Multiplan cyberknife

Within 35 days prior to randomization, either a WB MRI or a Ch-PET/CT is mandatory to confirm a diagnosis of oligorecurrent disease, with a maximum of 3 pelvic/extra-pelvic lymph nodes and/or bone metastases, and to exclude visceral disease.
According to SBRT technique, high doses will be delivered to small volumes in few fractions (≤5). In our framework, a schedule of 30 Gy in 3 fractions every other day (equivalent dose EQD2 = 98.6 Gy, considering α/β = 1.5 Gy), or equivalent regimens depending on disease site location will be used. Treatment planning and delivery will be performed using dedicated systems, such as Iplannet-Vero (Brainlab-Mitsubishi) and Multiplan-CyberKnife (Accuray), Eclipse-Trilogy (Varian) and Tomotherapy (Accuray). As far as image-guidance is concerned, Vero, Trilogy and Tomotherapy use a pre-treatment cone-beam CT whereas CyberKnife is based on intrafraction X-Rays. Thus, CyberKnife needs fiducials or spine tracking. CyberKnife is preferred when particular attention to critical structures is required and spine tracking is possible. Strict quality assurance protocols will be implemented to ensure the accuracy in dose delivery.

Treatments were administered in five fractions, with 8 Gy per fraction prescribed to the periphery of the PTV. Treatment planning was performed using the MultiPlan CyberKnife^® planning system version 2.1.0 (Accuray, Inc.). The dose constraint for the ipsilateral uninvolved kidney was less than a third of the volume of the unilateral normal kidney that received >15 Gy. Other organs, with dose limitations and their constraints, have previously been reported and are shown in Table II (9 (link)). With these dose-volume limitations, the PTVs were encompassed by the 72.0, 83.3 and 83.9% isodose curves. Dose-volume histograms provided the required data on dose distribution, and a conformity index (CI) and dose heterogeneity index (HI) were used for planning evaluation. The CI is defined as the ratio of the tissue volume that receives equal to or more than the prescription dose, to the tumor volume, which receives equal to or more than the prescription dose. The HI is defined as the ratio of the maximum dose to the prescription dose. The planning data are shown in Table III.