Beam direction arrangement using a superconducting rotating gantry in carbon ion treatment for pancreatic cancer

objectives: Carbon ion radiotherapy provides a concen- trated dose distribution to the target and has several advantages over photon radiotherapy. This study aimed to evaluate the optimal beam direction in carbon ion pencil beam scanning and compare dose distributions between the rotating gantry system (RGS) and fixed- beam port system (FBPS).methods: Patients with locally advanced pancreatic cancer were randomly selected. First, dose-volume parameters of 7-beam directions in the prone position were evaluated. Second, a composite plan developed using 4-beam directions in RGS was compared with that developed using FBPS, with a total prescribed dose of 55.2 Gy (relative biological effectiveness, RBE) in 12 fractions.results: Target coverages in the composite plan did not widely differ. For the first and second segments of the duodenum, the mean dose of D2cc was not significantlychanged (23.80 ± 11.90 Gy [RBE] and 25.63 ± 10.41 Gy [RBE] for RGS and FBPS, respectively). However, the dose-volume histogram curve in RGS showed a promi- nent dose reduction in the low-dose region. No signifi- cant differences were observed in the stomach, third and fourth segments of the duodenum, and spinal cord. The mean dose of the total kidney was similar between RGS and FBPS.conclusions: Compared with that of FBPS, the 4-beam arrangement in the prone position using RGS provides comparable or superior dose distribution in the surrounding normal organ while achieving the same target coverage. In addition, RGS allows for single-pa- tient positioning.advances in knowledge: RGS is beneficial in delivering radiotherapy doses to the duodenum and allows for single-patient positioning and a simple planning process

Proof-of-Concept Comparative Dosimetric Analysis of Coplaner Horizontal-Port Carbon-Ion Radiotherapy in the Head and Neck

Purpose/Objective(s)Carbon-ion radiotherapy (CIRT) may offer improved treatment of radioresistant disease in complex anatomy, such as in head and neck (H&N) cancer. Nonetheless, center cost remains prohibitive. A compact center implementing only horizontal ports has been theorized; coplaner irradiation may improve target coverage. As proof of concept, horizontal+coplaner (H+C) treatment was dosimetrically compared in variously located, complex H&N cases, to evaluate feasibility of this approach.Materials/Methods3 previously-treated patients with adenoid cystic carcinoma (ACC) (L. maxillary sinus, R. parotid, upper R. sinus), 1 with R. nasal angiosarcoma, and 1 with R. parotid adenocarcinoma, were selected. A H+C plan was developed on identical CIRT software per standard. Prescription dose was maintained (64-70.4 Gy (RBE)). Bed roll of +/-30 degrees and off-medial transcranial irradiation were employed to improve targeting and organ at risk (OAR) protection. OAR limits included a Dmax 40 Gy (RBE) with V40 20% for optic nerves and chiasm and Dmax 30 Gy (RBE) for brain stem. Individual dose-volume histograms (DVH) were qualitatively compared.ResultsPTV and GTV coverage varied <1% in all cases, with comparable DVHs. Stem dose was below Dmax 30 Gy (RBE) in all patients, with reduced H+C dose noted in the upper R. sinus and L maxillary sinus ACC patients (Dmax 6.8 vs 14.7 Gy (RBE) and 1.3 vs 17.8 Gy (RBE), respectively). H+C unilateral optic nerve dose was above the Dmax limit of 40 Gy (RBE) in the upper R sinus and L maxillary sinus ACC cases as well (40.4 vs 37.0 Gy (RBE) and 45.7 vs 46.2 Gy (RBE), respectively). In the latter case, left H+C optic nerve V40 dose exceeded the 20% limit, at 21.6% vs 3.6% standard. In the former, the upper sinus location increased bilateral eye irradiation: V10 rose from 57% and 0% to 100% each, with Dmax increased to 51.7 from 47 Gy (RBE) in the right, and 30.9 from 8 Gy (RBE) in the left. The sarcoma case experienced increased H+C chiasm Dmax to 28.7 from 1.8 Gy (RBE), below the 40 Gy (RBE) limit. H+C irradiation raised all V5, V10, and V20 brain dosages, with averages of 16.2 vs 2.2%, 10.9 vs 1.5%, and 2.8 vs 0.8%, respectively. Maximums of 25%, 20%, and 7% were noted in the right parotid ACC.ConclusionAdequate CIRT dose delivery with protection of key OARs in complex H&N cancer appears feasible using only a horizontal port with coplaner approach. Dose increase could be seen in optic nerves and eyes when near or obstructing tumor from the port, highlighting disease location and anatomical limitations of treating solely within the horizontal plane. Increased brain dosage was noted in all cases. The impact of low-dose high-LET CIRT on neural tissue requires further exploration prior to deployment of a coplaner approach. Potentials such as sitting-up immobilization for anteroposterior delivery may mitigate the limitations seen here. A larger cohort analysis is in progress.The American Society for Radiation Oncology (ASTRO) Annual meeting 202

