Optimization of dose distributions of target volumes and organs at risk during stereotactic body radiation therapy for pancreatic cancer with dose-limiting auto-shells

Yangsen Cao,Xueling Guo,Chunshan Yu,Zhitao Dai,Xiaofei Zhu,Yongjian Sun,Huojun Zhang,Xiaoping Ju,Yongming Liu

doi:10.1186/s13014-018-0956-7

Abstract

BackgroundTo identify optimization of dose distributions of target volumes and decrease of radiation doses to normal tissues during stereotactic body radiation therapy (SBRT) for pancreatic cancer with dose-limiting auto-shells.MethodsWith the same prescription dose, dose constraints of normal organs and calculation algorithm, treatment plans of each eligible patient were re-generated with 3 shells, 5 shells and 7 shells, respectively. The prescription isodose line and beam number of each patient in 3-shell, 5-shell and 7-shell plan remained the same. Hence, a triplet data set of dosimetric parameters was generated and analyzed.ResultsAs the increase of shell number, the conformal index, volumes encompassed by 100% prescription isodose line and 30% prescription isodose line significantly decreased. The new conformal index was higher in 3-shell group than that in 5-shell and 7-shell group. A sharper dose fall-off was found in 5-shell and 7-shell group compared to 3-shell group. And the tumor coverage in 7-shell was better than that of 3-shell and 5-shell. Lower D5cc of the intestine, D10cc of the stomach, Dmax of the spinal cord and smaller V10 of the spleen was confirmed in 7-shell group compared to 3-shell group.ConclusionsMore conformal dose distributions of target volumes and lower radiation doses to normal organs could be performed with the increase of dose-limiting auto-shells, which may be more beneficial to potential critical organs without established dose constraints.

Highlights

To identify optimization of dose distributions of target volumes and decrease of radiation doses to normal tissues during stereotactic body radiation therapy (SBRT) for pancreatic cancer with dose-limiting auto-shells
All of the treatment plans were generated with pre-selection of constraints, some of which were even stricter than those recommended, and optimization of planning target volume (PTV) coverage (OCO), in order to comply with ALARA
The results of our study indicate that with the increase of the shells, conformity index (CI), volumes encompassed by different isodose lines, doses to organs at risk (OAR) with a certain volume and V10 of the spleen decreased while dose conformity was better

Summary

Introduction

To identify optimization of dose distributions of target volumes and decrease of radiation doses to normal tissues during stereotactic body radiation therapy (SBRT) for pancreatic cancer with dose-limiting auto-shells. High doses may be required to achieve local control attributable to inherent radio-resistance of pancreatic cancer. Collimators are nontrivial for controlling dose conformity and dose fall-off. While multiple fixed collimators may allow better conformity and fewer hot spots around the tumor boundary than a single one, but it is time-consuming and a large number of collimators could even impair plan quality. The Iris collimator can reduce treatment time [8], but may not necessarily lead to better dosimetric plan quality [9]. A larger tumor volume indicated a larger aperture collimator, contributing to a larger penumbra and slow dose fall-off, detrimental to normal organs

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