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TLD POSTAL DOSE QUALITY AUDIT FOR 6MV AND 15MV PHOTON BEAMS IN RADIOTHERAPY CLINICAL PRACTICE

TLD POSTAL DOSE QUALITY AUDIT FOR 6MV AND 15MV PHOTON BEAMS IN RADIOTHERAPY CLINICAL PRACTICE. Sonja Petkovska 1 , Margarita Ginovska 2 , Hristina Spasevska 2 , Nadica Dimitrovska 1 , 1 University Clinic for Radiotherapy and Oncology, Skopje, RM

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TLD POSTAL DOSE QUALITY AUDIT FOR 6MV AND 15MV PHOTON BEAMS IN RADIOTHERAPY CLINICAL PRACTICE

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  1. TLD POSTAL DOSE QUALITY AUDIT FOR 6MV AND 15MV PHOTON BEAMS IN RADIOTHERAPY CLINICAL PRACTICE Sonja Petkovska1, Margarita Ginovska2, Hristina Spasevska2 , Nadica Dimitrovska1, 1University Clinic for Radiotherapy and Oncology, Skopje, RM 2Faculty of Electrical Engineering and Information Technologies, Ss Ciril and Metodious University, Skopje, RM RAD 2012, 24-27 April, Nish

  2. INTRODUCTION Radiation therapy is the modality of choice for about half of the cancer patients at some stage during their treatment. • Radiotherapy aim: • delivering as high dose as possible • at the tumor volume • spearing the health tissue as much as • possible. RAD 2012, 24-27 April, Nish

  3. INTRODUCTION • Delivered dose should • provide the highest • probability to cure the • patient without inducing • severe complications in • normal tissues. • Delivered dose should be • equal to prescribed one TCP – Tumor Control Probability NTCP – Normal Tissue Complication probability TSP – Probability for Succesfful Treatment RAD 2012, 24-27 April, Nish

  4. INTRODUCTION QA programme • Mechanical checks provide geometrical accuracy • Dosimetry checks provide dose distribution accuracy • Beam calibrations provide prescribed dose accuracy RAD 2012, 24-27 April, Nish

  5. INTRODUCTION External comparison with an independent dosimetry laboratory • Check the dose delivered by radiotherapy unit • Comparison in different beam parameters in clinical practice • Allows detecting dosimetric errors RAD 2012, 24-27 April, Nish

  6. ESTRO QUALity Assurance network (EQUAL) 2Gy 2Gy 2Gy 2Gy 2Gy 2Gy Compare beam parameters measured in the same conditions in different radiotherapy centers RAD 2012, 24-27 April, Nish

  7. MATERIALS AND MEASUREMENTS Thermoluminescent Dosimeters (TLDs) with lithium fluoride powder (LiF) TLD holder Water phantom RAD 2012, 24-27 April, Nish

  8. MATERIALS AND MEASUREMENTS • 4 TLDs per unit • are irradiated one by one • 2 for 6MV photon beam • 2 for 15MV photon beam geometry setup for TLD irradiation RAD 2012, 24-27 April, Nish

  9. MATERIALS AND MEASUREMENTS 6MV photon beam 299MU D = 2Gy at reference depth 15MV photon beam 251MU RAD 2012, 24-27 April, Nish

  10. MATERIALS AND MEASUREMENTS Dcalc is TPS calculated dose Dm is measured dose with ionisation chamber RAD 2012, 24-27 April, Nish

  11. RESULTS • The levels of deviation between measured and stated quantities (Qm/Qs) and the corresponding EQUAL actions are specified as follows: • Qm/Qs < 3% optimal level • 3% < Qm/Qs < 5% tolerance level • 5% < Qm/Qs < 10% a level outside tolerance level • Qm/Qs > 10% an emergency level RAD 2012, 24-27 April, Nish

  12. RESULTS Deviation for high energy photon beams RAD 2012, 24-27 April, Nish

  13. CONCLUSION • The results from ML show that the relative deviation Qm/Qs for these analyzed 6MV and 15MV photon beams, do not exceed 3%. This evaluation shows significant absorbed dose reproducibility which confirmed the capability of the linear accelerator to deliver real treatments with an acceptable stability. RAD 2012, 24-27 April, Nish

  14. CONCLUSION The purpose of this TLD audit is to check the dose delivered by radiotherapy unit, so this independent and trustworthy verification of dose delivery improve internal QA and help to detect some dosimetric errors. Dose accuracy is just one segment of external quality procedures… RAD 2012, 24-27 April, Nish

  15. RAD 2012, 24-27 April, Nish

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