Application of gradient dose segmented analysis as a treatment quality indicator for patients undergoing volumetric modulated arc radiotherapy
Date
2022-12
Authors
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Journal ISSN
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH SUMMARY: The gamma analysis metric is a commonly used metric for volumetric modulated arc radiotherapy (VMAT) plan evaluation. The major drawback of this metric is the lack of correlation between gamma passing rates and dose-volume histogram (DVH) values for planning target volumes (PTV). The novel gradient dose segmented analysis (GDSA) metric was developed by Steers et al. to quantify changes in the PTV mean dose (Dmean) for patients undergoing VMAT. In this study, the GDSA metric was applied to 115 head-and-neck cancer patients treated on the Varian Halcyon v2.0 linear accelerator between August 2019 and July 2020 in the Division of Radiation Oncology. The GDSA indicated that a total of 13 patients had received at least one treatment fraction where the PTV Dmean exceeded 3% compared to the first treatment fraction. The kilovoltage cone-beam computed tomography (kV CBCT) images of these patients were analysed to determine the cause. The maximum predicted change in the PTV Dmean was 4.83%. Measurable changes in anterior-posterior and lateral separations were observed for 8 out the 13 patients (62%) where the change in PTV Dmean exceeded 3%. The maximum calculated effective separation change diameter was calculated as 3.86 cm. In cases where the change in PTV Dmean was less than 3%, no measurable separation changes were observed. The pitch-, roll- and yaw-rotational errors were quantified as the Halcyon treatment couch does not allow for online rotational corrections. The maximum pitch, roll and yaw rotational errors were 3.91º ± 0.89º, 3.07º ± 0.51º and 2.62º ± 0.40º, respectively. The mean errors were 0.9º, 0.45º, and 0.43º, for pitch, roll and yaw, respectively.
The obtained results demonstrated that large deviations in PTV Dmean (>3%) were more likely due to change in effective diameter, whereas small deviations in PTV Dmean combined with separation changes less than 1 cm, were more likely caused by errors in pitch for long treatment fields. Weight loss during radiotherapy is well documented and proven to be the highest among head-and-neck cancer patients. The GDSA easily be implemented to identify setup/immobilization errors, as well as aid the department in scheduling new CT scans for patients experiencing continuous weight loss before significant differences in dose delivery occur.
AFRIKAANSE OPSOMMING: Die gamma-analise word oor die algemeen as ‘n plan evaluasie metode vir Volumetriese Gemoduleerde Boogterapie (VGBT, “VMAT”) gebruik. Die grootste nadeel daarvan is die gebrek aan korrelasie tussen die gamma-analise en beplannings-teikenvolumes (BTV) van dosis-volume histogramme (DVH). Steers et al. het ‘n nuwe metode ontwikkel om hierdie probleem te oorkom. Die gesegmenteerde-dosis-gradient-analise (GDGA) kan direk gebruik word om die gemiddelde dosis-verandering in die BTV te bereken vir pasiente wat VGBT ondergaan Die GDGA is retrospektief op 115 kop-en-nek kanker pasiente toegepas wat tussen Augustus 2019 en Julie 2020 op die Varian Halcyon v2.0 lineere versneller behandel is. Die GDGA analise het getoon dat ‘n totaal van 13 pasiente ten minste een fraksie van radioterapie ontvang het, waar die gemiddelde dosis-verandering in die BTV hoer as 3% is vergelyke met die eerste behandelingsfraksie. Die Keelstraal-rekenaartomografiese beelde van hierdie pasiente is analiseer om die oorsprong van hierdie dosis-veranderinge te ondersoek. Die maksimum gemiddelde dosis-verandering in die BTV was 4.83%. Vir agt uit die dertien pasiente (62%) was daar merkbare veranderinge in hul anterior-posterior en laterale separasies. Die maksimum berekende effektiewe separasie diameter verandering is 3.86 cm. Geen merkbare veranderinge in separasie is bereken vir pasiente waar die gemiddelde dosis-verandering in die BTV onder 3% is nie. Die Halcyon se pasient bed laat nie vir rotasie verstellings toe nie en daarom is die hei, rol en gier foute bereken. Die maksimum hei, rol en gier rotasie foute is onderskeidelik as 3.91º ± 0.89º, 3.07º ± 0.51º en 2.62º ± 0.40º, bereken. Die gemiddelde foute vir hei, rol en gier is onderskeidelik bereken as 0.9º, 0.45º en 0.43º. Die resultate toon merkbare veranderinge in die pasiente se effektiewe diameter as die gemiddelde dosis-verandering van die BTV hoer as 3% is. Verder, word klein veranderinge in die gemiddelde dosis-verandering van die BTV tesame met separasie veranderinge kleiner as 1 cm, in alle waarskynlikheid deur foute in die hei van die pasiente veroorsaak. Gewigsverlies tydens radioterapie vir kop-en-nek kankers word volledig in die literatuur omskryf. Dit is maklik om die GDGA in praktyk te implementeer om foute in opstelling/immobilisasie en stelselmatige gewigsverlies in pasiente te monitor voordat merkbare veranderinge in gegewe radioterapie dosisse voorkom.
