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Section of Radiation Safety and Quality Assurance

Tetsuo Akimoto, Hidenobu Tachibana, Kenji Hotta, Hiromi Baba, Koichi Nemoto


Radiation therapy technologies have improved recently and will continue to progress. However, while advanced technology has provided higher accuracy and precision in radiotherapy, it has introduced more complex situations and difficulties in performing the treatment adequately. Radiotherapy errors can occur at several time points from planning through treatment. The accuracy and precision of dose delivery in radiation therapy is important because there is evidence that a 7-10% change in the dose to the target volume may result in a significant change in tumor control probability. “Quality assurance in radiotherapy” is for all procedures that ensure consistency of the medical prescription, and safe fulfillment of that prescription, as regards the dose to the target volume, together with the minimal dose to normal tissue, minimal exposure of personnel and adequate patient monitoring aimed at determining the end result of the treatment.

The primary aim of the Section of Radiation Safety and Quality Assurance is to develop quality assurance programs for photon and proton therapy machines as well as to check that quality requirements in photon and proton therapy products are met and to adjust and correct performance if the requirements are found not to have been met. The second aim is to install and establish advanced technologies in clinical practices in the radiation oncology department. Other goals are to develop high-precision radiotherapy as intensity modulated radiation therapy (IMRT), volumetric modulated arc therapy (VMAT), respiratory-gating radiation therapy, marker-tracking radiation therapy, image-guided radiation therapy (IGRT), stereotactic RT and proton beam therapy (PBT) in cancer treatment.

Routine activities

At present, the staff of the Section of Radiation Safety and Quality Assurance consists of one radiation oncologists, three medical physicists and one radiological technologist. We have more than 1,000 new patients for photon and proton therapy every year. The section is responsible for four linear accelerators, two CT simulators and four different treatment planning systems in photon/ electron therapy. In proton therapy, one accelerator, two treatment units, and one planning system are managed.

Quality assurance programs have been established for photon and proton therapy by the medical physicists. The daily, monthly and annual programs are performed by the medical physicists and radiological technologists. In addition, the medical physicists perform radiotherapy planning for IMRT/VMAT in prostate and head and neck sites, stereotactic RT in the liver and lungs, and proton therapy in the head and neck, esophagus, lung, liver, prostate and infants. The medical physicists support conventional radiotherapy planning and also check the quality and safety for all treatment plans.

Research activities

In the Radiation Safety and Quality Assurance Section, the following research activities are ongoing:

  1. Design and development of new proton beam irradiation system
  2. Design and development of monitor unit calculation for proton therapy
  3. Design and development of a Monte Carlobased dose calculation algorithm for proton therapy
  4. Design and development of a CT-based image guided and adaptive proton therapy system.
  5. Design and development of four-dimensional planning for motion synchronized dose delivery for photon therapy.
  6. Design and development of CT-pulmonary ventilation imaging
  7. Design and development of quality assurance system for gated radiotherapy
  8. Multi-institutional study of independent MU/ Dose verification for conventional, stereotactic RT, IMRT, VMAT as well as for Vero, CyberKnife and Tomotherapy in photon therapy

Clinical trials

The following multi-institutional clinical trials are ongoing:

  1. Establishment of safety for radiotherapy planning of photon therapy


We established an on-the job-training program for quality assurance programs for a photon linear accelerator and over 100 medical physicists and radiological technologists have taken the educational program. We held a meeting for independent MU/dose verification and over 180 medical physicists and radiological technologists participated in the meeting. We trained graduated students from Tsukuba University and Komazawa University for a quality assurance program in photon therapy

Future prospects

We maintain the quality of photon/electron and proton therapy machines and also establish new technologies to improve patient outcomes. In addition, we will work on radiotherapy as well as radiology including establishment of a quality assurance program for diagnostic instruments and management of radioactive materials.

List of papers published in 2015


  1. Kohno R, Yamaguchi H, Motegi K, Tanaka F, Akita T, Nagata Y, Hotta K, Miyagishi T, Nishioka S, Dohmae T, Akimoto T. Position verification of the RADPOS 4-D in-vivo dosimetry system. Int J Med Phys Clin Eng Radiat Oncol, 4:318-325, 2015
  2. Hotta K, Kohno R, Nagafuchi K, Yamaguchi H, Tansho R, Takada Y, Akimoto T. Evaluation of monitor unit calculation based on measurement and calculation with a simplified Monte Carlo method for passive beam delivery system in proton beam therapy. J Appl Clin Med Phys, 16:228-238, 2015