ON RADIOTHERAPY DOSE VERIFICATION WITH A FLAT-PANEL IMAGER

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TUESDAY ,SEPTEMBER 1, 2009 SYMPOSIUM S 49 IMRT. Symposium Recent PhD projects in medical physics and RTT 132 speaker ON RADIOTHERAPY DOSE VERIFICATION WITH A FLAT-PANEL IMAGER L. McDermott 1 1 THE NETHERLANDS CANCER I NSTITUTE, Amsterdam, Netherlands The purpose of this thesis was to 1) investigate the dose characteristics of the amorphous silicon electronic portal imaging device (a-Si EPID), 2) develop an algorithm to determine the 2D dose distribution within a patient or phantom based on images of treatment fields and 3) implement EPID dosimetry into the clinic for the verification of IMRT, both prior to (pre-treatment) and during (in vivo) radiotherapy. The EPID response was found to be stable (±0.5%) over 2 years, with corrections (eg temperature). Corrections were also de- termined for ghosting and image-lag based on irradiation time, characteristic of all commercial a-Si panels available. A ’back-projection’ algorithm, already developed for liquid-filled EPIDs, was extended. The algorithm converts im- ages to an absolute 2D dose distribution in the patient isocentric plane. EPID dosimetry was introduced into the clinic in 2005. Clinically relevant errors were found and resolved in the treatment planning system, related to pre-set MLC parameters. Daily EPID images were used to determine the range and influence of anatomy changes for in vivo dosimetry. It was found that respi- ratory motion, variation in rectal gas pockets and patient positioning were the main anatomy changes that would affect the dose delivered to patients. Var- ious aspects of clinical EPID dosimetry were addressed, including manage- ment of 2D data, analysis of discrepancies observed, automation of analysis and development of action levels. Results for the first 75 patients revealed an average agreement within 1% (1 SD) of the total plan for both pre-treatment and in vivo verification. Combining 2D gamma images from 3 fractions (in vivo data) filtered out random errors due to anatomy variation and rendered similar results as phantom pre-treatment verification. In vivo replaced pre-treament checks for most cases. Two to four clinically relevent errors were detected and resolved with EPID dosimetry per year. The EPID is therefore suitable for reliable and accurate absolute dose verification during radiotherapy. In addi- tion, the EPID can replace traditional dosimetry devices to verify patient plans before treatment, being sufficiently efficient and accurate. The method devel- oped in this thesis is a safety net, providing radiation oncologists with the con- fidence to raise dose levels and introduce sophisticated treatment techniques, which will eventually lead to higher cure rates for patients. Thesis Publica- tionsL McDermott, R Louwe, J Sonke et al "Dose-response and ghosting ef- fects of an amorphous silicon electronic portal imaging device" Med Phys 31 2004R Louwe, L McDermott, J Sonke et al "The long-term stability of amor- phous silicon flat panel imaging devices for dosimetry purposes" Med Phys 31 2004M Wendling, R Louwe, L McDermott et al "Accurate two-dimensional IMRT verification using a back-projection EPID dosimetry method" Med Phys 33 2006L McDermott, M Wendling, J Sonke et al "Anatomy changes in ra- diotherapy detected using portal imaging" RadOnc 79 2006L McDermott, S Nijsten, J Sonke et al "A comparison of ghosting effects for three commercial a-Si EPIDs" Med Phys 33 2006L McDermott, M Wendling, B van Asselen et al "Clinical experience with EPID dosimetry for prostate IMRT pre-treatment dose verification" Med Phys 33 2006L McDermott, M Wendling, J Sonke et al "Replacing pre-treatment verification with in vivo EPID dosimetry for prostate IMRT" Int J Radiat Oncol Biol Phys 67 2007 133 speaker APPLICATION OF MOSFET DOSIMETRY FOR IN VIVO DOSIMETRY IN RADIOTHERAPY E. Bloemen- van Gurp 1 1 MAASTRO CLINIC, Maastricht, Netherlands The research work performed by Esther Bloemen- van Gurp, investigating the application of MOSFET dosimetry for in vivo dosimetry in radiotherapy, resulted in a broad application of MOSFET dosimetry in clinical practice and will be finished in June 2009. The first publication discusses the result of a study to determine the accuracy of the MOSFET detector for dose measure- ments in a junction field technique, using split beams. The goal of this study was to evaluate the dose across the split line. The accuracy of the detector was determined by an extended set of phantom measurements and the re- sults of this phantom study were used for patient measurements, performed on 5 patients receiving loco-regional treatment for breast cancer, during 10 sequential treatment fractions. The influence of factors related to mechanical properties and QC procedures of the linear accelerator are also discussed. (Bloemen-van Gurp E.J., du Bois W.F.J., Visser P.A., Bruinvis I., Jalink D., Hermans J. and Lambin P. Clinical dosimetry with MOSFET dosimeters to de- termine the dose along the field junction in a split beam technique. Radiother- apy and Oncology 67 (2003) 351357).The second publication describes the use of MOSFET dosimeters for entrance in vivo dose verification during elec- tron beam treatments, performed without build-up material on the detector to prevent the target volume from shadowing effects by the detector. A compre-