AFRIKAANSE OPSOMMING: Die gamma-analise word oor die algemeen as ‘n plan evaluasie metode vir Volumetriese Gemoduleerde Boogterapie (VGBT, “VMAT”) gebruik. Die grootste nadeel daarvan is die gebrek aan korrelasie tussen die gamma-analise en beplannings-teikenvolumes (BTV) van dosis-volume histogramme (DVH). Steers et al. het ‘n nuwe metode ontwikkel om hierdie probleem te oorkom. Die gesegmenteerde-dosis-gradient-analise (GDGA) kan direk gebruik word om die gemiddelde dosis-verandering in die BTV te bereken vir pasiente wat VGBT ondergaan Die GDGA is retrospektief op 115 kop-en-nek kanker pasiente toegepas wat tussen Augustus 2019 en Julie 2020 op die Varian Halcyon v2.0 lineere versneller behandel is. Die GDGA analise het getoon dat ‘n totaal van 13 pasiente ten minste een fraksie van radioterapie ontvang het, waar die gemiddelde dosis-verandering in die BTV hoer as 3% is vergelyke met die eerste behandelingsfraksie. Die Keelstraal-rekenaartomografiese beelde van hierdie pasiente is analiseer om die oorsprong van hierdie dosis-veranderinge te ondersoek. Die maksimum gemiddelde dosis-verandering in die BTV was 4.83%. Vir agt uit die dertien pasiente (62%) was daar merkbare veranderinge in hul anterior-posterior en laterale separasies. Die maksimum berekende effektiewe separasie diameter verandering is 3.86 cm. Geen merkbare veranderinge in separasie is bereken vir pasiente waar die gemiddelde dosis-verandering in die BTV onder 3% is nie. Die Halcyon se pasient bed laat nie vir rotasie verstellings toe nie en daarom is die hei, rol en gier foute bereken. Die maksimum hei, rol en gier rotasie foute is onderskeidelik as 3.91º ± 0.89º, 3.07º ± 0.51º en 2.62º ± 0.40º, bereken. Die gemiddelde foute vir hei, rol en gier is onderskeidelik bereken as 0.9º, 0.45º en 0.43º. Die resultate toon merkbare veranderinge in die pasiente se effektiewe diameter as die gemiddelde dosis-verandering van die BTV hoer as 3% is. Verder, word klein veranderinge in die gemiddelde dosis-verandering van die BTV tesame met separasie veranderinge kleiner as 1 cm, in alle waarskynlikheid deur foute in die hei van die pasiente veroorsaak. Gewigsverlies tydens radioterapie vir kop-en-nek kankers word volledig in die literatuur omskryf. Dit is maklik om die GDGA in praktyk te implementeer om foute in opstelling/immobilisasie en stelselmatige gewigsverlies in pasiente te monitor voordat merkbare veranderinge in gegewe radioterapie dosisse voorkom.
Description
Thesis (MSc)--Stellenbosch University, 2022.
Keywords
Cancer -- Radiotherapy, Neck -- Cancer -- Patients, Head -- Cancer -- Patients, UCTD