Radiation Oncology/Stereotactic radiosurgery

Stereotactic Radiosurgery (SRS)

Clinical Sites

Overview

Malignant

Benign:

Thieme; 2018 (PMID 29699833): Voxel-Based Homogeneity Index (VHI)
- VHI = k ∫ ∫ ∫ (D(x,y,z)/PD - 1)² / TV
- D(x,y,z) = Dose at coordinates (x,y,z)
- PD = prescribed dose
- TV = Target volume size
- k = 10^4
- Sensitive homogeneity index which uses voxel information for score calculation

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

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

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

The CyberKnife System is a radiation therapy device manufactured by Accuray Incorporated
The system is used to deliver radiosurgery for the treatment of benign tumors, malignant tumors and other medical conditions

Stereotactic radiosurgery using charged-particle beams has been the subject of biomedical research and clinical development for almost 60 years
Energetic beams of charged particles of proton mass or greater (e.g., nuclei of hydrogen, helium or carbon atoms) manifest unique physical and radiobiological properties that offer advantages for neurosurgical application and for neuroscience research
These beams can be readily collimated to any desired cross-sectional size and shape
At higher kinetic energies, the beams can penetrate entirely through the patient in a similar fashion to high-energy photon beams but without exponential fall-off of dose
At lower kinetic energies, the beams exhibit increased dose-deposition (Bragg ionization peak) at a finite depth in tissue that is determined by the beam’s energy as it enters the patient
These properties enable highly precise, 3-dimensional placement of radiation doses to conform to uniquely shaped target volumes anywhere within the brain