Comparative Analysis of Recurrent Glioblastoma Target Contours via 11C-Methionine, 68Ga-Prostate-Specific Membrane Antigen Positron Emission Tomography, and Magnetic Resonance Imaging: Implications for Precision Radiotherapy Planning.

Purpose: Glioblastoma (GBM) recurrence poses challenges in radiation therapy treatment planning because reirradiation has limited leeway needed for precise target delineation. Although effective radiotracers are emerging for treatment planning, comparisons of 11C-methionine positron emission tomography (MET-PET), 68Ga-prostate-specific membrane antigen PET (PSMA-PET), and magnetic resonance imaging (MRI) for contouring recurrent GBMs are lacking in the literature. This case study aimed to highlight the differences and similarities in target contours delineated from 3 examinations, aiming to raise doubts about the adequacy of current radiation therapy planning practices. Methods and Materials: A 37-year-old female patient with recurrent Isocitrate dehydrogenase (IDH)1/2 wild-type GBM underwent MRI, MET-PET, and PSMA-PET scans. Target delineations were performed, and volumes were compared using the Dice similarity coefficient, conformity index, and overlap volume, considering different planning target volume margins. Results: We found that MET-PET and MRI volumes showed superior agreement compared with PSMA-PET across all similarity parameters, indicating a more marked discrepancy between PSMA-PET and other modalities. Increasing planning target volume margins demonstrated progressive convergence in intervolume discrepancies. Notably, PSMA-PET delineated larger volumes extending beyond MRI-based volumes. Conclusions: MRI alone may not suffice for target delineation in recurrent GBMs. PET imaging modalities offer complementary insights. Combined PET-MRI guidance could improve tumor boundary detection in target delineation for reirradiation. Prospective trials are necessary to ascertain its impact on patient outcomes.

Therapeutic efficacy of platinum/etoposide regimens in the treatment of advanced poorly differentiated neuroendocrine carcinomas of the lung: A retrospective analysis.

Background: Lung neuroendocrine neoplasms (NENs) are rare malignancies developed from bronchial mucosa. Because of its rarity and complex histopathology, there is limited data on the role of chemotherapy in this subset of tumors. Few studies regarding the treatment of poorly differentiated lung NENs, known as neuroendocrine carcinomas (NECs), are available and many limits are detectable as heterogeneity of tumor samples including different origins and different clinical behaviors, moreover, no evidence of therapeutic advances have been achieved along the last thirty years. Method: We performed a retrospective analysis of 70 patients affected by poorly differentiated lung NECs: half of patients underwent a first line therapy with a combination of cisplatin plus etoposide; the remaining patients receiving carboplatin instead of cisplatin, plus etoposide. Results: In our analysis, the outcomes of patients treated with either cisplatin or carboplatin schedule are similar in terms of ORR (44% versus 33%), DCR (75% versus 70%), PFS (6.0 versus 5.0 months) and OS (13.0 versus 10 months). Median number of chemotherapy cycles was 4 (range 1-8). The 18% of patients required a dose reduction. Main toxicities reported were hematological (70.5%), gastrointestinal (26.5%) and fatigue (18%). Conclusion: Survival rate in our study suggests that high grade lung NENs are characterized by an aggressive behavior and a poor prognosis, despite the treatment with platinum/etoposide according to available data. Clinical results of present study contribute to strengthen available data on the usefulness of platinum/etoposide regimen in the treatment of poorly differentiated lung NENs.

Innovations in Positron Emission Tomography and State of the Art in the Evaluation of Breast Cancer Treatment Response.

The advent of hybrid Positron Emission Tomography/Computed Tomography (PET/CT) and PET/Magnetic Resonance Imaging (MRI) scanners resulted in an increased clinical relevance of nuclear medicine in oncology. The use of [18F]-Fluorodeoxyglucose ([18F]FDG) has also made it possible to study tumors (including breast cancer) from not only a dimensional perspective but also from a metabolic point of view. In particular, the use of [18F]FDG PET allowed early confirmation of the efficacy or failure of therapy. The purpose of this review was to assess the literature concerning the response to various therapies for different subtypes of breast cancer through PET. We start by summarizing studies that investigate the validation of PET/CT for the assessment of the response to therapy in breast cancer; then, we present studies that compare PET imaging (including PET devices dedicated to the breast) with CT and MRI, focusing on the identification of the most useful parameters obtainable from PET/CT. We also focus on novel non-FDG radiotracers, as they allow for the acquisition of information on specific aspects of the new therapies.

A Novel Radiotherapeutic Approach to Treat Bulky Metastases Even From Cutaneous Squamous Cell Carcinoma: Its Rationale and a Look at the Reliability of the Linear-Quadratic Model to Explain Its Radiobiological Effects.

Introduction: Metastatic cutaneous squamous cell carcinoma (cSCC) is a very rare condition. The lack of definition of an oligometastatic subgroup means that there is no consensus for its treatment, unlike the mucosal head and neck counterpart. Like the latter, the cutaneous form is able to develop bulky tumor masses. When this happens, the classic care approach is just for palliative intent due to a likely unfavorable benefit-risk balance typical of aggressive treatments. Here we proposed a novel radiotherapy (RT) technique to treat bulky metastases from cSCC in the context of an overall limited tumor burden and tried to explain its clinical outcome by the currently available mathematical radiobiological and ad hoc developed models. Methods: We treated a case of facial cSCC with three metastases: two of them by classic stereotactic RT and the other by lattice RT supported by metabolic imaging (18F-FDG PET) due to its excessively large dimensions. For the latter lesion, we compared four treatment plans with different RT techniques in order to define the best approach in terms of normal tissue complication probability (NTCP) and tumor control probability (TCP). Moreover, we developed an ad hoc mathematical radiobiological model that could fit better with the characteristics of heterogeneity of this bulky metastasis for which, indeed, a segmentation of normoxic, hypoxic, and necrotic subvolumes might have been assumed. Results: We observed a clinical complete response in all three disease sites; the bulky metastasis actually regressed more rapidly than the other two treated by stereotactic RT. For the large lesion, NTCP predictions were good for all four different plans but even significantly better for the lattice RT plan. Neither the classic TCP nor the ad hoc developed radiobiological models could be totally adequate to explain the reported outcome. This finding might support a key role of the host immune system. Conclusions: PET-guided lattice RT might be safe and effective for the treatment of bulky lesions from cSCC. There might be some need for complex mathematical radiobiological models that are able to take into account any immune system's role in order to explain the possible mechanisms of the tumor response to radiation and the relevant key points to enhance it.

Non-Homogeneous Tumor Growth and Its Implications for Radiotherapy: A Phenomenological Approach.

Tumor regrowth and heterogeneity are important clinical parameters during radiotherapy, and the probability of treatment benefit critically depends on the tumor progression pattern in the interval between the fractional irradiation treatments. We propose an analytic, easy-to-use method to take into account clonal subpopulations with different specific growth rates and radiation resistances. The different strain regrowth effects, as described by Gompertz law, require a dose-boost to reproduce the survival probability of the corresponding homogeneous system and for uniform irradiation. However, the estimate of the survival fraction for a tumor with a hypoxic subpopulation is more reliable when there is a slow specific regrowth rate and when the dependence on the oxygen enhancement ratio of radiotherapy is consistently taken into account. The approach is discussed for non-linear two-population dynamics for breast cancer and can be easily generalized to a larger number of components and different tumor phenotypes.