Dosimetric evaluation of photon dose calculation under jaw and MLC shielding

Fogliata, A.; Clivio, Alessandro; Vanetti, Eugenio; Nicolini, G.; Belosi, M.F.; Cozzi, Luca

doi:10.1118/1.4820443

Cited by 16 publications

(13 citation statements)

References 29 publications

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“…While agreeing with aforementioned retrospective reports, our clinically optimized synchronous JT‐VMAT plan exhibits superior OAR protection for normal lung doses as well as other OAR sparing prospectively compared to no JT‐VMAT for the given complexity of single‐isocenter/two‐lesion lung SBRT setting. By tracking the jaws during SBRT VMAT plan optimization, the magnitude of normal lung dose reductions (the OAR closest to the multiple targets) observed in this study were generally consistent with previous studies, yet relatively higher differences (up to 11%) were observed, perhaps due to the unique complexity of the clinical situations and the distance between the tumors. It is worthwhile to mention that MLC transmission of our 6 MV‐FFF beam was 1.2% and was modeled by the TPS and incorporated in the dose calculation.…”

Section: Discussionsupporting

confidence: 89%

Potential reduction of lung dose via VMAT with jaw tracking in the treatment of single‐isocenter/two‐lesion lung SBRT

Pokhrel

Sanford

Halfman

et al. 2019

J Applied Clin Med Phys

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Purpose/objectives Due to higher radiosensitivity, non‐target normal tissue dose is a major concern in stereotactic body radiation therapy (SBRT) treatment. The aim of this report was to estimate the dosimetric impact, specifically the reduction of normal lung dose in the treatment of single‐isocenter/two‐lesion lung SBRT via volumetric modulated arc therapy with jaw tracking (JT‐VMAT). Materials/methods Twelve patients with two peripherally located early‐stage non‐small‐cell‐lung cancer (NSCLC) lung lesions underwent single‐isocenter highly conformal non‐coplanar JT‐VMAT SBRT treatment in our institution. The mean isocenter to tumors distance was 5.6 ± 1.9 (range 4.3–9.5) cm. The mean combined planning target volume (PTV) was 38.7 ± 22.7 (range 5.0–80.9) cc. A single isocenter was placed between the two lesions. Doses were 54 and 50 Gy in three and five fractions, respectively. Plans were optimized in Eclipse with AcurosXB algorithm utilizing jaw tracking options for the Truebeam with a 6 MV‐FFF beam and standard 120 leaf millennium multi‐leaf collimators. For comparison, the JT‐VMAT plans were retrospectively re‐computed utilizing identical beam geometry, objectives, and planning parameters, but without jaw tracking (no JT‐VMAT). Both plans were normalized to receive the same target coverage. The conformity and heterogeneity indices, intermediate‐dose spillage [D2cm, R50, Gradient Index (GI), Gradient Distance (GD)], organs at risks (OAR) doses including normal lung as well as modulation factor (MF) were compared for both plans. Results For similar target coverage, GI, R50, GD, as well as the normal lung V5, V10, V20, mean lung dose (MLD), and maximum dose received by 1000 cc of lungs were statistically significant. Normal lung doses were reduced by 8%–11% with JT‐VMAT. Normal lung dose increased as a function of tumor distance from isocenter. For the other OAR, up to 1%–16% reduction of non‐target doses were observed with JT‐VMAT. The MF and beam‐on time were similar for both plans, however, MF increased as a function of tumors distance, consequently, delivering higher dose to normal lungs. Conclusion Utilizing jaw tracking options during optimization for single‐isocenter/two‐lesion lung SBRT VMAT plans reduced doses to the normal lung and other OAR, reduced intermediate‐dose spillage and provided superior/similar target coverage. Application of jaw tracking did not affect delivery efficiency and provided excellent plan quality with similar MF and beam‐on time. Jaw tracking is recommended for future clinical SBRT plan optimization.

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Section: Discussionsupporting

confidence: 89%

Potential reduction of lung dose via VMAT with jaw tracking in the treatment of single‐isocenter/two‐lesion lung SBRT

Pokhrel

Sanford

Halfman

et al. 2019

J Applied Clin Med Phys

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“…Also, PD of FFF beams has been studied for the treatment plans generated for the intensity modulated radiation therapy (IMRT), stereotactic body radiotherapy (SBRT), and stereotactic radiosurgery (SRS) 4,8 as well as for square and rectangular open fields. 7,11,19 Similar to the MC studies, these publications have suggested that the PD of unflattened beams is lower than flattened beams of the same nominal energy and that the relative difference in PD increases with energy.…”

