Evaluation of pencil beam convolution and anisotropic analytical algorithms in stereotactic lung irradiation

Herman, Terence; Hibbitts, Kerry; Herman, Terence S.; Ahmad, Salahuddin

doi:10.4103/0971-6203.89974

Cited by 10 publications

(3 citation statements)

References 17 publications

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“…Thus, a recommendation to readjust the Dpr could be suggested. This finding agrees with international recommendations indicating that a decrease of Dpr should be suggested [ 33 , 34 ]. Therefore, a reduction of Dpr from 5 to 10% is recommended when moving from type (A) algorithms to type (B) algorithms.…”

Section: Resultssupporting

confidence: 91%

Dosimetrical and radiobiological approach to manage the dosimetric shift in the transition of dose calculation algorithm in radiation oncology: how to improve high quality treatment and avoid unexpected outcomes?

et al. 2018

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BackgroundFor a given prescribed dose of radiotherapy, with the successive generations of dose calculation algorithms, more monitor units (MUs) are generally needed. This is due to the implementation of successive improvements in dose calculation: better heterogeneity correction and more accurate estimation of secondary electron transport contribution. More recently, there is the possibility to report the dose-to-medium, physically more accurate compared to the dose-to-water as the reference one. This last point is a recent concern and the main focus of this study.MethodsIn this paper, we propose steps for a general analysis procedure to estimate the dosimetric alterations, and the potential clinical changes, between a reference algorithm and a new one. This includes dosimetric parameters, gamma index, radiobiology indices based on equivalent uniform dose concept and statistics with bootstrap simulation. Finally, we provide a general recommendation on the clinical use of new algorithms regarding the dose prescription or dose limits to the organs at risks.ResultsThe dosimetrical and radiobiological data showed a significant effect, which might exceed 5–10%, of the calculation method on the dose the distribution and clinical outcomes for lung cancer patients. Wilcoxon signed rank paired comparisons indicated that the delivered dose in MUs was significantly increased (> 2%) using more advanced dose calculation methods as compared to the reference one.ConclusionThis paper illustrates and explains the use of dosimetrical, radiobiologcal and statistical tests for dosimetric comparisons in radiotherapy. The change of dose calculation algorithm may induce a dosimetric shift, which has to be evaluated by the physicists and the oncologists. This includes the impact on tumor control and on the risk of toxicity based on normal tissue dose constraints. In fact, the alteration in dose distribution makes it hard to keep exactly the same tumor control probability along with the same normal tissue complication probability.

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Section: Resultssupporting

confidence: 91%

Dosimetrical and radiobiological approach to manage the dosimetric shift in the transition of dose calculation algorithm in radiation oncology: how to improve high quality treatment and avoid unexpected outcomes?

et al. 2018

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“…Therefore, the possible advantages of the second protocol were dose escalation by 2 to 4 Gy and the use of AAA for T1a/b tumors and the latter alone for T2a tumors. Pencil beam algorithm tends to overestimate the dose distribution in PTV, and AAA can provide more accurate dose distributions [ 19 , 20 ]. Using AAA could actually lead to higher dose delivery, and the isocenter dose is usually allowed to be considerably higher in order to deliver as low doses as possible to surrounding structures [ 21 ].…”

Section: Discussionmentioning

confidence: 99%

Stereotactic body radiotherapy for stage I non-small-cell lung cancer using higher doses for larger tumors: results of the second study

