Advances in medical devices have allowed the use of CT, MRI, and PET-CT for the diagnosis of tumors and the detailed evaluation of the extent of lesions. For several decades, CT has been established as the gold standard modality for the treatment planning of radiotherapy, while MRI has emerged as a tool to evaluate the functional characteristics of tumors without radiation exposure. To further optimize precision radiation therapy, we should consider how functional images can be used in the workflow for radiation therapy. In this regard, MRI, as a modality without the need for a contrast agent, may allow more frequent scans and more detailed dose painting, such as increasing the dose to viable lesion parts while reducing the dose to less aggressive parts. Thus, a more personalized treatment based on precision radiation medicine might be realized. In recent years, MR-Linac systems (MRI integrated linear accelerator radiation therapy systems) have been applied in clinical settings by fusing MRI with Linac planning, and further development of radiation therapy utilizing MRI-derived functional images is expected. The use of MR-Linac techniques allows the characteristics of the tumor to be evaluated in more detail before treatment, and the treatment planning can be modified according to the position and characteristics of the tumor (which may change daily during irradiation) to avoid harming normal tissue. Compared with conventional cone beam CT, MR-Linac can offer MR images with much better contrast of soft tissue for image-guided radiation therapy, even when acquired at 0.35 T. A multicenter study of liver tumors using MR-Linac was recently reported. In current tumor imaging, various MRI sequences can be used to evaluate tumor functional information such as tumor heterogeneity, cell density, microenvironment, angiogenesis, necrosis, hypoxic status, and microstructure. In this article, we introduce state-of-the-art acquisition methods for MRI imaging, and discuss how the functional information obtained from these imaging methods can be useful for radiation therapy.

PET and SPECT provide us with information about biological quantitative values at localized area, even at the deep component of human. They usually have been used for diagnosis, but when combining with radiotherapy, PET and SPECT images would be helpful to make a decision on radiation-dose distribution for treatment because the patient images can be obtained in the similar condition under radiation therapy. In addition, anti-tumor effect of radiation therapy is now precisely controlled for target. Therefore, precise information of tumor, such as extent of tumor and heterogeneity within tumor, would make the treatment more effective, while normal organ functions are preserved. What nuclear medicine can do for the ideal treatment is discussed in this section.

Hypoxia has been known to be a feature associated with tumor radioresistance. So far, clinical strategies to overcome chronic hypoxia due to the limitation of the oxygen diffusion have been designed. However, intermittent or acute/cycling hypoxia, whose frequency can range between a few cycles per minutes to hours, is receiving increased attention, because this type of hypoxia has been reported to have an influence on tumor malignancy as well as treatment resistance via increased expression of pro-survival pathways. Therefore, a priori information on fluctuating hypoxia can be important in clinical treatment planning, but complicated dynamics makes it difficult to elucidate biological significance of intermittent hypoxia.

Here, we illustrate the use of pulsed electron spin resonance imaging (ESRI) as a novel imaging method to directly monitor fluctuating oxygenation i.e. cycling hypoxia in transplanted tumors. A common resonator platform for both ESRI and magnetic resonance imaging (MRI) provided pO₂ maps with anatomical guidance without positional movement. Oxygen images every 3 min in pO₂ could visualize the rapid oxygen fluctuation and distinguish the cycling hypoxia and chronic hypoxia. Furthermore, we have examined the vascular renormalization process by longitudinally pO₂ mapping during treatments with a multi-tyrosine kinase inhibitor sunitinib. Transient improvement in tumor oxygenation and the decrease of cycling tumor hypoxia were visualized by ESRI 2 to 4 days following antiangiogenic treatments. Radiation treatment during this time period of improved oxygenation by antiangiogenic therapy resulted in a synergistic delay in tumor growth.

In conclusion, this ESRI technique combined with MRI, may offer a powerful clinical tool to noninvasively detect variable hypoxic status in tumors and to identify a window of vascular renormalization to maximize the effects of combination therapy with antiangiogenic drugs.

After the end of human genome project, the cost of genetic analysis has rapidly declined with the advancement of next-generation sequencers. In addition, the relationship between various diseases and genes has been clarified. Therefore, it is likely that genetic testing may be performed in daily clinical practice in the near future. In such background, a novel research ‘radiomics’ is spreading to offer a new viewpoint for the use of genotype in radiological field which has traditionally focused on the analysis of imaging phenotypes. Radiomics is applied to the molecular classification or treatment strategy. This paper explains what radiomics is and what kind of changes it would bring.

The biological effectiveness of charged-particle beams depends not only on dose but also on radiation quality. The radiation quality of charged-particle beams has been most commonly represented by the linear energy transfer (LET) in radiation biology studies. We investigated a new therapeutic technique of charged-particle therapy in which two or more ion species are delivered in one treatment session for optimizing the dose and LET distributions in a patient. We refer the therapeutic technique as an Intensity Modulated composite PArtiCle Therapy (IMPACT). Helium, carbon, oxygen and neon ions are considered as ion species for the IMPACT. To demonstrate the effectiveness of the IMPACT for simultaneous optimization of dose and LET distributions, an IMPACT plan was made for a prostate case. In accordance with the prescriptions, LETs in prostate, planning target volume (PTV), and rectum could be adjusted at 80 keV/μm, at 50 keV/μm, and below 30 keV/μm, respectively, while keeping the dose to the PTV at 2 Gy uniformly. The IMPACT enables the optimization of the dose and the LET distributions in a patient, which will maximize the potential of charged-particle therapy by expanding the therapeutic window.

In 2016, the American Association of Physicists in Medicine (AAPM) has published a report of task group (TG) 100 with a completely new concept, entitled “application of risk analysis methods to radiation therapy quality management.” TG-100 proposed implementation of risk analysis in radiotherapy to prevent harmful radiotherapy accidents. In addition, it enables us to conduct efficient and effective quality management in not only advanced radiotherapy such as intensity-modulated radiotherapy and image-guided radiotherapy but also new technology in radiotherapy. It should be noted that treatment process in modern radiotherapy is absolutely more complex and it needs skillful staff and adequate resources. TG-100 methodology could identify weakness in radiotherapy procedure through assessment of failure modes that could occur in overall treatment processes. All staff in radiotherapy have to explore quality management in radiotherapy safety.