Guidance on Evaluation of Accelerator Neutron Irradiation Device System for Boron
Neutron Capture Therapy (Draft)
1. Introduction
Boron neutron capture therapy (BNCT) is radiation therapy that is based on the nuclear capture
reaction that occurs when the 10B compound is irradiated with thermal neutrons to yield alpha particles
and lithium nuclei to selectively destroy the cancer cells.
The track ranges of the two emitted particles within the body are extremely short at approximately 10µm, and this distance is not greater than the diameter of the cancer cell. The emitted particles thus destroy
only the nuclei of the cancer cells and do not reach normal cells, even those immediately adjacent to thecancer cells. The two particles used for therapeutic effect are heavy ions, and hence, have a potent
cytotoxic effect on cancer cells. Therefore, in principle, damage is suppressed to normal cells, which do
not uptake boron, while selectively destroying the cancer cells. BNCT is expected to have significant
therapeutic effects against invasive cancers with unclear margins, such as malignant brain tumors andcancers resistant to radiation therapy. In addition, because there is limited radiation effect from theneutron beam on normal tissue, it can also be used as an indicator of for recurrent cancer afterconventional radiation therapy.
Japan is the world leader in the field of BNCT. Since the world’s first BNCT accelerator began
operating in the country in 2010, BNCT has been rapidly transforming from clinical studies using
research reactors, and now faces a significant turning point. An accelerator –based BNCT phase I clinicalstudy on brain tumors and cancer of the head and neck has been completed, and research is progressing tophase II clinical studies. It is important to set signposts for evaluation to contribute to expedited approval
review to enable the delivery of this cutting-edge therapeutic equipment to patients as soon as possible.
The major point of difference between BNCT, conventional radiotherapy and particle beam therapy is theuse of boron agents and neutron beams. A variety of technologies are also available to generate neutron
beams, including research reactors, and accelerators using nuclear reactions. Therefore, during the clinicalapplication of BNCT, it will be necessary to extract characteristics that differ from those of conventionalradiation therapy and evaluate this technology based on a consideration of the associated technologicalissues and limitations.
Considering the above background, this working group investigated the research and development,
usage trends, and standards related to BNCT accelerator neutron irradiation device and treatment planningdevice both in Japan and overseas, and created a draft guidance to enable appropriate and expedited
evaluation of the efficacy, safety, and quality of this therapy on scientific grounds.

2. Scope
The targets of this guidance are compact accelerator-based neutron sources for BNCT and thetreatment planning device used in combination with the applicable device.

3. Role of This GuidanceThis guidance has presented items considered important at present, based on the consideration that it
pertains to the development of important device. The guidance will be revised based on futuretechnological innovations and amassed knowledge and does not have binding force over the content ofapproval applications. The flexible application of this guidance is essential when evaluating products
subject to it. The evaluation must reflect full understanding of the characteristics of the given product andbe based on reasonable scientific basis. Referencing other, related guidelines both in Japan and overseas
should also be considered in addition to using this guidance. It is also necessary to comply with thevarious laws related to radiation safety (Atomic Energy Basic Act, Act on Prevention of Radiation
Hazards, Industrial Safety and Health Act, etc.).