Proof-of-Concept Comparative Dosimetric Analysis of Coplanar Horizontal-Port Carbon-Ion Radiotherapy in the Head and Neck

- Adequate CIRT dose delivery with protection of key OARs in complex H&N cancer appears feasible with the horizontal + coplanar approach. - Dose increase in optic nerves and eyes when near or obstructing tumor from the port were noted. - Increased brain dosage was noted in all cases. The impact of low-dose high-LET CIRT on neural tissue requires further exploration. - Potentials such as sitting-up immobilization for anteroposterior delivery may mitigate the limitations seen here. A larger cohort analysis is in progress.American Society for Radiation Oncology (ASTRO) Annual meeting 202

Mapping Land Use/Land Cover Changes and Forest Disturbances in Vietnam Using a Landsat Temporal Segmentation Algorithm

Accurately mapping land use/land cover changes (LULCC) and forest disturbances provides valuable information for understanding the influence of anthropogenic activities on the environment at regional and global scales. Many approaches using satellite remote sensing data have been proposed for characterizing these long-term changes. However, a spatially and temporally consistent mapping of both LULCC and forest disturbances at medium spatial resolution is still limited despite their critical contributions to the carbon cycle. In this study, we examined the applicability of Landsat time series temporal segmentation and random forest classifiers to mapping LULCC and forest disturbances in Vietnam. We used the LandTrendr temporal segmentation algorithm to derive key features of land use/land cover transitions and forest disturbances from annual Landsat time series data. We developed separate random forest models for classifying land use/land cover and detecting forest disturbances at each segment and then derived LULCC and forest disturbances that coincided with each other during the period of 1988–2019. The results showed that both LULCC classification and forest disturbance detection achieved low accuracy in several classes (e.g., producer’s and user’s accuracies of 23.7% and 78.8%, respectively, for forest disturbance class); however, the level of accuracy was comparable to that of existing datasets using the same reference samples in the study area. We found relatively high confusion between several land use/land cover classes (e.g., grass/shrub, forest, and cropland) that can explain the lower overall accuracies of 67.6% and 68.4% in 1988 and 2019, respectively. The mapping of forest disturbances and LULCC suggested that most forest disturbances were followed by forest recovery, not by transitions to other land use/land cover classes. The landscape complexity and ephemeral forest disturbances contributed to the lower classification and detection accuracies in this study area. Nevertheless, temporal segmentation and derived features from LandTrendr were useful for the consistent mapping of LULCC and forest disturbances. We recommend that future studies focus on improving the accuracy of forest disturbance detection, especially in areas with subtle landscape changes, as well as land use/land cover classification in ambiguous and complex landscapes. Using more training samples and effective variables would potentially improve the classification and detection accuracies

Four-dimensional carbon-ion pencil beam treatment planning comparison between robust optimization and range-adapted internal target volume for respiratory-gated liver and lung treatment.

