Exploration and application of phenomenological RBE models for proton therapy

Rørvik, Eivind; Fjæra, Lars Fredrik; Dahle, Tordis Johnsen; Dale, Jon Espen; Engeseth, Grete May; Stokkevåg, C.H.; Thörnqvist, S.; Ytre-Hauge, Kristian S.

doi:10.1088/1361-6560/aad9db

Cited by 104 publications

(144 citation statements)

References 123 publications

Supporting

Mentioning

118

Contrasting

Order By: Relevance

“…In addition, the difference of

Δ D_{truemax}

between the optimization techniques was larger when the OAR was closer to the CTV. Among the RBE models, Wilkens et al showed largest

Δ D_{truemax}

, followed by Wedenberg et al and McNamara et al This is the same trend observed in RBE for low

{(α / β)}_{x}

in the high LET region reported in the literature . Figure 6(a) and 6(b) shows the comparison of the

Δ D_{99}

for the CTV in the case of

{()(, α false/ β)}_{x} = 3

and

{()(, α false/ β)}_{x} = 12

, respectively.…”

Section: Discussionsupporting

confidence: 69%

See 1 more Smart Citation

Difference in LET‐based biological doses between IMPT optimization techniques: Robust and PTV‐based optimizations

Hirayama

Matsuura

Yasuda

et al. 2020

J Applied Clin Med Phys

View full text Add to dashboard Cite

Purpose: While a large amount of experimental data suggest that the proton relative biological effectiveness (RBE) varies with both physical and biological parameters, current commercial treatment planning systems (TPS) use the constant RBE instead of variable RBE models, neglecting the dependence of RBE on the linear energy transfer (LET). To conduct as accurate a clinical evaluation as possible in this circumstance, it is desirable that the dosimetric parameters derived by TPS (D RBE¼1:1 ) are close to the "true" values derived with the variable RBE models (D vRBE ). As such, in this study, the closeness of D RBE¼1:1 to D vRBE was compared between planning target volume (PTV)-based and robust plans.Methods: Intensity-modulated proton therapy (IMPT) treatment plans for two Radiation Therapy Oncology Group (RTOG) phantom cases and four nasopharyngeal cases were created using the PTV-based and robust optimizations, under the assumption of a constant RBE of 1.1. First, the physical dose and dose-averaged LET (LET d ) distributions were obtained using the analytical calculation method, based on the pencil beam algorithm. Next, D vRBE was calculated using three different RBE models. The deviation of D vRBE from D RBE¼1:1 was evaluated with D 99 and D max , which have been used as the evaluation indices for clinical target volume (CTV) and organs at risk (OARs), respectively. The influence of the distance between the OAR and CTV on the results was also investigated. As a measure of distance, the closest distance and the overlapped volume histogram were used for the RTOG phantom and nasopharyngeal cases, respectively.Results: As for the OAR, the deviations of D vRBE max from D RBE¼1:1 max were always smaller in robust plans than in PTV-based plans in all RBE models. The deviation would tend to increase as the OAR was located closer to the CTV in both optimization techniques. As for the CTV, the deviations of D vRBE 99 from D RBE¼1:1 99 were comparable between the two optimization techniques, regardless of the distance between the CTV and the OAR.---

show abstract

“…In addition, the difference of

Δ D_{truemax}

between the optimization techniques was larger when the OAR was closer to the CTV. Among the RBE models, Wilkens et al showed largest

Δ D_{truemax}

, followed by Wedenberg et al and McNamara et al This is the same trend observed in RBE for low

{(α / β)}_{x}

in the high LET region reported in the literature . Figure 6(a) and 6(b) shows the comparison of the

Δ D_{99}

for the CTV in the case of

{()(, α false/ β)}_{x} = 3

and

{()(, α false/ β)}_{x} = 12

, respectively.…”

Section: Discussionsupporting

confidence: 69%

“…In the case of

{()(, α false/ β)}_{x} = 3

, the

Δ D_{99}

calculated with the Wedenberg RBE model was smaller than McNamara RBE model. This probably resulted from the fact that in the case of low

{(α / β)}_{x}

, the Wedenberg model gives a smaller RBE than the McNamara model in uniform dose regions where LET is small …”

Section: Discussionmentioning

confidence: 99%

Difference in LET‐based biological doses between IMPT optimization techniques: Robust and PTV‐based optimizations

Hirayama

Matsuura

Yasuda

et al. 2020

J Applied Clin Med Phys

View full text Add to dashboard Cite

show abstract

“…We used the LQ‐based RBE model developed by McNamara et al Due to the large variation in the RBE estimates because of the fundamental differences in experimental databases, model assumptions, and regression techniques, we estimated the model dependence of our results using two other models . Different RBE models give different RBE ; however, in both models, the magnitude of RBE increase is not significant (lower than 0.03 and 0.06 at the water surface and 0.003 and 0.005 at the target center, respectively).…”

Section: Discussionmentioning

confidence: 99%

Physical and biological impacts of collimator‐scattered protons in spot‐scanning proton therapy

