An atlas for clinical target volume definition, including elective nodal irradiation in definitive radiotherapy of biliary cancer

Abstract

Radiotherapy (RT) is a treatment option for advanced biliary tract cancer (BTC), often combined with sequential and/or concurrent chemotherapy. The use of modern RT techniques requires accurate clinical target volume (CTV) definition and delineation. However, guidelines for CTV delineation in BTC are lacking. Therefore, the aim of this study was to propose a computer tomography (CT) atlas for CTV definition of BTC. We previously proposed guidelines to define the nodal CTV (CTV-N) in BTC. In this study, based on a literature analysis, we defined the margins to be added to the gross tumor volume (GTV; subclinical and microscopic disease) to define the primary tumor CTV (CTV-T). An abdominal contrast enhanced planning CT scan was performed on three different patients with unresectable intrahepatic cholangiocarcinoma (CC), extrahepatic CC and gallbladder cancer. The GTV and anatomical reference structures were outlined on CT images. Then, based on our guidelines, the CTV-T and CTV-N were delineated and merged to define the final CTV in the three patients. An atlas, showing the defined CTV, was generated from the reference CT images to illustrate the CTV for intra-hepatic CC, extra-hepatic CC and gallbladder cancer. This atlas can be used as an aid for CTV definition in patients with BTC treated with modern RT techniques.

Nodal CTV selection according to primary tumour location and pT stage for biliary tract cancer

“…Despite the widespread use of adjuvant CRT in BTC, there is no consensus on the appropriate definition of the CTV in this setting . Our previous study reported on the nodal areas of potential geographic error in adjuvant RT for BTC .…”

“…Essentially, the overall picture of the pattern of nodal spread emerging from that study seems to correspond well to our findings; however, it lacks important data on the relation between the tumour T‐stage and subsite and the risk of nodal involvement. Our more detailed analysis revealed some meaningful differences and pitfalls, influencing the CTV design: firstly, for IHC, the differences in the pattern of spread between rIHC and l/hIHC result in significant reduction in the CTV for rIHC when compared to that proposed in the atlas—as inclusion of left gastric, lesser curvature and paracardial LNS is not necessary (Fig. ).…”

“…Similarly, Ao LNS is at high risk of involvement only for pT3‐4 stage in dEHC and pEHC. SMA LNS, which is not included in the atlas has a risk of involvement of 33.3% for pT3‐4 dEHC. It is worth noting that both data sets (ours and that of Marinelli et al…”

“…According to the latest ASCO guidelines for adjuvant therapy for resected BTC, an R1 resection status is the indication for postoperative CRT in EHC and gallbladder cancer (GBC) . However, only limited data are still available to guide the clinical target volume (CTV) delineation in BTC, especially with respect to the subsite of disease and the T‐stage of the tumour . The most common pattern of locoregional recurrence in BTC is nodal .…”

“…5 However, only limited data are still available to guide the clinical target volume (CTV) delineation in BTC, especially with respect to the subsite of disease and the Tstage of the tumour. [6][7][8][9] The most common pattern of locoregional recurrence in BTC is nodal. 7 Our previous study compared pathological-surgical data on the pattern of nodal spread with the extent of elective nodal CTV used in published studies on RT for BTC.…”