4. Points to Consider in Evaluation(1) Basic items
1) Clearly show the developmental background, development product specifications,development product and usage status of similar products in Japan and overseas, theequipment design and system principles (including algorithms), standard usage methods, etc.
2) Stipulate and evaluate evaluation items required for overall system installation and operation,referencing the following items:(i) Software (including OS: operating system and algorithms)(ii) Installation conditions(a) Weight (load-bearing conditions required for the floor where equipment is used)(b) Dimensions (including when housed)(c) Anti-tip measures(iii) Target material(a) Physical and chemical safety of the target material and methods of handling(b) Deterioration due to charged particle irradiation and neutron generation of the target
material (blistering, etc.), safety measures for damaged material (measures for dust andevaporation of the material, etc.) and replacement frequency(c) Procedures for replacement of target material(iv) Noise and vibration(v) Maintenance inspections and details thereof(vi) Measures for activation of apparatus and incidental equipment(a) Maintenance methods for activated equipment (Hands on, use of specialized jigs)(b) Replacement frequency of activated parts and replacement method(c) Safe waste disposal methods(vii) Necessity of training plans and details thereof(viii) Documentation of user operating manuals, etc., and details thereof(ix) Methods for patient monitoring during irradiation(x) Troubleshooting protocols (measures for dealing with sudden changes in patients andremoval of patients from the apparatus, radiation problems, leakage of coolant into thetarget vacuum box, measures for power outages, and measures for emergency stop)(xi) Software life science process (See: JIS T 2304)(xii) Risk management (See: ISO 14971)
It is essential to examine measures based on the worst-case scenario, where thisexamination is not limited to equipment risks, but also includes accidents during treatment.
Refer to the appendix for other main points to note regarding the targets of this evaluationindex.

3) Equivalence of final product and testing apparatus
When nonclinical and clinical studies are implemented using the test equipment, evaluate
equivalence with the final product.

(2) Nonclinical studies

These include the conduct-appropriate evaluation of the safety and efficacy of the system as awhole, and of the safety and efficacy of the neutron irradiation field through the bench tests andbiological studies shown below. When necessary, the performance and quality of the patient
irradiation system, the radiation measurement monitor in the treatment room and the treatment
planning device that comprise the treatment system are also evaluated according to related
guidelines and industry standards.
1) Safety evaluation of accelerator neutron irradiation device(i) Electrical safety (See: JIS T 0601-1)(ii) Electromagnetic compatibility (See: JIS T 0601-2)(iii) Radiation safety (See: JIS T 0601-2-64)(iv) Mechanical safety (See: JIS T 0601-1)(a) Alarm(b) Interlock(c) Emergency stop mechanism(d) Excess irradiation prevention mechanism(e) Incorrect operation prevention mechanism(f) Other necessary mechanisms(v) Biological safety (See: JIS T 0993-1)(vi) Safety for exposure by leakage radiation besides the beam port
Because high intensity neutron beam is generated and used for treatment, there is apossibility that radiation (neutron beams, gamma rays and residual gamma rays) leak fromthe equipment or the walls outside the beam port. Whenever possible, therefore, take noteof the following matters, with reference to JIS T0601-2-64:(a) Ascertain the characteristics of the leaking radiation (type of radiation, dose rate, etc.).
Assume an operational history of approximately 10 years for the residual gamma rays.
(b) Ensure that the disadvantage to the patient through exposure outside the treatment area
is sufficiently smaller than the advantages of treatment.
(vii) Safety for exposure of medical staffs (including equipment maintenance worker) to residual
radiation due to activated equipment (See: Act on Prevention of Radiation Hazards)
Residual radiation may be emitted from the accelerator and the neutron irradiation device
with the activated components even when the accelerator is stopped and neutron beams are
not generated. Thus, the following points must be noted:(a) Ascertain the characteristics of the residual radiation (dose rate, spatial distribution,and temporal change). Assume an operational history of approximately 10 years.
(b) Ensure that the exposure of medical staffs is sufficiently small compared with the limit
value stipulated by law (conduct appropriate exposure management).
(viii) Safety for exposure of worker from the activated components such as target during
maintenance and inspection of the therapeutic device.
Ensure that the equipment is designed so that the exposure of radiation worker involved in
the operation and maintenance management of the equipment is sufficiently small
compared with the limit value stipulated by law.
2) Performance evaluation of accelerator neutron irradiation equipment(i) Stability, reproducibility, and feasible and continuous operating time of the energy andcurrent of the charged particle beam generated and accelerated in the accelerator

