The characteristic of stem-related genes with pancreatic carcinoma cell after irradiation

Purpose

To investigate stem-related differentially expressed genes (DEGs) and their potential mechanism in pancreatic cancer cells (MIAPaCa-2) exposed to x-ray and proton radiation, as well as how these factors affected the prognosis of patients with pancreatic adenocarcinoma (PADC).

Methods

The stem-related DEGs were screened using the online tool Stemchecker after protons and x-rays were used to irradiate MIAPaCa-2 cells. Analysis was done on the probable processes and prognostic significance of the DEGs in PAC patients.

Results

Four datasets containing 401 DEGs were filtered, and the stem-related DEGs for each irradiation type indicated a variety of radiobiological characteristics. In pancreatic cancer cells, a number of stem-related DEGs may serve as biomarkers of radiation effects. Patients with pancreatic cancer demonstrated predictive significance for GRB7, B2M, and PMAIP1.

Conclusions

MIAPaCa-2 cells exposed to x-rays and protons repeatedly displayed heterogeneous expression of stem-related DEGs involved in complex radiosensitivity, radio-resistance, and radio-induced mortality pathways. GRB7 and B2M were considered potential radiation sensitivity indicators for pancreatic cancer.

Three-dimensional dose and LETD prediction in proton therapy using artificial neural networks

PURPOSE

Challenges in proton therapy include identifying patients most likely to benefit; ensuring consistent, high-quality plans as its adoption becomes more widespread; and recognizing biological uncertainties that may be related to increased relative biologic effectiveness driven by linear energy transfer (LET). Knowledge-based planning (KBP) is a domain that may help to address all three.

METHODS

Artificial neural networks were trained using 117 unique treatment plans and associated dose and dose-weighted LET (LET_D ) distributions. The data set was split into training (n = 82), validation (n = 17), and test (n = 18) sets. Model performance was evaluated on the test set using dose- and LET_D -volume metrics in the clinical target volume (CTV) and nearby organs at risk and Dice similarity coefficients (DSC) comparing predicted and planned isodose lines at 50%, 75%, and 95% of the prescription dose.

RESULTS

Dose-volume metrics significantly differed (α = 0.05) between predicted and planned dose distributions in only one dose-volume metric, D_2% to the CTV. The maximum observed root mean square (RMS) difference between corresponding metrics was 4.3 Gy_RBE (8% of prescription) for D_1cc to optic chiasm. DSC were 0.90, 0.93, and 0.88 for the 50%, 75%, and 95% isodose lines, respectively. LET_D -volume metrics significantly differed in all but one metric, L_0.1cc of the brainstem. The maximum observed difference in RMS differences for LET_D metrics was 1.0 keV/μm for L_0.1cc to brainstem.

CONCLUSIONS

We have devised the first three-dimensional dose and LET_D -prediction model for cranial proton radiation therapy has been developed. Dose accuracy compared favorably with that of previously published models in other treatment sites. The agreement in LET_D supports future investigations with biological doses in mind to enable the full potential of KBP in proton therapy.

Treatment-planning approaches to intensity modulated proton therapy and the impact on dose-weighted linear energy transfer

PURPOSE

We quantified the effect of various forward-based treatment-planning strategies in proton therapy on dose-weighted linear energy transfer (LETd). By maintaining the dosimetric quality at a clinically acceptable level, we aimed to evaluate the differences in LETd among various treatment-planning approaches and their practicality in minimizing biologic uncertainties associated with LETd.

METHOD

Eight treatment-planning strategies that are achievable in commercial treatment-planning systems were applied on a cylindrical water phantom and four pediatric brain tumor cases. Each planning strategy was compared to either an opposed lateral plan (phantom study) or original clinical plan (patient study). Deviations in mean and maximum LETd from clinically acceptable dose distributions were compared.

RESULTS

In the phantom study, using a range shifter and altering the robust scenarios during optimization had the largest effect on the mean clinical target volume LETd, which was reduced from 4.5 to 3.9 keV/μm in both cases. Variations in the intersection angle between beams had the largest effect on LETd in a ring defined 3 to 5 mm outside the target. When beam intersection angles were reduced from opposed laterals (180°) to 120°, 90°, and 60°, corresponding maximum LETd increased from 7.9 to 8.9, 10.9, and 12.2 keV/μm, respectively. A clear trend in mean and maximum LETd variations in the clinical cases could not be established, though spatial distribution of LETd suggested a strong dependence on patient anatomy and treatment geometry.

