Experience of micromultileaf collimator linear accelerator based single fraction stereotactic radiosurgery: Tumor dose inhomogeneity, conformity, and dose fall off

Hong, Linda; Garg, Madhur; Lasala, Patrick; Kim, Mimi; Mah, Dennis; Chen, Chin Cheng; Yaparpalvi, Ravindra; Mynampati, D; Kuo, Hsiang-Chi; Guha, Chandan

doi:10.1118/1.3549764

Cited by 28 publications

(32 citation statements)

References 46 publications

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“…The associated steep dose fall off degrades the dose coverage disproportionately for small tumors, requiring an increase in the block margin, as shown in Figure 7. A similar trend with rapid fall in the homogeneity index (=maximum PTV dose/Rx dose) with increasing block margin (referred as "beam margin") was seen with the small brain lesions in a stereotactic radiosurgery study (SRS) by Hong et al 15 We found that the only method by which the volume irradiated by a certain dose level can be reduced is to prescribe to a lower isodose line as shown in Figure 8. As indicated in Figure 9, this results in an increase in the global maximum dose and the volume of all absolute dose levels.…”

Section: Discussionmentioning

confidence: 60%

CBCT-based dosimetric verification and alternate planning techniques to reduce the normal tissue dose in SBRT of lung patients

Narayanasamy

Feddock

Gleason

et al. 2015

Int J Cancer Ther Oncol

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Original ArticleAbstract Purpose: Confirmation of treatment delivery accuracy in stereotactic body radiotherapy (SBRT) of lung tumors suggests the possibility of treatment margin, or aperture reduction. In this investigation, the dose delivery to lung tumors using SBRT techniques was verified, and the feasibility of normal tissue sparing via aperture reduction or altered prescription isodose line was assessed. Methods: Planned and delivered doses to the gross tumor volume (GTV) and planning target volume (PTV) were compared for 10 patients using planning CT and conebeam CT image. Potential for reduction in normal tissue dose were assessed using 2 alternate treatment plans -reduced PTVs and alternate prescription techniques. Plans were assessed using conformity index, homogeneity index and the ratio of 50% / 100% isodose volumes (R50%). Results: The planned and delivered mean doses were consistent to within 4%. However, the mean dose delivered to the GTV exceeded the prescription dose (Rx) by 19% and is consistent with our planning technique of prescribing to the 80% isodose line. When reducing treatment margins and retaining a constant dose-volume constraint, block margins had to be increased which produced a constant effective field aperture outside of the GTV. Prescription to a lower isodose line using stereotactic-like planning techniques yielded the only method by which the volume of the prescription isodose could be affected, although this yielded increases in normal tissue dose due to the increased monitor units required. Conversely, conventional prescription techniques using wider field apertures were effective in reducing absolute values of normal tissue dose. Although dose conformity was similar across different prescription isodose lines, homogeneity index and R50% values were significantly different in the 60%-70% prescription isodose line plans than the 80%, 90% prescription plans. Conclusion: Traditional margin reduction techniques did not affect a reduction in the volume of normal tissue irradiated to the prescribed dose. Prescribing to low isodose lines yields reduced volumes of the prescribed dose, but at the expense of normal tissue dose.

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Section: Discussionmentioning

confidence: 60%

CBCT-based dosimetric verification and alternate planning techniques to reduce the normal tissue dose in SBRT of lung patients

Narayanasamy

Feddock

Gleason

et al. 2015

Int J Cancer Ther Oncol

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“…Not only did we demonstrate the feasibility of AV node ablation using SRS, but our results also establish the safety of this cardiac radioablation procedure, at least in pigs, with no radiation injury detected in nearby healthy tissues. The radiation dose falloff in SRS is around 10% to 15% per millimeter, with a resulting dose falloff of 50% at 2 to 5 mm, with only 0.05% of the dose remaining at 1 m from the target lesion . Therefore, SRS is associated with a sharp falloff in radiation dose.…”

Section: Discussionmentioning

confidence: 99%

Swine Atrioventricular Node Ablation Using Stereotactic Radiosurgery: Methods and In Vivo Feasibility Investigation for Catheter‐Free Ablation of Cardiac Arrhythmias

