Benefits of online in vivo dosimetry for single-fraction total body irradiation

Objective: The aim of this study is to implement a new treatment technique in total body irradiation (TBI) using the manual field-in-field-TBI (MFIF-TBI) technique and dosimetrically verifying its results with respect to compensator-based TBI (CB-TBI) and open field TBI technique. Materials and Methods: A rice flour phantom (RFP) was placed on TBI couch with knee bent position at 385 cm source to surface distance. Midplane depth (MPD) was calculated for skull, umbilicus, and calf regions by measuring separations. Three subfields were opened manually for different regions using the multi-leaf collimator and jaws. The treatment Monitor unit (MU) was calculated based on each subfield size. In the CB-TBI technique, Perspex was used as a compensator. Treatment MU was calculated using MPD of umbilicus region and the required compensator thickness was calculated. For open field TBI, treatment MU was calculated using MPD of umbilicus region, and the treatment was executed without placing compensator. The diodes were placed on the surface of RFP to measure the delivered dose and the results were compared. Results: The MFIF-TBI results showed that the deviation was within ± 3.0% for the different regions, except for the neck for which the deviation was 8.72%. In the CB-TBI delivery, the dose deviation was ± 3.0% for different regions in the RFP. The open field TBI results showed that the dose deviation was not within the limit ± 10.0%. Conclusion: The MFIF-TBI technique can be implemented for TBI treatment as no TPS is required, and laborious process of making a compensator can be avoided while ensuring that the dose uniformity in all the regions within the tolerance limit.

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“…The in vivo dosimetry can be performed with MOSFET and diodes. [ 17 21 29 ] In this study, we used in vivo diodes for accurate dose measurement.…”

Section: Discussionmentioning

confidence: 99%

A Phantom Study on Feasibility of Manual Field-in-Field Clinical Implementation for Total Body Irradiation and Comparison of Midplane Dose with Different Bilateral TBI Techniques

Khanna

Pandu

Mohandass

et al. 2023

Journal of Medical Physics

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“…Various detectors can be used for such processes. Some of these have included TLD's,[ 1 ] diodes,[ 2 3 4 ] and MOSFET devices. [ 5 ] Su et al .,[ 6 ] used Gafchromic EBT film for analysis and found that agreement within 4.1% could be achieved compared to TLD measurements.…”

Section: Introductionmentioning

confidence: 99%

Build-up material requirements in clinical dosimetry during total body irradiation treatments

Butson¹,

Pope²,

Haque³

et al. 2016

J Med Phys

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Total body irradiation (TBI) treatments are mainly used in a preparative regimen for hematopoietic stem cell (or bone marrow) transplantation. Our standard clinical regimen is a 12 Gy/6 fraction bi-daily technique using 6MV X-rays at a large extended source to surface distance (SSD). This work investigates and quantifies the dose build-up characteristics and thus the requirements for bolus used for in vivo dosimetry for TBI applications. Percentage dose build-up characteristics of photon beams have been investigated at large extended SSDs using ionization chambers and Gafchromic film. Open field measurements at different field sizes and with differing scatter conditions such as the introduction of standard Perspex scattering plates at different distances to the measurement point were made in an effort to determine the required bolus/build-up material required for accurate determination of applied dose. Percentage surface dose values measured for open fields at 300 cm SSD were found to range from 20% up to 65.5% for fields 5 cm × 5 cm to 40 cm × 40 cm, respectively. With the introduction of 1 cm Perspex scattering plates used in TBI treatments, the surface dose values increased up to 83–90% (93–97% at 1 mm depth), depending on the position of the Perspex scattering plate compared to the measurement point. Our work showed that at least 5 mm water equivalent bolus/scatter material should be placed over the EBT3 film for accurate dose assessment for TBI treatments. Results also show that a small but measurable decrease in measured dose occurred with 5 mm water equivalent thick bolus material of areas '3 cm2. As such, we recommend that 3 cm × 3 cm × 5 mm bolus build-up is the smallest size that should be placed over EBT3 Gafchromic film when used for accurate in vivo dosimetry for TBI applications.

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Clinical use of Gafchromic EBT4 film for in vivo dosimetry for total body irradiation

Draeger,

Guan,

Lee

et al. 2024

J Applied Clin Med Phys

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PurposeIn vivo dosimetry is a common requirement to validate dose accuracy/uniformity in total body irradiation (TBI). Several detectors can be used for in vivo dosimetry, including thermoluminescent dosimeters (TLDs), diodes, ion chambers, optically stimulated luminescent dosimeters (OSLDs), and film. TLDs are well established for use in vivo but required expertise and clinical system availability may make them impractical for multifractionated TBI. OSLDs offer quick readout, but recalls have restricted their use. The purpose of this work was to validate the newly available Gafchromic EBT4 film for TBI in vivo dosimetry.MethodsFilm calibration curves were created under standard conditions (6MV/15MV, 1.5/3.0 cm depth, 100 cm source‐to‐surface distance (SSD), 10 × 10 cm2 field), and films were scanned at several time points (0.5–24 h) to determine the shortest development time that yielded accurate dose measurements. 4 × 4 cm2 films were placed under 1.5 cm thick bolus on the anterior and posterior sides of a solid water phantom to measure entrance and exit dose under TBI conditions (∼600 cm SSD, 39.5 × 39.5 cm2 field, 6 MV/15 MV). These measurements were compared to ion chamber and diode readings for validation. Film measurements were also compared to OSLD measurements for three TBI patients.ResultsThe shortest development time that resulted in accurate dosimetry and allowed for adequate physician review time was 4 h (± 4% dose accuracy). Film entrance and exit dose measurements were within ± 3.8% of ion chamber and diode readings for 6MV and 15MV beams. Patient film measurements were within ∼ ± 5% for the majority of anatomical measurement locations; however, film and OSLD readings for some anatomic locations deviated by > 10%.ConclusionsThese results indicate that EBT4 film can be utilized for accurate in vivo dosimetry for TBI patients and shows good agreement with diode and ion chamber measurements. Further investigation into film and OSLD differences was not possible due to OSLD recalls.

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Benefits of online in vivo dosimetry for single-fraction total body irradiation

Cited by 6 publications

References 16 publications

A Phantom Study on Feasibility of Manual Field-in-Field Clinical Implementation for Total Body Irradiation and Comparison of Midplane Dose with Different Bilateral TBI Techniques

A Phantom Study on Feasibility of Manual Field-in-Field Clinical Implementation for Total Body Irradiation and Comparison of Midplane Dose with Different Bilateral TBI Techniques

Build-up material requirements in clinical dosimetry during total body irradiation treatments

Clinical use of Gafchromic EBT4 film for in vivo dosimetry for total body irradiation

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