Circular collimator arc versus dynamic conformal arc treatment planning for linac-based stereotactic radiosurgery of an intracranial small single lesion: a perspective of lesion asymmetry

Background: Although circular collimator arcs (CCA) and dynamic conformal arcs (DCA) are commonly used linear accelerator-based treatment planning techniques for intracranial stereotactic radiosurgery (SRS) of a small single lesion, these two techniques have not been rigorously compared in terms of tumor shape. Therefore, this study compared clinical CCA plans with re-planned DCA plans using conformity index (CI) and V12Gy (volume of normal brain tissue receiving 12 Gy or higher) from a perspective of asymmetry (Asym) of planning target volume (PTV). Methods: Ninety-five clinical CCA plans delivered for a small single lesion with PTV size < 1.4 cm3 were selected and re-planned using DCA. PTV Asym (%) was defined and calculated from three dimensions of PTV. A pair of the 95 plans was first considered as one group without grouping and then categorized into two groups with respective to either PTV size or PTV Asym, and four groups with respect to PTV size and PTV Asym. For grouping, median values of PTV size and PTV Asym were used. A non-parametric paired test was performed for CI and V12Gy to compare CCA and DCA plans in each group. Results: Median values of PTV size and PTV Asym were 0.415 cm3 (range: 0.076 cm3–1.369 cm3) and 6.12% (range: 0.52–25.74%), respectively. DCA plans had a lower average CI value than CCA plans for all groups. CCA plans had a smaller average V12Gy value than DCA plans for lesions with PTV Asym ≤6.12%, while CCA and DCA plans had similar average V12Gy values for lesions with PTV Asym > 6.12%. Conclusions: The DCA technique is recommended when a lesion has PTV Asym > 6.12% regardless of PTV size. For lesions with PTV Asym ≤6.12%, a technique choice would depend on the preference of CI or V12Gy.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Optic disc dose reduction in ocular brachytherapy using(125)I notched COMS plaques: A simulation study based on current clinical practice

Purpose Although notched Collaborative Ocular Melanoma Study (COMS) plaques have been widely used, optic disc dose reduction by notched COMS plaques has not been discussed in the literature. Therefore, this study investigated optic disc dose reduction in ocular brachytherapy using(125)I notched COMS plaques in comparison with optic disc dose for(125)I standard COMS plaques. Methods For this simulation study, an in-house brachytherapy dose calculation program was developed using MATLAB software by incorporating the American Association of Physicists in Medicine Task Group-43 Update (AAPM TG-43U1) dosimetry formalism with a line source approximation in a homogeneous water medium and COMS seed coordinates in the AAPM TG 129. Using this program, optic disc doses for standard COMS plaques (from 12 to 22 mm in diameter in 2 mm increments) and notched COMS plaques with one seed removed (Case #1, from 12 to 22 mm) and with two seeds removed (Case #2, from 14 to 22 mm) were calculated as a function of tumor margin-to-optic disc distance (DT) for various tumor basal dimensions (BDs) for prescription depths from 1 to 10 mm in 1 mm intervals. A dose of 85 Gy for an irradiation time of 168 h was prescribed to each prescription depth. Then absolute and relative optic disc dose reduction by notched COMS plaques (Cases #1 and #2) was calculated for all prescription depths. Results Optic disc dose reduction by notched COMS plaques (Cases #1 and #2) had five unique trends related to maximum optic disc dose reduction and corresponding optimal DT for each BD in each plaque. It increased with increasing prescription depth. Conclusions The results presented in this study would enable the clinician to choose an adequate plaque type among standard and notched(125)I COMS plaques and a prescription depth to minimize optic disc dose.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

A practical approach to estimating optic disc dose and macula dose without treatment planning in ocular brachytherapy using I COMS plaques

It has been reported that proximity of the tumor to the optic disc and macula, and radiation dose to the critical structures are substantial risk factors for vision loss following plaque brachytherapy. However, there is little dosimetry data published on this. In this study, therefore, the relationship between distance from tumor margin and radiation dose to the optic disc and macula in ocular brachytherapy using 125I Collaborative Ocular Melanoma Study (COMS) plaques was comprehensively investigated. From the information, this study aimed to allow for estimation of optic disc dose and macula dose without treatment planning.Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

OptImal Gamma kNife lIghTnIng sOlutioN (IGNITION) score to characterize the solution space of the Gamma Knife FIP optimizer for stereotactic radiosurgery

ObjectivesThe objective of this study is to evaluate the user-defined optimization settings in the Fast Inverse Planning (FIP) optimizer in Leksell GammaPlan® and determine the parameters that result in the best stereotactic radiosurgery (SRS) plan quality for brain metastases, benign tumors, and arteriovenous malformations (AVMs).MethodsThirty patients with metastases and 30 with benign lesions-vestibular schwannoma, AVMs, pituitary adenoma, and meningioma-treated with SRS were evaluated. Each target was planned by varying the low dose (LD) and beam-on-time (BOT) penalties in increments of 0.1, from 0 to 1. The following plan quality metrics were recorded for each plan: Paddick conformity index (PCI), gradient index (GI), BOT, and maximum organ-at-risk (OAR) doses. A novel objective score matrix was calculated for each target using a linearly weighted combination of the aforementioned metrics. A histogram of optimal solutions containing the five best scores was extracted.ResultsA total of 7260 plans were analyzed with 121 plans per patient for the range of LD/BOT penalties. The ranges of PCI, GI, and BOT across all metastatic lesions were 0.58-0.97, 2.1-3.8, and 8.8-238 min, respectively, and were 0.13-0.97, 2.1-3.8, and 8.8-238 min, respectively, for benign lesions. The objective score matrix showed unique optimal solutions for metastatic lesions and benign lesions. Additionally, the plan metrics of the optimal solutions were significantly improved compared to the clinical plans for metastatic lesions with equivalent metrics for all other cases.ConclusionIn this study, FIP optimizer was evaluated to determine the optimal solution space to maximize PCI and minimize GI, BOT and OAR doses simultaneously for single metastatic/benign/non-neoplastic targets. The optimal solution chart was determined using a novel objective score which provides novice and expert planners a roadmap to generate the most optimal plans efficiently using FIP