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 Thieme; 2018 (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 (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 (17194494): Radical Dose Homogeneity Index rDHI = Dmin / Dmax Dmin = minimum dose within target volume Dmax = maximum dose within target volume Oliver; 2007 (17194494): Moderate Dose Homogeneity Index mDHI = D95% / D5% D95% = dose to 95% of target volume D5% = dose to 5% of target volume Paddick; 2006 (18503356): Dose Gradient Index GI = PIVhalf / PIV PIVhalf = 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 (14575847): Conformity Gradient Index CGI = (CGIc + CGIg) / 2 CGIc = TV / PIV * 100 CGIg = UF Gradient Index (see below) Wagner; 2003 (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 (11728692): New Conformity Index NCI = (TV x PIV) / (TVPIV)2 Inverse Paddick Conformity Index Paddick; 2000 (11143252): Paddick Conformity Index Paddick CI = (TVPIV)2 / (TV x PIV) TVPIV = Target Volume covered by Prescription Isodose Volume TV = Target Volume PIV = Prescription Isodose Volume This is two separate ratios multiplied together: Undertreatment ratio: TVPIV / TV Overtreatment ratio: TVPIV / 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 (9869245): Radiation Conformity Index RCIi = PTV / PIV PTV: Planning target volume = CTV + IM + SM PIV = Prescription Isodose Volume Inverse of RTOG Conformity Index RTOG; 1993 (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 (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 (8262852): Coverage Coverage = Dmin / PD Dmin = minimum dose within target volume PD = prescribed dose Minor deviation if <0.9, major deviation if <0.8 Wu; 1988 (3352544): Dose Homogeneity Index DHI: (VTDR - VHDR) / VTDR VTDR = total treatment volume enclosed by prescribed treatment dose rate (PIV) VHDR = volume enclosed by high-dose rate which is 1.5x TDR or greater (PIV1.5x) Used for high dose rate brachytherapy implants, but applicable to SRS Other literature Lomax; 2003 (12654454) van't Riet; 1997 (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 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 CyberKnife System 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 Charged-Particle Radiosurgery 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 Toxicity Please see the toxicity page for further information