Radiation Doses used in Gamma Knife

**Radiation Dose Recommendations for Gamma Knife Radiosurgery (Pitt) (as of 2002)**
Disorder	Marginal Dose (50% IDL)	Comments
AVM	15-25Gy	varies by size and location goal should be 24Gy (15-16 min) see AVM chart
Acoustic Neuroma	11-15Gy	13Gy is usual (11-12 if 3cm) 12-13Gy at Cleveland
Meningioma	11-18Gy	atypical (50-56Gy EBT + 12-16Gy) malignant (60Gy EBT + 12-16Gy) 14-15Gy goal
Metastases	14-24Gy	varies by size or combined with whole brain (see below)
Glial Tumors	12-20Gy	EBT 55-60 Gy + 15.5 - 16Gy
Trigeminal Neuralgia	40Gy	80Gy maximum
Thalamotomy	60-70Gy	120-140Gy maximum
Pituitary	11-25Gy	functional 16-25Gy nonfunctional 12-16Gy limit optic nerve and chiasm to 8Gy

The dose ranges above are from U Pitt. Other sites (e.g. Cleveland Clinic) have standard doses: acoustic neuroma of 12-13Gy, meningioma 14-15Gy if < 35mm and at least 5mm from the optic chiasm, and pituitary15-20Gy (higher if functional.) Volume is critical so in an AVM consider dose adjustments like: < 2cc (24Gy) 2.1- 5cc (22-23Gy) 5-8cc (21Gy) 8 - 13.5cc (18Gy) and > 13.5cc. The AVM (Pitt) data used 12Gy volume to predict toxicity and volumes up to 20cc had a low risk (< 10%) except brain stem sites. See the tables on doses for single fraction or three fractions or five fractions

Brain Metastases Doses
Size	Pit	RTOG	Other
2cm	20Gy	24Gy	24Gy
2.1-3cm	15-16Gy	18Gy	22-24
3.1-4cm	13.5 - 14Gy	15Gy	16Gy
whole + RS	16Gy		18Gy-20Gy

Karolinska Policy on Brain Mets
(assumes no whole brain/adjusts for critical structures)
Tumor Diameter	Prescription Dose (40-60%IDL)
< 15mm	25Gy
15- 20mm	20-25Gy
20-25mm	20Gy
25-30mm	18Gy
>30mm	don't treat

Some protocols for patients with brain metastases combine whole brain irradiation (WB) with radiosurgery as noted below:

RTOG 95-08 (for patient with 1-3 brain mets up to 4cm in size) randomized patients between whole brain radiation alone (250cGy X 15 or 3750cGy) or WB followed by radiosurgery the dose as noted:

2cm = 24Gy
2.1 - 3cm = 18Gy
3.1 - 4cm = 15Gy

ACOSOG Z0300, for patients with 1-3 brain mets (all less than 3cm) all patients received radiosurgery and were then randomized to half of them receiving whole brain irradiation (250cGy X 12 or 3000cGy) which was given after the radiosurgery. The radiosurgery dose was adjusted lower for patients getting WB as noted below:

Radiosurgery Dose from ACOSOG Z0300
Tumor Size	No Whole Brain	Combined with Whole Brain
< 2cm	24Gy	22Gy
2 - 2.9cm	20Gy	18Gy

the dose for a brain metastases may be better chosen based on the volume rather than the diameter. For small volume lesions (up to 4-5 cc) full doses can probably be given (e.g. 22-24Gy, if over the motor strip 22Gy) for somewhat larger (5-8cc) the dose can be dialed down a bit (20-22Gy, but it may be useless to treat radioresistant mets to < 20Gy) for larger lesions (>8cc) then lower doses (16Gy) may be necessary. There are some studies with brain mets that showed better results with a dose of at least 20Gy in terms of increased survival. There may be still be a palliative benefit gained even if lower doses have to be used.

Diameter (cm)	Volume (cc) (4/3 pi r^3)
0.25	.0082
0.5	.06545
.75	.2209
1.0	.5236
1.25	1.02265
1.5	1.767
1.75	2.806
2.0	4.1888
2.25	5.9641
2.5	8.18
2.75	10.889
3.0	14.137
3.25	17.974

Other dose guidelines from the Karolinska (as 2002)
GBM: 30Gy/10fx (EBT) + 15-18Gy (50% IDL) but 20% may require reoperation for radionecrosis, RTOG class III/IV may benefit Low grade glioma: 10-12Gy (50% IDL) after surgery if residual Meningioma:12-15Gy (50% IDL) lower dose if near critical structure, do not include dural tail Malignant meningioma: 18Gy minimum , same dose/volume as mets Acoustic neuroma: 12Gy (50% IDL) outline cochlea and plug to reduce fall-off, maximum volume 10cc Pituitary: 12-15Gy (50% IDL) functional need higher dose, limit optic chiasm to 8Gy AVM: 15-24Gy periphery, location more important than volume, cover entire nidus, embolize first if too big, limit brain stem to 15-18Gy Trigeminal neuralgia:85Gy Dmax (4mm) shot placed at periphery and 50% ISD adjacent to brain stem Epilepsy: 20-24Gy (50% IDL) / 4mm shot, collateral sulcus, parahypocampal area, limit BS to 12Gy and OC to 8Gy Dose Limits to Critical Structure: Optic: 8Gy (6Gy if combined with external); Brain Stem: 12-18Gy, and Trigeminal: < 19Gy Quality Assurance: the goal of planning as per RTOG 95-08 would be to have tumor coverage of 90% (Vpd minimum 80%) and Conformality Index (CI = PIV/TV) of < 2 (up to 3.5)

Diameter (mm)	Volume (cc)	Gy (1% K)	Gy (3% ILF)
12.5	1.02	27.5	34
15.0	1.77	25.0	29
17.5	2.81	22.5	23
20.0	4.10	20.0	18
22.5	5.96	18.7	16.5
25.0	8.18	17.5	14.5
27.5	10.89	16.5	13.5
30.0	14.14	15.0	13