Efficacy and feasibility of re-irradiation using carbon ions for pancreatic cancer that recurs after carbon-ion radiotherapy

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Carbon-ion re-irradiation for pancreatic cancer; feasibility and efficacy.

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Adjuvant chemotherapy improve local control of re-irradiation using carbon ions.

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Carbon-ion radiotherapy for recurrent pancreatic cancer; reasonable option.

Background and purpose

Patients who receive carbon-ion radiotherapy (C-ion RT) for primary pancreatic cancer may experience locoregional recurrence; however, the treatment options for such patients are limited. We aimed to investigate the feasibility and efficacy of carbon-ion re-irradiation for patients with pancreatic cancer who experienced recurrence after initial C-ion RT.

Materials and methods

Twenty-one patients with recurrent pancreatic cancer who underwent repeat C-ion RT between December 2010 and November 2016 at our institute were retrospectively evaluated. The sites of post-initial C-ion RT failure were in-field central in 16 patients (76.2%) and marginal in 5 (23.8%). The median doses of initial and repeat C-ion RT were both 52.8 Gy (relative biological effectiveness [RBE]). Thirteen patients (61.9%) received concurrent chemotherapy with re-irradiation, while 11 (52.4%) received adjuvant chemotherapy.

Results

The median follow-up period after re-irradiation was 11 months. The 1-year local control, progression-free survival, and overall survival rates were 53.5%, 24.5%, and 48.7%, respectively. Toxicity data was obtained from the patients’ charts. Only 1 patient (4.8%) developed grade 3 acute toxicities and none developed grade ≥3 late toxicities. Univariate analysis indicated that patients who received adjuvant chemotherapy had significantly improved local control rates compared with those who did not; the 1-year local control rates were 80.0% and 0.0%, respectively (P = 0.0469).

Conclusion

Repeating C-ion RT may be a reasonable option with tolerable toxicity for patients with recurrent pancreatic cancers. Adjuvant chemotherapy appears to improve the local control rate. This is the first study to examine re-irradiation using C-ion for recurrent pancreatic cancer after initial C-ion RT.

Proton beam therapy delivered using pencil beam scanning vs. passive scattering/uniform scanning for localized prostate cancer: Comparative toxicity analysis of PCG 001-09

Background and purpose

Patient-level benefits of proton beam therapy (PBT) relative to photon therapy for prostate cancer (PC) continue to be the focus of debate. Although trials comparing the two modalities are underway, most are being conducted using "conventional" PBT (passive scattering/uniform scanning [PS/US]) rather than pencil beam scanning (PBS). The dosimetric benefits of PBS are well-known, but comparative data are limited. This analysis compares PBS toxicity rates with those of PS/US in a prospective multicenter registry.

Methods

We evaluated acute/late gastrointestinal (GI) and genitourinary (GU) toxicity rates for men with low-to-intermediate risk PC enrolled in PCG 001-09. Acute toxicities with the two techniques were compared using χ² tests, and the cumulative incidence methods for late toxicity. Multivariable analyses (MVAs) for acute toxicity were performed using logistic regression, and cox proportional hazards models for late toxicity.

Results

Patients were treated using PS/US (n = 1105) or PBS (n = 238). Acute grade ≥2 GI toxicity in PBS did not significantly differ from that with PS/US (2.9% and 2.1%, respectively; P = 0.47). Acute grade ≥2 GU toxicity was significantly higher with PBS (21.9% and 15.1%; P < 0.01). In MVA, PBS was significantly associated with increased acute grade ≥2 GU toxicity (RR = 1.57, p < 0.001). Late grade ≥2 GI and GU toxicities did not differ significantly between groups.

Conclusions

This is the first multi-institutional comparative effectiveness evaluation of PBT techniques in PC. Differences in acute GU toxicity warrant further evaluation, and highlight the urgent need for prospective data using PBT.

