Microsoft Excel Workbook for Dosimetry Calculations

To accompany “Dosimetry System for SIT: Manual for Gafchromic® film”

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Contents Contents .............................................................................................................................1 Introduction .......................................................................................................................1 Form SIT 1.........................................................................................................................2 Form SIT 2.........................................................................................................................3 Form SIT 3.........................................................................................................................4 Form SIT 4A......................................................................................................................5 Form SIT 4B......................................................................................................................6 Form SIT 4C......................................................................................................................7 Form SIT 4D......................................................................................................................8 Form SIT 4E ....................................................................................................................10 Form SIT 5.......................................................................................................................11 Form SIT 6.......................................................................................................................12 Form SIT 7.......................................................................................................................13 Form SIT 8A & B ............................................................................................................14 Form SIT 9.......................................................................................................................16

Introduction The spreadsheet file dosimetry_v13.xls provides a simple way to perform all the calculations required in the Dosimetry System for SIT: Manual for Gafchromic® film. The workbook is organised in the same manner and following the sequence of the recommended data forms contained in Appendix B of the manual. All places where entries are required are indicated by cells highlighted with yellow. Either single forms or the complete workbook can be printed to provide a permanent record.

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Form SIT 1

This form merely provides a convenient format for recording the neutral density filter readings. Record the serial number of the Radiachromic reader you are using at the head of the form. Readings should be taken at the start and finish of each session of taking OD readings.

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Form SIT 2

This calculates the mean and standard deviation of the background OD measurements. The date must be entered correctly as this is used later to check that this measurement is still valid.

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Form SIT 3

Use this form to record the irradiation conditions for the transfer standard dosimeters and the subsequent results. Also record the type of source you are using, 60Co or 137Cs using the buttons at the top of the sheet. The half-life will be entered automatically allowing the spreadsheet to calculate the dose rate for any day.

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Form SIT 4A

Enter the date at the head and the required calibration dosages in column A. The calibration dosages should be adjusted to span the expected operational dose. For fruit flies and tsetse which use 120 Gy the calibration dosages should range from 40 to 240 Gy. For Lepidoptera, which require dosages in the range 250 – 500 Gy depending on species, the calibration dosages should range from 100 to 600 Gy If the calibration data has been entered (Form SIT 3) the sheet will calculate the required irradiation times. These exact times may be used, or convenient times close to these values. Enter the actual times used in column C and the minimum and maximum temperature of the dosimeters during each exposure in columns E and F. The effective temperatures will be used to correct the dosimeter response readings by the appropriate temperature compensation, and the mean of all the temperatures will become the reference temperature for all future readings T(ref). Also record information about the timer at the foot of the sheet.

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Form SIT 4B

When the calibration dosimeters are read, 24 to 30 hours after exposure, enter the readings for each dosimeter strip as appropriate. The OD(mean), OD(std dev), CV(%), response, corrected response and mean corrected response for each dose will be calculated.

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Form SIT 4C

For the determination of transit dose, enter the times T1 - T4 in seconds and the constants N1 and N2 appropriate for your irradiator set up in column T. The value of T1 – T4 should match the lowest four doses from SIT4A. The values of N1 and N2 should be chosen such that T1 plus N1 times the estimated transit time is approximately equal to T2, with N2 twice N1. Enter the dosimeter OD values in columns V – X. The actual transit time will be calculated, and the graph of the relationship displayed. If the dose rate of your machine is less than 4 Gy/min the effect of the transit dose will be insignificant. In this case you may choose not to perform the transit dose calculation by clicking on the appropriate button at the top right of this sheet; the transit time will be set to zero and you may proceed with the next step. This button will only work if the dose rate is less than 4 Gy/min.

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Form SIT 4D

This form is completed automatically, with the actual dose taking into account the transit time. Using the mean corrected response the spreadsheet calculates linear, quadratic and power regression fits, and the residuals for each.

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Select the fit which gives a random arrangement of the residuals. In this example the power series fit produces a noticeable pattern in the residuals and should not be used. If more than one fit gives a random arrangement for preference select the linear fit.

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Form SIT 4E

When you have chosen an appropriate fit, select it with the buttons at the top of Form SIT 4E. The rest of this form shows the residuals for the three possible fits. This completes the calibration of the system. At this point the spreadsheets SIT 1, SIT 2, SIT 3 and SIT 4 should be printed and stored as part of the record for quality control audit purposes.

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Form SIT 5

This form is used for determining the dose actually received during routine treatment. The date and desired dose are entered at the head of the form and the calculated exposure time (allowing for the transit time) is calculated. The routine monitoring dosimeter readings are then entered in column D, with the exposure temperature in C and the actual dose recorded by the dosimeter is indicated in column G.

The spreadsheet will warn you if the background OD measurement (6 months) or system calibration (12 months) are out of date.

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Form SIT 6

This form is for checking the homogeneity of the dosimeter batch. When the target dose is entered in C9 the approximate exposure time is calculated (C11). The exact time (dose) used however is not critical for the batch homogeneity, but should be close to the normal exposure dose used in routine treatment. After irradiating a set of three dosimeter strips, record the OD values on the form. The Coefficient of variation will be calculated.

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Form SIT 7

Use this form to record the data from a dose mapping exercise. Unless you have multiple thermocouple thermometers available you will have to estimate a single temperature for all the dosimeters to enter in column B. A warning also appears on this sheet if either calibration is out of date.

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Form SIT 8A & B

The Form SIT 8A is similar to forms SIT 5 and 7, but records the dosimeter readings either from the reference location, minimum dose point or other location (see Manual section 5.4, page 23). It provides for up to three dosimeters placed together in one location, allowing the readings to be average to give a lower uncertainty.

The spreadsheet will warn you if the background or system calibration is out of date.

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Form SIT 8B records process parameters. These two sheets together (SIT-8A & SIT-8B) should be complete for each shipment of insects send from the rearing facility and a copy included with the shipment.

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Form SIT 9

Insert the date when the dosimeter Lot was received at the head of the form. Form SIT 9 brings together information on the calibration of the system and the uncertainty in the dose values arising from various sources. These include dose rate uncertainty (from the transfer dosimeter reading), uncertainty in the Gafchromic® film calibration, and from non-homogeneity in the dosimeters. The main remaining uncertainty arises from determining the temperature of the dosimeter at the time of irradiation. The measured temperature of the dosimeters entered on the forms SIT 5, 6 or 7 are used to compensate for differences in the response of the dosimeter at different temperatures, but if the temperature is not constant during irradiation the response of the dosimeter will be varying during the exposure and this gives rise to additional uncertainty. Measure with a thermocouple thermometer or estimate the likely maximum range of dosimeter temperature during irradiation and enter the maximum and minimum temperature of a typical exposure. This is then used to estimate the uncertainty due to temperature variation. An overall uncertainty Utotal is calculated from these uncertainty terms. Utotal is an estimate of the standard deviation of the dose estimation by your system, and can be used to provide confidence intervals for the point estimate of dose. The 95% confidence interval is approximately ±2 x Utotal.