The impact of dose escalation using fiducial markers in image guided Volumetric Modulated Arc radiotherapy to the focal lesion micro boost of localized prostate cancer / Radwa Fawzy Saleh Ahmed ; Supervised Ahmed Seleem Fouad , Raafat Ragaey Abdelmalek , Omar Abdelaziz Hamada

Thesis (Ph.D.) - Cairo University - Faculty of Medicine - Department of Oncology (Clinical)

Purpose/objective:Measurement of systemic & random errors introduced by the online marker match, the offline marker match & the offline bone match verification and consequently estimating the PTV needed if treatment verification was done guided by: (i) The fiducial markers match (PTVmarker), (ii) The bone structure match (PTVbone) and (iii) The laser markers on the skin only (PTVlaser). Methods/materials:Thirty localized prostate cancer patients treated with dose escalation VMAT giving 78 Gy/35# to the whole prostate & 87Gy simultaneous boost to the focal lesion.Three fiducial markers were inserted US guided; two at the base & the 3rd at the apex. For each patient, two daily MV images were acquired; one pre-online marker match for offline bone match, while the second was acquired post online marker match and was utilized for offline marker as well. Systematic and random errors were calculated for each verification method to estimate the PTV needed. In order to composite the PTVmarker, the online & offline marker matches were compared to check the uncertainty of the marker match process, while CT scans were repeated weekly to estimate the marker migration. The PTVmarker was then added to the evaluated PTV from the online marker match to obtain the PTVlaser. The offline bone match was used to estimate the PTV due to skin marks migration (PTVskin marks migration), which was then deducted from the PTVlaser to acquire the PTVbone

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