| (II) If a licensed medical physicist does not perform
the spot check measurements, the results of the spot check measurements
shall be reviewed by a licensed medical physicist with a specialty
in therapeutic radiological physics within 5 treatment days and a
record made of the review. If the output varies by more than 5.0%
from the expected value, a licensed medical physicist with a specialty
in therapeutic radiological physics shall be notified immediately.
(III) The written spot check procedures shall specify
the frequency that tests or measurements are to be performed and that
the spot check shall be performed during the calibration specified
in clause (ii) of this subparagraph. The acceptable tolerance for
each parameter measured when compared to the value for that parameter
determined in the calibration specified in clause (ii) of this subparagraph
shall be stated.
(IV) The written spot check procedures shall include
special operating instructions that shall be carried out whenever
a parameter in subclause (III) of this clause exceeds an acceptable
tolerance.
(V) Whenever a spot check indicates a significant change
in the operating characteristics of a system, as specified in the
procedures, the system shall be recalibrated, as required in clause
(ii) of this subparagraph.
(VI) Records of written spot checks and any necessary
corrective actions shall be maintained by the registrant in accordance
with subsection (l) of this section for inspection by the agency.
A copy of the most recent spot check shall be available at a designated
area within the therapy facility housing that therapeutic radiation
system.
(VII) Spot checks shall be obtained using a system
satisfying the requirements of clause (ii)(IV) of this subparagraph.
(3) Therapeutic radiation machines capable of operating
at energies of 1 MeV and above.
(A) Equipment requirements.
(i) For operating conditions producing maximum leakage
radiation, the absorbed dose in rads (mGy) due to leakage radiation,
including x rays, electrons, and neutrons, at any point in a circular
plane of 2 m radius centered on and perpendicular to the central axis
of the beam at the isocenter or normal treatment distance and outside
the maximum useful beam size shall not exceed 0.1% of the maximum
absorbed dose in rads (mGy) of the unattenuated useful beam measured
at the point of intersection of the central axis of the beam and the
plane surface. Measurements excluding those for neutrons shall be
averaged over an area up to, but not exceeding, 100 square centimeters
(cm2 ) at the positions specified. Measurements
of the portion of the leakage radiation dose contributed by neutrons
shall be averaged over an area up to, but not exceeding, 200 cm2 . For each system, the registrant shall determine
or obtain from the manufacturer the leakage radiation existing at
the positions specified for the specified operating conditions. Records
on leakage radiation measurements shall be maintained in accordance
with subsection (l) of this section for inspection by the agency.
(ii) Each wedge filter that is removable from the system
shall be clearly marked with an identification number. Documentation
available at the control panel shall contain a description of the
filter. The wedge angle shall appear on the wedge or wedge tray (if
permanently mounted to the tray). If the wedge tray is damaged, the
wedge transmission factor shall be redetermined. Equipment manufactured
after March 1, 1989, shall meet the following requirements.
(I) Irradiation shall not be possible until a selection
of a filter or a positive selection to use "no filter" has been made
at the treatment console, either manually or automatically.
(II) An interlock system shall be provided to prevent
irradiation if the filter selected is not in the correct position.
(III) A display shall be provided at the treatment
console showing the beam quality in use.
(IV) An interlock shall be provided to prevent irradiation
if any filter selection operation carried out in the treatment room
does not agree with the filter selection operation carried out at
the treatment console.
(iii) The registrant shall determine data sufficient
to assure that the following beam quality requirements in tissue equivalent
material are met.
(I) The absorbed dose resulting from x rays in a useful
electron beam at a point on the central axis of the beam 10 cm greater
than the practical range of the electrons shall not exceed the values
stated in the following Table II. Linear interpolation shall be used
for values not stated.
Attached Graphic
(II) Compliance with subclause (I) of this clause shall
be determined using:
(-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.
Cont'd... |
