68Ga-fibroblast activation protein inhibitor PET/CT on gross tumour volume delineation for radiotherapy planning of oesophageal cancer

BACKGROUND AND PURPOSE

To compare ⁶⁸Ga-fibroblast activation protein inhibitor (FAPI) and ¹⁸F-FDG PET/CT in imaging locally advanced oesophageal cancer, and evaluate the potential usefulness of ⁶⁸Ga-FAPI PET/CT on gross target volume (GTV) delineation aimed at radiotherapy planning for oesophageal cancer as compared with contrast-enhanced CT (CE-CT) and ¹⁸F-FDG PET/CT.

MATERIALS AND METHODS

Twenty-one patients with newly diagnosed oesophageal cancer who underwent both ¹⁸F-FDG and ⁶⁸Ga-FAPI PET/CT scans were selected. GTVs of the primary tumours based on CE-CT (GTV_CT), PET/CT, and CE-CT plus PET/CT were delineated. Gross tumour lengths were measured by GTVs and endoscopy and recorded.

RESULTS

The ⁶⁸Ga-FAPI PET showed significantly higher radiotracer uptake than ¹⁸F-FDG PET (median SUVmax 16.71 vs. 11.23; P = 0.002) in the primary tumours. SUV thresholds of FAPI ×20%, 30%, 40%, and FDG ×40% showed similar lesion lengths compared with that in endoscopic examination (P > 0.05). GTV_CT demonstrated the largest volume (median: 48.80 mm³, range: 14.83-162.23 mm³) than PET-based GTVs. For PET/CT-guided complementary contouring of GTV_CT, four patients (19%) were increased by FAPI ×20% and 30%, two patients (9.5%) were increased by FAPI ×40%, and only one patient was increased by FDG ×40%. Furthermore, the volume of GTV based on CE-CT plus FAPI ×20%, 30%, and 40% showed no significant difference with GTV_CT and planning target volume based CE-CT plus FAPI-PET and meets the organ at risk standard.

CONCLUSION

The ⁶⁸Ga-FAPI PET/CT methodology showed favourable tumour-to-background contrast in oesophageal cancer and might provide additional information for target volume delineation and help avoid tumour geographic misses.

Aspects of dosimetry and clinical practice of skin brachytherapy: The American Brachytherapy Society working group report

PURPOSE

Nonmelanoma skin cancers (NMSCs) are the most common type of human malignancy. Although surgical techniques are the standard treatment, radiation therapy using photons, electrons, and brachytherapy (BT) (radionuclide-based and electronic) has been an important mode of treatment in specific clinical situations. The purpose of this work is to provide a clinical and dosimetric summary of the use of BT for the treatment of NMSC and to describe the different BT approaches used in treating cutaneous malignancies.

METHODS AND MATERIALS

A group of experts from the fields of radiation oncology, medical physics, and dermatology, who specialize in managing cutaneous malignancies reviewed the literature and compiled their clinical experience regarding the clinical and dosimetric aspects of skin BT.

RESULTS

A dosimetric and clinical review of both high dose rate ((192)Ir) and electronic BT treatment including surface, interstitial, and custom mold applicators is given. Patient evaluation tools such as staging, imaging, and patient selection criteria are discussed. Guidelines for clinical and dosimetric planning, appropriate margin delineation, and applicator selection are suggested. Dose prescription and dose fractionation schedules, as well as prescription depth are discussed. Commissioning and quality assurance requirements are also outlined.

CONCLUSIONS

Given the limited published data for skin BT, this article is a summary of the limited literature and best practices currently in use for the treatment of NMSC.

The effectiveness of gadolinium MRI to improve target delineation for radiotherapy in hepatocellular carcinoma: a comparative study of rigid image registration techniques

To achieve consistent target delineation in radiotherapy for hepatocellular carcinoma (HCC), image registration between simulation CT and diagnostic MRI was explored. Twenty patients with advanced HCC were included. The median interval between MRI and CT was 11 days. CT was obtained with shallow free breathing and MRI at exhale phase. On each CT and MRI, the liver and the gross target volume (GTV) were drawn. A rigid image registration was taken according to point information of vascular bifurcation (Method[A]) and pixel information of volume of interest only including the periphery of the liver (Method[B]) and manually drawn liver (Method[C]). In nine cases with an indefinite GTV on CT, a virtual sphere was generated at the epicenter of the GTV. The GTV from CT (VGTV[CT]) and MRI (VGTV[MR]) and the expanded GTV from MRI (V+GTV[MR]) considering geometrical registration error were defined. The underestimation (uncovered V[CT] by V[MR]) and the overestimation (excessive V[MR] by V[CT]) were calculated. Through a paired T-test, the difference between image registration techniques was analyzed. For method[A], the underestimation rates of VGTV[MR] and V+GTV[MR] were 16.4 ± 8.9% and 3.2 ± 3.7%, and the overestimation rates were 16.6 ± 8.7% and 28.4 ± 10.3%, respectively. For VGTV[MR] and V+GTV[MR], the underestimation rates and overestimation rates of method[A] were better than method[C]. The underestimation rates and overestimation rates of the VGTV[MR] were better in method[B] than method[C]. By image registration and additional margin, about 97% of HCC could be covered. Method[A] or method[B] could be recommended according to physician preference.