Transcript of ON RADIOTHERAPY DOSE VERIFICATION WITH A FLAT-PANEL IMAGER

Page 1: ON RADIOTHERAPY DOSE VERIFICATION WITH A FLAT-PANEL IMAGER

TUESDAY, SEPTEMBER 1, 2009 SYMPOSIUM S 49

IMRT. SymposiumRecent PhD projects in medical physics and RTT132 speaker

ON RADIOTHERAPY DOSE VERIFICATION WITH A FLAT-PANELIMAGERL. McDermott11 THE NETHERLANDS CANCER INSTITUTE, Amsterdam, Netherlands

The purpose of this thesis was to 1) investigate the dose characteristics of theamorphous silicon electronic portal imaging device (a-Si EPID), 2) develop analgorithm to determine the 2D dose distribution within a patient or phantombased on images of treatment fields and 3) implement EPID dosimetry intothe clinic for the verification of IMRT, both prior to (pre-treatment) and during(in vivo) radiotherapy. The EPID response was found to be stable (±0.5%)over 2 years, with corrections (eg temperature). Corrections were also de-termined for ghosting and image-lag based on irradiation time, characteristicof all commercial a-Si panels available. A ’back-projection’ algorithm, alreadydeveloped for liquid-filled EPIDs, was extended. The algorithm converts im-ages to an absolute 2D dose distribution in the patient isocentric plane. EPIDdosimetry was introduced into the clinic in 2005. Clinically relevant errorswere found and resolved in the treatment planning system, related to pre-setMLC parameters. Daily EPID images were used to determine the range andinfluence of anatomy changes for in vivo dosimetry. It was found that respi-ratory motion, variation in rectal gas pockets and patient positioning were themain anatomy changes that would affect the dose delivered to patients. Var-ious aspects of clinical EPID dosimetry were addressed, including manage-ment of 2D data, analysis of discrepancies observed, automation of analysisand development of action levels. Results for the first 75 patients revealed anaverage agreement within 1% (1 SD) of the total plan for both pre-treatmentand in vivo verification. Combining 2D gamma images from 3 fractions (in vivodata) filtered out random errors due to anatomy variation and rendered similarresults as phantom pre-treatment verification. In vivo replaced pre-treamentchecks for most cases. Two to four clinically relevent errors were detectedand resolved with EPID dosimetry per year. The EPID is therefore suitable forreliable and accurate absolute dose verification during radiotherapy. In addi-tion, the EPID can replace traditional dosimetry devices to verify patient plansbefore treatment, being sufficiently efficient and accurate. The method devel-oped in this thesis is a safety net, providing radiation oncologists with the con-fidence to raise dose levels and introduce sophisticated treatment techniques,which will eventually lead to higher cure rates for patients. Thesis Publica-tionsL McDermott, R Louwe, J Sonke et al "Dose-response and ghosting ef-fects of an amorphous silicon electronic portal imaging device" Med Phys 312004R Louwe, L McDermott, J Sonke et al "The long-term stability of amor-phous silicon flat panel imaging devices for dosimetry purposes" Med Phys31 2004M Wendling, R Louwe, L McDermott et al "Accurate two-dimensionalIMRT verification using a back-projection EPID dosimetry method" Med Phys33 2006L McDermott, M Wendling, J Sonke et al "Anatomy changes in ra-diotherapy detected using portal imaging" RadOnc 79 2006L McDermott, SNijsten, J Sonke et al "A comparison of ghosting effects for three commerciala-Si EPIDs" Med Phys 33 2006L McDermott, M Wendling, B van Asselen etal "Clinical experience with EPID dosimetry for prostate IMRT pre-treatmentdose verification" Med Phys 33 2006L McDermott, M Wendling, J Sonke et al"Replacing pre-treatment verification with in vivo EPID dosimetry for prostateIMRT" Int J Radiat Oncol Biol Phys 67 2007

133 speaker

APPLICATION OF MOSFET DOSIMETRY FOR IN VIVO DOSIMETRYIN RADIOTHERAPYE. Bloemen- van Gurp1

1 MAASTRO CLINIC, Maastricht, Netherlands

The research work performed by Esther Bloemen- van Gurp, investigatingthe application of MOSFET dosimetry for in vivo dosimetry in radiotherapy,resulted in a broad application of MOSFET dosimetry in clinical practice andwill be finished in June 2009. The first publication discusses the result of astudy to determine the accuracy of the MOSFET detector for dose measure-ments in a junction field technique, using split beams. The goal of this studywas to evaluate the dose across the split line. The accuracy of the detectorwas determined by an extended set of phantom measurements and the re-sults of this phantom study were used for patient measurements, performedon 5 patients receiving loco-regional treatment for breast cancer, during 10sequential treatment fractions. The influence of factors related to mechanicalproperties and QC procedures of the linear accelerator are also discussed.(Bloemen-van Gurp E.J., du Bois W.F.J., Visser P.A., Bruinvis I., Jalink D.,Hermans J. and Lambin P. Clinical dosimetry with MOSFET dosimeters to de-termine the dose along the field junction in a split beam technique. Radiother-apy and Oncology 67 (2003) 351357).The second publication describes theuse of MOSFET dosimeters for entrance in vivo dose verification during elec-tron beam treatments, performed without build-up material on the detector toprevent the target volume from shadowing effects by the detector. A compre-