It is essential for quality assurance to verify the safety of each individual patient's plan in radiation therapy. The tolerance level for independent verification of monitor unit calculations for non-IMRT clinical radiotherapy has been shown in the AAPM TG114. Thus, we investigated the precision of independent MU (dose) verification considering a wedge off-axis calculation and we conducted a study at twelve institutes for independent verification with the wedge off-axis calculation. The results obtained with the wedge off-axis calculation showed better agreement with the treatment planning system calculation results than those without the former calculation in a phantom study and in the patient retrospective study. The confidence limits with the wedge off-axis calculation were 2.2±3.4% and 2.0±4.3% for the plans with a physical wedge and a non-physical wedge in the patient study, respectively. However, the confidence limits were over 5% without the off-axis calculation. From our multi-institutional study, the results suggested that the tolerance level for the wedge off-axis plan would be 5% when considering the wedge off-axis calculation and the level was similar to that of the treatment planning system using other conventional irradiation techniques.

Purpose: A multi-institutional study was performed to identify the impact of different independent dose verification programs on independent dose verification software program.

Methods: Data for 1,543 treatment fields were collected in three institutions. RADCALC and Simple MU Analysis (Simple MU) using the Clarkson-based algorithm were used. RADCALC needs the input of radiological path length (RPL) from radiotherapy treatment planning systems (RTPSs) (Eclipse or Pinnacle³). The Simple MU computes the RPL using CT images independently from the RTPSs. Ion-chamber measurements were performed for commissioning the two programs and the RTPSs. Next, the results of the two programs were compared to the RTPSs obtained in the clinically-approved plans in all three institutions.

Results: The commissioning results showed ±1.5% variation in the ion-chamber measurements and there was slight difference between the institutions. The RADCALC (0.9±2.2%) and the Simple MU (1.7±2.1%) results showed a slight systematic difference. Pinnacle³ computed longer RPLs because it used CT-physical density tables. Thus, there was an impact on the accuracy in the treatment plans involving bone and other high-density materials.

Conclusion: Dose calculation algorithms in different dose verification programs provided similar results. However, care must be taken because different RPL calculation methods in the RTPSs may affect dose difference between different independent dose verification programs by 1%.

To foster medical physicists, we introduce the achievement we made since 2011 under the national research project of the Japan Society for the Promotion of Science (JSPS) Core-to-Core program; ‘Forming Research and Educational Hubs of Medical Physics.’ On this basis and under the JSPS program, we promoted research and educational exchange with Indiana University (IU) in USA, University of Groningen (The UG) in the Netherland and other cooperating institutions such as University of Minnesota (UM).

A total of 23 students and researchers were sent. UG accepted the most among three institutions. In turn, 12 foreign researchers including post-doctor fellows came to Japan for academic seminars or educational lectures.

Fifteen international seminars were held; 8 in Japan, 4 in USA, and 3 in the Netherland.

Lots of achievement were made through these activities in 5 years. Total of 23 research topics at the international conferences were presented. Total of 12 articles were published in international journals.

This program clearly promoted the establishment of international collaboration, and many young researchers and graduate students were exchanged and collaborated with foreign researchers.

High precision radiation therapy (HPRT) has been improved by utilizing conventional image engineering technologies. However, different frameworks are necessary for further improvement of HPRT. This review paper attempted to define the multidimensional image and what multidimensional image analysis is, which may be feasible for increasing the accuracy of HPRT. A number of researches in radiation therapy field have been introduced to understand the multidimensional image analysis. Multidimensional image analysis could greatly assist clinical staffs in radiation therapy planning, treatment, and prediction of treatment outcomes.

Polymer gel dosimeters are devices that utilize the radiation-induced polymerization reactions of vinyl monomers in a gel to store information of radiation dose. They have some advantages over other dosimeters as the visual conformation and the direct read-out of three-dimensional (3D) radiation dose information for the dosimetric verification of intensity modulated radiotherapy (IMRT), volumetric modulated arc therapy (VMAT), and stereotactic radiotherapy (SRT) with steep dose gradients. In this report, the dosimetric uncertainties and potential for clinical applications of polymer gel dosimetry by the in-house developed 3D dose verification system for IMRT and VMAT QA is outlined.

Current status of MR-Linac System was reported. First, we introduced the history of development about MR-Linac System. We discussed the advantage of MR-Linac for radiotherapy. Next, we explained the electron return effect caused by magnetic field, resulting in different dose distribution, compared to dose distribution with no magnetic field. Our explanation about MR-Linac will help for understanding this system.