(ii) Operational stability of charged particle beam charge monitor(iii) Soundness of target material (cooling system, temperature monitoring, etc.)(a) Safety measures should be adopted to prevent adverse reactions caused byunanticipated excessive beam irradiating to the target material.
(b) Measures should be adopted to prevent blistering.
(c) Safety measures should be adopted in consideration of such events as when the coolingof the target material stops, or when there is leakage of the coolant (including on thevacuum side).
(d) Safety measures should be adopted for events such as the leakage of the target material
when using a liquid target material like liquid lithium.
(iv) Stability and reproducibility of characteristics of the neutron beam emitted from the beam
port(v) Stability and reproducibility of characteristics of the gamma ray mixed in the neutron beam(vi) Feasibility of irradiation
Output the results implemented according to the irradiation schedule.
(vii) Safety and reproducibility of the methods for observing and controlling the neutron beamand mixed gamma rays during irradiation(a) When directly measuring the generated neutron beam and mixed gamma rays in realtime
• reliability and stability of measurement monitor(b) When indirectly observing or controlling the generated neutron beam based on charged
particle output (current value)• uniformity of characteristics of the neutron beam generated relative to the current of
the charged particle• methods for ascertaining soundness of target material• method for estimating the characteristics of the neutron beam generated during
treatment when there is a large change in the characteristics of the beam relative to thecurrent of the incident charged particle, and neutron flux may change compared withthat immediately before treatment(viii) Size of irradiation field of neutron beam, treatable depth, and irradiation time
Present the equipment’s performance such as the treatable range and depth, neutron flux,
mixed gamma ray rate, and the targeted irradiation time for each irradiation case. The dose
distribution and irradiation time for each case is determined by the physical characteristicsof the beam generated by the equipment and can change depending on the boron
concentration in each tissue. When presenting these performance values, also show theboron concentration value used for calculation, the relative biological effectiveness (RBE)value, and the compound biological effectiveness (CBE) value.
(ix) Change in position of patient and focus during treatment
If the position of the patient and the focus change during neutron beam irradiation, there
may be fluctuation in the dose delivered to the patient. In principle, thus, the position of thepatient must not be changed.
When the position of the patient and the focus are allowed to change during irradiation,
monitor the position of the patient and the focus, and demonstrate that it is possible tocontrol the irradiation by considering the effect of such elements as the change in dose
caused by the change. In addition, demonstrate the stability and reliability of the monitor
measuring positional changes of the patient and the focus.

(x) The method of calculation used to evaluate the dose of the neutron beam and the dose
effect in human body
When using calculation methods for dose evaluation related to the neutron beam and in
human body based on the Monte Carlo method, present the calculation method (calculation
code, nuclear data used for transport calculations, dose conversion factor, etc.).
3) Safety and performance evaluation of treatment planning device
Unlike conventional radiation treatment, BNCT uses continuous energy (white) neutrons, andthe dose from mixed gamma rays and secondary gamma rays generated by the reaction of the
body tissue and neutrons must be evaluated. The factor (RBE value) to convert from theabsorbed dose to gray-equivalent (Gy-Eq) dose changes depending upon the kind of tissue andorgan, and also on neutron energy. Basically, Monte Carlo method is used for dose evaluationof BNCT, furthermore a display function is also necessary to show the dose distribution to thetumor and normal tissue. BNCT is also characterized by the use of boron drug and thetreatment is completed with a single irradiation. It is also necessary to consider settings of thepatient’s irradiation position, possibility of respiratory movement, and changes in irradiation
conditions during irradiation, and the activation of the patient and building.
Evaluate the treatment planning device by considering these matters that are unique to BNCT,
as well as taking note of the following: When the device has functions other than calculating
the dose in human body, clearly state the principles used to achieve these functions and theperformance.
(i)

