Biological impact of geometric uncertainties: what margin is needed for intra-hepatic tumors?

Wen-Shan Liu,Shalom Kalnicki,Hsiang-Chi Kuo,Keh-Shih Chuang,Chandan Guha,Dennis Mah,Ravi Yaparpalvi,Linda Hong,Andrew Wu

doi:10.1186/1748-717x-5-48

Abstract

BackgroundTo evaluate and compare the biological impact on different proposed margin recipes for the same geometric uncertainties for intra-hepatic tumors with different tumor cell types or clinical stages.MethodThree different margin recipes based on tumor motion were applied to sixteen IMRT plans with a total of twenty two intra-hepatic tumors. One recipe used the full amplitude of motion measured from patients to generate margins. A second used 70% of the full amplitude of motion, while the third had no margin for motion. The biological effects of geometric uncertainty in these three situations were evaluated with Equivalent Uniform Doses (EUD) for various survival fractions at 2 Gy (SF2).ResultsThere was no significant difference in the biological impact between the full motion margin and the 70% motion margin. Also, there was no significant difference between different tumor cell types. When the margin for motion was eliminated, the difference of the biological impact was significant among different cell types due to geometric uncertainties. Elimination of the motion margin requires dose escalation to compensate for the biological dose reduction due to the geometric misses during treatment.ConclusionsBoth patient-based margins of full motion and of 70% motion are sufficient to prevent serious dosimetric error. Clinical implementation of margin reduction should consider the tumor sensitivity to radiation.

Highlights

To evaluate and compare the biological impact on different proposed margin recipes for the same geometric uncertainties for intra-hepatic tumors with different tumor cell types or clinical stages
There was no significant difference in the biological impact between the full motion margin and the 70% motion margin
When the margin for motion was eliminated, the difference of the biological impact was significant among different cell types due to geometric uncertainties

Summary

Introduction

To evaluate and compare the biological impact on different proposed margin recipes for the same geometric uncertainties for intra-hepatic tumors with different tumor cell types or clinical stages. Primary hepatocellular carcinoma (HCC) and liver metastases are common in East Asia and Africa. The volume of liver cancer patients in the United States increases each year [1]. Advanced RT techniques (3D conformal & stereotactic radiotherapy) have been applied to unresectable focal intrahepatic cancer to improve the local control rate without serious radiation-induced liver disease (RILD) [2,3]. Michigan's group [2] has showed that HCC treatment with RT is promising. The response rate, measured by the shrinkage of the tumor volume, could be as high as 90%. In 2002, HC Park et al [4] found the response rates of HCC were 29.2%, 68.6%, and 77.1% for doses 40 Gy, 40-50 Gy, and 50 Gy, respectively

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