| (-a-) a measurement within a tissue equivalent phantom
with the incident surface of the phantom at the normal treatment distance
and normal to the central axis of the beam;
(-b-) a field size of 10 cm by 10 cm; and
(-c-) a phantom whose cross-sectional dimensions exceed
the measurement radiation field by at least 5 cm and whose depth is
sufficient to perform the required measurement.
(III) The absorbed dose at a surface located at the
normal treatment distance, at the point of intersection of that surface
with the central axis of the useful beam during x-ray irradiation,
shall not exceed the limits stated in the following Table III. Linear
interpolation shall be used for values not stated.
Attached Graphic
(IV) Compliance with subclause (III) of this clause
shall be determined by measurements made as follows:
(-a-) within a tissue equivalent phantom using an instrument
that will allow extrapolation to the surface absorbed dose;
(-b-) using a phantom whose size and placement meet
the requirements of subclause (II) of this clause;
(-c-) after removal of all beam modifying devices that
can be removed without the use of tools, except for beam scattering
or beam-flattening filters; and
(-d-) using the largest field size available that does
not exceed 15 cm by 15 cm.
(iv) All therapeutic radiation systems shall be provided
with radiation detectors in the radiation head. These shall include
the following, as appropriate.
(I) Equipment manufactured after March 1, 1989, shall
be provided with at least 2 independent radiation detectors. The detectors
shall be incorporated into 2 independent dose monitoring systems.
(II) Equipment manufactured on or before March 1, 1989,
shall be provided with at least 1 radiation detector. This detector
shall be incorporated into a primary dose monitoring system.
(III) The detector and the system into which that detector
is incorporated shall meet the following requirements.
(-a-) Each detector shall be removable only with tools
and shall be interlocked to prevent incorrect positioning.
(-b-) Each detector shall form part of a dose monitoring
system from whose readings in dose monitor units the absorbed dose
at a reference point in the treatment volume can be calculated.
(-c-) Each dose monitoring system shall be capable
of independently monitoring, interrupting, and terminating irradiation.
(-d-) For equipment manufactured after March 1, 1989,
the design of the dose monitoring systems shall assure that the malfunctioning
of 1 system shall not affect the correct functioning of the secondary
system; and failure of any element common to both systems that could
affect the correct function of both systems shall terminate irradiation.
(-e-) Each dose monitoring system shall have a legible
display at the treatment console. For equipment manufactured after
March 1, 1989, each display shall:
(-1-) maintain a reading until intentionally reset
to zero;
(-2-) have only one scale and no scale multiplying
factors;
(-3-) utilize a design such that increasing dose is
displayed by increasing numbers and shall be so designed that, in
the event of an overdosage of radiation, the absorbed dose may be
accurately determined; and
(-4-) retain the dose monitoring information in at
least one system for a 15-minute period of time in the event of a
power failure.
(v) In equipment manufactured after March 1, 1989,
inherently capable of producing useful beams with unintentional asymmetry
exceeding 5.0%, the asymmetry of the radiation beam in two orthogonal
directions shall be monitored before the beam passes through the beam-limiting
device. If the difference in dose rate between one region and another
region symmetrically displaced from the central axis of the beam exceeds
5.0% of the central axis dose rate, indication of this condition shall
be at the console; and if this difference exceeds 10% of the central
axis dose rate, the irradiation shall be terminated.
(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.
Cont'd... |
