Intensity modulated neutron radiotherapy for the treatment of adenocarcinoma of the prostate

Fast and Furious: Fast Neutron Therapy in Cancer Treatment

Fast neutron therapy has been used for decades. In conjunction with recent advances in photonic techniques, fast neutrons are no longer of much oncologic interest, which is not unequivocally positive, given their undoubted therapeutic value. This mini-review recalls the history of medical research on fast neutrons, considers their physical and radiobiological properties alongside their benefits for cancer treatment, and discusses their place in modern radiation oncology.

Hadrontherapy techniques for breast cancer

Radiotherapy plays a key role in breast cancer treatment, and recent technical advances have been made to improve the therapeutic window by limiting the risk of radiation-induced toxicity or by increasing tumor control. Hadrontherapy is a form a radiotherapy relying on particle beams; compared with photon beams, particle beams have specific physical, radiobiological and immunological properties, which can be valuable in diverse clinical situations. To date, available hadrontherapy techniques for breast cancer irradiation include proton therapy, carbon ion radiation therapy, fast neutron therapy and boron neutron capture therapy. This review analyzes the current rationale and level of evidence for each hadrontherapy technique for breast cancer.

Comparisons of 3-Dimensional Conformal and Intensity-Modulated Neutron Therapy for Head and Neck Cancers

PURPOSE

Neutron therapy is a high linear energy transfer modality that is useful for the treatment of radioresistant head and neck (H&N) cancers. It has been limited to 3-dimensioanal conformal-based fast-neutron therapy (3DCNT), but recent technical advances have enabled the clinical implementation of intensity-modulated neutron therapy (IMNT). This study evaluated the comparative dosimetry of IMNT and 3DCNT plans for the treatment of H&N cancers.

MATERIALS AND METHODS

Seven H&N IMNT plans were retrospectively created for patients previously treated with 3DCNT at the University of Washington (Seattle). A custom RayStation model with neutron-specific scattering kernels was used for inverse planning. Organ-at-risk (OAR) objectives from the original 3DCNT plan were initially used and were then systematically reduced to investigate the feasibility of improving a therapeutic ratio, defined as the ratio of the mean tumor to OAR dose. The IMNT and 3DCNT plan quality was evaluated using the therapeutic ratio, isodose contours, and dose volume histograms.

RESULTS

When compared with the 3DCNT plans, IMNT reduces the OAR dose for the equivalent tumor coverage. Moreover, IMNT is most advantageous for OARs in close spatial proximity to the target. For the 7 patients with H&N cancers examined, the therapeutic ratio for IMNT increased by an average of 56% when compared with the 3DCNT. The maximum OAR dose was reduced by an average of 20.5% and 20.7% for the spinal cord and temporal lobe, respectively. The mean dose to the larynx decreased by an average of 80%.

CONCLUSION

The IMNT significantly decreases the OAR doses compared with 3DCNT and provides comparable tumor coverage. Improvements in the therapeutic ratio with IMNT are especially significant for dose-limiting OARs near tumor targets. Moreover, IMNT provides superior sparing of healthy tissues and creates significant new opportunities to improve the care of patients with H&N cancers treated with neutron therapy.

Dose escalation in prostate cancer using intensity modulated neutron radiotherapy

BACKGROUND AND PURPOSE

Initial promising results of 3D conformal neutron radiotherapy (3D-CNRT) were subsequently limited by high normal tissue toxicities. It is now possible to deliver intensity modulated neutron radiotherapy (IMNRT). The present work compares photon IMRT, 3D-CNRT and IMNRT for three prostate patients to quantify the benefits of IMNRT.

MATERIALS AND METHODS

We compare updated 3D-CNRT plans, IMNRT plans, and conventional IMRT plans by translating neutron DVHs into effective photon DVHs using the dose dependent radiobiological effectiveness (RBE) for each structure. RBE curves are parameterized for a range of normal tissue and prostate tumor values. Generalized equivalent uniform dose (gEUD) and gEUD in 2Gy fractions (gEUD(2)) is calculated for each structure, plan, and parameterization. Rectal sparing and dose to prostate-GTV are compared for 3D-CNRT, IMNRT, and IMRT as a function of normal tissue and prostate RBE.

RESULTS

The closer the RBE values of prostate tumor and normal tissue, the greater the advantage of IMNRT over 3D-CNRT. The rectal sparing achieved using IMNRT ranged from ∼5% to 13% depending upon the choice of RBE for rectum and the α/β value of prostate tumor. IMNRT may provide a theoretical dose advantage over photon IMRT if the α/β value of prostate is 1.5 and the RBEs of prostate and rectum differ by more than 5%. For higher values of prostate α/β any advantages of IMNRT over IMRT could require that the RBEs of prostate and rectum differ by as much as 20%.

CONCLUSIONS

IMNRT provides a clear normal tissue sparing advantage over 3D-CNRT. The advantage increases when the RBEs of the target structure and the normal tissue are similar. This RBE translation method could help identify clinical sites where the dose sparing advantages of IMNRT would allow for the exploitation of the radiobiological advantages of high-LET neutron radiotherapy.

Dose-dependent onset of regenerative program in neutron irradiated mouse skin

Background

Tissue response to irradiation is not easily recapitulated by cell culture studies. The objective of this investigation was to characterize, the transcriptional response and the onset of regenerative processes in mouse skin irradiated with different doses of fast neutrons.

Methodology/Principal Findings

To monitor general response to irradiation and individual animal to animal variation, we performed gene and protein expression analysis with both pooled and individual mouse samples. A high-throughput gene expression analysis, by DNA oligonucleotide microarray was done with three months old C57Bl/6 mice irradiated with 0.2 and 1 Gy of mono-energetic 14 MeV neutron compared to sham irradiated controls. The results on 440 irradiation modulated genes, partially validated by quantitative real time RT-PCR, showed a dose-dependent up-regulation of a sub-class of keratin and keratin associated proteins, and members of the S100 family of Ca²⁺-binding proteins. Immunohistochemistry confirmed mRNA expression data enabled mapping of protein expression. Interestingly, proteins up-regulated in thickening epidermis: keratin 6 and S100A8 showed the most significant up-regulation and the least mouse-to-mouse variation following 0.2 Gy irradiation, in a concerted effort toward skin tissue regeneration. Conversely, mice irradiated at 1 Gy showed most evidence of apoptosis (Caspase-3 and TUNEL staining) and most 8-oxo-G accumulation at 24 h post-irradiation. Moreover, no cell proliferation accompanied 1 Gy exposure as shown by Ki67 immunohistochemistry.

Conclusions/Significance

The dose-dependent differential gene expression at the tissue level following in vivo exposure to neutron radiation is reminiscent of the onset of re-epithelialization and wound healing and depends on the proportion of cells carrying multiple chromosomal lesions in the entire tissue. Thus, this study presents in vivo evidence of a skin regenerative program exerted independently from DNA repair-associated pathways.