Chapter DHS 157

DHS 157.85(1)(b) (b) Leakage radiation from contact therapy systems may not exceed one mGy (103 mR) per hour at 5 centimeters from the surface of the tube housing assembly. Contact therapy tube housing assemblies shall have a removable shield of material, equivalent in attenuation to 0.5 millimeters of lead at 100 kV, which may be positioned over the entire useful beam exit port during periods when the beam is not in use.

DHS 157.85(1)(c) (c) Leakage radiation from systems operating at 150 kV or less may not exceed one mGy (103 mR) per hour at one meter from the tube housing.

DHS 157.85(1)(d) (d) Leakage radiation from systems operating above 150 kV may not exceed 0.1% of the useful beam one meter from the source housing for any of its operating conditions.

DHS 157.85(2) (2) Permanent beam-limiting devices. Permanent, non-adjustable collimators used for limiting the useful beam shall provide at least the same degree of attenuation as required for the tube housing assembly.

DHS 157.85(3) (3) Adjustable or removable beam-limiting devices.

DHS 157.85(3)(a) (a) All removable beam-limiting devices or diaphragms may not transmit more than one percent of the useful beam for the most penetrating beam used. This paragraph does not apply to beam shaping blocks or shaping materials.

DHS 157.85(3)(b) (b) When adjustable beam-limiting devices are used, the position and shape of the useful beam shall be indicated by a light beam. These devices may transmit not more than 5% of the useful beam.

DHS 157.85(4) (4) Filter systems. The filter system shall be designed to meet all of the following requirements:

DHS 157.85(4)(a) (a) Accidental displacement of filters is not possible at any tube orientation.

DHS 157.85(4)(b) (b) If the proper filter is not in place, an interlock system shall prevent irradiation.

DHS 157.85(4)(c) (c) The air kerma rate escaping from the filter placement opening slot in the tube head may not exceed 100 mGy (one rad) per hour at one meter under any operating conditions.

DHS 157.85(4)(d) (d) Each filter shall be marked as to its material of construction and its thickness.

DHS 157.85(4)(e) (e) Each wedge filter that is removable from the system shall be clearly marked with an identification number. For removable wedge filters, the nominal wedge angle shall appear on the wedge or wedge tray. If the wedge or wedge tray is significantly damaged, the wedge transmission factor shall be reestablished.

DHS 157.85(4)(f) (f) If the absorbed dose rate information relates exclusively to operation with a field flattening filter or beam scattering foil in place, that foil or filter shall be removable only by the use of tools.

DHS 157.85(5) (5) Tube immobilization.

DHS 157.85(5)(a) (a) An x-ray tube shall be mounted so that it cannot accidentally turn or slide with respect to the opening in the tube housing through which radiation is emitted.

DHS 157.85(5)(b) (b) The tube housing assembly shall be capable of being immobilized.

DHS 157.85(6) (6) Emergency switches. At least one emergency power cutoff switch shall be present. If more than one emergency power cutoff switch is installed and not all switches are tested at once, each switch shall be tested on a rotating basis. Safety quality control checks of the emergency power cutoff switches may be conducted at the end of the treatment day to minimize possible stability problems with the therapeutic radiation machine.

DHS 157.85(7) (7) Source marking. An x-ray tube housing assembly shall be marked so that it is possible to determine the location of the focal spot to within 5 millimeters and the marking shall be readily accessible for use during calibration procedures.

DHS 157.85(8) (8) Timer.

DHS 157.85(8)(a) (a) A suitable irradiation control device shall be provided to terminate the irradiation after a preset time interval or after a preset radiation dose has been delivered.

DHS 157.85(8)(b) (b) A timer with a display shall be provided at the treatment control panel. The timer shall have a pre-set time selector and an elapsed time or time remaining indicator.

DHS 157.85(8)(c) (c) A timer shall be a cumulative timer that activates with an indication of “BEAM-ON” and retains its reading after irradiation is interrupted or terminated. After irradiation is terminated and before irradiation may be reinitiated, it shall be necessary to reset the elapsed time indicator.

DHS 157.85(8)(d) (d) A timer shall terminate irradiation when a pre-selected time has elapsed, if any dose monitoring system present has not previously terminated irradiation.

DHS 157.85(8)(e) (e) A timer may not permit an exposure if set at zero.

DHS 157.85(8)(f) (f) A timer may not activate until the shutter is opened when irradiation is controlled by a shutter mechanism unless calibration includes a timer end effect correction to compensate for mechanical lag.

