Radiation Oncology/Stereotactic radiosurgery

Stereotactic Radiosurgery (SRS)

Clinical Sites

Overview

• CNS Page

Malignant

• Brain Metastases
• Pineal Gland tumors

Benign:

• Meningioma
• Acoustic Neuroma (Vestibular Schwannoma)
• Pituitary Adenoma
• Trigeminal Neuralgia
• Sphenopalatine Neuralgia
• Chronic Cluster Headaches
• Arteriovenous Malformation (AVM)
• Cavernous Malformation
• Glomus Jugulare (Paraganglioma)
• Epilepsy
• Cancer pain

Treatment planning indices

• Yomo; 2010 (PMID 19809786): Energy Index
  • EI = ID / (TV x PD)
  • ID = integral dose within target volume
  • PD = prescribed dose
  • Measure of dose homogeneity within target volume

• Oliver; 2007 (PMID 17194494): Radical Dose Homogeneity Index
  • rDHI = D_min / D_max
  • D_min = minimum dose within target volume
  • D_max = maximum dose within target volume

• Oliver; 2007 (PMID 17194494): Moderate Dose Homogeneity Index
  • mDHI = D_95% / D_5%
  • D_95% = dose to 95% of target volume
  • D_5% = dose to 5% of target volume

• Paddick; 2006 (PMID 18503356): Dose Gradient Index
  • GI = PIV_half / PIV
  • PIV_half = Prescription isodose volume, at half the prescription isodose (e.g. at 25%)
  • PIV = Prescription isodose volume (e.g. at 50%)
  • Simplified UF Gradient Index

• Wagner; 2003 (PMID 14575847): Conformity Gradient Index
  • CGI = (CGIc + CGIg) / 2
  • CGIc = TV / PIV * 100
  • CGIg = UF Gradient Index (see below)

• Wagner; 2003 (PMID 14575847): UF Gradient Index
  • CGIg = 100 - (100 * ((REff,50%Rx - REff,Rx) - 0.3 cm))
  • REff,50%Rx = Effective radius of the isodose line that is equal to one-half of the prescription isodose volume
  • REff,Rx = Effective radius of the prescription volume
  • Evaluates the steepness of the gradient between prescription isodose line (e.g 50%) and half prescription isodose line (e.g. 25%)

• Nakamura; 2001 (PMID 11728692): New Conformity Index
  • NCI = (TV x PIV) / (TV_PIV)²
  • Inverse Paddick Conformity Index

• Paddick; 2000 (PMID 11143252): Paddick Conformity Index
  • Paddick CI = (TV_PIV)² / (TV x PIV)
  • TV_PIV = Target Volume covered by Prescription Isodose Volume
  • TV = Target Volume
  • PIV = Prescription Isodose Volume
  • This is two separate ratios multiplied together:
    • Undertreatment ratio: TV_PIV / TV
    • Overtreatment ratio: TV_PIV / PIV

• ICRU; 1999 (ICRU Report): Conformity Index
  • CI = TV / PTV
  • TV: Treated volume = volume eclosed by a given isodose surface (e.g. 50%, 95%)
  • PTV: Planning target volume = CTV + IM + SM
  • RTOG conformity index with ICRU terminology

• Knoos; 1998 (PMID 9869245): Radiation Conformity Index
  • RCI_i = PTV / PIV
  • PTV: Planning target volume = CTV + IM + SM
  • PIV = Prescription Isodose Volume
  • Inverse of RTOG Conformity Index

• RTOG; 1993 (PMID 8262852): Conformity Index
  • Conformity Index PITV = PIV / TV
  • PI = prescription isodose volume
  • TV = target volume
  • Normal 1.0-2.0, minor deviation if >2.0 or <1.0, major deviation if >2.5 or <0.9

• RTOG; 1993 (PMID 8262852): Homogeneity
  • Homogeneity MDPD = MD / PD
  • MD = maximum dose within target volume
  • PD = prescribed dose
  • Minor deviation if >2.0, major deviation if >2.5

• RTOG; 1993 (PMID 8262852): Coverage
  • Coverage = D_min / PD
  • D_min = minimum dose within target volume
  • PD = prescribed dose
  • Minor deviation if <0.9, major deviation if <0.8

• Wu; 1988 (PMID 3352544): Dose Homogeneity Index
  • DHI: (V_TDR - V_HDR) / V_TDR
  • V_TDR = total treatment volume enclosed by prescribed treatment dose rate (PIV)
  • V_HDR = volume enclosed by high-dose rate which is 1.5x TDR or greater (PIV_1.5x)
  • Used for high dose rate brachytherapy implants, but applicable to SRS

Other literature

• Lomax; 2003 (PMID 12654454)
• van't Riet; 1997 (PMID 9112473)

Dose overview

Doses are prescribed to the 50% isodose line unless stated otherwise

• Brain metastases: 24 Gy, 18 Gy, 15 Gy for tumors <2 cm, 2.1-3cm, and 3.1-4 cm.
• Trigeminal neuralgia: 40 Gy (80 Gy Dmax), using 4mm collimator
• Acoustic neuroma (vestibular schwannoma): 12.5 Gy
• Meningioma: 12-14 Gy
• Arteriovenous malformation: 18-20 Gy

Gamma Knife Machines

• Hopital Timone, Marseille (2006) -- GKS 4C vs PerfeXion
  • Randomized. 200 patients. Arm 1) GammaKnife 4C vs Arm 2) GammaKnife PerfeXion
  • 2009 PMID 19190462 -- "Radiosurgery with the world's first fully robotized Leksell Gamma Knife PerfeXion in clinical use: a 200-patient prospective, randomized, controlled comparison with the Gamma Knife 4C." (Regis J, Neurosurgery. 2009 Feb;64(2):346-55; discussion 355-6.)
    • Outcome: No technical failures. Median # of collimator sizes 4C 1 vs PerfeXion 2. Median treatment time 60 min vs 40 min (SS), but median beam-on time 33.4 vs 34.0 minutes (NS). Single run 42% vs. 99%. Collision risk requiring gamma angle 24% vs 0%.
    • Toxicity: Less dose with PerfeXion to vertex (8x), thyroid (10x), sternum (13x), and gonads (15X)
    • Conclusion: Technological advances with PerfeXion

Toxicity

• Please see the toxicity page for further information