BELdART. Belgian dosimetry Audits in RadioTherapy

Transcription

1 Belgian dosimetry Audits in RadioTherapy B. Schaeken, R. Cuypers, S. Lelie, W. Schroeyers, F. Sergent, S. Vynckier, A. Rijnders, D. Verellen, H. Janssens

2 Organisation: national audit - 31 locations - 79 linac s photon beams electron beams Visited audits / 3 y time span; all Belgian clinical beams Basic mechanical checks: isocentrum; lasers; telemeter; light field correspondence Basic dosimetry checks: dose measurements in water on beam axis at pre-defined depths - photon beams: 11 dose measurements all types - electron beams: 2 dose measurements in reference conditions

3 first large-scale audit based on alanine/ EPR dosimetry requested dose: 4 Gy, 4 pellets: u c (D w ) = 1.1 % (k =1) MU should be calculated with TPS as would be done for patients sad ssd dref alanine 1 cm x 1 cm dref sad set-up ssd set-up δ (D meas -D center )/ D center within optimal level: δ 3% dose determined with individual base functions Anton: Appl.Rad.Isot 62, 25; Phys.Med.Biol 51, 26 measured dose expressed as dose normalized amplitudes

4 sleeve b fading fading b T T Q Q M j j M j j b b m D k k k k k k k with k D m m A = = Α = =, 1 1 PTB-traceable

5 Dosimetry audits: photon beams Exp. Experiment Depth N r (cm) Irradiation distance Field size Accessory N r det Requested dose ref 1 Ref. field dref ssd or sad 1cm x 1cm no 1 4 Gy Tray factor dref ssd or sad 1cm x 1cm tray 2 4 Gy Energy open beam 4 Energy wedged beam 1&2 ssd or sad 1cm x 1cm no 3,4 4 Gy 3.3 1&2 ssd or sad 1cm x 1cm wedge 5,6 4 Gy Output factor1 8 ssd or sad 6cm x 6cm no 7 4 Gy Output factor2 8 ssd or sad 8cm x 2cm no 8 4 Gy Output factor3 8 ssd or sad 2cm x 8cm no 9 4 Gy Output factor4 8 sad or ssd 2cm x 2cm no 1 4 Gy MLC 1 symm/irreg 1 MLC 2 asymm/irreg 11 MLC 3 asymm/irreg.+ wedge 8 ssd or sad circular no 11 4 Gy ssd or sad 15cm x 12cm no 12 4 Gy ssd or sad 12cm x 8 cm wedge 13 4 Gy 3.11

6 Dosimetry audits: electron beams BELdART Exp Nr Experiment Depth (cm) Irradiation distance Field size accesso ry Nr det Requested dose ref 12 Ref. field_ MeV1 dref ssd or clinical practice 1cm x 1cm no 14 4 Gy Ref. field_ MeV2 (R 5 > 7 cm) dref ssd or clinical practice 1cm x 1cm no 15 4 Gy 4.14 involving 68 alanine pellets

7 1. Actual status: 36 linacs: Varian: 11; Siemens: 7; Elekta: 16; Novalis: 1; BrainLabAB/MHI Vero : 1 Dosimetry was checked in 64 photon beams: 4x 4MV; 1x 5MV; 32x 6MV; 1x 1MV; 17x 15MV; 9x 18MV 54 electron beams: 2x 4MeV; 1x 5MeV; 18x 6MeV; 1x 7MeV; 3x 8MeV; 2x 9MeV; 3x 12MeV; 1x 14MeV; 9x 15MeV; 12x 18MeV; 1x 2MeV; 1x 25MeV For 1 st and 2 nd run measurements in photon beams: D meas / D stated =.999, σ =.13 (#83) D alanine / D ionometry = 1.1, σ =.8 (#98)

8 2. Traceability: Alanine vs. ionisation cham ber: re fe re nce and non re fe re nce beams N = 98 mean = 1,1 σ =,6 range =,31 Alanine vs. ionisation chamber: ref. beams N = 17 mean =,998 σ =,5 range =,16 5,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 D w, alanine /D w, ion chamber

9 3.Results MV: Photon ref beam output N = 56 mean = 1, σ =,1 range =, Quality Index N = 62 mean =,997 σ =,1 range =, ,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 D w, meas /D w, center,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 QI meas /QI center (TPR2/1)

10 3.Results MV: Photon wedged beam output N = 12 mean =,998 σ =,17 range =, Photon beam output with collimator opening N = 372 mean = 1, σ =,15 range =,85 5 2,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 D w, meas /D w, center,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 D w, meas /D w, center

11 3.Results MV: MLC1 MLC2 MLC3 Photon irr. Field output MLC1 MLC2 MLC3 N = mean = 1,,998,993 σ =,16,15,17 range =,71,77,72,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 D w, meas /D w, center

12 kq,q in high-energy electron beams: SL25: 4, 6, 8, 1, 12, 15, 18, 2, 22 MeV ROOS chamber cross calibrated vs. Farmer at 18 MeV / NCS-18 protocol Roos/Farmer = 1.18 Alanine (8 Gy): ur(dw) =.3%; Roos/Farmer: ur(dw) = 1.8% (NCS-18/pp69) Two types of holder MeV kq,q

13 Results MeV: All electron beams N = 57 mean =,994 σ =,25 range =, Low energy electron beams N = 29 mean =,996 σ =,21 range =,94,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 4 2,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 D w, meas /D w, center D w, meas /D w, center High energy electron beams N = 28 mean =,992 σ =,28 range =,133 2,9,92,94,96,98 1, 1,2 1,4 1,6 1,8 1,1 D w, meas /D w, center

14 3.Results summary (latest): output measurements Dmeas/ Dcenter 1sd R(min max) # photon ref beam QI (open beam) wedged photon beam regular field sizes MLC electron beams Results are incl. 2 nd and 3 th run measurements If deviations are observed, it s likely that they are systematic, even within optimal level Finding explanations for a deviation needs a detailed look-up Out of tolerance situations disappear in a 2 nd run, although a clear explanation is difficult to find

15 4. Conclusion: alanine/epr was successfully used as transfer dosimetry system allowing sufficient accurate dose measurements results into accordance with (reference) ionometry beam data are well modeled in TPS for the visited centers suits well for mailed dosimetry (practicalities) but the true benefit of alanine/epr lays in complex dose deliveries (helical, IMRT, SRS, brachytherapy...)

16 Acknowledgments: Hilde Beutjens (lab ass) and Mathias Anton (PTB); fully supported by FANC-AFCN Visit us at Info