DHS 157.85(8)(g) (g) A timer shall be accurate to within one percent of the selected value or one second, whichever is greater.

DHS 157.85(9) (9) Control panel indicators. An x-ray unit shall have all of the following:

DHS 157.85(9)(a) (a) An indication at the control panel of whether electrical power is on and if activation of the x-ray tube is possible.

DHS 157.85(9)(b) (b) An indication of whether x-rays are being produced.

DHS 157.85(9)(c) (c) A means for indicating x-ray tube potential and current.

DHS 157.85(9)(d) (d) A means for terminating an exposure at any time.

DHS 157.85(9)(e) (e) A locking device that will prevent unauthorized use of the therapeutic radiation machine.

DHS 157.85(10) (10) Target to skin distance. There shall be a means of determining the central axis target to skin distance to within 2 millimeters and of reproducing this measurement to within 2 millimeters thereafter.

DHS 157.85(11) (11) Shutters. Unless it is possible to bring the x-ray tube output to the prescribed exposure parameters within 5 seconds after the x-ray “ON” switch is energized, the beam shall be attenuated by a shutter having a shielding equivalency not less than that of the tube housing assembly. In addition, after the unit is at operating parameters, the shutter shall be controlled by the operator from the control panel. An indication of shutter position shall appear at the control panel.

DHS 157.85(12) (12) Low filtration machines. Each therapeutic radiation machine equipped with a beryllium or other low filtration window shall be clearly labeled on the tube housing assembly and shall be provided with a permanent warning device on the control panel that is activated when no additional filtration is present, to indicate that the dose rate is very high.

DHS 157.85(13) (13) Full calibration measurements.

DHS 157.85(13)(a) (a) Full calibration of a therapeutic radiation machine shall be performed by or under the direct supervision of a medical physicist under all of the following conditions:

DHS 157.85(13)(a)1. 1. Before the first medical use following installation or reinstallation of the therapeutic radiation machine.

DHS 157.85(13)(a)2. 2. At intervals not exceeding 12 months.

DHS 157.85(13)(a)3. 3. Before medical use under all of the following conditions:

DHS 157.85(13)(a)3.a. a. Whenever quality control check measurements indicate that the radiation output differs by more than 5% from the value obtained at the last full calibration and the difference cannot be reconciled.

DHS 157.85(13)(a)3.b. b. Following any component replacement, major repair or modification of components that could significantly affect the characteristics of the radiation beam.

DHS 157.85(13)(b) (b) Full calibration of therapeutic radiation machines with multi-energy capabilities is required only for those operational modes or radiation energies that are not within their acceptable range.

DHS 157.85(13)(c) (c) If the repair, replacement or modification does not affect all energies, full calibration shall be performed on the affected energy that is in most frequent clinical use at the facility. The remaining energies may be validated with quality control check procedures.

DHS 157.85(13)(d) (d) Full calibration shall include all measurements recommended for annual calibration by protocols approved by recognized national or international organizations. An acceptable protocol is the “Protocol for clinical reference dosimetry of high-energy photon and electron beams” as stated in AAPM Report No. 67, American Association of Physicists in Medicine, 1999.

DHS 157.85 Note Note: Report No. 67 “Protocol for Clinical Reference Dosimetry of High-Energy Photon and Electron Beams,” was published in Medical Physics, 26 (9), September 1999, pp. 1847-70. The report may also be obtained from: Medical Physics Publishing, 4531 Vernon Blvd., Madison WI 53705-4964 or ordered from their website: www.medicalphysics.org.

DHS 157.85(13)(e) (e) A registrant shall maintain a record of each calibration for the duration of the registration. The record shall include all of the following:

DHS 157.85(13)(e)1. 1. The date of the calibration.

DHS 157.85(13)(e)2. 2. The manufacturer’s name, model and serial number for both the therapeutic radiation machine and the x-ray tube.

DHS 157.85(13)(e)3. 3. The model and serial numbers of the instruments used to calibrate the therapeutic radiation machine.

DHS 157.85(13)(e)4. 4. The signature of the medical physicist responsible for performing the calibration.

DHS 157.85(13)(em) (em) Full calibration for electronic brachytherapy units shall include all of the following:

DHS 157.85(13)(em)1. 1. Timer accuracy and linearity over the typical range of use.

DHS 157.85(13)(em)2. 2. Proper operation of back-up exposure control devices. External testing protocol is acceptable as long as the back-up exposure control is tested per the manufacturer’s scheduled calibration cycle.