Section: Introductionmentioning

confidence: 55%

“…Peripheral doses are also relevant when considering the risk of secondary malignancies or the potential failure of the implanted electronic devices (e.g., pacemakers, defibrillators). 5,12,15,[17][18][19] Numerous studies have investigated the trends in PD for flattened photon beams with varying field sizes, depth, and distances from the field edge, as well as the effects of beam modifiers [e.g., multileaf collimators (MLCs)] and collimator rotation. 12,[14][15][16][20][21][22][23][24] The removal of the flattening filter changes the profile and dosimetric characteristics of photon beams.…”

Section: Introductionmentioning

confidence: 99%

Technical Report: Evaluation of peripheral dose for flattening filter free photon beams

et al. 2016

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Purpose: To develop a comprehensive peripheral dose (PD) dataset for the two unflattened beams of nominal energy 6 and 10 MV for use in clinical care. Methods: Measurements were made in a 40 × 120 × 20 cm 3 (width × length × depth) stack of solid water using an ionization chamber at varying depths (dmax, 5, and 10 cm), field sizes (3 × 3 to 30 × 30 cm 2 ), and distances from the field edge (5-40 cm). The effects of the multileaf collimator (MLC) and collimator rotation were also evaluated for a 10 × 10 cm 2 field. Using the same phantom geometry, the accuracy of the analytic anisotropic algorithm (AAA) and Acuros dose calculation algorithm was assessed and compared to the measured values. Results: The PDs for both the 6 flattening filter free (FFF) and 10 FFF photon beams were found to decrease with increasing distance from the radiation field edge and the decreasing field size. The measured PD was observed to be higher for the 6 FFF than for the 10 FFF for all field sizes and depths. The impact of collimator rotation was not found to be clinically significant when used in conjunction with MLCs. AAA and Acuros algorithms both underestimated the PD with average errors of −13.6% and −7.8%, respectively, for all field sizes and depths at distances of 5 and 10 cm from the field edge, but the average error was found to increase to nearly −69% at greater distances. Conclusions: Given the known inaccuracies of peripheral dose calculations, this comprehensive dataset can be used to estimate the out-of-field dose to regions of interest such as organs at risk, electronic implantable devices, and a fetus. While the impact of collimator rotation was not found to significantly decrease PD when used in conjunction with MLCs, results are expected to be machine model and beam energy dependent. It is not recommended to use a treatment planning system to estimate PD due to the underestimation of the out-of-field dose and the inability to calculate dose at extended distances due to the limits of the dose calculation matrix. C 2016 American Association of Physicists in Medicine. [http://dx

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“…Kron et al 26 and Fogliata et al 27 assessed the accuracy of the AXB11 and the AAA under the shielding by the jaw, the MLC or the both with varying static and VMAT fields. In general, good results were obtained for both algorithms, the largest discrepancies being for the smallest fields.…”

Section: The Axb Algorithm and Homogeneous Phantomsmentioning

confidence: 99%

The accuracy of the Acuros XB algorithm in external beam radiotherapy – a comprehensive review

Ojala

2014

Int J Cancer Ther Oncol

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Review Article AbstractThe accuracy of dose calculation algorithms has been a topic of interest among the radiotherapy community throughout last decades. On one hand the advancements in computers and algorithms has improved the accuracy, but on the other hand the developments in other parts of treatment process, in treatment delivery techniques and in treatment devices have always pushed the requirements to the next level. In this review article a comprehensive overview on the accuracy of a new type 'c' dose calculation algorithm, the Acuros XB (AXB) algorithm (Varian Medical Systems, Inc., Palo Alto, CA, USA), is provided. All the articles that have applied the AXB algorithm in terms of external beam radiotherapy are included and the research frames with reported deviations to reference methods are described. For the homogeneous water phantoms the reported accuracy was from 1% to 2%, being of similar level for heterogeneous phantoms, in rare occasions lower. In anthropometric and anthropomorphic phantoms the mean deviations were about 2% and slightly larger for single points and/or small regions. With patient plans the reported average discrepancies were less than from 3% to 5%. Almost without exceptions, the algorithm has proven to perform better than other existing commercial dose calculation algorithms. The number of such papers, in which the AXB algorithm is the only dose determination method, is already notable, which indicates that the accuracy of the algorithm is trusted for reference use and it also, with reported dosimetric results, implies that the AXB algorithm has reached its maturity.

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Dosimetric evaluation of photon dose calculation under jaw and MLC shielding

Abstract: The two algorithms analyzed showed encouraging results in predicting out-of-field region dose for clinical use.

Cited by 16 publications

References 29 publications

Potential reduction of lung dose via VMAT with jaw tracking in the treatment of single‐isocenter/two‐lesion lung SBRT

Potential reduction of lung dose via VMAT with jaw tracking in the treatment of single‐isocenter/two‐lesion lung SBRT

Technical Report: Evaluation of peripheral dose for flattening filter free photon beams

The accuracy of the Acuros XB algorithm in external beam radiotherapy – a comprehensive review

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