Review of surface dose detectors in radiotherapy

O'Shea, E.; McCavana, Patrick

doi:10.1017/s1460396903000049

Cited by 13 publications

(7 citation statements)

References 23 publications

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“…There have been several studies comparing different detector types for measurements including the buildup region . The scintillator Exradin W1 was shown to produce depth dose curves in water in close agreement to Monte Carlo calculated curves .…”

Section: Introductionmentioning

confidence: 71%

Detector response in the buildup region of small MV fields

2020

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Purpose The model used to calculate dose distributions in a radiotherapy treatment plan relies on the data entered during beam commissioning. The quality of these data heavily depends on the detector choice made, especially in small fields and in the buildup region. Therefore, it is necessary to identify suitable detectors for measurements in the buildup region of small fields. To aid the understanding of a detector's limitations, several factors that influence the detector signal are to be analyzed, for example, the volume effect due to the detector size, the response to electron contamination, the signal dependence on the polarity used, and the effective point of measurement chosen. Methods We tested the suitability of different small field detectors for measurements of depth dose curves with a special focus on the surface‐near area of dose buildup for fields sized between 10 × 10 and 0.6 × 0.6 cm2. Depth dose curves were measured with 14 different detectors including plane‐parallel chambers, thimble chambers of different types and sizes, shielded and unshielded diodes as well as a diamond detector. Those curves were compared with depth dose curves acquired on Gafchromic film. Additionally, the magnitude of geometric volume corrections was estimated from film profiles in different depths. Furthermore, a lead foil was inserted into the beam to reduce contaminating electrons and to study the resulting changes of the detector response. The role of the effective point of measurement was investigated by quantifying the changes occurring when shifting depth dose curves. Last, measurements for the small ionization chambers taken at opposing biasing voltages were compared to study polarity effects. Results Depth‐dependent correction factors for relative depth dose curves with different detectors were derived. Film, the Farmer chamber FC23, a 0.13 cm3 scanning chamber CC13 and a plane‐parallel chamber PPC05 agree very well in fields sized 4 × 4 and 10 × 10 cm2. For most detectors and in smaller fields, depth dose curves differ from the film. In general, shielded diodes require larger corrections than unshielded diodes. Neither the geometric volume effect nor the electron contamination can account for the detector differences. The biggest uncertainty arises from the positioning of a detector with respect to the water surface and from the choice of the detector's effective point of measurement. Depth dose curves acquired with small ionization chambers differ by over 15% in the buildup region depending on sign of the biasing voltage used. Conclusions A scanning chamber or a PPC40 chamber is suitable for fields larger than 4 × 4 cm2. Below that field size, the microDiamond or small ionization chambers perform best requiring the smallest corrections at depth as well as in the buildup region. Diode response changes considerably between the different types of detectors. The position of the effective point of measurement has a huge effect on the resulting curves, therefore detector specific rather than general shifts of half th...

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Section: Introductionmentioning

confidence: 71%

Detector response in the buildup region of small MV fields

2020

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“…An extrapolation chamber is one category of parallel-plate ionization chamber, with a small sensitive volume which can be varied. Its response is reported to be very good in the non-electronic equilibrium region [21]. Therefore, the surface dose can be estimated by measuring the ionization per unit volume as a function of electrode spacing, and then extrapolating the data to a zero electrode spacing.…”

Section: Introductionmentioning

confidence: 99%

An investigation of the depth dose in the build-up region, andsurface dose for a 6-MV therapeutic photon beam: Monte Carlo simulation and measurements

Apipunyasopon

Srisatit

Phaisangittisakul

2012

Journal of Radiation Research

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The percentage depth dose in the build-up region and the surface dose for the 6-MV photon beam from a Varian Clinac 23EX medical linear accelerator was investigated for square field sizes of 5 × 5, 10 × 10, 15 × 15 and 20 × 20 cm2using the EGS4nrc Monte Carlo (MC) simulation package. The depth dose was found to change rapidly in the build-up region, and the percentage surface dose increased proportionally with the field size from approximately 10% to 30%. The measurements were also taken using four common detectors: TLD chips, PFD dosimeter, parallel-plate and cylindrical ionization chamber, and compared with MC simulated data, which served as the gold standard in our study. The surface doses obtained from each detector were derived from the extrapolation of the measured depth doses near the surface and were all found to be higher than that of the MC simulation. The lowest and highest over-responses in the surface dose measurement were found with the TLD chip and the CC13 cylindrical ionization chamber, respectively. Increasing the field size increased the percentage surface dose almost linearly in the various dosimeters and also in the MC simulation. Interestingly, the use of the CC13 ionization chamber eliminates the high gradient feature of the depth dose near the surface. The correction factors for the measured surface dose from each dosimeter for square field sizes of between 5 × 5 and 20 × 20 cm2are introduced.

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“…Due to the complexity of build-up region dosimetry and the lack of consideration given to the skin dose, physical data related to surface dosimetry are insufficient. [3] Megavoltage photon beams have a skin-sparing effect because the surface dose is usually much lower than the maximum dose that occurs under the skin. [4] Although advanced radiotherapy techniques help to reduce normal tissue damage, unwanted skin reactions still occur.…”

Section: Surface Dosementioning

confidence: 99%

In Vivo Dosimetry In External Radiotherapy

Kesen¹

2017

TJ Oncol

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SUMMARYRadiotherapy is a cancer treatment that uses ionizing radiation to kill or prevent the proliferation of cancerous cells, while also aiming to minimize the damage to healthy tissue. To achieve this in the most effective manner, many radiotherapy machines and treatment techniques have been developed. Today, advanced radiotherapy techniques, such as intensity-modulated radiotherapy, image-guided radiotherapy, and intensity-modulated arc therapy, are frequently being used in cancer treatments. These techniques are applied via computer-controlled devices; therefore, they need to be closely monitored to ensure the dose administered to the patient is as planned. It is important to check the accuracy of the plan to ensure that the correct dose is administered to the patient during treatment. The accuracy of the administered dose can be determined by in vivo dosimetry (IVD). Different measurement devices are used for IVD. In this article, the characteristics of IVD and its measurement systems will be reviewed.

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Review of surface dose detectors in radiotherapy

Cited by 13 publications

References 23 publications

Detector response in the buildup region of small MV fields

Detector response in the buildup region of small MV fields

An investigation of the depth dose in the build-up region, andsurface dose for a 6-MV therapeutic photon beam: Monte Carlo simulation and measurements

In Vivo Dosimetry In External Radiotherapy

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