Improvement in the neutron beam collimation for application in boron neutron capture therapy of the head and neck region

In June 2020, the Japanese government approved boron neutron capture therapy for the treatment of head and neck cancer. The treatment is usually performed in a single fraction, with the neutron irradiation time being approximately 30–60 min. As neutrons scatter in air and loses its intensity, it is preferable to bring the patient as close to the beam port as possible to shorten the irradiation time. However, this can be a challenge, especially for patients with head and neck cancer, as the shoulders are an obstacle to a clean positioning. In this study, a novel neutron collimation system for an accelerator based neutron source was designed to allow for a more comfortable treatment, without compromising the irradiation time. Experimental measurements confirmed the simulation results and showed the new collimator can reduce the irradiation time by approximately 60% (under the same condition where the distance between the source and the patient surface was kept the same). The dose delivered to the surrounding healthy tissue was reduced with the new collimator, showing a 25% decrease in the D₅₀ of the mucosal membrane. Overall, the use of the newly designed collimator will allow for a more comfortable treatment of the head and neck region, reduce the treatment time, and reduce the dose delivered to the surrounding healthy tissue

A validated proton beam therapy patch-field protocol for effective treatment of large hepatocellular carcinoma

Development of a curative local treatment for large hepatocellular carcinoma (HCC) is an important issue. Here, we investigated the dose homogeneity, safety and antitumor effectiveness of proton beam therapy (PBT) using a patch-field technique for large HCC. Data from nine patients (aged 52–79 years) with large HCC treated with patch-field PBT were investigated. The cranial–caudal diameters of the clinical target volumes (CTVs) were 15.0–18.6 cm (median 15.9). The CTV was divided cranially and caudally while both isocenters were aligned along the cranial–caudal axis and overlap of the cranial and caudal irradiation fields was set at 0–0.5 mm. Multileaf collimators were used to eliminate hot or cold spots. Total irradiation doses were 60–76.4 Gy equivalents. Irradiation doses as a percentage of the prescription dose (from the treatment planning system) around the junction were a minimum of 93–105%, a mean of 99–112%, and a maximum of 105–120%. Quality assurance (QA) was assessed in the cranial and caudal irradiation fields using imaging plates. Acute adverse effects of Grade 3 were observed in one patient (hypoalbuminemia), and a late adverse effect of Grade 3 was observed in one patient (liver abscess). Child–Pugh class elevations were observed in four patients (A to B: 3; B to C: 1). Overall survival rates at 1 and 2 years were 55 and 14%, respectively, with a median overall survival of 13.6 months. No patients showed local recurrence. Patch-field PBT supported by substantial QA therefore is one of the treatment options for large HCC

Registration error of the liver CT using deformable image registration of MIM Maestro and Velocity AI

BackgroundUnderstanding the irradiated area and dose correctly is important for the reirradiation of organs that deform after irradiation, such as the liver. We investigated the spatial registration error using the deformable image registration (DIR) software products MIM Maestro (MIM) and Velocity AI (Velocity).MethodsImage registration of pretreatment computed tomography (CT) and posttreatment CT was performed in 24 patients with liver tumors. All the patients received proton beam therapy, and the follow-up period was 4–14 (median: 10) months. We performed DIR of the pretreatment CT and compared it with that of the posttreatment CT by calculating the dislocation of metallic markers (implanted close to the tumors).ResultsThe fiducial registration error was comparable in both products: 0.4–32.9 (9.3 ± 9.9) mm for MIM and 0.5–38.6 (11.0 ± 10.0) mm for Velocity, and correlated with the tumor diameter for MIM (r = 0.69, P = 0.002) and for Velocity (r = 0.68, P = 0.0003). Regarding the enhancement effect, the fiducial registration error was 1.0–24.9 (7.4 ± 7.7) mm for MIM and 0.3–29.6 (8.9 ± 7.2) mm for Velocity, which is shorter than that of plain CT (P = 0.04, for both).ConclusionsThe DIR performance of both MIM and Velocity is comparable with regard to the liver. The fiducial registration error of DIR depends on the tumor diameter. Furthermore, contrast-enhanced CT improves the accuracy of both MIM and Velocity

Proton beam therapy for liver metastases from gastric cancer

Liver metastases from gastric cancer (LMGC) is a non-curable, fatal disease with a 5-year survival rate of <10%. Although various local treatments have been applied, their clinical utility has not been established. The purpose of this study was to investigate the safety and effectiveness of proton beam therapy (PBT) for the treatment of patients with LMGC. A total of nine patients (seven men, two women; aged 56–78 years) with LMGC who received PBT between 2002 and 2012 were retrospectively reviewed. Patients who had tumors confined to the liver were investigated, and patients who had extrahepatic tumors were excluded. Six of the patients had solitary tumors, and three patients had multiple tumors. The total irradiation dose was 64–77 Gy relative biological effectiveness (RBE), and three patients received concurrent chemotherapy. The overall and progression-free survival (OS and PFS) rates, local control (LC) rate, and adverse effects were investigated. All patients completed treatment without interruption, and late adverse effects of higher than Grade 3 were not observed. The OS rates at 1, 3 and 5 years were 100%, 78% and 56%, respectively (median, 5.5 years); the PFS rates were 67%, 40% and 40% (median, 2.6 years); and the LC rates were 89%, 71% and 71%. PBT was demonstrated to be a safe treatment, and the OS and PFS rates were not inferior to those for other types of local treatment. Therefore, PBT should be considered as an effective local treatment option for patients with LMGC