Radiant energy – Radiation controlling means – Shields
Patent
1987-07-09
1989-01-17
Fields, Carolyn E.
Radiant energy
Radiation controlling means
Shields
378 65, 378145, H05G 102
Patent
active
047989610
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to radiation field shielding in a radiotherapy apparatus, and more particularly to a device for shielding the radiation field from a collimator unit which is included in the radiotherapy apparatus and which in a per se known manner is rotatable about its axis and rotatable in its entirety about an axis of rotation spaced from the collimator unit, such that this is rotatable about a patient to be subjected to radiation, the device being exchangeably mounted on the collimator unit and supporting in a holder at least one radiation shield means spaced from the collimator unit.
In radiotherapy, it is most essential that the patient be held in a correct position in relation to the radiotherapy apparatus. Also, very high demands are placed on the shielding of the radiation field from the collimator of the radiotherapy apparatus in order that radiation should be confined to the intended, clearly defined treatment area. Incomplete or incorrect radiation field shielding may cause damage to tissues outside the treatment area.
The collimator unit itself is generally provided with a so-called primary diaphragm for producing rectangular or square radiation fields. Often, it is however desired to have a shielding aperture of irregular shape, to which end use is made of a so-called satellite diaphragm in the form of a holder device which is mounted on the collimator and in which radiation shield means, such as lead blocks, are fixed for providing final shielding.
On the market, there are several different types of such holder devices having a similar basic design. One previously known holder device consists of a frame mounted on the collimator and supporting a slotted plexiglass plate spaced from the aperture of the collimator. Lead blocks, which can be fixed by different clamping means, are placed on or suspended from this plate. For example, the lead blocks have projecting threaded pins which are inserted through a slot in the plate, whereupon the blocks are fixed by screwing a wing nut on the pin and tightening it against the plate.
The known shielding and holder devices suffer from a number of drawbacks as regards both the handling of the lead blocks by the personnel and the radiotherapeutic treatment itself. First, the handling of the lead blocks involves heavy lifting since these blocks weigh up to about 20 kg. The personnel working at a radiotherapy apparatus may handle about 1000 kg lead during one working day, sometimes at an aergonomically very tiring height above the floor. Secondly, the blocks must be shifted when a certain part of the patient's body should be subjected to radiation from two directions and to a certain depth. The patient is in fact lying permanently fixed on the treatment table and if the patient after radiation in a first direction should be subjected to radiation in the opposite direction, the collimator is turned together with the shield device through 180.degree. about the patient. The shield means are however then mirror-inverted and, thus, must be shifted in order to obtain the same desired orientation of the shield aperture as in connection with radiation in the first direction. Shifting the shield means is both physically tiring and time-consuming. Further, it is difficult to achieve high accuracy after mirror-inversion of the blocks since they must be dismounted and/or turned on the plexiglass plate.
The very fixing of the lead blocks is a problem since the blocks will easily loosen at oblique directions of radiation, i.e. when the axis of the collimator is oblique in relation to the vertical plane. If a lead block loosens during irradiation, this must be interrupted.
The apertured or slotted plexiglass plate is a problem itself since it gives an inhomogeneous radiation field. In the optimum case, no objects apart from the shield means must be in the zone between the aperture of the collimator and the part of the patient to be subjected to radiation.
One object of the present invention is to provide a device for supplementary shielding of the radiation fi
REFERENCES:
patent: 3723743 (1973-03-01), Brackenbrough et al.
patent: 3982133 (1976-09-01), Jupa et al.
patent: 4027167 (1977-05-01), Pollermann
patent: 4158779 (1979-06-01), Rommel et al.
patent: 4214167 (1980-07-01), Gade
patent: 4233519 (1980-11-01), Coad
Fields Carolyn E.
Miller John A.
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