Current status of high linear energy transfer irradiation

Exposure to hyperbaric oxygen induces cell cycle perturbation in prostate cancer cells

Cell cycle synchronization of tumor cells by exposure to hyperbaric oxygenation (HBO) may increase the efficacy of chemotherapy or radiation by placing cells into a chemosensitive portion of the cycle. The purpose of the current study was to examine oxygen pressure-dependent relationships with respect to the cell cycle in prostate tumor cells in vitro. LNCaP cells were grown in an incubator at 21% O2 and then exposed to 100% oxygen at pressures up to 6 atmospheres (atm) for 1.5 h. Cells were then returned to the incubator and evaluated for DNA content by propidium iodide and new DNA synthesis with a pulse-chase experiment. Cell cycle effects were evaluated by flow cytometry. Exposure to HBO increased the percentage of cells synthesizing new DNA in a dose-dependent fashion: 0 atm, 44%; 6 atm, 65%. Cells that synthesize new DNA accumulate in G2/M as a function of partial pressure of oxygen. These results suggest that HBO induces cells to enter the cell cycle and accumulate in G2/M. Cell cycle synchronization and entry of senescent cells into the cell cycle suggest that HBO may be a useful adjuvant to chemotherapy or radiation in the treatment of prostate cancer. There are two potential mechanisms of action that may make HBO efficacious in the treatment of prostate cancer. HBO may potentiate cancer chemotherapeutic agents that cause damage to DNA during DNA synthesis or HBO may inhibit cell division causing accumulation in G2/M.

The response of quiescent cell populations in murine solid tumors to irradiation with fast neutrons

5-bromo-2'-deoxyuridine (BUdR) was injected into SCC VII tumor-bearing mice intraperitoneally to label all proliferating tumor cells. The mice were irradiated with fast neutrons or x-rays. Immediately, or 24 h after irradiation, the tumors were excised, minced and trypsinized. The tumor cell suspensions were incubated with cytochalasin-B (a cytokinesis blocker). The micronucleus frequency was determined using immunofluorescence staining to BUdR. The cells that were not labeled with BUdR could be regarded as the quiescent cells. The micronucleus frequency in total tumor cells was determined from the irradiated tumors that were not pretreated with BUdR. The difference in radiosensitivity between total and quiescent cells was markedly reduced with fast neutrons, especially at higher doses of radiation. Potentially lethal damage repair by total and quiescent cells was inhibited more strongly with neutrons than with x-rays. When using fast neutrons, the radiosensitivity of solid tumors depends on their heterogeneity less critically than for x-rays.

Development of fast neutron therapy worldwide. Radiobiological, clinical and technical aspects

Radiobiological data indicate that fast neutrons could bring a benefit in the treatment of some tumour types, and suggest mechanisms through which this benefit could be achieved. However, radiobiology also clearly indicates that there is a need for patient selection as well as for a high-physical selectivity. The main difficulty when interpreting the results of neutron therapy are the poor technical conditions in which the first treatments were applied. This explains why the value and the place of neutron therapy are not universally recognized, although more than 15,000 patients have been treated so far worldwide. There are, however, clinical indications of fast neutrons bringing a benefit for the following tumour sites: salivary glands, paranasal sinuses, soft tissue sarcomas, prostatic adenocarcinomas, palliative treatment of melanoma and rectum. These tumours represent about 10-15% of all patients currently referred to the radiation therapy departments.

Review of the clinical results of fast neutron therapy

The clinical results reported from the different neutron therapy centres are reviewed. Fast neutrons were shown to be useful in the treatment of locally extended inoperable salivary gland tumours (average local control rates 67% for neutrons compared to 28% for photons). For paranasal sinuses and some tumours of the head and neck area, especially extended tumours with large fixed lymph nodes, neutrons could also be of interest. By contrast, the results obtained for brain tumours were, in general, disappointing. Neutrons were shown to be beneficial in the treatment of well differentiated soft tissue sarcomas, as well as to bone- and chondrosarcomas. For locally extended prostatic adenocarcinoma, a RTOG randomized trial gave local control rates of 77% for mixed schedule compared to 31% for photons. Neutrons could be useful also for palliative treatment of melanomas. Further studies are needed in order to evaluate the benefit of fast neutrons for other localizations such as uterine cervix, bladder and rectum. It can be concluded that fast neutrons could be of interest for about 10% of the radiotherapy patients, but it is likely that the new high-energy hospital-based cyclotrons will further extend the indications of neutron therapy. However, patient selection remains one of the main problems and there is a need for development of individual predictive tests.

[Perioperative radiotherapy of bone and soft tissue tumors]

The goal of pre- and/or postoperative irradiation of soft tissue sarcoma combined with conservative surgery is to reduce the local failure rate comparable to that of radical surgery but with substantial less morbidity and loss of function; this is realized, so that local control and survival rates following combined therapy are comparable to those achieved by radical surgery alone. The high effect of fast neutrons is mentioned especially in large tumors. In osteosarcoma fast neutron therapy may give better chance for inactivation of tumor cells resistant against chemotherapy.

Neutron therapy for malignant tumours of the salivary glands. A report of the Edinburgh experience

A group of 28 patients with malignant tumours of the salivary glands have been treated by d(15) + Be neutron irradiation. Nineteen patients had inoperable cancers. Three had gross recurrent cancer and three had measurable residual cancer after surgery. Three patients were treated post-operatively for microscopic residual disease. Seven different histological types of tumour were included. Six out of 8 patients with adenoid cystic carcinomas have lasting local tumour control. 54.5% of the gross tumours were locally controlled. All three of those classified as microscopic residual disease have no evidence of local recurrence. 11/14 cancers given 16.0 Gy or more in 20 fractions in 4 weeks were controlled compared with only 1/8 given a lower dose. 12/19 cancers less than 10.0 cm maximum diameter were controlled. The radiation-related morbidity was similar to that observed after photon therapy.