Refaat

Ballout

Zakka

et al. 2017

JAHA

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BackgroundLinear accelerator–based stereotactic radiosurgery delivered to cardiac arrhythmogenic foci could be a promising catheter‐free ablation modality. We tested the feasibility of in vivo atrioventricular (AV) node ablation in swine using stereotactic radiosurgery.Methods and ResultsFive Large White breed swine (weight 40–75 kg; 4 females) were studied. Single‐chamber St Jude pacemakers were implanted in each pig. The pigs were placed under general anesthesia, and coronary/cardiac computed tomography simulation scans were performed to localize the AV node. Cone beam computed tomography was used for target positioning. Stereotactic radiosurgery doses ranging from 35 to 40 Gy were delivered by a linear accelerator to the AV node, and the pigs were followed up with weekly pacemaker interrogations to observe for potential electrocardiographic changes. Once changes were observed, the pigs were euthanized, and pathology specimens of various tissues, including the AV node and tissues surrounding the AV node, were taken to study the effects of radiation. All 5 pigs had disturbances of AV conduction with progressive transition into complete heart block. Macroscopic inspection did not reveal damage to the myocardium, and pigs had preserved systolic function on echocardiography. Immunostaining revealed fibrosis in the target region of the AV node, whereas no fibrosis was detected in the nontargeted regions.ConclusionsCatheter‐free radioablation using linear accelerator–based stereotactic radiosurgery is feasible in an intact swine model.

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“…For Cyberknife, the value of P‐IDL is often between those values . Previous studies showed that using either noncoplanar conformal static field or dynamic conformal arcs the optimal P‐IDL is around 77%. With development of volumetric arc therapy (VMAT) technique on LINAC, in which the beams are modulated for dose rate, MLC aperture and gantry angle continuously, more variables are introduced in the inverse planning and delivery process for SRS treatment.…”

Section: Introductionmentioning

confidence: 99%

“…SRS treatment for brain tumors requires conformity in both high and intermediate dose regions for better sparing normal brain tissue. The toxicities of SRS have been linked to V12, the volume of brain tissue irradiated with 12 Gy and conformity index . The dose prescription practice differs significantly among the modalities: Gamma Knife, Cyber Knife, and LINAC.…”

Section: Introductionmentioning

confidence: 99%

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Strategies to optimize stereotactic radiosurgery plans for brain tumors with volumetric‐modulated arc therapy

Wang

DeNittis

2020

J Applied Clin Med Phys

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Purpose Prescription practice in SRS plans for brain tumors differs significantly for different modalities. In this retrospective study, the strategies to optimize SRS plans for brain tumors with volumetric arc therapy (VMAT) were presented. Methods Fifty clinically treated cases were stratified by the maximum target size into two groups (≥ 2 cm in 25 cases and <2 cm but ≥1 cm in 25 cases), which were optimized using traditional LINAC MLC‐based approaches with the average prescription isodose line (P‐IDL) of (91.4 ± 0.6)%. Four to five plans have been created for each case with variation of the P‐IDL from 65% to 90%. The optimization strategies to select an optimal P‐IDL, to use tuning structures within the target and beyond as well as to use NTO (normal tissue objectives), were applied to all new plans. Results The optimal P‐IDL was found to be around 75%. After applying the new optimization strategies with an average P‐IDL of 74.8%, the mean modified gradient index (mGI) and V12 were reduced by 25% and 35%, respectively for both groups. The Paddick conformity index (PCI) was averagely improved by 8%. The average homogeneity index (HI) and focal index (FI) were increased by 22% and 50%, respectively. The mGI was inversely proportional to the PTV volumes. The shape of the dose distribution in target was also changed from concave to convex. The comparison of PCI with historical data from other institutes and modalities shows that the plans in this study have the best conformity near the target. Conclusions With the new optimization strategies for VMAT SRS plan of brain tumor more conformal plans in both high and intermediate dose region (~50% of the PD) were created, in which the dose in the core of the target was notably increased while V12 and mGI were significantly decreased, and PCI was improved. The mGI was inversely proportional to the PTV volumes. The optimal P‐IDL is around 75%. The average PCI is the best in this study compared with the published historical data. These strategies are applicable to treatment planning for multiple brain and liver tumors where sparing the tissue peripheral to the target is critical.

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Experience of micromultileaf collimator linear accelerator based single fraction stereotactic radiosurgery: Tumor dose inhomogeneity, conformity, and dose fall off

Cited by 28 publications

References 46 publications

CBCT-based dosimetric verification and alternate planning techniques to reduce the normal tissue dose in SBRT of lung patients

CBCT-based dosimetric verification and alternate planning techniques to reduce the normal tissue dose in SBRT of lung patients

Swine Atrioventricular Node Ablation Using Stereotactic Radiosurgery: Methods and In Vivo Feasibility Investigation for Catheter‐Free Ablation of Cardiac Arrhythmias

Strategies to optimize stereotactic radiosurgery plans for brain tumors with volumetric‐modulated arc therapy

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