CONCLUSION

Changes in LETd from treatment-plan setup follow intuitive trends in a controlled phantom experiment. Anatomical and other patient-specific considerations, however, can preclude generalizable strategies in clinical cases. For pediatric cranial radiation therapy, we recommend using opposed lateral treatment fields to treat midline targets.

Spot-scanning hadron arc (SHArc) therapy: A proof of concept using single and multi-ion strategies with helium, carbon, oxygen and neon ions

PURPOSE

To present particle arc therapy treatments using single and multi-ion therapy optimization strategies with helium (⁴ He), carbon (¹² C), oxygen (¹⁶ O) and neon (²⁰ Ne) ion beams.

METHODS AND MATERIALS

An optimization procedure and workflow were devised for spot-scanning hadron arc therapy (SHArc) treatment planning in the PRECISE (PaRticle thErapy using single and Combined Ion optimization StratEgies) treatment planning system (TPS). Physical and biological beam models were developed for helium, carbon, oxygen and neon ions via FLUKA MC simulation. SHArc treatments were optimized using both single ion (¹² C, ¹⁶ O, or ²⁰ Ne) and multi-ion therapy (¹⁶ O+⁴ He or ²⁰ Ne+⁴ He) applying variable relative biological effectiveness (RBE) modeling using a modified microdosimetric kinetic model (mMKM) with (α/β)_x values of 2Gy, 5Gy and 3.1Gy respectively, for glioblastoma, pancreatic adenocarcinoma, and prostate adenocarcinoma patient cases. Dose, effective dose, linear energy transfer (LET) and RBE were computed with the GPU-accelerated dose engine FRoG and dosimetric/biophysical attributes were evaluated in the context of conventional particle and photon-based therapies (e.g., volumetric modulated arc therapy [VMAT]).

RESULTS

All SHArc plans met the target optimization goals (3GyRBE) and demonstrated increased target conformity and substantially lower low-dose bath to surrounding normal tissues than VMAT. SHArc plans using a single ion species (¹² C, ¹⁶ O, or ²⁰ Ne) exhibited favorable LET distributions with the highest-LET components centralized in the target volume, with values ranging from ∼80-170keV/μm, ∼130-220keV/μm and ∼180-350keV/μm, for ¹² C, ¹⁶ O, or ²⁰ Ne, respectively, exceeding mean target LET of conventional particle therapy (¹² C:∼60, ¹⁶ O:∼78 ²⁰ Ne:∼100 keV/μm). Multi-ion therapy with SHArc delivery (SHArc_MIT ) provided a similar level of target LET enhancement as SHArc compared to conventional planning, however, with additional benefits of homogenous physical dose and RBE distributions.

CONCLUSION

Here, we demonstrate that arc delivery of light and heavy ion beams, using either a single ion species (¹² C, ¹⁶ O, or ²⁰ Ne) or combining two ions in a single fraction (¹⁶ O+⁴ He or ²⁰ Ne+⁴ He), affords enhanced physical and biological distributions (e.g., LET) compared with conventional delivery with photons or particle beams. SHArc marks the first single and multi-ion arc therapy treatment optimization approach using light and heavy ions. This article is protected by copyright. All rights reserved.

Biological Dose Optimization for Particle Arc Therapy using Helium and Carbon Ions

PURPOSE

To present biological dose optimization for particle arc therapy using helium and carbon ions.

METHODS

Treatment plan planning and optimization procedures were developed for spot-scanning hadron arc (SHArc) delivery using the RayStation TPS and a GPU-accelerated dose engine (^†TPS-XXX). The SHArc optimization algorithm is applicable for charged particle beams and determines angle-dependencies for spot/energy selection with three main initiatives: i) achieve standard clinical optimization goals and constraints for target and OARs, ii) target dose robustness and iii) increasing LET in the target volume. Three patient cases previously treated at the ^†INSTITUTION-XXX were selected for evaluation of conventional versus arc delivery for the two clinical particle beams (helium [⁴He] and carbon [¹²C] ions): glioblastoma, prostate-adenocarcinoma and skull-base chordoma. Biological dose and dose-averaged linear energy transfer (LET_d) distributions for SHArc were evaluated against conventional planning techniques (VMAT and IMPT_2F) applying the modified microdosimetric kinetic model (mMKM) for considering bio-effect with (α/β)_x=2Gy. Clinical viability and deliverability were assessed via evaluation of plan quality, robustness and irradiation time.

