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NI FEATURE: THE EDITORIAL DEBATE I-- PROS AND CONS
Year : 2017  |  Volume : 65  |  Issue : 4  |  Page : 701-702

Fractionated gamma knife radiosurgery for large brain arteriovenous malformations


Department of Neurosurgery and Gamma Knife Center, All India Institute of Medical Sciences, New Delhi, India

Date of Web Publication5-Jul-2017

Correspondence Address:
Manmohan Singh
Department of Neurosurgery and Gamma Knife Center, All India Institute of Medical Sciences, New Delhi
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/neuroindia.NI_519_17

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How to cite this article:
Singh M. Fractionated gamma knife radiosurgery for large brain arteriovenous malformations. Neurol India 2017;65:701-2

How to cite this URL:
Singh M. Fractionated gamma knife radiosurgery for large brain arteriovenous malformations. Neurol India [serial online] 2017 [cited 2019 Oct 17];65:701-2. Available from: http://www.neurologyindia.com/text.asp?2017/65/4/701/209520




Large brain arteriovenous malformations (AVMs) are one of the most challenging neurosurgical lesions. There are no standardized treatment options or protocols to be offered to such patients. Most of the patients present with seizures, chronic headaches, progressive neurological deficits or hemorrhage. Due to their shear size and invariable involvement of eloquent areas, any treatment offered, potentially leads to significant morbidity in these patients. However, offering no treatment and simply following up these patients with a large AVM may not be a good option in many patients as progressive neurological deficits and chronic headache often incapacitate them. The risk of hemorrhage is a reality and a significant number of patients land up in the psychiatry clinics due to this fear.

The surgical option in large (Spetzler-Martin Grade 4/5) AVMs carries a significant risk of mortality and morbidity. Embolization in multiple sittings also does not yield desirable results. Fractionated radiation therapy is associated with significant radiation side effects and invariably does not lead to nidus obliteration. Single fraction stereotactic radiosurgery (SRS) carries significant radiation injury to the surrounding normal brain as rapid dose fall off of sterotactic radiosurgery (SRS) starts to disappear as the volume of target increases.

In the backdrop of the large experience gained in the field of stereotactic radiosurgery, especially in gamma knife radiosurgery, fractionation using gamma knife radiosurgery is being tried in large brain AVMs with very encouraging results. Due to better confomality and rapid dose fall off, fractionated SRS has opened up new frontiers in the management of large brain lesion or lesions located in critical areas of the brain. Fractionated gamma knife therapy is typically being used in large brain AVMs, functional pituitary adenomas or even in small AVMs located in eloquent areas of the brain.

Dose fractionation and volume fractionation techniques are used to treat large AVMs. In dose fractionation technique, the total radiation dose is delivered to the target in 4 or 5 fractionations (hypofractionation) on consecutive days. In volume fractionation technique, a large target is divided into smaller volume targets and full radiation dose is delivered to each of these small volume targets spaced over a few months. The benefits of fractionation include less radiation damage to the surrounding normal brain while maintaining the efficacy of nidus obliteration. The most important aspect of preventing radiation damage to surrounding brain during the radiosurgery procedure is to keep the radiation exposure to the surrounding normal brain to the minimum. To achieve this the 'volume of normal brain receiving 12 Gy' should be adopted as a standard baseline value and this volume should be kept around 10 cc.[1]

Dose fractionation is a good modality to reduce radiation toxicity and to increase the efficacy while treating larger AVMs. Studies have shown that upto 50% obliteration rates occur in AVMs larger than 10cc volume.[2] There are, however, scant studies showing reasonable obliteration rates in AVMs larger than 30 or 40 cc volumes, the treatment of which is a real challenge. Such AVMs are not rare to be seen at referral centres. Dose fractionation by various gamma knife techniques like gamma knife extend using the relocatable frame, or keeping stereotactic frame attached to head for 3 to 4 days is cumbersome and adds to patient discomfort. This technique has no superiority over volume staging.

There are a rising number of studies published in literature, which point out that volume fractionation of a larger target e.g. a volume more than 30 cc, has a superior efficacy as compared to dose fractionation technique. In a study by Fogh et al.,[3] when hypofractionated values were matched with volume-staged values for the biological effective dose, only conservative dose fractionation schemes, such as 27.3 Gy in 5 fractions and 25 Gy in 4 fractions, were comparable to the volume-staged treatments. This represented a mean 18.7% ±7.3% reduction in the single-fraction biologically equivalent dose for hypofractionated treatments versus the reference volume-staged treatments (P < 0.001). This study has categorically concluded that volume fractionation/staging has superiority over dose fractionation (hypofractionation) in delivering a higher dose to the target while sparing the surrounding normal brain in treating large brain AVMs. Kondziolka et al., have also shown excellent obliteration rates following volume staged gamma knife treatment. They have reported an obliteration rate of 50% after 36 months without new onset deficits developing, with an additional 29% of the AVMs showing near total obliteration.[4] The residual nidus may further be subjected to surgical excision; or, another gamma knife dose may be delivered for achieving its obliteration.

Further studies are needed to validate the technique of dose/volume fractionation radiosurgery in the obliteration of large AVMs and to assess the various factors that help to minimize the complication rate.[5]



 
  References Top

1.
Lawrence YR, Li XA, el Naqa I, Hahn CA, Marks LB, Merchant TE, Dicker AP Radiation dose-volume effects in the brain. Int J Radiat Oncol Biol Phys 2010;76 (3 Suppl):S20-7  Back to cited text no. 1
    
2.
Lindvall P, Bergström P, Löfroth PO, Marwan H, Henriksson R, Jonasson P, et al. Hypofractionated conformal stereotactic radiotherapy for arteriovenous malformations. Neurosurgery 2003; 53:1036-43.  Back to cited text no. 2
    
3.
Fogh S, Ma L, Gupta N, Sahgal A, Nakamura JL, Barani I, et al. High-precision volume-staged Gamma Knife surgery and equivalent hypofractionation dose schedules for treating large arteriovenous malformations. J Neurosurg 2012;117 Suppl:115-9.  Back to cited text no. 3
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4.
Sirin S, Kondziolka D, Niranjan A, Flickinger JC, Maitz AH, Lunsford LD: Prospective staged volume radiosurgery for large arteriovenous malformations: Indications and outcomes in otherwise untreatable patients. Neurosurgery 2006;58:17–27.  Back to cited text no. 4
    
5.
Mukherjee KK, Kumar N, Tripathi M, Oinam AS, Ahuja CK, Dhandapani S, et al. Dose fractionated gamma knife radiosurgery for large arteriovenous malformations on daily or alternate day schedule outside the linear quadratic model: Proof of concept and early results. A substitute to volume fractionation. Neurol India 2017;65:826-35.  Back to cited text no. 5
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