referring to the drawing in greater detail and initially to fig1 and 2 , a shipping box 12 is used to hold product containers 14 and dry ice substitute 16 . dosimeters 18 are placed on the product containers and inside the product containers . the dosimeters are fixed in the center of product containers 14 by agar 20 and taped to the sides of the product containers . shipping boxes 12 , as seen in fig1 and 2 , are used to hold product containers 14 and dry ice substitute 16 . shipping box 12 can be formed of any rigid material which will hold the product containers and the dry ice substitute . in the preferred embodiment , the shipping boxes are made of polyfoam . the product containers 14 are used to hold the agar 20 . dosimeters 18 are taped to the outside of the product containers 14 in addition to being fixed in a center position inside the product containers . the product containers must be the same containers used to hold actual product . dry ice substitute 16 is used as a substitute for dry ice in shipping box 12 . the dry ice substitute can be made of anything having a shape and density similar to dry ice . dry ice is solid carbon dioxide . the dry ice used has a shape of 13 / 8 × 3 / 4 × 1 / 2 inch and a density of 0 . 785 g / ml . the dry ice substitute comprises dried animal food and salt pellets . the dried animal food has a density of 0 . 642 g / ml with a shape of 13 / 8 × 5 / 8 × 1 / 2 inch . the salt pellets have a density of 1 . 102 g / ml and a shape of 1 - 1 / 6 × 5 / 8 × 3 / 8 inch . these two components are combined in a ratio of seven parts dried animal food with three parts salt pellets to yield an average density that is equivalent to the average density of dry ice . in one embodiment the dried animal food is purina ® labdiet and the salt pellets are morton ® system saver pellets , 99 . 5 % pure salt . additionally , the labdiet is not brittle and lasts for many experiments , thus saving money . the dry ice substitute is then packed into shipping boxes and packed around the product containers . dosimeters 18 are used to determine the amount of radiation received at particular points in carrier 22 . dosimeters are taped to the outside of product containers 14 . additionally , dosimeters are inserted into product containers where they are fixed into a center position by agar 20 . dosimeters can be any type of device that can detect specific amounts of radiation and are small enough for use in the dose mapping system . in the preferred embodiment , the dosimeters are effective in a range of 5 to 50 kgy . the dosimeters are supplied by the irradiation facility . any semisolid substance can be used to fix dosimeter 18 in the approximate center of product container 14 . in the preferred embodiment agar 20 is used as a product substitute to fix the dosimeter in the approximate center of the product container . agar is a mucilaginous complex sulfated polymer of galactose units . the agar allows the dosimeters to be fixed approximately in the center of product containers 14 . the agar further acts as a shield against the radiation source whereby the dosimeters receive an amount of radiation that would be approximately equal to the amount received during product irradiation . the agar must have a gel point less than 50 ° c . and a melting point greater than 85 ° c . the significance of these two points is that it allows for filling of plastic bottles with agar without melting the bottle . additionally , the agar will remain a solid during irradiation . in the preferred embodiment , the agar preparation should have a density of approximately 1 . 2 kg / l which is approximately the density of frozen serum . the density of agar is variable depending on its preparation . in the preferred embodiment , the agar is prepared by autoclaving 15 liters of water with 250 grams of agar mixed in with the water . fig3 illustrates the general floor plan 10 of the radiation facility . shipping boxes 12 are packed with product containers 14 containing agar 20 . dosimeters 18 are taped to the product containers and inserted into the center of the product containers where they are fixed into position by the agar . the shipping boxes are then packed with a dry ice substitute 16 and placed onto a carrier 22 . the carrier holds seven to fifteen shipping boxes , depending on the size of the box . the carrier is attached to a conveyor system 24 . the conveyor system brings the carrier into a room containing a gamma radiation source 26 . carrier 22 can be any device which will hold a number of shipping boxes 12 . the carrier is a metal structure capable of carrying several shipping boxes . in the preferred embodiment , the carrier holds seven to fifteen shipping boxes . conveyor system 24 is used to transport carriers 22 to the radiation source 26 . the conveyor system can be any means by which the carriers are brought to and from the radiation source 26 . in the preferred embodiment , the conveyor system brings a carrier to the radiation source in an orientation where a first side of the shipping boxes receives radioactivity on the first pass of the radiation source , then the conveyor system brings the carrier by the radiation source a second time in an orientation where a second , opposite , side of shipping boxes receives radioactivity . the conveyor system moves the carriers to one of eleven positions . the conveyor system has a means for varying the time at which the carriers are held at each of the eleven positions . each carrier is held at each position for a specified time . this means is used to control the length of exposure to the radiation source and to reduce variability in exposure . radiation source 26 is any source of radiation . in the preferred embodiment , the radiation source produces gamma radiation from cobalt 60 . generally , product containers 14 are filled with agar 20 . the agar is prepared by mixing the