We investigated the dose differences between robust optimization-based treatment planning (4DRO) and range-adapted internal target volume (rITV). We used 4DCT dataset of 20 lung cancer and 20 liver cancer patients, respectively, who had been treated with respiratory-gated carbon-ion pencil beam scanning therapy. 4DRO and rITV plans were created with the same clinical target volume (CTV) and organs at risk (OAR) contours. Four-dimensional dose distribution was calculated using deformable image registration. Dose metrics (e.g. D95, V20) were analyzed. Statistical significance was assessed by the Wilcoxon signed-rank test. For the lung cases, the mean CTV-D95 value for the rITV plan (=98.5%) was same as that for the 4DRO plan (=98.5%, P = 0.106), while the mean D95 value for the CTV + setup margin contour for the rITV plan (=98.2%) was higher than that for the 4DRO plan (95.2%, P < 0.001). For the liver cases, the mean CTV-D95 value for the rITV plan (=98.1%) was slightly lower than that for the 4DRO plan (=98.5%, P < 0.01), while the mean D95 value for the CTV + setup margin contour for the rITV plan (=98.0%) was higher than that for the 4DRO plan (94.1%, P < 0.001). For the doses to the organs at risk (OARs), the ipsilateral lung-V20/liver-V20 values for the rITV plan (=10.1%/19.7%) was significantly higher than that for the 4DRO plan (=8.6%/17.6, P < 0.001). Although the target coverage for 4DRO plan may be worse than that for rITV plan in the presence of the setup error, the 4DRO plan can improve OAR dose while preserving acceptable target dose coverage

Pelvic insufficiency fractures following carbon-ion radiotherapy for uterine carcinomas

Background and purpose: There is growing evidence on the role of carbon-ion radiotherapy (C-ion RT) for gynaecological tumours. Pelvic insufficiency fracture (PIF) decreases the quality of life after photon beam radiotherapy (RT). However, there is little information on PIF after C-ion RT. This study retrospectively assessed incidence of PIF after C-ion RT for uterine carcinomas (UCs) and the associations of clinical and dosimetric parameters with PIF incidence. Material and methods: We performed a pooled analysis of 102 patients with UCs who underwent definitive C-ion RT alone and were followed up for >6 months without any additional RT in the pelvic region. PIF occurrence was surveyed using magnetic resonance imaging and/or computed tomography. Associations of clinical and dosimetric parameters with PIF incidence were analysed. Results: The 2- and 5-year actuarial incidences of ≥grade 1 PIF in all pelvic regions were 22.3% and 42.4%, respectively. The most frequent site of involvement was the sacrum. Log-rank tests showed that higher volumes receiving >10 Gy (relative biological effectiveness) (V10), V20, V30, and V40, body mass index (BMI) under 18.5, and current smoking were associated with increased incidence of ≥grade 1 PIF in the sacrum. Conclusions: We clarified the actuarial incidence of PIF after C-ion RT for UCs. Higher V10, V20, V30, V40, D50%, Dmean, current smoking, BMI <18.5, and using the anterior-posterior direction in whole pelvic irradiation were associated with higher incidences of PIF in the sacrum. The present results may lead to further improvement of C-ion RT for UCs

Dose-averaged linear energy transfer per se does not correlate with late rectal complications in carbon-ion radiotherapy

Background and purpose: Several studies have focused on increasing the linear energy transfer (LET) within tumours to achieve higher biological effects in carbon-ion radiotherapy (C-ion RT). However, it remains unclear whether LET affects late complications. We assessed whether physical dose and LET distribution can be specific factors for late rectal complications in C-ion RT. Materials and methods: Overall, 134 patients with uterine carcinomas were registered and retrospectively analysed. Of 134 patients, 132 who were followed up for >6 months were enrolled. The correlations between the relative biological effectiveness (RBE)-weighted dose based on the Kanai model (the ostensible "clinical dose"), dose-averaged LET (LETd), or physical dose and rectal complications were evaluated. Rectal complications were graded according to the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria. Results: Nine patients developed grade 3 or 4 late rectal complications. Linear regression analysis found that D2cc in clinical dose was the sole risk factor for ≥grade 3 late rectal complications (p = 0.012). The receiver operating characteristic analysis found that D2cc of 60.2 Gy (RBE) was a suitable cut-off value for predicting ≥grade 3 late rectal complications. Among 35 patients whose rectal D2cc was ≥60.2 Gy (RBE), no correlations were found between severe rectal toxicities and LETd alone or physical dose per se. Conclusion: We demonstrated that severe rectal toxicities were related to the rectal D2cc of the clinical dose in C-ion RT. However, no correlations were found between severe rectal toxicities and LETd alone or physical dose per se