| (vi) Selection and display of dose monitor units shall
meet the following requirements.
(I) Irradiation shall not be possible until a selection
of a number of dose monitor units has been made at the treatment console.
(II) The preselected number of dose monitor units shall
be displayed at the treatment console until reset manually for the
next irradiation.
(III) After termination of irradiation, it shall be
necessary to reset the dosimeter display to zero before subsequent
treatment can be initiated.
(IV) For equipment manufactured after March 1, 1989,
after termination of irradiation, it shall be necessary to manually
reset the preselected dose monitor units before irradiation can be
initiated.
(vii) Termination of irradiation by the dose monitoring
system or systems during stationary beam therapy shall meet the following
requirements.
(I) Each primary system shall terminate irradiation
when the preselected number of dose monitor units has been detected
by the system.
(II) If original design of the equipment includes a
secondary dose monitoring system, that system shall be capable of
terminating irradiation when not more than 15% or 40 dose monitor
units, whichever is smaller, above the preselected number of dose
monitor units set at the console has been detected by the secondary
dose monitoring system.
(III) For equipment manufactured after March 1, 1989,
a secondary dose monitoring system shall be present. That system shall
be capable of terminating irradiation when not more than 10% or 25
dose monitoring units, whichever is smaller, above the preselected
number of dose monitor units set at the console has been detected
by the secondary dose monitoring system.
(IV) For equipment manufactured after March 1, 1989,
an indicator on the console shall show which dose monitoring system
has terminated irradiation.
(viii) A locking device shall be provided in the system
to prevent unauthorized use of the x-ray system. A computerized password
system would also constitute a locking device.
(ix) It shall be possible to interrupt irradiation
and equipment movements at any time from the operator's position at
the treatment console. Following an interruption, it shall be possible
to restart irradiation by operator action without any reselection
of operating conditions. If any change is made of a preselected value
during an interruption, irradiation and equipment movements shall
be automatically terminated.
(x) It shall be possible to terminate irradiation and
equipment movements or go from an interruption condition to termination
conditions at any time from the operator's position at the treatment
console.
(xi) Timers shall meet the following requirements.
(I) A timer that has a display shall be provided at
the treatment console. The timer shall have a preset time selector
and an elapsed time indicator.
(II) The timer shall be a cumulative timer that activates
with the production of radiation and retains its reading after irradiation
is interrupted or terminated. After irradiation is terminated and
before irradiation can be reinitiated, it shall be necessary to reset
the elapsed time indicator to zero.
(III) For equipment manufactured after March 1, 1989,
after termination of irradiation and before irradiation can be reinitiated,
it shall be necessary to manually reset the preset time selector.
(IV) The timer shall terminate irradiation when a preselected
time has elapsed if the dose monitoring systems have not previously
terminated irradiation.
(xii) Equipment capable of producing more than 1 radiation
type shall meet the following additional requirements.
(I) Irradiation shall not be possible until a selection
of radiation type has been made at the treatment console.
(II) An interlock system shall be provided to:
(-a-) ensure that the equipment can emit only the radiation
type that has been selected;
(-b-) prevent irradiation if any selected operations
carried out in the treatment room do not agree with the selected operations
carried out at the treatment console;
(-c-) prevent irradiation with x-rays except to obtain
a port film when electron applicators are fitted; and
(-d-) prevent irradiation with electrons when accessories
specific for x-ray therapy are fitted.
(III) The radiation type selected shall be displayed
at the treatment console before and during irradiation.
(xiii) Equipment capable of generating radiation beams
of different energies shall meet the following requirements.
(I) Irradiation shall not be possible until a selection
of energy has been made at the treatment console.
(II) An interlock system shall be provided to prevent
irradiation if any selected operations carried out in the treatment
room do not agree with the selected operations carried out at the
treatment console.
(III) The nominal energy value selected shall be displayed
at the treatment console before and during irradiation.
(xiv) Equipment capable of both stationary beam therapy
and moving beam therapy shall meet the following requirements.
(I) Irradiation shall not be possible until a selection
of stationary beam therapy or moving beam therapy has been made at
the treatment console.
(II) An interlock system shall be provided to prevent
irradiation if any selected operations carried out in the treatment
room do not agree with the selected operations carried out at the
treatment console.
(III) The selection of stationary or moving beam shall
be displayed at the treatment console. An interlock system shall be
provided to ensure that the equipment can only operate in the mode
that has been selected.
(IV) For equipment manufactured after March 1, 1989,
an interlock system shall be provided to terminate irradiation if
movement of the gantry occurs during stationary beam therapy or stops
during moving beam therapy unless such stoppage is a preplanned function.
(V) Moving beam therapy shall be controlled to obtain
the selected relationships between incremental dose monitor units
and incremental angle of movement.
(-a-) For equipment manufactured after March 1, 1989,
an interlock system shall be provided to terminate irradiation if
the number of dose monitor units delivered in any 10 degrees of arc
differs by more than 20% from the selected value.
(-b-) For equipment manufactured after March 1, 1989,
where gantry angle terminates the irradiation in arc therapy, the
dose monitor units shall differ by less than 5.0% from the value calculated
from the absorbed dose per unit angle relationship.
(VI) Where the dose monitor system terminates the irradiation
in moving beam therapy, the termination of irradiation shall be as
required by clause (vii) of this subparagraph.
(xv) For equipment manufactured after March 1, 1989,
a system shall be provided from whose readings the absorbed dose rate
at a reference point in the treatment volume can be calculated. The
radiation detectors specified in subparagraph (iv) of this paragraph
may form part of this system. In addition, the dose monitor unit rate
shall be displayed at the treatment console. If the equipment can
deliver under any conditions an absorbed dose rate at the normal treatment
distance more than twice the maximum value specified by the manufacturer
for any machine parameters utilized, a device shall be provided that
terminates irradiation when the absorbed dose rate exceeds a value
twice the specified maximum. The dose rate at which the irradiation
will be terminated shall be in a record maintained by the registrant
in accordance with subsection (l) of this section for agency inspection.
(xvi) The registrant shall determine, or obtain from
the manufacturer, the location with reference to an accessible point
on the radiation head of the x-ray target or the virtual source of
x-rays and the electron window or the virtual source of electrons
if the system has electron beam capabilities.
(xvii) Capabilities shall be provided so that all radiation
safety interlocks can be checked for correct operation.
(B) Facility and shielding requirements.
(i) Each installation shall be provided with primary
and/or secondary barriers as are necessary to assure compliance with
§289.231(m) and (o) of this title.
(ii) All protective barriers shall be fixed except
for entrance doors or beam interceptors.
(iii) The console shall be located outside the treatment
room and all emergency buttons/switches shall be clearly labeled as
to their functions.
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