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

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