RESULTS

For all investigated patient cases, SHArc treatment optimizations met planning goals and constraints for target coverage and OARs, exhibiting acceptable target coverage and reduced normal tissue volumes with effective dose >10GyRBE compared to conventional 2F planning. For carbon ions, LET_d was increased in the target volume from ∼40-60keV/µm to ∼80-140keV/µm for SHArc compared to conventional treatments. Favorable LET_d distributions were possible with the SHArc approach, with maximum LET_d in CTV/GTV and potential reductions of high-LET regions in normal tissues and OARs. Compared to VMAT, SHArc affords substantial reductions in normal tissue dose (40-70%).

CONCLUSION

SHArc therapy offers potential treatment benefits such as increased normal tissue sparing from higher doses >10GyRBE, enhanced target LET_d, and potential reduction in high-LET components in OARs. Findings justify further development of robust SHArc treatment planning towards potential clinical translation.

How can we consider variable RBE and LETd prediction during clinical practice? A pediatric case report at the Normandy Proton Therapy Centre using an independent dose engine

Background

To develop an auxiliary GPU-accelerated proton therapy (PT) dose and LET_d engine for the IBA Proteus®ONE PT system. A pediatric low-grade glioma case study is reported using FRoG during clinical practice, highlighting potential treatment planning insights using variable RBE dose (D_vRBE) and LET_d as indicators for clinical decision making in PT.

Methods

The physics engine for FRoG has been modified for compatibility with Proteus®ONE PT centers. Subsequently, FRoG was installed and commissioned at NPTC. Dosimetric validation was performed against measurements and the clinical TPS, RayStation (RS-MC). A head patient cohort previously treated at NPTC was collected and FRoG forward calculations were compared against RS-MC for evaluation of 3D-Γ analysis and dose volume histogram (DVH) results. Currently, treatment design at NPTC is supported with fast variable RBE and LET_d calculation and is reported in a representative case for pediatric low-grade glioma.

Results

Simple dosimetric tests against measurements of iso-energy layers and spread-out Bragg Peaks in water verified accuracy of FRoG and RS-MC. Among the patient cohort, average 3D-Γ applying 2%/2 mm, 3%/1.5 mm and 5%/1 mm were > 97%. DVH metrics for targets and OARs between FRoG and RayStation were in good agreement, with ∆D_50,CTV and ∆D_2,OAR both ⪅1%. The pediatric case report demonstrated implications of different beam arrangements on D_vRBE and LET_d distributions. From initial planning in RayStation sharing identical optimization constraints, FRoG analysis led to plan selection of the most conservative approach, i.e., minimized D_vRBE,max and LET_d,max in OARs, to avoid optical system toxicity effects (i.e., vision loss).

Conclusion

An auxiliary dose calculation system was successfully integrated into the clinical workflow at a Proteus®ONE IBA facility, in excellent agreement with measurements and RS-MC. FRoG may lead to further insight on D_vRBE and LET_d implications to help clinical decision making, better understand unexpected toxicities and establish novel clinical procedures with metrics currently absent from the standard clinical TPS.

Towards harmonizing clinical linear energy transfer (LET) reporting in proton radiotherapy: a European multi-centric study

BACKGROUND

Clinical data suggest that the relative biological effectiveness (RBE) in proton therapy (PT) varies with linear energy transfer (LET). However, LET calculations are neither standardized nor available in clinical routine. Here, the status of LET calculations among European PT institutions and their comparability are assessed.

MATERIALS AND METHODS

Eight European PT institutions used suitable treatment planning systems with their center-specific beam model to create treatment plans in a water phantom covering different field arrangements and fulfilling commonly agreed dose objectives. They employed their locally established LET simulation environments and procedures to determine the corresponding LET distributions. Dose distributions D1.1 and DRBE assuming constant and variable RBE, respectively, and LET were compared among the institutions. Inter-center variability was assessed based on dose- and LET-volume-histogram parameters.

RESULTS

Treatment plans from six institutions fulfilled all clinical goals and were eligible for common analysis. D1.1 distributions in the target volume were comparable among PT institutions. However, corresponding LET values varied substantially between institutions for all field arrangements, primarily due to differences in LET averaging technique and considered secondary particle spectra. Consequently, DRBE using non-harmonized LET calculations increased inter-center dose variations substantially compared to D1.1 and significantly in mean dose to the target volume of perpendicular and opposing field arrangements (p < 0.05). Harmonizing LET reporting (dose-averaging, all protons, LET to water or to unit density tissue) reduced the inter-center variability in LET to the order of 10-15% within and outside the target volume for all beam arrangements. Consequentially, inter-institutional variability in DRBE decreased to that observed for D1.1.

