Statistical analysis of the gamma evaluation acceptance criteria : A simulation study of 2D dose distributions under error free conditions
(2018) In Physica Medica 52. p.4247 Abstract
Purpose: To investigate the statistical distribution of the gamma value under errorfree conditions, in order to study the relation between the gamma evaluation failure rate and statistically significant deviations in the general situation. Methods: The 2D absorbed dose distribution for 30 clinical headandneck IMRT fields were calculated in a QC phantom. For the same fields, dose measurements were simulated by assuming that the calculated value represented the expectation value, and by adding a random spatial uncertainty of 1–9 mm (1SD) and a random dose uncertainty of 1%–3% (1SD). The simulated measurements were then compared to the calculated dose using the gamma evaluation, and the distribution of the failure rate (i.e. the... (More)
Purpose: To investigate the statistical distribution of the gamma value under errorfree conditions, in order to study the relation between the gamma evaluation failure rate and statistically significant deviations in the general situation. Methods: The 2D absorbed dose distribution for 30 clinical headandneck IMRT fields were calculated in a QC phantom. For the same fields, dose measurements were simulated by assuming that the calculated value represented the expectation value, and by adding a random spatial uncertainty of 1–9 mm (1SD) and a random dose uncertainty of 1%–3% (1SD). The simulated measurements were then compared to the calculated dose using the gamma evaluation, and the distribution of the failure rate (i.e. the probability of gamma values above unity) was analysed. Results: For a wide range of the random measurement uncertainty, a distinct peak in the failure rate distribution was observed. The presence of higher failure rates was associated with large values of the second order derivative of the dose distribution. For spatial uncertainties larger than or equal to the resolution of the dose matrix, and for reasonable dose uncertainties, the median value of the failure rate distribution was fairly constant. Conclusions: Simulations showed, in the general case, that the probability of having a gamma value above unity under errorfree conditions was not spatially uniform. We believe that this shortcoming may be partly responsible for the limited ability of the gamma evaluation method to detect errors in clinically relevant situations.
(Less)
 author
 Sunjic, Svjetlana; Ceberg, Crister ^{LU} and Bokulic, Tomislav
 organization
 publishing date
 20180801
 type
 Contribution to journal
 publication status
 published
 subject
 keywords
 Gamma index, IMRT, Treatment planning system
 in
 Physica Medica
 volume
 52
 pages
 6 pages
 publisher
 ISTITUTI EDITORIALI E POLGRAFICI INTERNAZIONALI
 external identifiers

 scopus:85048708666
 ISSN
 11201797
 DOI
 10.1016/j.ejmp.2018.06.633
 language
 English
 LU publication?
 yes
 id
 0fa411d559594c22aa43b7f412f9dcd2
 date added to LUP
 20180627 16:33:16
 date last changed
 20181121 21:40:34
@article{0fa411d559594c22aa43b7f412f9dcd2, abstract = {<p>Purpose: To investigate the statistical distribution of the gamma value under errorfree conditions, in order to study the relation between the gamma evaluation failure rate and statistically significant deviations in the general situation. Methods: The 2D absorbed dose distribution for 30 clinical headandneck IMRT fields were calculated in a QC phantom. For the same fields, dose measurements were simulated by assuming that the calculated value represented the expectation value, and by adding a random spatial uncertainty of 1–9 mm (1SD) and a random dose uncertainty of 1%–3% (1SD). The simulated measurements were then compared to the calculated dose using the gamma evaluation, and the distribution of the failure rate (i.e. the probability of gamma values above unity) was analysed. Results: For a wide range of the random measurement uncertainty, a distinct peak in the failure rate distribution was observed. The presence of higher failure rates was associated with large values of the second order derivative of the dose distribution. For spatial uncertainties larger than or equal to the resolution of the dose matrix, and for reasonable dose uncertainties, the median value of the failure rate distribution was fairly constant. Conclusions: Simulations showed, in the general case, that the probability of having a gamma value above unity under errorfree conditions was not spatially uniform. We believe that this shortcoming may be partly responsible for the limited ability of the gamma evaluation method to detect errors in clinically relevant situations.</p>}, author = {Sunjic, Svjetlana and Ceberg, Crister and Bokulic, Tomislav}, issn = {11201797}, keyword = {Gamma index,IMRT,Treatment planning system}, language = {eng}, month = {08}, pages = {4247}, publisher = {ISTITUTI EDITORIALI E POLGRAFICI INTERNAZIONALI}, series = {Physica Medica}, title = {Statistical analysis of the gamma evaluation acceptance criteria : A simulation study of 2D dose distributions under error free conditions}, url = {http://dx.doi.org/10.1016/j.ejmp.2018.06.633}, volume = {52}, year = {2018}, }