Total target volume is a better predictor of whole brain dose from gamma stereotactic radiosurgery than the number, shape, or location of the lesions

Narayanasamy, Ganesh; Smith, Adam J. T.; Meter, Emily Van; McGarry, Ronald C.; Molloy, J

doi:10.1118/1.4818825

Cited by 13 publications

(15 citation statements)

References 18 publications

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“…As shown by previous publications, the volume of tissue receiving specific isodose is proportional to the total target volume raised to an exponent [15, 17]. The primary framework is thus to define irradiated volume for a series of HF-RT patients as [15, 17]:where V primary (P) is volume of the external contour (EXT, entire volume inside the patient surface, including skull, skin, etc.)…”

Section: Methodsmentioning

confidence: 99%

“…The primary framework is thus to define irradiated volume for a series of HF-RT patients as [15, 17]:where V primary (P) is volume of the external contour (EXT, entire volume inside the patient surface, including skull, skin, etc.) or Brain-Minus-PTV (BMP, the brain contour minus all target volumes) receiving dose P (percentage of prescription), PTV is the total target volume, and a(P) and b(P) are empirically determined fit-parameters for single, regularly-shaped targets.…”

Section: Methodsmentioning

confidence: 99%

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Investigation of irradiated volume in linac-based brain hypo-fractionated stereotactic radiotherapy

et al. 2017

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BackgroundEmerging techniques such as brain hypo-fractionated radiotherapy (HF-RT) involve complex cases with limited guidelines for plan quality and normal tissue tolerances. The purpose of the present study was to statistically parameterize irradiated volume independently of dose prescription, or margin to determine what spread in achievable irradiated volume one may expect for a given case.MethodsWe defined EXT as the total tissue within the external contour of the patient (including the target) and we defined BMP as the contour of the brain minus PTV. Irradiated volumes of EXT and BMP at specific doses (i.e. 50, 60%, etc., of the prescribed dose) were extracted from 135 single-target HF-RT clinical cases, each planned with a single-arc, homogeneous (SAHO) approach in which target maximum dose (Dmax) was constrained to <130% of the prescribed dose. Irradiated volumes were subsequently measured for cases involving 2 targets (N = 29), 3 targets (N = 7) and >3 targets (N = 10) to investigate the effect of target number. We also examined the effect of shape complexity. A series of best fit curves with confidence and prediction intervals were generated for irradiated volume versus total target volume and the resulting model was subsequently validated on a subsequent set of 23 consecutive prospective cases not originally used in curve-fitting. A subset of 30 HF-RT cases were re-planned with a well-published four-arc, heterogeneous (FAHE) radiosurgery planning approach (Dmax could exceed 130%) to demonstrate how technique affects irradiated volume.ResultsFor SAHO, strong correlation (R2 > 0.98) was found for predicting irradiated volumes. For a given total target volume, irradiated-volume increased by a range of 1.4–2.9× for >3 versus single-targets depending on isodose level. Shape complexity had minor impact on irradiated volume. There was no statistical difference in irradiated volumes between validation and input data (p > 0.2). The FAHE-generated irradiated volumes yielded curves and prediction and confidence bands that agreed well with published data indicating that the proposed approach is feasible for cross-institutional comparisons.ConclusionsA description of irradiated volume for linac-based HF-RT is proposed based on population data. We have demonstrated that the proposed approach is feasible for inter and intra-institutional comparisons.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Investigation of irradiated volume in linac-based brain hypo-fractionated stereotactic radiotherapy

et al. 2017

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“…The authors concluded that a decrease of 1-2 Gy in the prescription dose was recommended when 5 or more lesions were treated in order to reduce the risk of radiation toxicity. Conversely, Narayanasamy et al [28] assessed the effect of the number, shape, location of lesions and the total target volume on V12 Gy and found that only the total tumor volume was a significant factor for the prediction of radiation-related toxicity. Also, Xue et al [24] reported that the mean normal brain dose was correlated with the total target volume not the number of tumors.…”

Section: Discussionmentioning

confidence: 99%

“…Although some studies have suggested that the number of lesions is a significant predictive factor for radiation toxicity [26,27,29], others have advocated that the total target volume is important for predicting radiation-related brain injury [24,28]. Takahashi et al [26] suggested that the dose to the normal brain tissue increased with increasing numbers of targets in patients with multiple brain metastases treated with linac-based SRS; therefore, they recommended not treating more than 7 metastatic lesions.…”