Ueno

Matsuura

Hirayama

et al. 2019

J Applied Clin Med Phys

View full text Add to dashboard Cite

To improve the penumbra of low‐energy beams used in spot‐scanning proton therapy, various collimation systems have been proposed and used in clinics. In this paper, focused on patient‐specific brass collimators, the collimator‐scattered protons' physical and biological effects were investigated. The Geant4 Monte Carlo code was used to model the collimators mounted on the scanning nozzle of the Hokkaido University Hospital. A systematic survey was performed in water phantom with various‐sized rectangular targets; range (5–20 cm), spread‐out Bragg peak (SOBP) (5–10 cm), and field size (2 × 2–16 × 16 cm2). It revealed that both the range and SOBP dependences of the physical dose increase had similar trends to passive scattering methods, that is, it increased largely with the range and slightly with the SOBP. The physical impact was maximized at the surface (3%–22% for the tested geometries) and decreased with depth. In contrast, the field size (FS) dependence differed from that observed in passive scattering: the increase was high for both small and large FSs. This may be attributed to the different phase‐space shapes at the target boundary between the two dose delivery methods. Next, the biological impact was estimated based on the increase in dose‐averaged linear energy transfer (LETd) and relative biological effectiveness (RBE). The LETd of the collimator‐scattered protons were several keV/μm higher than that of unscattered ones; however, since this large increase was observed only at the positions receiving a small scattered dose, the overall LETd increase was negligible. As a consequence, the RBE increase did not exceed 0.05. Finally, the effects on patient geometries were estimated by testing two patient plans, and a negligible RBE increase (0.9% at most in the critical organs at surface) was observed in both cases. Therefore, the impact of collimator‐scattered protons is almost entirely attributed to the physical dose increase, while the RBE increase is negligible.

show abstract

“…The uncertainties in the (α/β) x values should therefore be carefully assessed both when evaluating the RBE values presented here and when estimating normal tissue complication probability for specific endpoints. The RBE changes monotonously with (α/β) x for the ROR and MCN models 14 . The RBE for all (α/β) x values within the confidence intervals will therefore fall within the shaded regions in Fig.…”

Section: Resultsmentioning

confidence: 97%

“…However, for the purpose of evaluating RBE in a clinical setting, this approach could lead to artificially high RBE values in cases where the dose is inhomogeneous and low in parts of the organ. The low dose regions would then contribute to a significant increase in mean or median RBE as the RBE, for most models, is inversely proportional with dose 14 , and in addition, low dose regions often have high LET d due to low energy scattered or secondary ions or neutrons. Considering the dose and LET d distributions for the heart (Fig.…”

Section: Resultsmentioning

confidence: 99%

Inter-patient variations in relative biological effectiveness for cranio-spinal irradiation with protons

Ytre-Hauge

Fjæra

Rørvik

et al. 2020

Sci Rep

Self Cite

View full text Add to dashboard Cite

cranio-spinal irradiation (cSi) using protons has dosimetric advantages compared to photons and isexpected to reduce risk of adverse effects. The proton relative biological effectiveness (RBE) varies with linear energy transfer (LET), tissue type and dose, but a variable RBE has not replaced the constant RBE of 1.1 in clinical treatment planning. We examined inter-patient variations in RBE for ten proton CSI patients. Variable RBE models were used to obtain RBE and RBE-weighted doses. RBE was quantified in terms of dose weighted organ-mean RBE (RBE d = mean RBE-weighted dose/mean physical dose) and effective RBE of the near maximum dose (D 2% ), i.e., where subscripts RBE and phys indicate that the D 2% is calculated based on an RBE model and the physical dose, respectively. compared to the median RBE d of the patient population, differences up to 15% were observed for the individual RBE d values found for the thyroid, while more modest variations were seen for the heart (6%), lungs (2%) and brainstem (<1%). Large inter-patient variation in RBE could be correlated to large spread in LET and dose for these organs at risk (OARs). For OARs with small inter-patient variations, the results show that applying a population based RBE in treatment planning may be a step forward compared to using RBE of 1.1. OARs with large inter-patient RBE variations should ideally be selected for patient-specific biological or RBE robustness analysis if the physical doses are close to known dose thresholds.Proton therapy has been established as an important radiation treatment modality for cancer, offering improved sparing of normal tissue compared to conventional radiation therapy with photons 1 . The dosimetric advantages of protons have already been shown for medulloblastoma patients receiving cranio-spinal irradiation (CSI) 2,3 , and early clinical outcomes suggest that similar disease control can be achieved with reduced toxicity compared to photon therapy 4-6 . Longer follow-up and more clinical data are awaited to draw firm conclusions on the clinical benefits of proton CSI 7 .Dosimetric benefits of proton CSI include a significant dose reduction to organs anterior to the spinal column, including the cochlea, transverse colon, stomach, kidney, heart, and lungs 8 . Besides the different spatial patterns in physical dose deposition, protons also have an increased biological effect compared to photons, i.e. protons produce more damage than photons from the same physical dose. This difference is currently accounted for by a dose scaling factor; the relative biological effectiveness (RBE). Although contemporary clinical proton treatment planning is based on a constant RBE of 1.1 (RBE 1.1 ), the proton RBE is known to vary with linear energy transfer (LET), tissue type and physical dose 9-11 . In particular, the RBE increases due to the increase in LET towards the end of the proton beam range. The need to investigate the RBE further and to and to provide clinical solutions accounting for variations in the RBE has therefore recently bee...

show abstract

Exploration and application of phenomenological RBE models for proton therapy

Cited by 104 publications

References 123 publications

Difference in LET‐based biological doses between IMPT optimization techniques: Robust and PTV‐based optimizations

Difference in LET‐based biological doses between IMPT optimization techniques: Robust and PTV‐based optimizations

Physical and biological impacts of collimator‐scattered protons in spot‐scanning proton therapy

Inter-patient variations in relative biological effectiveness for cranio-spinal irradiation with protons

Contact Info

Product

Resources

About