A Novel Technique to Validate Dosimetry for Single-Isocenter Multiple-Target VMAT Stereotactic Radiosurgery

The purpose was to compare linac-based stereotactic radiosurgery and hypofractionated radiotherapy plan quality of automated planning, intensity modulated radiotherapy (IMRT) and manual dynamic conformal arc (DCA) plans as well as single- and multiple-isocenter techniques for multiple brain metastases (BM). For twelve patients with four to ten BM, seven non-coplanar linac-based plans were created: a manually planned DCA plan with a separate isocenter for each metastasis, a single-isocenter dynamic IMRT plan, an automatically generated single-isocenter volumetric modulated arc radiotherapy (VMAT) plan, four automatically generated single-isocenter DCA plans with three or five couch angles, with high or low sparing of normal tissue. Paddick conformity index, gradient index (GI), mean dose, total V12Gy and V5Gy of uninvolved brain, number of monitor units (MUs), irradiation time and pass rate were compared. The GI was significantly higher for VMAT than for separate-isocenter, IMRT, and all automatically generated plans. The number of MUs was lowest for VMAT, followed by automatically generated DCA and IMRT plans and highest for manual DCA plans. Irradiation time was the shortest for automatically planned DCA plans. Automatically generated linac-based single-isocenter plans for multiple BM reduce the number of MUs and irradiation time with at least comparable GI and V5Gy relative to the reference separate-isocenter DCA plans.

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Radiobiological evaluation considering setup error on single‐isocenter irradiation in stereotactic radiosurgery

Journal of Applied Clinical Medical Physics ◽

10.1002/acm2.13322 ◽

2021 ◽

Author(s):

Hisashi Nakano ◽

Satoshi Tanabe ◽

Ryuta Sasamoto ◽

Takeshi Takizawa ◽

Satoru Utsunomiya ◽

...

Keyword(s):

Stereotactic Radiosurgery ◽

Setup Error ◽

Single Isocenter

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[OA191] Influence of the degree of the geometric uncertainty on the quality of single isocenter VMAT multiple target treatments

Physica Medica ◽

10.1016/j.ejmp.2018.06.263 ◽

2018 ◽

Vol 52 ◽

pp. 73-74

Author(s):

Georgia Prentou ◽

Pantelis Karaiskos ◽

Panagiotis Papagiannis ◽

Evaggelos Pantelis ◽

Efi Koutsouveli

Keyword(s):

Multiple Target ◽

Geometric Uncertainty ◽

Single Isocenter

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A novel index for assessing treatment plan quality in stereotactic radiosurgery

Journal of Neurosurgery ◽

10.3171/2018.7.gks18694 ◽

2018 ◽

Vol 129 (Suppl1) ◽

pp. 118-124 ◽

Cited By ~ 4

Author(s):

Alexis Dimitriadis ◽

Ian Paddick

Keyword(s):

Stereotactic Radiosurgery ◽

Treatment Plan ◽

Efficiency Index ◽

Target Volume ◽

Surrounding Tissue ◽

Plan Quality ◽

Multiple Target ◽

Integral Dose ◽

Plan Optimization ◽

Dose Volume

OBJECTIVEStereotactic radiosurgery (SRS) is characterized by high levels of conformity and steep dose gradients from the periphery of the target to surrounding tissue. Clinical studies have backed up the importance of these factors through evidence of symptomatic complications. Available data suggest that there are threshold doses above which the risk of symptomatic radionecrosis increases with the volume irradiated. Therefore, radiosurgical treatment plans should be optimized by minimizing dose to the surrounding tissue while maximizing dose to the target volume. Several metrics have been proposed to quantify radiosurgical plan quality, but all present certain weaknesses. To overcome limitations of the currently used metrics, a novel metric is proposed, the efficiency index (η50%), which is based on the principle of calculating integral doses: η50% = integral doseTV/integral dosePIV50%.METHODSThe value of η50% can be easily calculated by dividing the integral dose (mean dose × volume) to the target volume (TV) by the integral dose to the volume of 50% of the prescription isodose (PIV50%). Alternatively, differential dose-volume histograms (DVHs) of the TV and PIV50% can be used. The resulting η50% value is effectively the proportion of energy within the PIV50% that falls into the target. This value has theoretical limits of 0 and 1, with 1 being perfect. The index combines conformity, gradient, and mean dose to the target into a single value. The value of η50% was retrospectively calculated for 100 clinical SRS plans.RESULTSThe value of η50% for the 100 clinical SRS plans ranged from 37.7% to 58.0% with a mean value of 49.0%. This study also showed that the same principles used for the calculation of η50% can be adapted to produce an index suitable for multiple-target plans (Gη12Gy). Furthermore, the authors present another adaptation of the index that may play a role in plan optimization by calculating and minimizing the proportion of energy delivered to surrounding organs at risk (OARη50%).CONCLUSIONSThe proposed efficiency index is a novel approach in quantifying plan quality by combining conformity, gradient, and mean dose into a single value. It quantifies the ratio of the dose “doing good” versus the dose “doing harm,” and its adaptations can be used for multiple-target plan optimization and OAR sparing.

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