Radiation-induced epilation due to couch transit dose for the Leksell Gamma Knife model C

Bradford, Carla; Morabito, Brian; Shearer, Douglas R.; Norén, Georg; Chougule, Prakash

doi:10.1016/s0360-3016(02)03025-0

Cited by 9 publications

(9 citation statements)

References 4 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The authors note that there is a sharp rise in dose at the 6 cm position; the dose they measured was 5.6 cGy per shot. (9) We also found a sharp increase in defocus dose and a rise in transit dose at this position (positions beyond this were not studied). Bradford et al attributed the high dose at the superior region of the head to the low attenuation of the unfocused beam by the 0.8 cm thick fiberglass helmet cap as the couch moves in and out of focus position for repositioning.…”

Section: B Previous Studiesmentioning

confidence: 61%

“…The transit dose increases at positions closer to the crown of the head because of the poorly shielded 23 cm diameter opening at the helmet's apex, which results in greater exposure from leakage and scatter at superior regions. (9) This is the reason for the behavior of the increased transit dose along the superior portion of the z-axis (Fig. 4).…”

Section: A Measured Datamentioning

confidence: 93%

“…With the model C Gamma Knife using an APS, Bradford et al (9) studied unaccounted dose at regions close to the scalp of the head to account for the cause of epilation. They found that the dose increases with proximity to the helmet cap -the transit dose increases with positions superior to the focus.…”

Section: B Previous Studiesmentioning

confidence: 99%

See 2 more Smart Citations

Target and peripheral dose during patient repositioning with the Gamma Knife automatic positioning system (APS) device

Tran

Stanley

Malhotra

et al. 2010

J Applied Clin Med Phys

View full text Add to dashboard Cite

The GammaPlan treatment planning system does not account for the leakage and scatter dose during APS repositioning. In this study, the dose delivered to the target site and its periphery from the defocus stage and intershot couch transit (couch motion from the focus to defocus position and back) associated with APS repositioning are measured for the Gamma Knife model 4C. A stereotactic head‐frame was attached to a Leksell 16 cm diameter spherical phantom with a calibrated ion chamber at its center. Using a fiducial box, CT images of the phantom were acquired and registered in the GammaPlan treatment planning system to determine the coordinates of the target (center of the phantom). An absorbed dose of 10 Gy to the 50% isodose line was prescribed to the target site for all measurements. Plans were generated for the 8, 14 and 18 mm collimator helmets to determine the relationship of measured dose to the number of repositions of the APS system and to the helmet size. The target coordinate was identical throughout entire study and there was no movement of the APS between various shots. This allowed for measurement of intershot transit dose at the target site and its periphery. The couch was paused in the defocus position, allowing defocus dose measurements at the intracranial target and periphery. Measured dose increases with frequency of repositioning and with helmet collimator size. During couch transit, the target receives more dose than peripheral regions; however, in the defocus position, the greatest dose is superior to the target site. The automatic positioning system for the Leksell Gamma Knife model 4C results in an additional dose of up to 3.87±0.07%,4.97±0.04%, and 5.71±0.07% to the target site; its periphery receives additional dose that varies depending on its position relative to the target. There is also dose contribution to the patient in the defocus position, where the APS repositions the patient from one treatment coordinate to another. This may be important for treatment areas around critical structures within the brain. Further characterization of the defocus and transit exposures and development of a dose calculation algorithm to account for these doses would improve the accuracy of the delivered plan.PACS numbers: 87.53.‐j, 87.53.Bn, 87.53.Dq, 87.53.Ly

show abstract

Section: B Previous Studiesmentioning

confidence: 61%

Section: A Measured Datamentioning

confidence: 93%

See 1 more Smart Citation

Target and peripheral dose during patient repositioning with the Gamma Knife automatic positioning system (APS) device

Tran

Stanley

Malhotra

et al. 2010

J Applied Clin Med Phys

View full text Add to dashboard Cite

show abstract

“…Also, as the helmet moves away from and towards the sources during repositioning, the unfocused beam will intersect the fiberglass helmet cap (where there is little attenuation of the beam) exposing the superior region of the phantom or patient to unintended radiation 24–25. The transit dose increases at positions closer to the crown of the head because of the poorly shielded 23 cm diameter opening at the helmet’s apex, which results in more exposure from leakage and scatter to the superior regions of the phantom 15,24. This is the reason for the behavior of the increased transit dose towards the superior portion of the z-axis for the model 4C.…”

Section: Discussionmentioning

confidence: 99%

Target and peripheral dose from radiation sector motions accompanying couch repositioning of patient coordinates with the Gamma Knife® Perfexion™

