| (IV) each filter is marked as to its material of construction
and its thickness. For wedge filters, the wedge angle shall appear
on the wedge or wedge tray.
(v) The tube housing assembly shall be capable of being
immobilized for stationary treatments.
(vi) The tube housing assembly shall be so marked that
it is possible to determine the location of the focal spot to within
5 millimeters (mm), and such marking shall be readily accessible for
use during calibration procedures.
(vii) Contact therapy tube housing assemblies shall
have a removable shield of at least 0.5 mm lead equivalency at 100
kVp that can be positioned over the entire useful beam exit port during
periods when the beam is not in use.
(viii) The timer shall:
(I) have a display provided at the treatment control
panel and a pre-set time selector;
(II) activate with the production of radiation and
retain its reading after irradiation is interrupted. After irradiation
is terminated and before irradiation can be reinitiated, it shall
be necessary to reset the elapsed time indicator to zero;
(III) terminate irradiation when a pre-selected time
has elapsed, if any dose monitoring system present has not previously
terminated irradiation;
(IV) permit selection of exposure times as short as
one second;
(V) not permit an exposure if set at zero;
(VI) not activate until the shutter is opened when
irradiation is controlled by a shutter mechanism unless calibration
includes a timer factor to compensate for mechanical lag; and
(VII) be accurate to within 1.0% of the selected value
or 1 second, whichever is greater.
(ix) The control panel, in addition to the displays
required in clause (viii)(I) of this subparagraph, shall have the
following:
(I) an indication of whether electrical power is available
at the control panel and if activation of the x-ray tube is possible;
(II) an indication of whether x rays are being produced;
(III) means for indicating x-ray tube potential and
current;
(IV) means for terminating an exposure at any time;
(V) a locking device that will prevent unauthorized
use of the therapeutic radiation system (a computerized pass-word
system would also constitute a locking device);
(VI) for therapeutic radiation systems manufactured
after March 1, 1989, a positive display of specific filters in the
beam; and
(VII) emergency buttons/switches that shall be clearly
labeled as to their functions.
(x) There shall be means of determining initially the
SSD to within 1 cm and of reproducing this measurement to within 2
mm thereafter.
(xi) Unless it is possible to bring the radiation output
to the prescribed exposure parameters within 5 seconds, the beam shall
be attenuated by a shutter having a lead equivalency not less than
that of the tube housing assembly. After the unit is at operating
parameters, the shutter shall be controlled electrically by the operator
from the control panel. An indication of shutter position shall appear
at the control panel.
(xii) Each therapeutic radiation system equipped with
a beryllium or other low-filtration window shall be clearly labeled
as such upon the tube housing assembly and at the control panel.
(B) Facility requirements for therapeutic radiation
systems capable of operating above 50 kVp.
(i) Provision shall be made for two-way aural communication
between the patient and the operator at the control panel.
(ii) Windows, mirrors, closed-circuit television, or
an equivalent system shall be provided to permit continuous observation
of the patient during irradiation and shall be so located that the
operator can observe the patient from the control panel.
(I) Should the viewing system described in clause (ii)
of this subparagraph fail or be inoperative, treatment shall not be
performed with the unit until the system is restored.
(II) In a facility that has a primary viewing system
by electronic means and an alternate viewing system, should both viewing
systems described in clause (ii) of this subparagraph fail or be inoperative,
treatment shall not be performed with the unit until one of the systems
is restored.
(C) Additional facility requirements for therapeutic
radiation systems capable of operation above 150 kVp.
(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. All protective barriers shall
be fixed except for entrance doors or beam interceptors.
(ii) The control panel shall be located outside the
treatment room or in an enclosed booth inside the room.
(iii) Interlocks shall be provided such that all entrance
doors shall be closed, including doors to any interior booths, before
treatment can be initiated or continued. If the radiation beam is
interrupted by any door opening, it shall not be possible to restore
the machine to operation without closing the door and reinitiating
irradiation by manual action at the control panel. When any door is
opened while the x-ray tube is activated, the exposure at a distance
of 1 m from the source shall be reduced to less than 100 mR/hr (1
mGy/hr).
(D) Surveys, calibrations, and spot checks.
(i) Surveys shall be performed as follows.
(I) All new and existing facilities not previously
surveyed shall have an initial survey made by a licensed medical physicist
with a specialty in therapeutic radiological physics, who shall provide
a written report of the survey to the registrant. Additional surveys
shall be done after any change in the facility, facility design, or
equipment that might cause a significant increase in radiation hazard.
(II) The registrant shall maintain a copy of the initial
survey report and all subsequent survey reports required by subclause
(I) of this clause in accordance with subsection (l) of this section
for inspection by the agency.
(III) The survey report shall indicate all instances
where the installation is in violation of applicable requirements
of this chapter.
(ii) Calibrations shall be performed as follows.
(I) The calibration of a therapeutic radiation system
shall be performed at intervals not to exceed 1 year and after any
change or replacement of components that could cause a change in the
radiation output. The calibrations shall be such that the dose at
a reference point in a water or plastic phantom can be calculated
to within an uncertainty of 5.0%.
(II) The calibration of the radiation output of the
therapeutic radiation system shall be performed by a licensed medical
physicist with a specialty in therapeutic radiological physics who
is physically present at the facility during such calibration.
(III) The calibration of the therapeutic radiation
system shall include, but not be limited to, the following determinations:
(-a-) verification that the radiation therapy system
is operating in compliance with the design specifications;
(-b-) HVL for each kV setting and filter combination
used;
(-c-) the exposure rates (air kerma rates) as a function
of field size, technique factors, filter, and treatment distance used;
and
(-d-) the degree of congruence between the radiation
field and the field indicated by the localizing device, if such device
is present, which shall be within 5 mm for any field edge.
(IV) Calibration of the radiation output of a therapeutic
radiation system shall be performed with a calibrated dosimetry system.
The dosimetry system calibration shall be traceable to a national
standard. The calibration interval shall not exceed 24 months.
(V) Records of calibration measurements specified in
clause (ii) of this subparagraph shall be maintained by the registrant
in accordance with subsection (l) of this section for inspection by
the agency.
(VI) A copy of the latest calibrated absorbed dose
rate measured on a particular therapeutic radiation system shall be
available at a designated area within the therapy facility housing
that therapeutic radiation system.
(iii) Spot checks shall be performed on therapeutic
radiation systems capable of operation at greater than 150 kVp. Such
measurements shall meet the following requirements.
(I) The spot check procedures shall be in writing,
or documented in an electronic reporting system, and shall have been
developed by a licensed medical physicist with a specialty in therapeutic
radiological physics.
Cont'd... |
