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Radiology


Figure 1: Elekta Synergy S System with Integrated Kilovoltage Cone-beam Computer Tomography Technology


Image Guidance for Prostate Cancer Rationale for Image-guided Radiotherapy Prostate cancer is one of the few cancer sites where clinical studies have clearly demonstrated the deleterious effects of systematic target displacements during RT treatment. Subgroup analyses of two randomised dose escalation trials studies reported biochemical control rates that decreased by 30 and 20% for patients with a distended rectum on planning CT,11,12


a situation that is not representative of the


treatment course, resulting in a systematic posterior displacement of the prostate and anterior rectal wall. Decreased doses to both the target and the organ at risk were the consequence, as no IGRT was performed to correct this systematic error.


The X-ray source (red) is installed orthogonal to the therapeutic MV beam (yellow) and a cone-beam computed tomography is acquired via rotation of the gantry around the patient.


Figure 2: Patient Set-up in External Beam Radiotherapy for Prostate Cancer


All of the studies used conventional or 3D-conformal RT (3D-CRT) treatment planning techniques and patient set-up was performed according to skin marks and portal imaging, which required rather large safety margins (~10mm). Consequences of large target volumes and suboptimal conformal dose distributions were increased rates of toxicity, especially late rectal toxicity,17 for the efforts to increase the accuracy of RT.


Several randomised trials have confirmed increased rates of biochemical control if irradiation doses were increased from 64 to β to 74 to 79.2Gy.13–16


providing the rationale


Precise patient set-up has been reported to be more difficult in obese patients. IGRT-based patient shifts were larger than 10mm in a left-to- right direction in 1 and 21% of normal weight and severely obese patients, respectively.18


This observation of less precise RT could


explain reports about decreased biochemical control in obese patients in some,19,20


although not all,21 clinical series, which suggests the particular need for IGRT in this patient cohort.


Clinical Results of Image-guided Radiotherapy There are no high-evidence-level data showing that IGRT improves outcome in EBRT for prostate cancer; however, promising studies have been reported by several groups. The deleterious effect of a distended rectum in EBRT without IGRT has been described above and two studies demonstrated that IGRT eliminated this ‘risk-factor’.22,23


Retrospective single-institution studies reported decreased rates of toxicity when IGRT was added to RT,24,25


low rates of toxicity when IGRT and intensity-modulated radiation therapy (IMRT) were practised in dose-escalated RT (see Figure 2).26


Image Guidance for Lung Cancer Rationale for Image-guided Radiotherapy Although RT is accepted as the treatment of choice for early-stage non-small-cell lung cancer (NSCLC) in medically inoperable patients, the rates of local tumour control have been disappointing with conventional RT techniques and conventional fractionation (see Figure 3). Local failure has been reported in 6–70% of the patients with stage I/II disease,27


which is substantially higher than the gold


standard in medically operable patients using open or video-assisted lobectomy.28


As a result of the well-established volume effect,29


control is even worse in advanced NSCLC. After simultaneous radiochemotherapy with irradiation doses of 60–66Gy, local tumour control is expected in only one-third of patients.30–32


A: Traditional patient set-up using alignment of skin marks (external markers) and room lasers; B: Image guidance using megavoltage portal imaging: patient set-up is based on the pelvic bones because of limited soft tissue contrast; C: Kilovotage cone-beam computed tomography with sufficient soft-tissue contrast for visualisation and precise targeting of the prostate.


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Achieving local tumour control is important even in advanced stages of disease with a high risk of systematic progression. Simultaneous treatment increased locoregional control by an absolute 6%, which


EUROPEAN ONCOLOGY & HAEMATOLOGY local and multiple studies reported


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