Mahsheed SabetROMP Registrar at Sir Charles Gairdner Hospital

ABG 2018

Outline

Introduction to VariSeed Planning System

Changes from Version 8.0.2 to Version 9.0.1

Test methods and Results

Conclusion

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Introduction to VariSeed Planning System• Variseed LDR treatment planning system (Varian Medical Systems, Palo Alto, CA)

• All I-125 seeds are the same size, type and strength

• Minimum distance between adjacent sources is 1 cm

• Calculations are based on AAPM TG 43

• Dose prescription: 144 Gy

• Lower doses to the centre of prostate due to presence of urethra

• When the plan is finalized, seeds are ordered:Preloaded needles, IsoAid (model: IAI-125A)

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Changes from Variseed Software Version 8.0.2 to Version 9.0.1

• The precise value of 1.0/ln(2) is used in Version 9.0.1 instead of approximation to 1.44

References used for post-upgrade tests• AAPM TG 53 report: Quality assurance for clinical radiotherapy treatment planning

• IAEA TRS 430: Commissioning and Quality Assurance of Computerized Planning Systems for

Radiation Treatment of Cancer

• In VariSeed 9.0.1 there is an option to automatically calculate the dose volume resolution. More calculation points are used to calculate DVH data for all of the Variseed functions. This means consistency of results for large structures and improved results for small structures

• The concept of regions is used in version 9.0.1 which means structures can be included or excluded from a region. The prostate region includes the urethra in this version.

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Initial checks

• Check the availability of release notes and necessary documents

• Backup of Version 8.0.2 and retrieve some plans in the new version

• Make sure artifacts on CT images don’t interfere with source identification

• Importing image sets

• Orientation

• Verify keyboard entry

• Source type

• Choice of source strength specification

Test Methods:• Manufacturer’s test procedures• Independent checks of volume calculations• Clinical tests

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Manufacturer’s test procedures

• Verification of source specification data, e.g. physical properties, radial dose function,

anisotropy factor and function

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• Dose point calculation to verify that dose calculations match the expected values at various

distances using the point model and the line model

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• Isodose level test: Nine isodose values (Gy) are defined around a seed with the Anisotropy

Factor (point model) in effect. Location of the isodose lines was compared with expected values.

• Report was printed

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• DVH values are used to verify that the system calculates isodose volumes as expected. A structure is defined and a seed is placed at the centre of it with Anisotropy Factor (point model) correction. Volumes from the Cumulative DVH table are compared with expected volumes.

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• Anisotropy function/Line source calculation test: Doses from two sources with known activities located at defined positions are compared at arbitrary distances and angles with the expected values.

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Independent checks of volume calculations

• A cube was defined in both versions of Variseed with dimensions of:4cm× 3cm× 3cm=36 cm3.

• TPS calculated volumes:

• Then a 1×1×0.5 cm3 volume was added to two sides of the cube.

• TPS calculated volumes:

• The volume calculated using version 9.0.1 agrees with hand calc.

• Difference in volumes between the two versions was 0.03 cc in both cases.

version 8.0.2: 35.97 cm3

version 9.0.1: 36.00 cm3

version 8.0.2: 40.30 cm3

version 9.0.1: 40.33 cm3

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More volume calculation checks:

• A single source was defined on a set of ultrasound images.

• Isodose volumes were calculated in both versions of the software using anisotropy factor

(point model) correction.

• Total volume was 216.55 cc in Version 9.0.1, and 216.68 cc in Version 8.0.2.

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Clinical tests

• Ten patient plans originally created in version 8.0.2 were re-calculated in version 9.0.1.

• Volumes and doses were compared pre- and post-implant in the two versions

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Comparison of the RMS values for gold seed locations• Post implant CT images are registered with pre-implant ultrasound images

• Gold seeds are marked on both image sets

• TPS calculates the RMS error which indicates the best fit to gold seed positions in pre- and post-

implant image sets

• Values of RMS error were compared in the two versions for the test patients.

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Conclusion

• Results of manufacturer’s test procedures were all within tolerance levels.

• Accuracy of volume calculations was slightly improved in version 9.0.1

• Isodose volumes agreed within 1 cm3 in the two versions of the software

• In all clinical cases pre- and post-implant volumes agreed within 0.15 cm3 and differences in

calculated doses were within 0.4 Gy. These small differences were clinically insignificant.

• RMS deviations of gold seed positions closely matched in the two versions

• Differences were attributed to the changes in volume calculation methods.

Thank you

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Recommended Tests in Reference Documents

• Check the source specifications

• Dose distribution from a single source

• Dose model input data

• Verify the correct seed bookkeeping

• Verify volumetric dose calculations

• Most of these requirements were covered in the manufacturer’s test procedures

Permanent LDR Implants at Sir Charles Gairdner Hospital (SCGH)

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Pre-implant: Volume study, trans rectal ultrasound imaging

• Slices are 5mm apart

• used for planning

• 4 gold seeds are also implanted :o 2 posterior to urethra: one near the base and one near the apex

o 2 lateral to the urethra at mid-gland

Planning• Variseed LDR treatment planning system (Varian Medical Systems, Palo Alto, CA)

• All I-125 seeds are the same size, type and strength

• Minimum distance between adjacent sources is 1 cm

• In the plan, base is filled first, then periphery of each slice

• Lower doses to the centre of prostate due to presence of urethra

• When the plan is finalized, seeds are ordered:Preloaded needles, IsoAid (model: IAI-125A)

• When sources arrive, they are imaged and calibrated

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Implant procedure:

• Trans-Rectal Ultrasound (TRUS) guided

• C-arm planar images:o Before the needles are inserted, with the US probe once at the base

and once at the apex;

o During the procedure;

o After the implant is complete: with the probe once at base and once at the apex

o Shifts in gold seed positions pre- and post-implant are detected in C-arm images for eachprobe position. Average shift for each seed is later used for post-implant dosimetry.

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Post-implant Dosimetry:

• To evaluate the quality of implant

• CT imaging on the day of implant or the day after

• Register with US images from the volume study, using the gold seeds as reference

• I-125 seeds are automatically identified by the Variseed software

• Dose distribution is calculated. DVHs are generated for the prostate, and urethra

• Dose report is produced• Results are recorded in the patient database

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