Open AccessElective nodal irradiation with simultaneous integrated boost stereotactic body radiotherapy for pancreatic cancer: Analyses of planning feasibility and geometrically driven DVH prediction model
Author(s) -
Nakamura Akira,
Prichard Hugh A.,
Wo Jennifer Y.,
Wolfgang John A.,
Hong Theodore S.
Publication year - 2019
Publication title -
journal of applied clinical medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.83
H-Index - 48
ISSN - 1526-9914
DOI - 10.1002/acm2.12528
Subject(s) - medicine , nuclear medicine , pancreatic cancer , radiation treatment planning , radiation therapy , radiology , cancer
Purpose We evaluate the feasibility of the elective nodal irradiation strategy in stereotactic body radiotherapy ( SBRT ) for pancreatic cancer. Methods Three simultaneous integrated boost ( SIB )‐ SBRT plans (Boost1, Boost2, and Boost3) were retrospectively generated for each of 20 different patients. Boost1 delivered 33 and 25 Gy to PTV 1 and PTV 2, respectively. Boost2 delivered 40, 33, and 25 Gy to boost CTV , PTV 1, and PTV 2, respectively. Boost3 delivered 33 and 25 Gy to PTV 1 and PTV 3, respectively. PTV 1 covered the initial standard SBRT plan (InitPlan) gross tumor volume ( GTV ). PTV 2 covered CTV geom which was created by a 10‐mm expansion (15 mm posterior) of GTV . PTV 3 covered CTV prop which included elective nodal regions. The boost CTV included GTV as well as involved vasculature. The planning feasibility in each scenario and dose–volume histograms ( DVH s) were analyzed and compared with the InitPlan (delivered 33 Gy only to PTV 1) by paired t ‐test. Next, a novel DVH prediction model was developed and its performance was evaluated according to the prediction accuracy (AC) of planning violations. Then, the model was used to simulate the impacts of GTV ‐to‐organs at risk ( OAR ) distance and gastrointestinal ( GI ) OAR volume variations on planning feasibility. Results Significant dose increases were observed in GI ‐ OAR s in SIB ‐ SBRT plans when compared with InitPlan. All dose constraints were met in 63% of cases in InitPlan, Boost1, and Boost2, whereas Boost3 developed DVH violations in all cases. Utilizing previous patient anatomy, the novel DVH prediction model achieved a high AC in the prediction of violations for GI ‐ OAR s; the positive predictive value, negative predictive value, and AC were 66%, 90%, and 84%, respectively. Experiments with the model demonstrated that the larger proximity volume of GI ‐ OAR at the shorter distance substantially impacted on planning violations. Conclusions SIB ‐ SBRT plan with geometrically defined prophylactic areas can be dosimetrically feasible, but including all nodal areas with 25 Gy in five fractions appears to be unrealistic.