Final PhD Oral Examination (Thesis Title: “Monte Carlo Modelling of Peripheral Dose and Risk of Secondary Malignancy in Flattening-Filter-Free and 10 MV Photon Beams for Paediatric Radiotherapy”)

Event Start:
Event End:
Event Location:
Room 203, Graduate Student Centre (6371 Crescent Road)
Intended Audience:
Public
Speaker:
YOUSSEF BEN BOUCHTA
Local Contact:

Physics and Astronomy

Event Information:

Abstract:
One of the most serious late side effects of cancer treatments is the development of a second malignant neoplasm (SMN). While the risk of SMN is influenced by many factors, radiation therapy (RT) during childhood and adolescence has been shown to be one of the most significant factors associated with the development of a second cancer. The work presented in this thesis aims at determining how to minimize the risk of RT-induced SMN without affecting the quality and efficacy of RT treatments. To properly assess dose to the entire body in patients, a Monte Carlo and measurements based model was developed. This model was used to determine the dose delivered to a cohort of pediatric patients by three different photon radiotherapy treatment modes: 6MV flattened, 6MV flattening-filter-free (FFF) and 10MV FFF. To establish the clinical significance of the dose difference between the three modes, the risk of SMN as calculated by four different risk models were assessed for whole lung irradiation (WLI), a treatment used to treat lung metastases in pediatric patients. The mixed Monte Carlo and measurements model was found to be accurate. The uncertainty on the dose was found to be below 9.4 % of the local dose. A comparison of the out-of-field dose delivered by the 6MV FFF and 10MV FFF beams relative to the 6MV flattened beam was presented. The data demonstrated dose reductions of 3.9% (95% CI[2.1,5.7]) and 9.8% (95% CI[8.0, 11.6]) at 5 cm from the planning treatment volume (PTV) and 21.9% (95% CI[13.7, 30.1]) and 25.6% ( 95% CI[17.6,33.6]) at 30 cm for 6MV FFF and 10 MV FFF beams respectively compared to the 6MV flattened beam. In pediatric patients who were treated with WLI, this dose reduction lead to a risk ratio of <0.90 and <0.95 for 10 MV FFF and 6MV FFF respectively compared to the 6MV flattened beam. In conclusion, the work presented in this thesis provides evidence that FFF beams, specifically 10MV FFF beams, deliver lower out-of-field dose than 6MV flattened beams. For WLI treatments, this dose reduction reduces the estimated risk of RT-induced thyroid cancers.

Add to Calendar Event Start: Wednesday, July 3, 2019 - 9:00 am Event End: 11:00 am Final PhD Oral Examination (Thesis Title: “Monte Carlo Modelling of Peripheral Dose and Risk of Secondary Malignancy in Flattening-Filter-Free and 10 MV Photon Beams for Paediatric Radiotherapy”) Event Information: Abstract: One of the most serious late side effects of cancer treatments is the development of a second malignant neoplasm (SMN). While the risk of SMN is influenced by many factors, radiation therapy (RT) during childhood and adolescence has been shown to be one of the most significant factors associated with the development of a second cancer. The work presented in this thesis aims at determining how to minimize the risk of RT-induced SMN without affecting the quality and efficacy of RT treatments. To properly assess dose to the entire body in patients, a Monte Carlo and measurements based model was developed. This model was used to determine the dose delivered to a cohort of pediatric patients by three different photon radiotherapy treatment modes: 6MV flattened, 6MV flattening-filter-free (FFF) and 10MV FFF. To establish the clinical significance of the dose difference between the three modes, the risk of SMN as calculated by four different risk models were assessed for whole lung irradiation (WLI), a treatment used to treat lung metastases in pediatric patients. The mixed Monte Carlo and measurements model was found to be accurate. The uncertainty on the dose was found to be below 9.4 % of the local dose. A comparison of the out-of-field dose delivered by the 6MV FFF and 10MV FFF beams relative to the 6MV flattened beam was presented. The data demonstrated dose reductions of 3.9% (95% CI[2.1,5.7]) and 9.8% (95% CI[8.0, 11.6]) at 5 cm from the planning treatment volume (PTV) and 21.9% (95% CI[13.7, 30.1]) and 25.6% ( 95% CI[17.6,33.6]) at 30 cm for 6MV FFF and 10 MV FFF beams respectively compared to the 6MV flattened beam. In pediatric patients who were treated with WLI, this dose reduction lead to a risk ratio of &lt;0.90 and &lt;0.95 for 10 MV FFF and 6MV FFF respectively compared to the 6MV flattened beam. In conclusion, the work presented in this thesis provides evidence that FFF beams, specifically 10MV FFF beams, deliver lower out-of-field dose than 6MV flattened beams. For WLI treatments, this dose reduction reduces the estimated risk of RT-induced thyroid cancers. Event Location: Room 203, Graduate Student Centre (6371 Crescent Road)

Source URL: https://phas.ubc.ca/final-phd-oral-examination-thesis-title-monte-carlo-modelling-peripheral-dose-and-risk-secondary