agar with water and then autoclaving . in the preferred embodiment , the agar is prepared by mixing 250 grams of agar with 15 liters of water and then autoclaving . after the agar mixture is removed from the autoclave it is a hot liquid . this liquid is allowed to cool and then poured into product containers , and it is further allowed to cool to room temperature . at room temperature the agar is a semisolid gel . additionally , the agar remains a semisolid during the irradiation process . dosimeters 18 are then taped to the outside of the product containers 14 . they are taped onto the product containers with scotch ® tape . each product container has a dosimeter 18 taped on a first side and a second opposite side as seen in fig2 . dosimeters are then fixed into the center of the product container . covers are then placed onto the product containers . product containers 14 are placed into shipping boxes 12 . the configurations of the product containers will be identical to actual irradiation conditions . an amount of dry ice substitute 16 equal to the amount of dry ice that would be present at the time of irradiation is then packed into the shipping boxes . in the preferred embodiment , ten pounds of dry ice substitute 16 is packed into the shipping boxes . the shipping boxes are then sealed shut with tape . shipping boxes 12 are then stacked onto carriers 22 . carriers 22 will hold up to 15 shipping boxes . a space is placed on the bottom of the carrier to elevate the shipping boxes . this space allows an accurate and consistent amount of radiation to reach the product containers . the amount of space is determined by evaluation of the non - product dose map data obtained from the irradiation facility . carriers 22 with shipping boxes 12 are then sent by conveyer system 24 to the radiation source 26 . the radiation source is contained in a separate radiation room . after exposure to radiation source , the carriers are returned on the conveyer system . after the radiation treatment the dosimeters 18 are collected and analyzed to create a dose map which can be used to ensure that each of the product containers 14 receive the proper amount of radiation . agar 20 was prepared by adding fourteen liters of tap water to a twenty liter capacity glass carboy . the water was rapidly mixed with a magnetic stir bar . 250 . 0 grams of agar was weighed out and slowly added to the carboy . the carboy opening was loosely covered with aluminum foil . the solution was allowed to mix for thirty minutes . the solution was then brought to fifteen liters with tap water . the solution was mixed for an additional thirty minutes . the solution was autoclaved at 121 ° c . for forty - five minutes . more than one carboy may be autoclaved at once . after the agar cooled , but before it gelled , the 500 ml , 1000 ml and / or 4000 ml product containers 14 were filled to a level similar to the level of product usually found in the container . the liquid agar was poured using a funnel . although , the agar could be transferred by a peristaltic pump and flexible tubing . the caps were loosely placed on the product containers while the agar solidified overnight at room temperature . the caps were tightened down once the agar 20 was solidified . this process was repeated until 140 × 500 ml , 112 × 1000 ml and 42 of each type of 4000 ml product containers were filled . the product containers of agar were stored at room temperature until needed . because delivered dose is directly dependent on density , mimicking the density of dry ice added to frozen products is essential for accurate dose mapping . for each of the 63 polyfoam shipping boxes 12 that were used , one bag containing ten pounds ( 4 . 53 kg ) of dry ice substitute 16 was required . ten pounds of dry ice substitute were made by mixing seven pounds labdiet with three pounds salt pellets in a plastic bag . the top of the bag was twisted to keep the contents from escaping . the bags of dry ice substitute were stored in a cool , dry place until needed . a cardboard divider was added to each of fourteen shipping boxes 12 . ten 500 ml product containers 14 of agar 20 were put into each of fourteen shipping boxes containing a divider . eight 1000 ml product containers 14 of agar 20 were put into each of the fourteen shipping boxes ( without dividers ). three 4000 ml berlin product containers of agar were put into each of fourteen shipping boxes ( without dividers ). three 4000 ml medical and veterinary supply product containers of agar were put into each of 21 shipping boxes ( without dividers ). one bag ( 10 pounds ) of dry ice substitute was added to each shipping box , the polyfoam lid was replaced , and sealed with packing tape . the shipping boxes 12 were labeled with the appropriate product container 14 labels . &# 34 ; 4000 m &# 34 ; for 4000 ml medical and veterinary supply product container . the labels were affixed to all the cases . the shipping boxes 12 were placed on pallets , 27 shipping boxes per pallet . the shipping boxes were then shipped to the irradiation facility . at the irradiation facility , the carrier 22 and carrier position ( level ) of each shipping box was labeled accordingly . each carrier can hold seven shipping boxes , numbered 1 ( bottom ) through 7 ( top ). the &# 34 ; 500 &# 34 ; shipping boxes were in carriers 1 and 2 , &# 34 ; 1000 &# 34 ; were in 3 and 4 , &# 34 ; 4000 b &# 34 ; were in 5 and 6 , and the &# 34 ; 4000 m &# 34 ; were in carriers 7 , 8 and 9 . at the irradiation facility , each dosimeter 18 was labeled with a white label containing the eventual location of the dosimeters within its shipping box 12 . included were the shipping box location ( carrier 22 and level ) plus a letter corresponding to the dosimeter map fig2 . each shipping box was opened and the bag of dry ice substitute 16 was removed . using fig2 as a guide , the dosimeters were attached