Optimal Planning Target Volume With Stereotactic Radiosurgery

• 12-month local control rate [ Time Frame: 1 yr ] [ Designated as safety issue: No ]
  

• Rate of radionecrosis at SRS treatment site [ Time Frame: 1 yr ] [ Designated as safety issue: Yes ]
  
• Rate of distant brain metastases [ Time Frame: 1 yr ] [ Designated as safety issue: No ]
  
• Overall survival [ Time Frame: 1 yr ] [ Designated as safety issue: No ]
  

Stereotactic radiosurgery (SRS) is used either as definitive treatment alone or as a "boost" in combination with whole-brain radiotherapy (WBRT) for the treatment of brain metastases. To establish a target for SRS, the gross tumor volume (GTV) is typically defined as the contrast-enhancing volume on T1-weighted axial MRI images. In turn, the volume chosen for treatment (the planning target volume or PTV) is generated by expanding the GTV to account for microscopic extension of tumor beyond the MRI-visualized volume and deviations in patient positioning at the time of treatment., However, the optimal PTV in patients undergoing SRS of brain metastases has not been established.

This pilot randomized study of 40 patients (representing a total of 80 brain metastases) should be sufficient to explore the effect of margin expansion about the GTV for brain metastases. The patients enrolled in this study will undergo radiosurgery to a planning treatment volume generated by expanding the gross tumor volume by either 1- or 3-mm. Each lesion will be randomized to receive either Arm 1 or Arm 2.

Arm 1: Planning target volume obtained by expanding the GTV 1mm ("1mm margin") Arm 2: Planning target volume obtained by expanding the GTV 3mm ("3mm margin")