In vitro sensitivity of malignant melanoma cells lines to photon and heavy ion radiation

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Superior proliferation inhibiting effects of heavy ions compared to photons.

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Increased G2/M arrest on heavy ion radiation compared to photon irradiation.

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Heavy ions might overcome radioresistance in malignant melanoma cells.

Background

The role of radiotherapy in malignant melanoma is still in discussion due to its relative resistance to radiation. In various literature, heavy ions show a higher relative biological effectiveness than photons. The aim of this work is to evaluate the radiotherapeutical effect from photons as well as heavy ions on malignant melanoma cells and to indicate the possible radiosensitivity based on its proliferation-inhibitory effect.

Methods

Two different cell lines of malignant melanoma, WM115 (primary tumor) and WM266-4 (metastatic site, skin) were used in this in vitro study. The cells were treated with photons or heavy ions (C₁₂ and O₁₆ ions). Cell-proliferation assay using hemocytometer was used for the quantitative and qualitative evaluation of cell growth. Furthermore, flow cytometry was also used to analyze the cell cycle distribution.

Results

Heavy ions compared to photons and between the two heavy ion modalities, O₁₆ ions showed an improved suppression of cell growth in both cell lines. Furthermore, a G2/M arrest was detected in both cell lines after all radiotherapy modalities – with the arrest increasing with the dose applied.

Conclusion

Heavy ions showed a greater inhibitory effect on cell proliferation compared to photons and an increased G2/M arrest. Therefore, C₁₂ and O₁₆ heavy ions might overcome the relative radioresistance of malignant melanoma to photons. Further research is warranted.

Determining RBE for development of lung fibrosis induced by fractionated irradiation with carbon ions utilizing fibrosis index and high-LET BED model

BACKGROUND AND PURPOSES

Carbon ion radiotherapy (CIRT) with raster scanning technology is a promising treatment for lung cancer and thoracic malignancies. Determining normal tissue tolerance of organs at risk is of utmost importance for the success of CIRT. Here we report the relative biological effectiveness (RBE) of CIRT as a function of dose and fractionation for development of pulmonary fibrosis using well established fibrosis index (FI) model.

MATERIALS AND METHODS

Dose series of fractionated clinical quality CIRT versus conventional photon irradiation to the whole thorax were compared in C57BL6 mice. Quantitative assessment of pulmonary fibrosis was performed by applying the FI to computed tomography (CT) data acquired 24-weeks post irradiation. RBE was calculated as the ratio of photon to CIRT dose required for the same level of FI. Further RBE predictions were performed using the derived equation from high-linear energy transfer biologically effective dose (high-LET BED) model.

RESULTS

The averaged lung fibrosis RBE of 5-fraction CIRT schedule was determined as 2.75 ± 0.55. The RBE estimate at the half maximum effective dose (RBE_ED50) was estimated at 2.82 for clinically relevant fractional sizes of 1-6 Gy. At the same dose range, an RBE value of 2.81 ± 0.40 was predicted by the high-LET BED model. The converted biologically effective dose (BED) of CIRT for induction of half maximum FI (BED_ED50) was identified to be 58.12 Gy_3.95. In accordance, an estimated RBE of 2.88 was obtained at the BED_ED50 level. The LQ model radiosensitivity parameters for 5-fraction was obtained as α_H = 0.3030 ± 0.0037 Gy^-1 and β_H = 0.0056 ± 0.0007 Gy^-2.

CONCLUSION

This is the first report of RBE estimation for CIRT with the endpoint of pulmonary fibrosis in-vivo. We proposed in present study a novel way to mathematically modeling RBE by integrating RBE_max and α/β_L based on conventional high-LET BED conception. This model well predicted RBE in the clinically relevant dose range but is sensitive to the uncertainties of α/β estimates from the reference photon irradiation (α/β_L). These findings will assist to eliminate current uncertainties in prediction of CIRT induced normal tissue complications and builds a solid foundation for development of more accurate in-vivo data driven RBE estimates.