Purpose of use, principles, etc.
(a) Purpose of use(b) Principles, algorithms(c) Function, performance(d) Usability(ii) Performance evaluation(a) Contour creation function• Able to perform region-splitting process by thresholding CT (computed
tomography) values.
• Setting function for region of interest, such as the focus site, and organ, where dose
evaluation is performed using CT imaging etc.
(b) Geometric parameter display function• Superimposed display function for radiation irradiation angle and range on 3D
patient models and medical imaging• Display to use for position matching at the time of irradiation (beam’s eye view,
digitally reconstructed radiograph (DRR), etc.)(c) Dose distribution computation function/dose distribution display function• Able to calculate dose distribution of the range of irradiation using geometricparameters relating to irradiation, using irradiation equipment used for treatment.
The calculated items include neutron flux, photon flux, absorption dose generated
by the reaction between the neutrons and 10B, absorption dose generated by thereaction between neutrons and elements comprising the body tissue (hydrogen,nitrogen, etc.), and the gamma ray absorption dose.
(d) Evaluation of dose-computing algorithm• The results of dose calculation are within the range of the design standard value
when tested based on methods stipulated by the manufacturer during development.
(e) Dose distribution analysis function• Able to display the equivalent dose and 3D distribution based on the calculated
physical dose (each absorption dose).
• Able to conduct general statistical processing, including the maximum dose,
minimum dose, mean dose, and deviation of the dose delivered to the focus andeach region of interest.
• Able to display the dose volume histogram (DVH) for the focus and each region ofinterest.
• Able to compare the dose distribution delivered to the focus and the normal tissue
against the same medical imaging slice.
(f) Irradiation dose parameter calculation/setting function• Calculate or set the irradiation time or neutron fluence and generate the charged
amount of charged particles to deliver the prescribed dose.
(g) Radiation treatment parameter optimization function• Find the combination of geometric parameters (position of incident beam, angle,
irradiation range, etc.) to ensure that dose distribution to surrounding importantorgans can be reduced while delivering as high a dose as possible to the focus,
considering the set focus and the surrounding organ.
(h) Re-planning function• Assist in the creation of new radiation treatment plans by calling up the contours
and parameters of already created radiation treatment plans on different medical
images.
(iii) Safety evaluation(a) Distance and length dimensions(b) Radiation dose(c) Date and time format(d) Preventing use by unauthorized personnel(e) Data limiting value(f) Protection from unauthorized changes(g) Accuracy of data transmission(h) Coordinate system and scale(i) Temporary storage and archiving of data(j) Soundness• Confirm that the calculated dose value is within an acceptable range of accuracy forthe computing time assumed for clinical use and the simulated system.
• Ensure that the region of interest (ROI) and dose distribution display match thecoordinates of the Digital Imaging and Communications in Medicine (DICOM)
images.
• Linkage with external computing software and nuclear data library
Confirm reproducibility when dose distribution calculations are outsourced.
Confirm versions of computing software and nuclear data library to be externallyoutsourced.

4) Biological effectConfirm that biological effect is expressed through neutron beam irradiation after exposure to
BNCT boron drugs in BNCT tests. Reports on this testing system have been published inliterature on the in vitro cytotoxicity effect and in vivo tumor proliferation suppression effect.
Therefore, construct the system by referencing these cases. In addition, evaluate the biologicaleffect (adverse events) of irradiation using neutrons alone.
5) Animal studies
Animal studies are to be appropriately evaluated, taking note of the following items:

