Liver Motion Case Study Answers

Organ Motion: RT of thoracic and abdomino-pelvic targets poses difficulties of precise target localisation and patient positioning. There is considerable variation in patient position and organ location during planning and treatment. This could be due to difficulties in precise positioning, and immobilisation, patient movement and organ motion. Consequently there is a chance of deviation in the dose absorbed from the actual planned dose to be delivered. Accurate understanding of the details of organ motion specific to the respective sites is necessary for successful planning and execution of RT with an acceptable therapeutic ratio.
The movements of liver during normal respiration are well known. Information on the extent of liver motion is
reported a study which investigated liver motion in 25 patients using a scintillation camera after administering Tc 99 isotope. The liver motion was 11mm +/- 3mm and 12 to 75 mm during regular respiration and deep breathing respectively. Mean liver motion assessed with ultra-sonogram by Suramo85 et al. was 25mm and 55 mm during normal respiration and deep breathing respectively. Davies et al. reported ultrasound based peak and trough liver motion estimates under normal respiration as 10 +/- 8mm (range 5-17mm). The mean movements in other directions were less than 2mm.
Other authors have investigated liver motion using CT and MRI scans. Shimizu89 et al. was the first to report three dimensional liver tumour motions using rapid sequence (one image in 1.5 seconds) MR images in 1999. Extend of movements was reported to be 2.1cms, 0.8 and 0.9 cm in cranio-caudal, ventro-dorsal and medio-lateral
It has multiple functions including production of bile, metabolism of nutrients, excretion of toxic wastes and plasma protein synthesis. It has an abundant blood supply and enormous capacity to regenerate. Radiobiologically, it has multiple functional subunits which are arranged in ‘parallel fashion’. Data from various surgical series has shown that at least 25% of normal liver is necessary for a successful resection . The minimum residual volume required may be higher in the presence of pre-existing liver dysfunction like cirrhosis.
Many of the sub-lethal injuries to liver parenchyma during irradiation to upper abdomen are repaired normally. With the available evidence, irradiation of liver tumour to higher doses of >50Gy is the corner stone in treating primary liver tumours with external RT. Irradiating normal liver to such higher doses and in larger volumes may result in significant damage to liver. The clinical syndrome of radiation induced liver disease (RILD) usually manifest if the mean normal liver dose exceeds 28-30Gy (5% chance of RILD)