DNA end resection is needed for the repair of complex lesions in G1-phase human cells

Repair of DNA double strand breaks (DSBs) is influenced by the chemical complexity of the lesion. Clustered lesions (complex DSBs) are generally considered more difficult to repair and responsible for early and late cellular effects after exposure to genotoxic agents. Resection is commonly used by the cells as part of the homologous recombination (HR) pathway in S- and G2-phase. In contrast, DNA resection in G1-phase may lead to an error-prone microhomology-mediated end joining. We induced DNA lesions with a wide range of complexity by irradiation of mammalian cells with X-rays or accelerated ions of different velocity and mass. We found replication protein A (RPA) foci indicating DSB resection both in S/G2- and G1-cells, and the fraction of resection-positive cells correlates with the severity of lesion complexity throughout the cell cycle. Besides RPA, Ataxia telangiectasia and Rad3-related (ATR) was recruited to complex DSBs both in S/G2- and G1-cells. Resection of complex DSBs is driven by meiotic recombination 11 homolog A (MRE11), CTBP-interacting protein (CtIP), and exonuclease 1 (EXO1) but seems not controlled by the Ku heterodimer or by phosphorylation of H2AX. Reduced resection capacity by CtIP depletion increased cell killing and the fraction of unrepaired DSBs after exposure to densely ionizing heavy ions, but not to X-rays. We conclude that in mammalian cells resection is essential for repair of complex DSBs in all phases of the cell-cycle and targeting this process sensitizes mammalian cells to cytotoxic agents inducing clustered breaks, such as in heavy-ion cancer therapy.

Concerted action of Nrf2-ARE pathway, MRN complex, HMGB1 and inflammatory cytokines - implication in modification of radiation damage

Whole body exposure to low linear energy transfer (LET) ionizing radiations (IRs) damages vital intracellular bio-molecules leading to multiple cellular and tissue injuries as well as pathophysiologies such as inflammation, immunosuppression etc. Nearly 70% of damage is caused indirectly by radiolysis of intracellular water leading to formation of reactive oxygen species (ROS) and free radicals and producing a state of oxidative stress. The damage is also caused by direct ionization of biomolecules. The type of radiation injuries is dependent on the absorbed radiation dose. Sub-lethal IR dose produces more of DNA base damages, whereas higher doses produce more DNA single strand break (SSBs), and double strand breaks (DSBs). The Nrf2-ARE pathway is an important oxidative stress regulating pathway. The DNA DSBs repair regulated by MRN complex, immunomodulation and inflammation regulated by HMGB1 and various types of cytokines are some of the key pathways which interact with each other in a complex manner and modify the radiation response. Because the majority of radiation damage is via oxidative stress, it is essential to gain in depth understanding of the mechanisms of Nrf2-ARE pathway and understand its interactions with MRN complex, HMGB1 and cytokines to increase our understanding on the radiation responses. Such information is of tremendous help in development of medical radiation countermeasures, radioprotective drugs and therapeutics. Till date no approved and safe countermeasure is available for human use. This study reviews the Nrf2-ARE pathway and its crosstalk with MRN-complex, HMGB1 and cytokines (TNF-a, IL-6, IFN-? etc.). An attempt is also made to review the modification of some of these pathways in presence of selected antioxidant radioprotective compounds or herbal extracts.

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Exposure to low linear energy transfer (LET) ionizing radiation (IR) causes intracellular oxidative stress and activate the Nrf2-ARE antioxidant pathway.

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Irradiation also causes inflammation and DNA damage which affect other pathways related to MRN complex and HMGB1 proteins.

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The antioxidant Keap1-Nrf2-ARE pathway most importantly regulates intracellular oxidative stress.

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The interaction of Keap1-Nrf2-ARE pathway with HMGB1 regulated inflammation; MRN complex regulated DNA repair is reviewed.