The impact of corrected field output factors based on IAEA/AAPM code of practice on small‐field dosimetry to the calculated monitor unit in eclipse™ treatment planning system

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Abstract

The objective of this study was to investigate the effect of field output factors (FOFs) according to the current protocol for small‐field dosimetry in conjunction to treatment planning system (TPS) commissioning. The calculated monitor unit (MU) for intensity‐modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT) plans in Eclipse™ TPS were observed. Micro ion chamber (0.01 CC) (CC01), photon field diode (shielded diode) (PFD), and electron field diode (unshielded diode) (EFD) were used to measure percentage depth doses, beam profiles, and FOFs from 1 × 1 cm ² to 10 × 10 cm ² field sizes of 6 MV photon beams. CC01 illustrated the highest percentage depth doses at 10 cm depth while EFD exhibited the lowest with the difference of 1.6% at 1 × 1 cm ². CC01 also produced slightly broader penumbra, the difference with other detectors was within 1 mm. For uncorrected FOF of three detectors, the maximum percent standard deviation (%SD) was 5.4% at 1 × 1 cm ² field size. When the correction factors were applied, this value dropped to 2.7%. For the calculated MU in symmetric field sizes, beam commissioning group from uncorrected FOF demonstrated maximum %SD of 6.0% at 1 × 1 cm ² field size. This value decreased to 2.2% when the corrected FOF was integrated. For the calculated MU in IMRT‐SRS plans, the impact of corrected FOF reduced the maximum %SD from 6.0% to 2.5% in planning target volume (PTV) less than 0.5 cm ³. Beam commissioning using corrected FOF also decreased %SD for VMAT‐SRS plans, although it was less pronounced in comparison to other treatment planning techniques, since the %SD remained less than 2%. The use of FOFs based on IAEA/AAPM TRS 483 has been proven in this research to reduce the discrepancy of calculated MU among three beam commissioning datasets in Eclipse™ TPS. The dose measurement of both symmetric field and clinical cases comparing to the calculation illustrated the dependence of the types of detector commissioning and the algorithm of the treatment planning for small field size.

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Most cited references 28

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Intensity-modulated radiation therapy, protons, and the risk of second cancers.

Eric J Hall (2006)

Intensity-modulated radiation therapy (IMRT) allows dose to be concentrated in the tumor volume while sparing normal tissues. However, the downside to IMRT is the potential to increase the number of radiation-induced second cancers. The reasons for this potential are more monitor units and, therefore, a larger total-body dose because of leakage radiation and, because IMRT involves more fields, a bigger volume of normal tissue is exposed to lower radiation doses. Intensity-modulated radiation therapy may double the incidence of solid cancers in long-term survivors. This outcome may be acceptable in older patients if balanced by an improvement in local tumor control and reduced acute toxicity. On the other hand, the incidence of second cancers is much higher in children, so that doubling it may not be acceptable. IMRT represents a special case for children for three reasons. First, children are more sensitive to radiation-induced cancer than are adults. Second, radiation scattered from the treatment volume is more important in the small body of the child. Third, the question of genetic susceptibility arises because many childhood cancers involve a germline mutation. The levels of leakage radiation in current Linacs are not inevitable. Leakage can be reduced but at substantial cost. An alternative strategy is to replace X-rays with protons. However, this change is only an advantage if the proton machine employs a pencil scanning beam. Many proton facilities use passive modulation to produce a field of sufficient size, but the use of a scattering foil produces neutrons, which results in an effective dose to the patient higher than that characteristic of IMRT. The benefit of protons is only achieved if a scanning beam is used in which the doses are 10 times lower than with IMRT.

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Accelerator beam data commissioning equipment and procedures: report of the TG-106 of the Therapy Physics Committee of the AAPM.

Indra J. Das, Chee-Wai Cheng, Ronald J. Watts … (2008)

For commissioning a linear accelerator for clinical use, medical physicists are faced with many challenges including the need for precision, a variety of testing methods, data validation, the lack of standards, and time constraints. Since commissioning beam data are treated as a reference and ultimately used by treatment planning systems, it is vitally important that the collected data are of the highest quality to avoid dosimetric and patient treatment errors that may subsequently lead to a poor radiation outcome. Beam data commissioning should be performed with appropriate knowledge and proper tools and should be independent of the person collecting the data. To achieve this goal, Task Group 106 (TG-106) of the Therapy Physics Committee of the American Association of Physicists in Medicine was formed to review the practical aspects as well as the physics of linear accelerator commissioning. The report provides guidelines and recommendations on the proper selection of phantoms and detectors, setting up of a phantom for data acquisition (both scanning and no-scanning data), procedures for acquiring specific photon and electron beam parameters and methods to reduce measurement errors (<1%), beam data processing and detector size convolution for accurate profiles. The TG-106 also provides a brief.discussion on the emerging trend in Monte Carlo simulation techniques in photon and electron beam commissioning. The procedures described in this report should assist a qualified medical physicist in either measuring a complete set of beam data, or in verifying a subset of data before initial use or for periodic quality assurance measurements. By combining practical experience with theoretical discussion, this document sets a new standard for beam data commissioning.

