Dosimetry of conformal dynamic arc radiotherapy and intensity modulated radiotherapy in unresectable cholangiocarcinoma

Background: Radiotherapy in cholangiocrcinoma has to overcome organ tolerance of the upper abdomen. Hi-technology radiotherapy may improve conformity and reduce dose to those organ. Objective: Quantitatively compare the dosimetry of conformal dynamic arc radiotherapy (CD-arcRT) and intensity modulated radiotherapy (IMRT) in unresectable cholangiocarcinoma. Material and methods: Eleven cases of unresectable cholangiocarcinoma were re-planned with IMRT and CDarcRT at King Chulalongkhorn Memorial Hospital between 20 September 2004 and 31 December 2005. Both the planning techniques were evaluated using the dose volume histogram of the planning target volume and organ at risk. The conformation number and dose to critical normal structures were used to determine the techniques. Results: IMRT technique was significantly conformed to the planning target volume than CD-arcRT in term of conformation number. For critical structure, IMRT significantly reduced the radiation dose to liver in terms of mean liver dose, V30Gy and V20Gy of the right kidney. Conclusion: The advantage of IMRT was more conformity and reduced dose to critical structure compared with CD-arcRT, but there was no difference between these techniques in terms of V20Gy of left kidney and maximum dose to the spinal cord.