CONCLUSION

Harmonizing the reported LET among PT centers is feasible and allows for consistent multi-centric analysis and reporting of tumor control and toxicity in view of a variable RBE. It may serve as basis for harmonized variable RBE dose prescription in PT.

Combined DNA Damage Repair Interference and Ion Beam Therapy: Development, Benchmark, and Clinical Implications of a Mechanistic Biological Model

PURPOSE

Our purpose was to develop a mechanistic model that describes and predicts radiation response after combined DNA damage repair interference (DDRi) and particle radiation therapy.

METHODS AND MATERIALS

The heterogeneous dose distributions of protons and ⁴He ions were implemented into the "UNIfied and VERSatile bio-response Engine" (UNIVERSE). Predictions for monoenergetic and mixed fields over clinically relevant dose and linear energy transfer range were compared with experimental in vitro survival data measured in this work as well as data available in the literature, including different cell lines and DDR interferences. Ultimately, UNIVERSE predictions were investigated in a patient plan.

RESULTS

UNIVERSE accurately predicts survival of cell lines with and without DDRi in clinical settings of ion beam therapy based only on 3 parameters derived from photon data. With increasing dose or linear energy transfer, the radiosensitizing effect of DDRi decreases, resulting in diminished relative biological effect of ion beam radiation for cells subjected to DDRi in comparison to cells that are not. Similar trends were observed in patient plan recalculations; however, this analysis also suggests that DDRi + particle radiation therapy may better preserve the therapeutic window in comparison to DDRi + photon radiation therapy.

CONCLUSIONS

The presented framework represents the first mechanistic model of combined DDRi and particle radiation therapy comprehensively benchmarked in clinically relevant scenarios and a step toward more personalized treatment. It reveals potential differences between DDRi + photon radiation therapy versus DDRi + particle radiation therapy, which have not been described so far. UNIVERSE could aid in appraising the clinical viability of combined administration of radiosensitizing drugs and charged particle therapy, as well as the identification of patients with known DDR deficiencies in the tumor who might benefit from therapy with light ions, freeing limited space at heavy ion therapy centers.

Spot-Scanning Hadron Arc (SHArc) Therapy: A Study With Light and Heavy Ions

PURPOSE

To evaluate the clinical potential of spot-scanning hadron arc (SHArc) therapy with a heavy-ion gantry.

METHODS AND MATERIALS

A series of in silico studies was conducted via treatment plan optimization in FRoG and the RayStation TPS to compare SHArc therapy against reference plans using conventional techniques with single, parallel-opposed, and 3-field configurations for 3 clinical particle beams (protons [p], helium [4He], and carbon [12C] ions). Tests were performed on water-equivalent cylindrical phantoms for simple targets and clinical-like scenarios with an organ-at-risk in proximity of the target. Effective dose and dose-averaged linear energy transfer (LETD) distributions for SHArc were evaluated against conventional planning techniques applying the modified microdosimetric kinetic model for considering bio-effect with (α/β)x = 2 Gy. A model for hypoxia-induced tumor radio-resistance was developed for particle therapy with dependence on oxygen concentration and particle species/energy (Zeff/β)2 to investigate the impact on effective dose.

RESULTS

SHArc plans exhibited similar target coverage with unique treatment attributes and distributions compared with conventional planning, with carbon ions demonstrating the greatest potential for tumor control and normal tissue sparing among the arc techniques. All SHArc plans exhibited a low-dose bath outside the target volume with a reduced maximum dose in normal tissues compared with single, parallel-opposed, and 3-field configuration plans. Moreover, favorable LETD distributions were made possible using the SHArc approach, with maximum LETD in the r = 5 mm tumor core (~8 keVμm-1, ~30 keVμm-1, and ~150 keVμm-1 for p, 4He, and 12C ions, respectively) and reductions of high-LET regions in normal tissues and organs-at-risk compared with static treatment beam delivery.

CONCLUSION

SHArc therapy offers potential treatment benefits such as increased normal tissue sparing. Without explicit consideration of oxygen concentration during treatment planning and optimization, SHArc-C may mitigate tumor hypoxia-induced loss of efficacy. Findings justify further development of robust SHArc treatment planning toward potential clinical translation.

