Elective nodal irradiation with simultaneous integrated boost stereotactic body radiotherapy for pancreatic cancer: Analyses of planning feasibility and geometrically driven DVH prediction model

Abstract

PurposeWe evaluate the feasibility of the elective nodal irradiation strategy in stereotactic body radiotherapy (SBRT) for pancreatic cancer.MethodsThree 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 PTV1 and PTV2, respectively. Boost2 delivered 40, 33, and 25 Gy to boostCTV, PTV1, and PTV2, respectively. Boost3 delivered 33 and 25 Gy to PTV1 and PTV3, respectively. PTV1 covered the initial standard SBRT plan (InitPlan) gross tumor volume (GTV). PTV2 covered CTVgeom which was created by a 10‐mm expansion (15 mm posterior) of GTV. PTV3 covered CTVprop which included elective nodal regions. The boostCTV included GTV as well as involved vasculature. The planning feasibility in each scenario and dose–volume histograms (DVHs) were analyzed and compared with the InitPlan (delivered 33 Gy only to PTV1) 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.ResultsSignificant dose increases were observed in GI‐OARs 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‐OARs; 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.

The timing and design of stereotactic radiotherapy approaches as a part of neoadjuvant therapy in pancreatic cancer: Is it time for change?

“…Elective nodal volumes (i.e., celiac trunk and superior mesenteric artery +/- hepatic artery, superior mesenteric vein, and portal vein) utilizing simultaneous integrated boost would be mandated to minimize marginal miss [15] , [17] , [34] , [55] . Five to fifteen fractions would be allowable on our sample schema while controlling for time to surgery from completion of radiotherapy, favoring the latter in the context of gross primary or nodal disease nearby to organs at risk [17] .…”

ESTRO ACROP guidelines for target volume definition in pancreatic cancer

“…This applies to all clinical situations except for adjuvant treatment for radiotherapy of the primary tumour. Posterior margins between the pancreas and the aorta as well as vena cava inferior are not described well enough in the literature to be recommended [44][45]. An exception might be locally recurrent cancer where the group from Johns Hopkins University systematically analysed high risk volume for recurrence [15].…”

Automated treatment planning as a dose escalation strategy for stereotactic radiation therapy in pancreatic cancer

“…10 The dosimetric feasibility of IMRT and VMAT with SIB for pancreatic cancer has been recently successfully demonstrated for conventional dose fractionation showing excellent tumor coverage, conformity of dose distribution, and sparing of OARs. [11][12][13] At the same time, the technological advancements in immobilization and imaging, together with the ability to deliver high conformal doses and to account for organ motion have led to a widespread implementation of stereotactic body radiotherapy (SBRT) in a number of clinical settings. 14 SBRT has garnered a major interest for pancreatic cancer patients since the delivery of ablative doses in a few fractions may improve downstaging and local control and also the shorter treatment time results in an easy integration with chemotherapy.…”

“…For pancreatic cancer, this strategy could deliver a boost dose to the portion of tumor infiltrating the peripancreatic vessels, with the aim of achieving tumor resectability, and a lower dose to the rest of the target volume, avoiding an overdosage to the portion of tumor overlapping the duodenal wall 10 . The dosimetric feasibility of IMRT and VMAT with SIB for pancreatic cancer has been recently successfully demonstrated for conventional dose fractionation showing excellent tumor coverage, conformity of dose distribution, and sparing of OARs 11–13 …”