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Dosimetric pre-treatment verification of IMRT using an EPID; clinical experience.
Radiother Oncol. 2006 Nov; 81(2):168-75.RO

Abstract

BACKGROUND AND PURPOSE

In our clinic a QA program for IMRT verification, fully based on dosimetric measurements with electronic portal imaging devices (EPID), has been running for over 3 years. The program includes a pre-treatment dosimetric check of all IMRT fields. During a complete treatment simulation at the linac, a portal dose image (PDI) is acquired with the EPID for each patient field and compared with a predicted PDI. In this paper, the results of this pre-treatment procedure are analysed, and intercepted errors are reported. An automated image analysis procedure is proposed to limit the number of fields that need human intervention in PDI comparison.

MATERIALS AND METHODS

Most of our analyses are performed using the gamma index with 3% local dose difference and 3mm distance to agreement as reference values. Scalar parameters are derived from the gamma values to summarize the agreement between measured and predicted 2D PDIs. Areas with all pixels having gamma values larger than one are evaluated, making decisions based on clinically relevant criteria more straightforward.

RESULTS

In 270 patients, the pre-treatment checks revealed four clinically relevant errors. Calculation of statistics for a group of 75 patients showed that the patient-averaged mean gamma value inside the field was 0.43 +/- 0.13 (1SD) and only 6.1 +/- 6.8% of pixels had a gamma value larger than one. With the proposed automated image analysis scheme, visual inspection of images can be avoided in 2/3 of the cases.

CONCLUSION

EPIDs may be used for high accuracy and high resolution routine verification of IMRT fields to intercept clinically relevant dosimetric errors prior to the start of treatment. For the majority of fields, PDI comparison can fully rely on an automated procedure, avoiding excessive workload.

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Authors+Show Affiliations

van Zijtveld M
Department of Radiation Oncology, Division of Medical Physics, Erasmus MC-Daniel den Hoed Cancer Center, Rotterdam, The Netherlands. M.vanzijtveld@erasmusmc.nl
Dirkx ML
No affiliation info available
de Boer HC
No affiliation info available
Heijmen BJ
No affiliation info available

MeSH

Electronic Data ProcessingFemaleFluoroscopyHumansMaleNeoplasmsRadiotherapy DosageRadiotherapy Planning, Computer-AssistedRadiotherapy, Intensity-Modulated

Pub Type(s)

Evaluation Study
Journal Article

Language

eng

PubMed ID

17055604

Citation

van Zijtveld, Mathilda, et al. "Dosimetric Pre-treatment Verification of IMRT Using an EPID; Clinical Experience." Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology, vol. 81, no. 2, 2006, pp. 168-75.
van Zijtveld M, Dirkx ML, de Boer HC, et al. Dosimetric pre-treatment verification of IMRT using an EPID; clinical experience. Radiother Oncol. 2006;81(2):168-75.
van Zijtveld, M., Dirkx, M. L., de Boer, H. C., & Heijmen, B. J. (2006). Dosimetric pre-treatment verification of IMRT using an EPID; clinical experience. Radiotherapy and Oncology : Journal of the European Society for Therapeutic Radiology and Oncology, 81(2), 168-75.
van Zijtveld M, et al. Dosimetric Pre-treatment Verification of IMRT Using an EPID; Clinical Experience. Radiother Oncol. 2006;81(2):168-75. PubMed PMID: 17055604.
* Article titles in AMA citation format should be in sentence-case
TY - JOUR T1 - Dosimetric pre-treatment verification of IMRT using an EPID; clinical experience. AU - van Zijtveld,Mathilda, AU - Dirkx,Maarten L P, AU - de Boer,Hans C J, AU - Heijmen,Ben J M, Y1 - 2006/10/19/ PY - 2005/11/04/received PY - 2006/09/07/revised PY - 2006/09/22/accepted PY - 2006/10/24/pubmed PY - 2007/2/21/medline PY - 2006/10/24/entrez SP - 168 EP - 75 JF - Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology JO - Radiother Oncol VL - 81 IS - 2 N2 - BACKGROUND AND PURPOSE: In our clinic a QA program for IMRT verification, fully based on dosimetric measurements with electronic portal imaging devices (EPID), has been running for over 3 years. The program includes a pre-treatment dosimetric check of all IMRT fields. During a complete treatment simulation at the linac, a portal dose image (PDI) is acquired with the EPID for each patient field and compared with a predicted PDI. In this paper, the results of this pre-treatment procedure are analysed, and intercepted errors are reported. An automated image analysis procedure is proposed to limit the number of fields that need human intervention in PDI comparison. MATERIALS AND METHODS: Most of our analyses are performed using the gamma index with 3% local dose difference and 3mm distance to agreement as reference values. Scalar parameters are derived from the gamma values to summarize the agreement between measured and predicted 2D PDIs. Areas with all pixels having gamma values larger than one are evaluated, making decisions based on clinically relevant criteria more straightforward. RESULTS: In 270 patients, the pre-treatment checks revealed four clinically relevant errors. Calculation of statistics for a group of 75 patients showed that the patient-averaged mean gamma value inside the field was 0.43 +/- 0.13 (1SD) and only 6.1 +/- 6.8% of pixels had a gamma value larger than one. With the proposed automated image analysis scheme, visual inspection of images can be avoided in 2/3 of the cases. CONCLUSION: EPIDs may be used for high accuracy and high resolution routine verification of IMRT fields to intercept clinically relevant dosimetric errors prior to the start of treatment. For the majority of fields, PDI comparison can fully rely on an automated procedure, avoiding excessive workload. SN - 0167-8140 UR - https://www.unboundmedicine.com/medline/citation/17055604/Dosimetric_pre_treatment_verification_of_IMRT_using_an_EPID L2 - https://linkinghub.elsevier.com/retrieve/pii/S0167-8140(06)00486-5 DB - PRIME DP - Unbound Medicine ER -