Tran¹,

Wu²,

Malhotra³

et al. 2011

Radiology and Oncology

View full text Add to dashboard Cite

BackgroundThe GammaPlan™ treatment planning system (TPS) does not fully account for shutter dose when multiple shots are required to deliver a patient’s treatment. The unaccounted exposures to the target site and its periphery are measured in this study. The collected data are compared to a similar effect from the Gamma Knife® model 4C.Materials and methods.A stereotactic head frame was attached to a Leksell® 16 cm diameter spherical phantom; using a fiducial-box, CT images of the phantom were acquired and registered in the TPS. Measurements give the relationship of measured dose to the number of repositions with the patient positioning system (PPS) and to the collimator size. An absorbed dose of 10 Gy to the 50% isodose line was prescribed to the target site and all measurements were acquired with an ionization chamber.ResultsMeasured dose increases with frequency of repositioning and with collimator size. As the radiation sectors transition between the beam on and beam off states, the target receives more shutter dose than the periphery. Shutter doses of 3.53±0.04 and 1.59±0.04 cGy/reposition to the target site are observed for the 16 and 8 mm collimators, respectively. The target periphery receives additional dose that varies depending on its position relative to the target.ConclusionsThe radiation sector motions for the Gamma Knife® Perfexion™ result in an additional dose due to the shutter effect. The magnitude of this exposure is comparable to that measured for the model 4C.

show abstract

“…4,5,9 Our ongoing evaluation of the radiocarcinogenic risk, based on phantom and in vivo measurements with GK-C shows, however, that although not apparently a major health problem, it should be kept in mind that increasing the numbers of shots to achieve better conformity also leads to a higher effective dose delivered to the patient. 19 Similarly, Bradford, et al, 1 have reported epilation at the top of the head in two patients with VS after undergoing fractionated GK-C-based radiosurgery. They found that the use of the APS increased the transit dose approximately 5 and 15% for a distance greater than 12 and 20.4 cm, respectively, and concluded that for treatments involving a large number of shots (Ͼ 50), off-target doses greater than 8 Gy were possible.…”

Section: Neurosurg Focus / Volume 14 / May 2003mentioning

confidence: 92%

Use of the Leksell gamma knife C with automatic positioning system for the treatment of meningioma and vestibular schwannoma

Levivier¹,

Lorenzoni²,

Massager³

et al. 2003

FOC

View full text Add to dashboard Cite

Object The authors report their experience using the Leksell gamma knife C (GK-C) for the treatment of meningioma and vestibular schwannoma (VS). Methods In December 1999, the first commercially available clinical GK-C was installed at the Université Libre de Bruxelles (Erasme Hospital, Brussels, Belgium). In January 2000, the system was upgraded and equipped with the automatic positioning system (APS). Between February 2000 and February 2003, the APS-equipped GK-C was used to perform 532 radiosurgical treatments, including those in 97 meningiomas and 101 VSs. Meningioma and VS represent 18 and 19%, respectively, of lesions in patients treated with GK-C at the authors' center. The mean number of isocenters per lesion was 9.5 (range 1–36): 18.1 (range 1–36) for meningioma and 12.8 (range 1–27) for VS. In 77.6% of the cases, the authors used a single helmet of collimators (55.5% in meningioma and 74.3% in VS). The most frequently used collimator size was 4 mm (46.7%). Whereas it was 4 mm in cases of VS (64.3%), it was 8 mm in cases of meningioma (41.6%). The APS could be used in 86% of the cases, either alone (79%) or in combination with trunnions (7%). There was a difference in the APS-based treatment success rate in meningiomas (85%) and VSs (94%). A significant difference was also noted in the conformity of the radiosurgical treatments between the two lesions. Conclusions The APS-equipped GK-C represents an evolutionary step in radiosurgery. It requires adjustments by the treating team for its specific limitations, which vary among indications, as exemplified by the differences inherent between meningioma and VS in this series.

show abstract

Radiation-induced epilation due to couch transit dose for the Leksell Gamma Knife model C

Cited by 9 publications

References 4 publications

Target and peripheral dose during patient repositioning with the Gamma Knife automatic positioning system (APS) device

Target and peripheral dose during patient repositioning with the Gamma Knife automatic positioning system (APS) device

Target and peripheral dose from radiation sector motions accompanying couch repositioning of patient coordinates with the Gamma Knife® Perfexion™

Use of the Leksell gamma knife C with automatic positioning system for the treatment of meningioma and vestibular schwannoma

Contact Info

Product

Resources

About