Browsing by Author "Burger, Hester"

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    A phantom based evaluation on the effects of patient breathing motion on Stereotactic Body Radiotherapy treatment volumes
    (2020) Coetzee, Nicolene; Burger, Hester; Joubert Nanette
    Aim: The aim of the study was to design an upper body phantom to mimic the movement of the lesion inside the lungs during a breathing cycle. Phantom design included an assessment of the motion observed for lung lesions, identification of suitable phantom materials as well as design of a motorized arm to mimic the movements observed inside the lung area of the phantom. Introduction: Expansion margins are added to clinical target volumes contoured by Oncologists in order to safeguard against under- or over-treatment of the target volume. They are designed to account for errors during setup, inaccuracies on the linear accelerator, and movement of targets inside the patient. If the margins are too small, there is a risk that the lesion/target may not receive the necessary dose, due to being partially missed. On the other hand, if the margins are too wide, the lesion will be covered, but normal tissue may receive unnecessary dose, resulting in additional side effects to the patient. Assessment of the impact of these margins is not possible in a static phantom and the availability of a low-cost motorized phantom would assist in the validation of these margins. Method: Previously treated patients' 4D CT scanning data were used to quantify the amount of movement seen for lesions within the lung. A phantom was then designed and built in an attempt to mimic both patient anatomy and movement. Materials were identified to replicate anatomical shape and densities of various organs in the thorax, as seen on CT scan data. Two treatment planning systems (Monaco, (Elekta) and Eclipse (Varian)) were used to determine the dosimetric characteristics of the materials. This was compared to actual dose as delivered by a linear accelerator (Elekta Synergy). Results: Paths were calculated from the breathing cycles during the 4D-CT scan sets and templates designed to mimic these movements. A thorax phantom was built with the appropriate materials suitable and matched densities to replicate a human thorax. Comparing transmission for these materials on a linear accelerator for 6MV and 10MV energy, the deviation from planned versus measured dose varied between 1.67% to 3.32% and 0.45% to 2.30%, respectively for the silicon material and between 0.77% to 3.22% and 0.17% to 2.57% for the 3D printed bone for 6MV and 10MV. iv Conclusion: The measurements done on the linear accelerator matched closely with the calculated values on the treatment planning system for transmission through the materials in the customised phantom. Various proposals were put forward to mimic the movement of the targets within the lung regions. However, it was not possible to manufacture a mechanically based working model due to the small movements observed (<5mm). It is recommended that a robotic solution be investigated as alternative to mimic these small movements.
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    Clinical symptoms and volumetric radiological responses of acoustic neuroma patients, treated with hypo-fractionated image guided radiotherapy (IGRT) at Groote Schuur hospital between 2013 and 2016
    (2018) Riddick, Alison; Parkes, J; Burger, Hester
    Background: Stereotactic radiosurgery (SRS) is the gold standard for treatment of small and medium sized tumours, although fractionated regimens are well described. Access is limited in resource-constrained settings. There are no South African data describing outcomes of AN patients treated with fractionated stereotactic radiotherapy (SRT) using photons. We describe clinical and radiological outcomes of AN patients treated with SRT at an academic centre in Cape Town, South Africa. Objectives: To describe patient demographics, tumour characteristics and patients’ symptoms and changes in symptoms at follow-up. To investigate tumour local control (LC) rates at last follow up MRI, and compare LC rates described for SRS in the literature. To correlate radiologists’ serial 2D maximum linear diameter (MLD) measurements with calculated 3D tumour volume (TV). Methods: Fifteen AN patients treated with modified SRT (18.0gy/3fractions, were identified from the planning database; 13 were included. Patient data and tumour characteristics (size, laterality and previous surgery) were retrospectively extracted from clinic folders. Initial planning data was accessed and checked. Tumour volumes were contoured by the author on all subsequent MRI’s per patient and validated by a second investigator; tumour volume (TV) was automatically calculated. Radiologist’s 2D MLDs were compared with 3D TV. Sensitivity and specificity of radiologist reported change of MLD as a measure of actual change in TV was calculated. LC was calculated, from time of treatment to time of last MRI or time of progression (defined as ≥20% increase in TV). Results: Mean age was 60.4years (range 45-79years), with 4 (30.8%) being female. Seven patients (53.8%) had left sided tumours and median tumour size was 1.15cm3 (mean 1.59 cm3; range 0.62-3.35 cm3). Nine patients (69.2%) had Koos stage 2 ANs, 3 (23.1%) had stage 3 tumours and 1 (7.7%) had a stage I tumour. Two patients had NF2.Median follow-up time 12 was 29 months (range 0-50 months). Median baseline TV, as was 1.15 cm3 (mean 1.59cm3 with range 0.62-3.35 cm3). Three patients had no follow-up MRIs: 2 demised and 1 declined further follow-up. In total 5 patients died, 4 of unrelated causes and 1 of unknown cause (median time to death after RT 24 months, range 6 - 36 months). LC was 74% at 36months. Hearing preservation rate was 67%. No new facial or trigeminal nerve symptoms were noted. Radiologists correctly reported tumour growth in 100% of tumours that grew, and specificity was 77.3% in those that were stable. Conclusion: This is the first local study in hypofractionated SRT using photons. We show lower LC rates than seen in literature; our numbers are small and short follow up time short, with high attrition rates. Acute treatment toxicities were absent. Longer term follow-up is needed to assess late RT effects. A prospective study using this method of treatment would better define LC.