Animal studies(a) Extrapolability of animal species to humans (anatomical and biological characteristics,
sensitivity to radiation, etc.)(b) Consideration comparing the procedures on animals with those in clinical practice, andextrapolability to humans(ii) Study protocol(a) Endpoint, evaluation criteria, evaluation method, evaluation period, and evaluator(b) Measurement data (physiological, mechanical and electrical data, radiation intensity,etc.)(c) Setting number of cases(iii) Points to note for evaluation(a) Treatment achievement status (gross pathological observation of the treated area andhistopathological evaluation, etc.)(b) Treatment status (level of achievement of treatment targets)(c) Extent and frequency of adverse events on the body(d) Equipment defects relating to items confirmed in animal studies(e) Differences between results obtained in animal studies and simulations(i)(3) Clinical studies
The concepts of setting the target sample size in clinical studies, endpoints to assess the efficacy ofthe obtained results, and the evaluation of adverse events may be implemented by referencing
clinical studies on conventional radiation therapy device, in line with each disease and irradiationsite. However, it is also necessary to conduct separate evaluations of adverse events caused by the
concurrent use of boron agents, as an item specific to BNCT.
In BNCT, the cytotoxic effect on tumor cells and adverse effects on normal tissue derive from theirradiation effect of two heavy particles with track ranges of 10 µm or less. It is necessary to
formulate treatment plans based on a scientific examination of nonclinical results from theperspective of efficacy and safety assurance in humans. Specifically, it is essential to evaluate thetumor size reduction (response) effect and the effects to the normal tissues would be affected by
the microscopic distribution of the boron agent on these tissues.
Conduct appropriate evaluation of clinical studies on BNCT by referencing the following:
1) Treatment protocol
Specifically, this can be created in the same manner as clinical trial / study protocols forconventional radiation or medical therapy. However, set efficacy and safety endpoints thatconsider concepts and processes specific to BNCT.

If the treatment planning system has functions other than in vivo dose calculations, and if theefficacy of these functions cannot be properly evaluated with nonclinical studies alone,
provide an explanation on the propriety of implementing the clinical study.
(1) Indicated diseases/sites
Explain the theoretical background for being able to anticipate that the effect is notinferior to or surpasses that of conventional treatment methods and explain the results ofprevious clinical studies that have applied BNCT to the respective diseases/sites as
grounds for setting the indicated diseases/sites.
(2) Setting endpoints
Set appropriate endpoints (survival rate, tumor response rate, palliative effect, etc.)
depending on the indicated diseases/sites based on the results of boron agent distribution
in the tumor verified in nonclinical studies. Set appropriate endpoints for adverse effects
on normal tissues based on the microscopic distribution of the boron agent in normal
tissue and the intra/extravascular distribution ratio verified in nonclinical studies.
(3) Grounds for setting the method of boron agent administration, irradiation timing, andneutron fluence during irradiation
Determine the method of boron agent administration and timing of irradiation based ondata on the cytotoxic effect and adverse effects on normal tissue due to the microscopic
distribution of the boron agent in the tumor and normal tissue, and the intra-/extracellularand intra-/extravascular distribution ratios in nonclinical studies. In addition, explain the
grounds for setting these items.
The neutron fluence irradiated to the patient is expected to differ depending on the boron
agent, target disease, and irradiation site. Thus, scientifically explain the grounds forsetting the parameters (boron concentration value and tolerable dose for normal tissue)
based on the results of nonclinical studies (RBE and CBE values) and the findings ofconventional radiation treatment.
(4) Treatment plan
The above evaluation items should be appropriately reflected in the treatment plan.

2) Accuracy of irradiation of neutron beam
(1) Evaluation of irradiation accuracy
The irradiation neutrons are more significantly affected by changes in patients position(example: slope of the neck) during irradiation compared with X-rays and particle beams.
Therefore, describe the method for evaluating differences in the irradiation position on thetreatment plan and at the start of treatment (set-up error). And also, describe the method
for evaluating changes in irradiation positions during irradiation (intra-fractional error)
because an irradiation session lasts approximately 30 minutes to one hour.
(2) Verification of irradiation neutron fluence
It is preferable to describe methods for evaluating safety based on previous nonclinicalstudies and clinical studies, as well as the grounds for determining the prescribed dose fornormal tissue or the tumor for the neutron fluence irradiated to the patient.

3) Defect (See: 4. (1) 2) (xii) Risk Management)
Evaluate the details, frequency, and seriousness of the defects. Explain the safety measures
adopted for defects.

