Brachytherapy has been proven to be an
effective radiotherapy modality for a number of treatment sites including the
breast, prostate and cervix. However, it is also recognized that amongst
patients who have received brachytherapy as part of their treatment that up to
15% of such procedures may result in sub-optimal dose distributions.
There has therefore been an increased focus within
the brachytherapy community in recent years towards more comprehensive
treatment validation. One form of treatment validation that is beginning to be
utilized is in-vivo source tracking, through the use of either two-dimensional
detector arrays or single point detectors.
A review of the literature reveals that in-vivo
source tracking techniques using two-dimensional arrays placed beneath a
patient have been shown to have the ability to track the brachytherapy source
to within 2 mm relative to the patient anatomy, whilst detector arrays
integrated into transrectal ultrasound imaging devices can measure a dwell
position with sub-millimetre accuracy, and point detectors placed within a
catheter or on an applicator have measured shifts in dwell positions (relative
to the detector) on the order of 0.5 mm.
In this talk I will discuss the potential
advantages of in-vivo source tracking using point dosimeter arrays as compared to performing in-vivo dosimetry,
particularly in the context of the steep dose gradients experienced in
brachytherapy. Desirable detector properties for performing in-vivo source
tracking will be outlined, with particular reference to the angular dependence
and detector sensitivity.
I will also give an overview of the evolution
and current status of novel detector systems developed at the Centre for
Medical Radiation Physics that have been applied to in-vivo source tracking in
HDR brachytherapy at St George Cancer Care Centre, Sydney and the Fondazione
IRCCS Istituto Nazionale Tumori, Milan.
Finally, beyond the suitability of the detector
type selected for in-vivo source tracking, there are several additional practical
and philosophical challenges that must be overcome when implementing a
successful in-vivo source tracking system. For example, the question of what is
an appropriate in-vivo source tracking error threshold. I’ll conclude this talk
by presenting the current status of in-vivo source tracking in overcoming these
challenges and discuss the outlook of in-vivo source tracking for HDR
brachytherapy as the community moves towards more comprehensive treatment