Technical Note: Improving the workflow in a carbon ion therapy center with custom software for enhanced patient care.

Carbon-ion radiation therapy (CIRT) is an up-and-coming modality for cancer treatment. Implementation of CIRT requires collaboration among specialists like radiation oncologists, medical physicists, and other healthcare professionals. Effective communication among team members is necessary for the success of CIRT. However, the current workflows involving data management, treatment planning, scheduling, and quality assurance (QA) can be susceptible to errors, leading to delays and decreased efficiency. With the aim of addressing these challenges, a team of medical physicists developed an in-house workflow management software using FileMaker Pro. This tool has streamlined the workflow and improved the efficiency and quality of patient care.

Prognostic analysis of radiation-induced liver damage following carbon-ion radiotherapy for hepatocellular carcinoma.

BACKGROUND: Radiation-induced liver damage (RILD) occasionally occurs following carbon-ion radiotherapy (CIRT) for liver tumors, such as hepatocellular carcinoma (HCC), in patients with impaired liver function disease. However, the associated risk factors remain unknown. The present study aimed to determine the risk factors of RILD after CIRT. METHODS: We retrospectively analyzed 108 patients with HCC treated with CIRT at the Osaka Heavy Ion Therapy Center between December 2018 and December 2022. RILD was defined as a worsening of two or more points in the Child-Pugh score within 12 months following CIRT. The median age of the patients was 76 years (range 47-95 years), and the median tumor diameter was 41 mm (range 5-160 mm). Based on the pretreatment liver function, 98 and 10 patients were categorized as Child-Pugh class A and B, respectively. We analyzed patients who received a radiation dose of 60 Gy (relative biological effectiveness [RBE]) in four fractions. The median follow-up period was 9.7 months (range 2.3-41.1 months), and RILD was observed in 11 patients (10.1%). RESULTS: Multivariate analysis showed that pretreatment Child-Pugh score B (p = 0.003, hazard ratio [HR] = 6.90) and normal liver volume spared from < 30 Gy RBE (VS30 < 739 cm3) (p = 0.009, HR = 5.22) were significant risk factors for RILD. The one-year cumulative incidences of RILD stratified by Child-Pugh class A or B and VS30 < 739 cm3 or ≥ 739 cm3 were 10.3% or 51.8% and 39.6% or 9.2%, respectively. CONCLUSION: In conclusion, the pretreatment Child-Pugh score and VS30 of the liver are significant risk factors for RILD following CIRT for HCC.

Validation of robust radiobiological optimization algorithms based on the mixed beam model for intensity-modulated carbon-ion therapy.

Currently, treatment planning systems (TPSs) that can compute the intensities of intensity-modulated carbon-ion therapy (IMCT) using scanned carbon-ion beams are limited. In the present study, the computational efficacy of the newly designed IMCT algorithms was analyzed for the first time based on the mixed beam model with respect to the physical and biological doses; moreover, the validity and effectiveness of the robust radiobiological optimization were verified. A dose calculation engine was independently generated to validate a clinical dose determined in the TPS. A biological assay was performed using the HSGc-C5 cell line to validate the calculated surviving fraction (SF). Both spot control (SC) and voxel-wise worst-case scenario (WC) algorithms were employed for robust radiobiological optimization followed by their application in a Radiation Therapy Oncology Group benchmark phantom under homogeneous and heterogeneous conditions and a clinical case for range and position errors. Importantly, for the first time, both SC and WC algorithms were implemented in the integrated TPS platform that can compute the intensities of IMCT using scanned carbon-ion beams for robust radiobiological optimization. For assessing the robustness, the difference between the maximum and minimum values of a dose-volume histogram index in the examined error scenarios was considered as a robustness index. The relative biological effectiveness (RBE) determined by the independent dose calculation engine exhibited a -0.6% difference compared with the RBE defined by the TPS at the isocenter, whereas the measured and the calculated SF were similar. Regardless of the objects, compared with the conventional IMCT, the robust radiobiological optimization enhanced the sensitivity of the examined error scenarios by up to 19% for the robustness index. The computational efficacy of the novel IMCT algorithms was verified according to the mixed beam model with respect to the physical and biological doses. The robust radiobiological optimizations lowered the impact of range and position uncertainties considerably in the examined scenarios. The robustness of the WC algorithm was more enhanced compared with that of the SC algorithm. Nevertheless, the SC algorithm can be used as an alternative to the WC IMCT algorithm with respect to the computational cost.

Treatment planning of carbon ion radiotherapy for prostate cancer based on cellular experiments with PC3 human prostate cancer cells.

