Respiratory Movement of Upper Abdominal Organs and its Effect on Radiotherapy Planning in Pancreatic Cancer

Aims: Radiotherapy for pancreatic cancer is complicated by the frequent overlapping of the planning target volume (PTV) and the organ at risk (OAR), limiting the dose that can be safely delivered to the tumour. Individualising the margins applied to the clinical target volume (CTV) may reduce OAR irradiation without increasing the risk of geographical miss. We quantified the movement of the pancreas with respiration and evaluated whether individualised margins based on this motion reduced the dose to OARs. Materials and methods: Planning computed tomography scans were acquired in quiet breathing, held expiration and held inspiration. Organ motion was evaluated from displacement of a reproducible point within the pancreas in all directions. Two sets of plans (standard plan: P-stan; individualised plan incorporating movement data: P-ind) were generated for each patient. The PTV and doses to OARs were evaluated for both sets of plans. Results: The mean (standard deviation) movement of the pancreas in the superior-inferior, lateral and anterior-posterior directions were 15.3mm (4.3), 5.2mm (3.5) and 9.7mm (6.1), respectively. The use of individualised margins reduced the mean PTV volume by 33.5% (9.8) (P = 0.0051). The proportional reductions in the percentage of kidney receiving > 10 Gy, small bowel > 45 Gy and liver > 30 Gy were 63.7% (P = 0.0051), 29.3% (P = 0.0125) and 29.2% (P = 0.0107), respectively. For the same level of OAR constraints, individualised margins allowed dose escalation in six of the 10 patients to a mean dose of 63.2 Gy. Conclusions: The present study shows a simple way of incorporating organ motion into the planning process and can be adopted by any centre without major strain on healthcare resources. The use of individualised margins reduced PTV volume and the dose to OARs. This may offer an opportunity for dose escalation to try and further improve local control. Gwynne, S. et at. (2009). Clinical Oncology 21, 713-719 (C) 2009 The Royal College of Radiologists. Published by Elsevier Ltd. All rights reserved.