A treatment planning study of proton arc therapy for para-aortic lymph node tumors: dosimetric evaluation of conventiona
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RESEARCH
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A treatment planning study of proton arc therapy for para-aortic lymph node tumors: dosimetric evaluation of conventional proton therapy, proton arc therapy, and intensity modulated radiotherapy Jeong-Eun Rah1, Gwe-Ya Kim2, Do Hoon Oh1, Tae Hyun Kim3, Jong Won Kim4, Dae Yong Kim3, Sung Yong Park5 and Dongho Shin3*
Abstract Background: The purpose of this study is to evaluate the dosimetric benefits of a proton arc technique for treating tumors of the para-aortic lymph nodes (PALN). Method: In nine patients, a proton arc therapy (PAT) technique was compared with intensity modulated radiation therapy (IMRT) and proton beam therapy (PBT) techniques with respect to the planning target volume (PTV) and organs at risk (OAR). PTV coverage, conformity index (CI), homogeneity index (HI) and OAR doses were compared. Organ-specific radiation induced cancer risks were estimated by applying organ equivalent dose (OED) and normal tissue complication probability (NTCP). Results: The PAT techniques showed better PTV coverage than IMRT and PBT plans. The CI obtained with PAT was 1.19 ± 0.02, which was significantly better than that for the IMRT techniques. The HI was lowest for the PAT plan and highest for IMRT. The dose to the OARs was always below the acceptable limits and comparable for all three techniques. OED results calculated based on a plateau dose–response model showed that the risk of secondary cancers in organs was much higher when IMRT or PBT were employed than when PAT was used. NTCPs of PAT to the stomach (0.29 %), small bowel (0.69 %) and liver (0.38 %) were substantially lower than those of IMRT and PBT. Conclusion: This study demonstrates that there is a potential role for PAT as a commercialized instrument in the future to proton therapy. Keywords: Proton arc therapy (PAT), Proton beam therapy (RBT), Intensity modulated radiation therapy (IMRT), Organ equivalent doses (OED), Normal tissue complication probability (NTCP)
Introduction New technologies in the delivery of radiation therapy have included the use of intensity-modulated radiation therapy (IMRT) or volumetric modulated arc therapy (VMAT) with linear accelerators, as well as the development of proton beam therapy (PBT), which has increased the ability to maximize the dose to the tumor while sparing normal structures. The VMAT approach has a number of potential * Correspondence: [email protected] 3 Proton Therapy Center, National Cancer Center, Goyang, Korea Full list of author information is available at the end of the article
advantages compared to IMRT, such as significantly reducing the treatment time and the number of MUs, as well as improving normal tissue sparing while keeping adequate coverage. Also, proton beams, unlike X-ray beams, have a low entrance dose, followed by a region of uniform high dose (the spread out Bragg peak) at the target, and then a steep fall-off to zero dose. These characteristics minimize the dose delivered to normal tissues while maximizing the dose delivered to the tumor. Better or comparable dose
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