et al. 2017

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BackgroundEfficacy of stereotactic body radiotherapy (SBRT) in stage I non–small-cell lung cancer (NSCLC) has almost been established. In Japan, the protocol of 48 Gy in 4 fractions over 4 days has been most often employed, but higher doses may be necessary to control large tumors. Previously, we conducted a clinical study using SBRT for stage I NSCLC employing different doses depending on tumor diameter, which was closed in 2008. Thereafter, a new study employing higher doses has been conducted, which is reported here. The purpose of this study was to review the safety and effectiveness of the higher doses.MethodsWe escalated the total dose for the improvement of local control for large tumors. In this study, 71 patients underwent SBRT between December 2008 and April 2014. Isocenter doses of 48, 50, and 52 Gy were administered for tumors with a longest diameter of < 1.5 cm, 1.5–3 cm, and > 3 cm, respectively. It was recommended to cover 95% of the PTV with at least 90% of the isocenter dose, and in all but one cases, 95% of the PTV received at least 80% of the prescribed dose. Treatments were delivered in 4 fractions, giving 2 fractions per week. SBRT was performed with 6-MV photons using 4 non-coplanar and 3 coplanar beams.ResultsThe median follow-up period was 44 months for all patients and 61 months for living patients. Overall survival (OS) was 65%, progression-free survival (PFS) was 55%, and cumulative incidence of local recurrence (LR) was 15% at 5 years. The 5-year OS was 69% for 57 stage IA patients and 53% for 14 stage IB patients (p = 0.44). The 5-year PFS was 55 and 54%, respectively (p = 0.98). The 5-year cumulative incidence of LR was 11 and 31%, respectively (p = 0.09). The cumulative incidence of Grade ≥ 2 radiation pneumonitis was 25%.ConclusionsOur newer SBRT study yielded reasonable local control and overall survival and acceptable toxicity, but escalating the total dose did not lead to improved outcomes.Trial registration UMIN000027231, registered on 3 May 2017. Retrospectively registered.

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“…It has been recently suggested that there is a need to adjust the prescribed dose of radiation especially after the implementation of the Anisotropic Analytical Algorithm (AAA) in the clinic. 21 However, in our department this question was raised with the transition from a Clarkson algorithm to a PBC algorithm without heterogeneity correction. 22 In fact the difference between MUs calculated using the Clarkson algorithm and PBC without heterogeneity correction was less than 1% for lung sites with a SD smaller than 1%.…”

Section: The Need To Adjust the Prescribed Dose In Radiotherapymentioning

confidence: 99%

A decision tool to adjust the prescribed dose after change in the dose calculation algorithm

Chaikh

Giraud

Marguet³

et al. 2014

Int J Cancer Ther Oncol

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Purpose: This work aims to introduce a method to quantify and assess the differences in monitor unites MUs when changing to new dose calculation software that uses a different algorithm, and to evaluate the need and extent of adjustment of the prescribed dose to maintain the same clinical results. Methods: Doses were calculated using two classical algorithms based on the Pencil Beam Convolution PBC model, using 6 patients presenting lung cancers. For each patient, 3 treatment plans were generated: Plan 1 was calculated using reference algorithm PBC without heterogeneity correction, Plan 2 was calculated using test algorithm with heterogeneity correction, and in plan 3 the dose was recalculated using test algorithm and monitor unites MUs obtained from plan 1 as input. To assess the differences in the calculated MUs, isocenter dose, and spatial dose distributions using a gamma index were compared. Statistical analysis was based on a Wilcoxon signed rank test. Results: The test algorithm in plan 2 calculated significantly less MUs than reference algorithm in plan 1 by on average 5%, (p < 0.001). We also found underestimating dose for target volumes using 3D gamma index analysis. In this example, in order to obtain the same clinical outcomes with the two algorithms the prescribed dose should be adjusted by 5%. Conclusion: This method provides a quantitative evaluation of the differences between two dose calculation algorithms and the consequences on the prescribed dose. It could be used to adjust the prescribed dose when changing calculation software to maintain the same clinical results as obtained with the former software. In particular, the gamma evaluation could be applied to any situation where changes in the dose calculation occur in radiotherapy.

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Evaluation of pencil beam convolution and anisotropic analytical algorithms in stereotactic lung irradiation

Cited by 10 publications

References 17 publications

Dosimetrical and radiobiological approach to manage the dosimetric shift in the transition of dose calculation algorithm in radiation oncology: how to improve high quality treatment and avoid unexpected outcomes?

Dosimetrical and radiobiological approach to manage the dosimetric shift in the transition of dose calculation algorithm in radiation oncology: how to improve high quality treatment and avoid unexpected outcomes?

Stereotactic body radiotherapy for stage I non-small-cell lung cancer using higher doses for larger tumors: results of the second study

A decision tool to adjust the prescribed dose after change in the dose calculation algorithm

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