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A new formalism for reference dosimetry of small and nonstandard fields.

R Capote, K Rosser, H Palmans … (2008)

The use of small fields in radiotherapy techniques has increased substantially, in particular in stereotactic treatments and large uniform or nonuniform fields that are composed of small fields such as for intensity modulated radiation therapy (IMRT). This has been facilitated by the increased availability of standard and add-on multileaf collimators and a variety of new treatment units. For these fields, dosimetric errors have become considerably larger than in conventional beams mostly due to two reasons; (i) the reference conditions recommended by conventional Codes of Practice (CoPs) cannot be established in some machines and (ii) the measurement of absorbed dose to water in composite fields is not standardized. In order to develop standardized recommendations for dosimetry procedures and detectors, an international working group on reference dosimetry of small and nonstandard fields has been established by the International Atomic Energy Agency (IAEA) in cooperation with the American Association of Physicists in Medicine (AAPM) Therapy Physics Committee. This paper outlines a new formalism for the dosimetry of small and composite fields with the intention to extend recommendations given in conventional CoPs for clinical reference dosimetry based on absorbed dose to water. This formalism introduces the concept of two new intermediate calibration fields: (i) a static machine-specific reference field for those modalities that cannot establish conventional reference conditions and (ii) a plan-class specific reference field closer to the patient-specific clinical fields thereby facilitating standardization of composite field dosimetry. Prior to progressing with developing a CoP or other form of recommendation, the members of this IAEA working group welcome comments from the international medical physics community on the formalism presented here.

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Author and article information

Contributors

Sivalee Suriyapee: ssivalee@yahoo.com

Journal

Journal ID (nlm-ta): J Appl Clin Med Phys

Journal ID (iso-abbrev): J Appl Clin Med Phys

Journal ID (doi): 10.1002/(ISSN)1526-9914

Journal ID (publisher-id): ACM2

Title: Journal of Applied Clinical Medical Physics

Publisher: John Wiley and Sons Inc. (Hoboken )

ISSN (Electronic): 1526-9914

Publication date (Electronic): 01 April 2020

Publication date Collection: May 2020

Volume: 21

Issue: 5 ( doiID: 10.1002/acm2.v21.5 )

Pages: 65-75

Affiliations

[ ¹ ] Medical Physics Program Department of Radiology Faculty of Medicine Chulalongkorn University Bangkok Thailand

[ ² ] Division of Radiation Oncology Department of Radiology King Chulalongkorn Memorial Hospital Bangkok Thailand

Author notes

[*] [* ] Authors to whom correspondence should be addressed: Sivalee Suriyapee

E‐mail: ssivalee@ 123456yahoo.com

Article

Publisher ID: ACM212855

DOI: 10.1002/acm2.12855

PMC ID: 7286014

PubMed ID: 32237215

SO-VID: 2f0b0cd6-12fb-449e-967b-ede2aadb7c86

License:

This is an open access article under the terms of the http://creativecommons.org/licenses/by/4.0/ License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

History

Date received : 07 February 2020

Date revision received : 13 December 2020

Date accepted : 08 February 2020

Page count

Figures: 7, Tables: 8, Pages: 11, Words: 8050

Funding

Funded by: Testing of the IAEA/AAPM Code of Practice on small-field dosimetry

Award ID: IAEA CRP E 2.40.21

Custom metadata

source-schema-version-number 2.0

cover-date May 2020

details-of-publishers-convertor Converter:WILEY_ML3GV2_TO_JATSPMC version:5.8.4 mode:remove_FC converted:10.06.2020

Keywords: eclipse™ tps,monitor unit,small field commissioning,small field detectors,small-field dosimetry,trs 483

Data availability:

Keywords: eclipse™ tps, monitor unit, small field commissioning, small field detectors, small-field dosimetry, trs 483

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The impact of corrected field output factors based on IAEA/AAPM code of practice on small‐field dosimetry to the calculated monitor unit in eclipse™ treatment planning system

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International Journal of Applied Technology in Medical Sciences

Most cited references 28

Intensity-modulated radiation therapy, protons, and the risk of second cancers.

Accelerator beam data commissioning equipment and procedures: report of the TG-106 of the Therapy Physics Committee of the AAPM.

A new formalism for reference dosimetry of small and nonstandard fields.

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