Appendix

Concept of risk management– Reference information –Matters relating to risk management are as follows, based on current technological limitations andconstraints:(1) Measurement of neutron beams and gamma rays(a) When directly measuring neutron beams and gamma rays: Regularly calibrate the value displayedon the measuring equipment and reduce risk by confirming that the measurements have been
conducted accurately.
(b) When not directly evaluating measurement of neutron beams and gamma rays: Check thecorrelation between the output (current value) of the charged particles and the generated neutron
flux, and indirectly monitor and control the generated neutron beam. In this method, the risk is
reduced by performing the irradiation to confirm the correlation between the generated neutron
flux and the output of charged particles, and performing measurement experiments to confirm thesoundness of the target material before and after irradiation. This method can also be applied forthe direct measurement of neutron flux described in (a), thus further reducing the risks of thedirect measurement method.
(2) Evaluating measurement of the dose applied to the patient
There is a possibility that the risk can be further reduced by setting and irradiating an
integrated/nonpower-based radiation detector such as activated foil and thermoluminescent dosimeters(TLD) around the radiation field of the patient. However, the measurement values of these methods
can change depending on such conditions as the measurement position and may be associated withsignificant errors. Thus, it must be understood that these data should be used only as an auxiliary
method and not be applied for absolute dose control.
(3) Soundness of target material
When it is difficult to directly confirm the conditions of the target material during treatment, indirect
monitoring is performed as much as possible by combining information, such as the temperature of
the cooling water of the target material and the extent of vacuum in the accelerating tube. In addition,risk is reduced by setting an interlock that can stop irradiation immediately when an anomaly isdetected.
(4) Leaked radiation outside the beam port
The results of measurement evaluations using gold foil and TLD have been reported in clinicalresearch on reactors1). No serious effects have been generated by leaked radiation in the results ofclinical studies to date2~5).
(5) Exposure by residual gamma rays after the irradiation by activation of the device
Manage and reduce the exposure dose by limiting the time to enter the irradiation room, taking a
distance from the beam port, combining equipment that remotely removes the patient from the beamport, etc.
(a) For the patient, the dose delivered during irradiation is quite higher, and the dose delivered byresidual gamma rays after irradiation is negligible.
(b) Manage the exposure dose for medical staffs such as doctors according to facility management
based on the related laws and regulations.
(6) Exit criteria
Examine the activation of patient as needed, referencing guidelines from related societies.

(7) Changes in patient position during irradiation
Basically, measures will be taken to suppress the movement of the patient as much as possible using afixing shell. Install a monitor that enables the sequential monitoring of the condition of the patient
during irradiation. Adopt measures that enable immediately stop irradiation when the patient’s
position changes significantly relative to the irradiation condition.
(8) Dynamics of boron during irradiation
Control the dose using a boron concentration estimation method that is as accurate as possible. A post
evaluation of boron concentration and neutron fluence during irradiation will be performed to confirm
the final given dose.

References
1.

Kinashi Y, et al., “Evaluation of micronucleus induction in lymphocytes of patients following BoronNeutron-Capture-Therapy: A comparison with thyroid cancer patients treated with radioinodine”, J.
Radiat. Res., 48, 197-204, 2007

2.

Fukuda H, et al., “Boron neutron capture therapy (BNCT) for malignant melanoma with specialreference to adsorbed doses to the normal skin and tumor”, Australas. Phys. Eng. Sci. Med., 26, 78-84,
2003

3.

Kankaanranta L, et al., “Boron neutron capture therapy in the treatment of locally recurred head andneck cancer”, Int. J. Radiat. Oncol. Biol. Phys., 69, 475-482, 2007

4.

Suzuki M, et al., “Boron neutron capture therapy outcomes for advanced or recurrent head and neckcancer”, J. Radiat. Res., 55, 146-153, 2013

5.

Yong Z, et al., “Boron neutron capture therapy for malignant melanoma: first clinical report in China”,
Chin. J. Cancer Res., 28, 634-640, 2016