on the outside of the bottles using scotch ® tape or equivalent . the dosimeters were laid as flat as possible against the bottle and positioned approximately in the middle of the product / agar , which is lower than the exact middle of the product container 14 itself . the dosimeters on the 500 ml product containers 14 were placed on the vertical edge of these product containers because of their orientation within the shipping box 12 . the cap was removed and the dosimeters were placed in the positions shown in fig2 . using a long pair of forceps , the dosimeters were submerged and fixed into the middle of the agar . the product container was recapped and placed into the shipping box in the proper configuration . one bag of dry ice substitute was emptied into each shipping box case and evenly distributed around the product containers . the lid was replaced and the shipping box was sealed with packaging tape . the shipping boxes were raised off the bottom of the carriers by foam sheets . the height that the shipping boxes were raised was determined from the initial dose map performed by personnel at the irradiation plant after each cobalt source reloading . different product container sizes must be evaluated separately , i . e ., shipping boxes of 1000 ml product containers 14 need to be 5 raised higher than shipping boxes of 500 ml product containers . this spacing reduced the minimum to maximum range and assured that all product containers fell within the specified exposure range of 25 - 35 kgy . the shipping boxes 12 were irradiated as specified . it was requested that the 0c1 position receive a target dose between 25 - 35 kgy , although for dose mapping purposes , the dosage range is not crucial . the 0c1 position is a designation for a specific portion of carrier 22 . these designations correspond to a map created by the irradiation facility . the maps allow for the identification of specific portions with in the carrier . once the shipping boxes 12 were unloaded , and the lids removed , the dosimeters were collected by removing the tape or recovering from the agar with forceps . the dosimeters were combined from each shipping box 12 separately with rubber bands and turned over for analysis . the dry ice substitute 16 was poured back into bags for future use . the dosimeter data was used to find the 0c1 values for each of the two carriers 22 of 500 ml product containers 14 and a mean value ( 0c1500 x ) was computed . the minimum and maximum delivered dosages for both carriers of 500 ml product containers was found . the minimum correction factor for 500 ml bottles ( cfmin500 ) was computed by dividing min500 by 0c1500 x . for example , if the minimum delivered dosage at any dosimeter 18 was 25 . 1 kgy and the average 0c1 reading was 28 . 7 kgy , then cfmin500 = 25 . 1 / 28 . 7 = 0 . 875 . next , the maximum correction factor for 500 ml product containers ( cfmax500 ) was computed by dividing max500 by 0c1500 x . for example , if the maximum delivered dosage at any dosimeter was 30 . 3 kgy and the average 0c1 reading was 28 . 7 kgy , then cfmax500 = 30 . 3 / 28 . 7 = 1 . 056 . these steps were repeated for all other product containers tested . the computed correction factors for each product container 14 size / configuration were used every time a target dose range was given to irradiating personnel while the same cobalt source was in use . the minimum target dosage level was computed by dividing the low end of the acceptable dosage range by the cfmin500 . for instance , if the acceptable range is 25 - 35 kgy and cfmin is 0 . 875 , then the new low end target dosage for the 0c1 position for 500 ml bottles is 25 / 0 . 875 = 28 . 6 kgy . next the maximum target dosage level was computed by dividing the high end of the acceptable dosage range by the cfmax500 . for instance , if the acceptable range is 25 - 35 kgy and cfmax500 is 1 . 056 , then the high target dosage for the 0c1 position for 500 ml bottles is 35 / 1 . 056 = 33 . 1 kgy . thus , using these numbers , a desired dosage range for serum in 500 ml product containers is 25 - 35 kgy ; therefore , 28 . 6 - 33 . 1 kgy needs to be delivered to the 0c1 position . thus , if the dosimeter record for this hypothetical run showed all 0c1 delivered dosage from all carriers to be between 28 . 6 and 33 . 1 kgy , than all product containers containing product were known to have actually received dosages within the desired 25 - 35 kgy range . from the foregoing , it will be seen that this invention is one well adapted to attain all the ends and objects hereinabove set forth together with other advantages which are obvious and which are inherent to the invention . it will be understood that certain features and subcombinations are of utility and may be employed without reference to other features and subcombinations . the above examples discussed the techniques and procedures used in the current invention , and it is understood that there are many other techniques and procedures that could be employed that would allow an individual of ordinary skill in the art to perform the claimed invention and that these other techniques and procedures are contemplated by and are within the scope of the claims . since many possible embodiments may be made of the invention without departing form the scope thereof , it is to be understood that all matter herein set forth , and shown in the drawings arc to be interpreted as illustrative and not in a limiting sense .
a method of dose mapping that simulates actual product irradiation conditions utilizing a semisolid to fix dosimeter inside product containers and a dry ice substitute to mimic the density of dry ice . the method comprising the steps of fixing dosimeter in a semisolid mixture inside product containers packed with a dry ice substitute and irradiating . the results are then calculated and analyzed to produce an accurate dose map .