Section: Discussionmentioning

confidence: 99%

“…Also, regarding the treatment of multiple targets in the brain with gamma knife radiosurgery, there is controversy in terms of whether the number of tumors or the total treated tumor volume is correlated with the radiation dose delivered to the brain. Narayanasamy et al [28] reported that the treated tumor volume is correlated with V12 Gy, rather than tumor number, tumor shape, or location. Unlikely, Sahgal et al [29] revealed that the number of tumors but not the total tumor volume significantly increases the V12 Gy.…”

Section: Introductionmentioning

confidence: 99%

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Evaluating Critical Brain Radiation Doses in the Treatment of Multiple Brain Lesions with Gamma Knife Radiosurgery

Hatiboğlu

Akdur²

2017

Stereotact Funct Neurosurg

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Background: Treatment of patients with multiple brain metastases has shifted to stereotactic radiosurgery, withholding whole-brain (WB) radiation therapy. However, radiation toxicity to the brain is a concern when treating multiple brain lesions with single-fraction stereotactic radiosurgery. Objective: The purpose of this study was todetermine the changes in brain radiation doses when treating various numbers of targets and lesion volumes. Methods: We simulated different treatment plans with different combinations of varying tumor volumes including 0.1, 0.5, 1, 2, and 5 cm³, and tumor numbers including 1, 3, 5, 10, 15, 20, and 25. Treatment planning was performed for all combinations in a computerized tomography of the head of a patient, using Leksell GammaPlan version 10.1.1 (Elekta AB, Stockholm, Sweden). Two different dosing strategies were used. In the lower-prescription dosing schedule, a marginal dose was given to the 50% isodose line, and 20 Gy were used when the number of lesions was less than 15 and 18 Gy were applied when the number of lesions was equal to or more than 15. In the higher-prescription dosing schedule, a marginal dose of 24 Gy was used for lesions of less than 5 cm³ and 20 Gy were applied for lesions equal to 5cm³. The mean WB dose, the WB integral dose, and the volume of brain receiving 12 Gy (V12 Gy) were calculated for each scenario. Also, the beam-on time of the Gamma Knife 4C unit was reported for all treatment scenarios. Results: Regression analysis showed that the total tumor volume was a more significant predictor of V12 Gy than the number of lesions, and a linear correlation between the total tumor volume and V12 Gy was found. We also found that the total tumor volume was a more significant predictor of the mean WB dose and the WB integral dose compared to the number of lesions. Conclusion: Our results suggest that multiple small to mid-sized lesions could be safely treated with a single-fraction gamma knife.

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A simple knowledge‐based tool for stereotactic radiosurgery pre‐planning

Goldbaum

Hurley

Hamilton

2019

J Applied Clin Med Phys

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We studied the dosimetry of single‐isocenter treatment plans generated to treat a solitary intracranial lesion using linac‐based stereotactic radiosurgery (SRS). A common metric for evaluating SRS plan quality is the volume of normal brain tissue irradiated by a dose of at least 12 Gy (V12), which is important because multiple studies have shown a strong correlation between V12 and incidence of radiation necrosis. Unrealistic expectations for values of V12 can lead to wasted planning time. We present a model that estimates V12 without having to construct a full treatment plan. This model was derived by retrospectively analyzing 50 SRS treatment plans, each clinically approved for delivery using circular collimator cone arc therapy (CAT). Each case was re‐planned for delivery via dynamic conformal arc therapy (DCAT), and then scaling arguments were used to extend dosimetric data to account for different prescription dose (PD) values (15, 18, 21, or 24 Gy). We determined a phenomenological expression for the total volume receiving at least 12 Gy (TV12) as a function of both planning target volume (PTV) and PD: TV12/1cc=n∗PD/1Gy+d∗][PTVfalse/)(1cca∗][PDfalse/)(1Gyc, where }{a,c,n,d are fit parameters, and a separate set of values is determined for each plan type. In addition, we generated a sequence of plots to clarify how the relationship between conformity index (CI) and TV12 depends on plan type (CAT vs DCAT), PTV, and PD. These results can be used to suggest realistic plan parameters and planning goals before the start of treatment planning. In the absence of access to more sophisticated pre‐planning tools, this model can be locally generated and implemented at relatively low cost with respect to time, money, and expertise.

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Total target volume is a better predictor of whole brain dose from gamma stereotactic radiosurgery than the number, shape, or location of the lesions

Cited by 13 publications

References 18 publications

Investigation of irradiated volume in linac-based brain hypo-fractionated stereotactic radiotherapy

Investigation of irradiated volume in linac-based brain hypo-fractionated stereotactic radiotherapy

Evaluating Critical Brain Radiation Doses in the Treatment of Multiple Brain Lesions with Gamma Knife Radiosurgery

A simple knowledge‐based tool for stereotactic radiosurgery pre‐planning

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