DHS 157.85(13)(em)3. 3. The output within the manufacturer’s specified tolerance of the expected value, if applicable, or the calculated output if there is no expected value.

DHS 157.85(13)(em)4. 4. Evaluation that the relative dose distribution about the source is within the manufacturer’s specified tolerance of the expected value.

DHS 157.85(13)(em)5. 5. For electronic brachytherapy systems where the source is moveable, the source position accuracy shall be within 1 millimeter within the applicator. Fixed x-ray source systems shall meet the manufacturer’s tolerances for source location and shape within the applicator.

DHS 157.85(13)(em)6. 6. For systems with transfer tubes and applicators, determination of the proper length of source transfer tubes and applicators.

DHS 157.85(13)(em)7. 7. For systems with transfer tubes and applicators, determination of the operability of the source transfer tubes, applicators and transfer tube-applicator interfaces.

DHS 157.85(14) (14) Quality control checks.

DHS 157.85(14)(a) (a) Quality control checks shall be performed on therapeutic radiation machines.

DHS 157.85(14)(b) (b) Quality control checks shall meet all of the following requirements:

DHS 157.85(14)(b)1. 1. A registrant shall perform quality control checks using written procedures established by a medical physicist.

DHS 157.85(14)(b)2. 2. The quality control check procedures shall specify all of the following:

DHS 157.85(14)(b)2.a. a. The frequency at which tests or measurements are to be performed.

DHS 157.85(14)(b)2.b. b. Which quality control checks are to be performed during calibration.

DHS 157.85(14)(b)2.c. c. The acceptable tolerance for each parameter measured in the quality control check when compared to the value for that parameter.

DHS 157.85(14)(c) (c) The cause for a parameter exceeding a tolerance set by the medical physicist shall be investigated and corrected before the system is used for patient irradiation.

DHS 157.85(14)(d) (d) Whenever a quality control check indicates a significant change in the operating characteristics of a system, as specified in the medical physicist’s quality control check procedures, the system shall be recalibrated.

DHS 157.85(14)(e) (e) A registrant shall have the medical physicist review and sign the results of each radiation output quality control check and notify the registrant of results within 10 working days of the date that the check was performed.

DHS 157.85(14)(f) (f) A registrant shall ensure that daily safety quality control checks of therapeutic radiation machines are performed.

DHS 157.85(14)(fm) (fm) If the results of the quality control checks indicate malfunction of any system, the registrant shall prevent clinical use of the system until repaired.

DHS 157.85(14)(g) (g) Safety quality control checks shall be performed prior to the first treatment of the day to ensure proper operation of all of the following:

DHS 157.85(14)(g)1. 1. Electrical interlocks at each external beam radiation therapy room entrance.

DHS 157.85(14)(g)2. 2. The “BEAM-ON” and termination switches.

DHS 157.85(14)(g)3. 3. Beam status indicator lights on the access doors, control console and in the radiation therapy room.

DHS 157.85(14)(g)4. 4. Viewing and intercom systems, if applicable.

DHS 157.85(14)(g)5. 5. If applicable, electrically operated treatment room doors from inside and outside the treatment room.

DHS 157.85(14)(g)6. 6. If applicable, the integrity of all cables, catheters or parts of the device that carry high voltages.

DHS 157.85(14)(gm) (gm) Daily quality control checks for adjustable source electronic brachytherapy shall include all the following:

DHS 157.85(14)(gm)1. 1. The output of the x-ray source falls within 3% of expected values, which includes output as a function of time or output as a function of setting on a monitor chamber.

DHS 157.85(14)(gm)2. 2. Verification of the consistency of the dose distribution to within 3% of that found during calibration.

DHS 157.85(14)(gm)3. 3. Validation of the operation of positioning methods to assure that the treatment dose exposes the intended location to within 1 mm.

DHS 157.85(14)(gm)4. 4. Inspection of all treatment components on the day of use.

DHS 157.85(14)(gr) (gr) Daily quality control checks for fixed source electronic brachytherapy shall include all the following:

DHS 157.85(14)(gr)1. 1. The probe shall be checked and adjusted for mechanical straightness to be less than or equal to 0.02 cm deflection.

DHS 157.85(14)(gr)2. 2. After the mechanical straightness of the probe is adjusted or checked, the beam itself shall be dynamically adjusted to be straight within the probe. This will center the beam to within 0.07mm upon the target.

DHS 157.85(14)(gr)3. 3. The beam shall be checked and adjusted for isotropy to within 12%.