[Purpose] Treatment plans for carbon ion radiotherapy (CIRT) in Japan are designed to uniformly deliver the prescribed clinical dose based on the radiosensitivity of human salivary gland (HSG) cells to the planning target volume (PTV). However, sensitivity to carbon beams varies between cell lines, that is, it should be checked that the clinical dose distribution based on the cell radiosensitivity of the treatment site is uniform within the PTV. [Methods] We modeled the linear energy transfer (LET) dependence of the linear-quadratic (LQ) coefficients specific to prostate cancer, which accounts for the majority of CIRT. This was achieved by irradiating prostate cancer cells (PC3) with X-rays from a 4 MV-Linac and carbon beams with different LETs of 11.1-214.3 keV/µm. By using the radiosensitivity of PC3 cells derived from cellular experiments, we reconstructed prostate-cancer-specific clinical dose distributions on patient computed tomography (CT). [Results] The LQ coefficient, α, of PC3 cells was larger than that of HSG cells at low (<50 keV/µm) LET and smaller at high (>50 keV/µm) LET, which was validated by cellular experiments performed on rectangular SOBPs. The reconstructed dose distribution on patient CT was sloped when 1 fraction incident from the one side of the patient was considered, but remained uniform from the sum of 12 fractions of the left-right opposing beams (as is used in clinical practice). [Conclusion] Our study reveals the inhomogeneity of clinical doses in single-field plans calculated using the PC3 radiosensitivity data. However, this inhomogeneity is compensated by using the combination of left-right opposing beams.

Carbon ion radiotherapy using fiducial markers for prostate cancer in Osaka HIMAK: Treatment planning.

PURPOSE: Carbon ion radiotherapy for prostate cancer was performed using two fine needle Gold Anchor (GA) markers for patient position verification in Osaka Heavy Ion Medical Accelerator in Kansai (Osaka HIMAK). The present study examined treatment plans for prostate cases using beam-specific planning target volume (bsPTV) based on the effect of the markers on dose distribution and analysis of target movements. MATERIALS AND METHODS: Gafchromic EBT3 film was used to measure dose perturbations caused by markers. First, the relationships between the irradiated film density and absolute dose with different linear energy transfer distributions within a spread-out Bragg peak (SOBP) were confirmed. Then, to derive the effect of markers, two types of markers, including GA, were placed at the proximal, center, and distal depths within the same SOBP, and dose distributions behind the markers were measured using the films. The amount of internal motion of prostate was derived from irradiation results and analyzed to determine the margins of the bsPTV. RESULTS: The linearity of the film densities against absolute doses was constant within the SOBP and the amount of dose perturbations caused by the markers was quantitatively estimated from the film densities. The dose perturbation close behind the markers was smallest (<10% among depths within the SOBP regardless of types of markers) and increased with depth. The effect of two types of GAs on dose distributions was small and could be ignored in the treatment planning. Based on the analysis results of internal motions of prostate, required margins of the bsPTV were found to be 8, 7, and 7 mm in left-right (LR), anterior-posterior (AP), and superior-inferior (SI) directions, respectively. CONCLUSION: We evaluated the dose reductions caused by markers and determined the margins of the bsPTV, which was applied to the treatment using fiducial markers, using the analysis results of prostate movements.

Impact of time-related factors on biologically accurate radiotherapy treatment planning.

BACKGROUND: The incomplete repair (IR) model expresses the cell repair effect from radiation-induced damage over time, which is given little consideration in actual treatment planning. By incorporating the IR model into the normal tissue complication probability (NTCP), the accuracy and safety of treatment plan evaluations concerning the effect of repair can be improved. This study aims to evaluate the impact of incorporating the IR model into the NTCP by varying time-related factors such as the repair half-time (T1/2) and the junction-shift sc3hedule in craniospinal irradiation (CSI). METHODS: CSI was planned retrospectively, and the NTCP of the spinal cord was calculated with the IR model for values of T1/2 from 1 to 10 h. The NTCP in the case of changing the junction-shift schedule was also examined in the same manner. RESULTS: The NTCP with the IR model increased with increasing T1/2, which is prominent for the larger T1/2. By changing the junction-shift schedule, the NTCP with the IR model decreased when adjacent fields overlapped. CONCLUSIONS: The IR model is a valuable addition to treatment planning because it enables the NTCP to be evaluated including the effect of repair and differences in scheduling to be reflected in the NTCP. However, these are largely dependent on the value of the T1/2.

Physics of epi-thermal boron neutron capture therapy (epi-thermal BNCT).

The physics of epi-thermal neutrons in the human body is discussed in the effort to clarify the nature of the unique radiologic properties of boron neutron capture therapy (BNCT). This discussion leads to the computational method of Monte Carlo simulation in BNCT. The method is discussed through two examples based on model phantoms. The physics is kept at an introductory level in the discussion in this tutorial review.