A systematic review on the usage of averaged LET in radiation biology for particle therapy

Linear Energy Transfer (LET) is widely used to express the radiation quality of ion beams, when characterizing the biological effectiveness. However, averaged LET may be defined in multiple ways, and the chosen definition may impact the resulting reported value. We review averaged LET definitions found in the literature, and quantify which impact using these various definitions have for different reference setups. We recorded the averaged LET definitions used in 354 publications quantifying the relative biological effectiveness (RBE) of hadronic beams, and investigated how these various definitions impact the reported averaged LET using a Monte Carlo particle transport code. We find that the kind of averaged LET being applied is, generally, poorly defined. Some definitions of averaged LET may influence the reported averaged LET values up to an order of magnitude. For publications involving protons, most applied dose averaged LET when reporting RBE. The absence of what target medium is used and what secondary particles are included further contributes to an ill-defined averaged LET. We also found evidence of inconsistent usage of averaged LET definitions when deriving LET-based RBE models. To conclude, due to commonly ill-defined averaged LET and to the inherent problems of LET-based RBE models, averaged LET may only be used as a coarse indicator of radiation quality. We propose a more rigorous way of reporting LET values, and suggest that ideally the entire particle fluence spectra should be recorded and provided for future RBE studies, from which any type of averaged LET (or other quantities) may be inferred.

Rapid effective dose calculation for raster-scanning 4He ion therapy with the modified microdosimetric kinetic model (mMKM)

PURPOSE

To develop and verify effective dose (D_RBE) calculation in ⁴He ion beam therapy based on the modified microdosimetric kinetic model (mMKM) and evaluate the bio-sensitivity of mMKM-based plans to clinical parameters using a fast analytical dose engine.

METHODS

Mixed radiation field particle spectra (MRFS) databases have been generated with Monte-Carlo (MC) simulations for ⁴He-ion beams. Relative biological effectiveness (RBE) and D_RBE calculation using MRFS were established within a fast analytical engine. Spread-out Bragg-Peaks (SOBPs) in water were optimized for two dose levels and two tissue types with photon linear-quadratic model parameters α_ph, β_ph, and (α/β)_ph to verify MRFS-derived database implementation against computations with MC-generated mixed-field α and β databases. Bio-sensitivity of the SOBPs was investigated by varying absolute values of β_ph, while keeping (α/β)_ph constant. Additionally, dose, dose-averaged linear energy transfer, and bio-sensitivity were investigated for two patient cases.

RESULTS

Using MRFS-derived databases, dose differences ≲2% in the plateau and SOBP are observed compared to computations with MC-generated databases. Bio-sensitivity studies show larger deviations when altering the absolute β_ph value, with maximum D_50% changes of ~5%, with similar results for patient cases. Bio-sensitivity analysis indicates a greater impact on D_RBE varying (α/β)_ph than β_ph in mMKM.

CONCLUSIONS

The MRSF approach yielded negligible differences in the target and small differences in the plateau compared to MC-generated databases. The presented analyses provide guidance for proper implementation of RBE-weighted ⁴He ion dose prescription and planning with mMKM. The MRFS-D_RBE calculation approach using mMKM will be implemented in a clinical treatment planning system.

RBE for proton radiation therapy - a Nordic view in the international perspective

BACKGROUND

This paper presents an insight into the critical discussions and the current strategies of the Nordic countries for handling the variable proton relative biological effectiveness (RBE) as presented at The Nordic Collaborative Workshop for Particle Therapy that took place at the Skandion Clinic on 14th and 15th of November 2019.

MATERIAL AND METHODS

In the current clinical practice at the two proton centres in operation at the date, Skandion Clinic, and the Danish Centre for Particle Therapy, a constant proton RBE of 1.1 is applied. The potentially increased effectiveness at the end of the particle range is however considered at the stage of treatment planning at both places based on empirical observations and knowledge. More elaborated strategies to evaluate the plans and mitigate the problem are intensely investigated internationally as well at the two centres. They involve the calculation of the dose-averaged linear energy transfer (LET_d) values and the assessment of their distributions corroborated with the distribution of the dose and the location of the critical clinical structures.

RESULTS

Methods and tools for LET_d calculations are under different stages of development as well as models to account for the variation of the RBE with LET_d, dose per fraction, and type of tissue. The way they are currently used for evaluation and optimisation of the plans and their robustness are summarised. A critical but not exhaustive discussion of their potential future implementation in the clinical practice is also presented.

CONCLUSIONS

The need for collaboration between the clinical proton centres in establishing common platforms and perspectives for treatment planning evaluation and optimisation is highlighted as well as the need of close interaction with the research academic groups that could offer a complementary perspective and actively help developing methods and tools for clinical implementation of the more complex metrics for considering the variable effectiveness of the proton beams.