more advantages in normal tissue sparing and delivery efficiency.