Exit dose studies in megavoltage photon therapy

Lambert, G.; Liversage, W. E.; Hirst, A.; Doughty, D.

doi:10.1259/0007-1285-56-665-329

Cited by 21 publications

(7 citation statements)

References 5 publications

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“…Since the fractional scatter contribution to depth dose is independent of the beam divergence, (32) we would expect the backscatter effect to be independent, as well. Our results confirmed that the BCF table was independent of SSD and the same was reported by Lambert et al (33) …”

Section: Discussionsupporting

confidence: 93%

Evaluation of six TPS algorithms in computing entrance and exit doses

Tan

Metwaly

Glegg

et al. 2014

J Applied Clin Med Phys

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Entrance and exit doses are commonly measured in in vivo dosimetry for comparison with expected values, usually generated by the treatment planning system (TPS), to verify accuracy of treatment delivery. This report aims to evaluate the accuracy of six TPS algorithms in computing entrance and exit doses for a 6 MV beam. The algorithms tested were: pencil beam convolution (Eclipse PBC), analytical anisotropic algorithm (Eclipse AAA), AcurosXB (Eclipse AXB), FFT convolution (XiO Convolution), multigrid superposition (XiO Superposition), and Monte Carlo photon (Monaco MC). Measurements with ionization chamber (IC) and diode detector in water phantoms were used as a reference. Comparisons were done in terms of central axis point dose, 1D relative profiles, and 2D absolute gamma analysis. Entrance doses computed by all TPS algorithms agreed to within 2% of the measured values. Exit doses computed by XiO Convolution, XiO Superposition, Eclipse AXB, and Monaco MC agreed with the IC measured doses to within 2%‐3%. Meanwhile, Eclipse PBC and Eclipse AAA computed exit doses were higher than the IC measured doses by up to 5.3% and 4.8%, respectively. Both algorithms assume that full backscatter exists even at the exit level, leading to an overestimation of exit doses. Despite good agreements at the central axis for Eclipse AXB and Monaco MC, 1D relative comparisons showed profiles mismatched at depths beyond 11.5 cm. Overall, the 2D absolute gamma (3%/3 mm) pass rates were better for Monaco MC, while Eclipse AXB failed mostly at the outer 20% of the field area. The findings of this study serve as a useful baseline for the implementation of entrance and exit in vivo dosimetry in clinical departments utilizing any of these six common TPS algorithms for reference comparison.PACS numbers: 87.55.‐x, 87.55.D‐, 87.55.N‐, 87.53.Bn

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Section: Discussionsupporting

confidence: 93%

Evaluation of six TPS algorithms in computing entrance and exit doses

Tan

Metwaly

Glegg

et al. 2014

J Applied Clin Med Phys

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“…Consequently, R exit will be influenced by the obliquity of the exit surface (19). It has been found previously (16) that R exit decreases with increasing obliquity, and corrections have been made for this effect in the clinical studies reported here.…”

Section: Lack Of Full Electronic Equilibrium and The Effect Of Exit Smentioning

confidence: 63%

Tumour Dose Estimation using Automated TLD Techniques

et al. 1998

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Lithium fluoride (TLD-700) dosimeters were used to measure exit surface absorbed doses in external beam radiotherapy using an automated TLD reader. Delivered tumour absorbed doses were derived from these measurements for head and neck, pelvis and breast treatments. For the head and neck treatments (first fraction only), the mean percentage difference between prescribed and delivered tumour absorbed doses was -0.15 +/- 3.0% (+/- 1 SD), for the pelvic treatments -0.83 +/- 2.8% and for the breast treatments +0.26 +/- 2.9%. The spread of results is approximately +/- 3% (+/- 1 SD). This is comparable with the estimated uncertainty in a single TLD absorbed dose measurement in phantom (+/- 2%; +/- 1 SD). Thus, ICRU recommended tolerances for absorbed dose delivery of +/- 5% may not be unequivocally detectable using this method. An action level of +/- 10% is suggested, allowing investigation of possible gross errors in treatment delivery at an early stage, before the course of treatment has progressed to a point at which absorbed dose compensation is impossible.

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“…By pro vid ing accurate data ab ou t the volum e o f the radiation patients should receive during the treatm ent, and de tecting possible dosim etric errors p rior to the session, in vivo dosim eters prevent patients from taking less or m ore radiation than the planned doses (4). To ensure th a t patients undergo targe ted doses accurately and reliably, practitioners make use o f in vivo dosim etry systems.…”

Section: Introductionmentioning

confidence: 99%

A Comparative study of radiation doses and treatment area dependence in thermoluminescence dosimetry systems and metal oxide semiconductor field effect transistors

2015

J Turgut Ozal Med Cent

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J o u rn a l O f T u rg u t O za l M e d ic a l C e n te r w w w .jto m c .o rgA C om parative Study o f Radiation Doses and Treatm ent Area Dependence in Thermolum inescence Dosim etry Systems and Metal O xide Sem iconductor Field Effect Transistors Eda Kaya Pepele1, Songül Barlaz Us2, Kadir Yaray3, Celalettin Eroğlu3, Bahar Dirican4, Serdar Soyuer3 1İnönü U niversity, Faculty o f M e d icin e , D e p a rtm e n t o f R adiation O n co lo g y, M alatya, T urkey 2M ersin U niversity, Faculty o f M e d icin e , D e p a rtm e n t o f R adiation O n co lo g y, M ersin, Turkey 3Erciyes U niversity, Faculty o f M e d icin e , D e p a rtm e n t o f R adiation O n co lo g y, Kayseri, Turkey 4G ülhane M ilita ry M e d icin e A cadem y, D e p a rtm e n t o f R adiation O n c o lo g y , A nkara, T urkey AbstractAim: This study aims at examining the differences between thermoluminescense dosimeters and metal oxide semiconductor field effect transistors in terms of radiation doses at different photon energies treatment area dependence in patients who recieved radiotherapy at the Department of Radiation Oncology, İnönü University. Material and Methods: Thermoluminescense dosimeter systems and metal oxide semiconductor field effect transistors were used at 6MV and 25MV in the range of 25-1000 cGy radiation doses to examine radiation dose dependence. Results were evaluated by taking measurements of treatment areas 5x5, 10x10, 15x15, 20x20, 25x25, 30x30, and 40x40 cm2, respectively, to specify treatment area dependence of these systems. Results: In both thermoluminescense dosimeters (TLD) and metal oxide semiconductor field effect transistors (MOSFET), reading values at 6 MV and 25 MV photon energies remained up to 800 cGy. We observed that both systems deviate from linearity at doses above 800 cGy. In TLDs, we recorded a %±1 (6 MV photon energy) and %+4 (25 MV photon energy) change in reading values. This change was %±1 (6 MV photon energy) and %+4 (25 MV photon energy) in MOSFETs. Conclusion: Both dosimeter systems have advantages and disadvantages in terms of accuracy and applicability. Being familiar with dosimeter systems is very important in identifying the accuracy of dose to be admisnistered.

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Exit dose studies in megavoltage photon therapy

Cited by 21 publications

References 5 publications

Evaluation of six TPS algorithms in computing entrance and exit doses

Evaluation of six TPS algorithms in computing entrance and exit doses

Tumour Dose Estimation using Automated TLD Techniques

A Comparative study of radiation doses and treatment area dependence in thermoluminescence dosimetry systems and metal oxide semiconductor field effect transistors

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