[Treatment with charged particles beams: hadrontherapy part I: physical basis and clinical experience of treatment with protons]

A Proteomic Study Suggests Stress Granules as New Potential Actors in Radiation-Induced Bystander Effects

Besides the direct effects of radiations, indirect effects are observed within the surrounding non-irradiated area; irradiated cells relay stress signals in this close proximity, inducing the so-called radiation-induced bystander effect. These signals received by neighboring unirradiated cells induce specific responses similar with those of direct irradiated cells. To understand the cellular response of bystander cells, we performed a 2D gel-based proteomic study of the chondrocytes receiving the conditioned medium of low-dose irradiated chondrosarcoma cells. The conditioned medium was directly analyzed by mass spectrometry in order to identify candidate bystander factors involved in the signal transmission. The proteomic analysis of the bystander chondrocytes highlighted 20 proteins spots that were significantly modified at low dose, implicating several cellular mechanisms, such as oxidative stress responses, cellular motility, and exosomes pathways. In addition, the secretomic analysis revealed that the abundance of 40 proteins in the conditioned medium of 0.1 Gy irradiated chondrosarcoma cells was significantly modified, as compared with the conditioned medium of non-irradiated cells. A large cluster of proteins involved in stress granules and several proteins involved in the cellular response to DNA damage stimuli were increased in the 0.1 Gy condition. Several of these candidates and cellular mechanisms were confirmed by functional analysis, such as 8-oxodG quantification, western blot, and wound-healing migration tests. Taken together, these results shed new lights on the complexity of the radiation-induced bystander effects and the large variety of the cellular and molecular mechanisms involved, including the identification of a new potential actor, namely the stress granules.

High LET Radiation Overcomes In Vitro Resistance to X-Rays of Chondrosarcoma Cell Lines

Chondrosarcomas are malignant tumors of the cartilage that are chemoresistant and radioresistant to X-rays. This restricts the treatment options essential to surgery. In this study, we investigated the sensitivity of chondrosarcoma to X-rays and C-ions in vitro. The sensitivity of 4 chondrosarcoma cell lines (SW1353, CH2879, OUMS27, and L835) was determined by clonogenic survival assays and cell cycle progression. In addition, biomarkers of DNA damage responses were analyzed in the SW1353 cell line. Chondrosarcoma cells showed a heterogeneous sensitivity toward irradiation. Chondrosarcoma cell lines were more sensitive to C-ions exposure compared to X-rays. Using D10 values, the relative biological effectiveness of C-ions was higher (relative biological effectiveness = 5.5) with cells resistant to X-rays (CH2879) and lower (relative biological effectiveness = 3.7) with sensitive cells (L835). C-ions induced more G2 phase blockage and micronuclei in SW1353 cells as compared to X-rays with the same doses. Persistent unrepaired DNA damage was also higher following C-ions irradiation. These results indicate that chondrosarcoma cell lines displayed a heterogeneous response to conventional radiation treatment; however, treatment with C-ions irradiation was more efficient in killing chondrosarcoma cells, compared to X-rays.

[Is proton beam therapy the future of radiotherapy? Part I: clinical aspects]

Proton beam therapy uses positively charged particles, protons, whose physical properties improve dose-distribution (Bragg peak characterized by a sharp distal and lateral penumbra) compared with conventional photon-based radiation therapy (X-ray). These ballistic advantages apply to the treatment of deep-sited tumours located close to critical structures and requiring high-dose levels. [60-250 MeV] proton-beam therapy is now widely accepted as the "gold standard" in specific indications in adults--ocular melanoma, chordoma and chondrosarcoma of the base of skull --and is regarded as a highly promising treatment modality in the treatment of paediatric malignancies (brain tumours, sarcomas…). This includes the relative sparing of surrounding normal organs from low and mid-doses that can cause deleterious side-effects such as radiation-induced secondary malignancies. Other clinical studies are currently testing proton beam in dose-escalation evaluations, in prostate, lung, hepatocellular cancers, etc. Clinical validation of these new indications appears necessary. To date, over 60,000 patients worldwide have received part or all of their radiation therapy program by proton beams, in approximately 30 treatment facilities.

[An original contention system for hadron therapy]

In hadron therapy centers that have only fixed horizontal beams (i.e. most carbon ions centers and protons centers of first generation), the angulations of the beam remain technically limited, especially for the treatment of children under general anaesthesia with posterior-oblique (40 degrees or so) beams in supine position. We have been developing recently an original positioning system allowing for treatment with posterior-oblique beams, either from right or left directions, by keeping the child in the adequate position.

Particle beam radiotherapy for head and neck tumors: radiobiological basis and clinical experience

BACKGROUND

Head and neck tumors are often located near critical organs, making it impossible to deliver a dose of conventional radiotherapy high enough to eradicate the disease. Our aim was to review the potential benefits and available clinical experience of particle beam therapy (hadrontherapy) in the treatment of these tumors.

METHODS

A review of the literature was carried out through a MEDLINE search (publications between 1980 and 2005).

RESULTS

A review of the available clinical data shows that particle beam therapy can offer several radiobiological and physical advantages over conventional photon radiotherapy: improved dose distribution permits dose escalation within the target and optimal sparing of normal tissue. Preclinical and clinical studies suggest that there may be benefits to using hadrontherapy for tumors characterized by poor radiosensitivity and critical location. At present, the most used hadrons are protons and, as yet on an experimental basis, carbon ions. It is now well accepted that there are certain indications for using proton therapy for skull base tumors (chordoma and chondrosarcoma), paranasal sinus carcinomas, selected nasopharyngeal tumors, and neutron/ion therapy for salivary gland carcinomas (in particular, adenoid cystic tumors). Its viability in other cases, such as locally advanced squamous cell carcinoma, melanoma, soft tissue sarcoma, and bone sarcoma, is still under investigation.

CONCLUSIONS

Hadrontherapy can be beneficial in the treatment of tumors characterized by poor radiosensitivity and critical location. Further clinical and radiobiological studies are warranted for improved selection of patient population.

Clinical complementarities between proton and carbon therapies

Protons are characterised by low LET, but compared with photons and electrons have an improved physical depth dose distribution. Some indications for protons, i.e., ocular melanoma, chordoma and chondrosarcoma of the base of skull or cervical spine, are now accepted by the radiation oncology community as the treatment of choice. Others are still under evaluation, e.g. meningioma, locally advanced nasopharynx tumours, paediatric tumours. Neutrons have the biological advantage of a high LET, but their distribution of dose is in most cases suboptimal. Despite this, there are radiobiological arguments leading to expect that neutrons might be of some benefit in patients with tumours that are resistant to photons, slowly growing or containing a high proportion of hypoxic cells. There is some clinical evidence or rationale for a potential high LET advantage for locally extensive (I think that the current (jargon) word is extended in English..) salivary gland tumours, locally extensive(extended) prostate carcinoma, slowly growing inoperable soft tissue sarcoma, adenocarcinoma, adenoid cystic carcinoma of the paranasal sinuses, melanoma and rectal carcinoma. Light ions combine the high LET advantage of neutrons and the improved physical depth dose distribution of protons. The opportunity offered by an optimised distribution of dose should open a new era for high-LET particles, especially in deeply situated x-ray resistant tumours, where the use of neutron beams was restricted by the low quality of their depth-dose profiles. Preliminary results are encouraging.