Purpose The target volume for radiotherapy of anal cancer is complex, with the added challenge of it being surrounded by several critical organs at risk (OARs). In this study, we review the dosimetric advantage that can be achieved with intensity modulated proton therapy (IMPT) over intensity modulated radiotherapy (IMRT) and derive the dose constraints for OARs. Materials and Methods Ten consecutive patients of anal cancer treated using rotational IMRT (Rapid Arc; Varian Medical Systems, Palo Alto, USA) in 2023 were reviewed. The contours of the target volumes and OARs (bowel, bladder, marrow, bilateral femoral heads, and external genitalia) were reviewed on Eclipse (v16.1) treatment planning system for adherence to contouring guidelines. The clinical plans were re-evaluated for OAR doses and target volume coverage.The scans with structure sets were exported to RayStation treatment planning system (v12A) for intensity modulated proton therapy (IMPT) planning. The dose for IMPT planning was prescribed to the CTV with 5 mm robustness, keeping dose prescription similar to the clinical IMRT plan (45-50 Gy to pelvis and 55-60 Gy simultaneous boost to any gross disease and gross nodes). The 4 beam class solution was identified as best for IMPT planning. The IMPT plan objective was set 10% to 20% below the lower threshold of RTOG 05–29 and UK guidelines, followed by principles of ALARA for OARs without compromising target coverage. The dose-volume parameters, conformity index (CI) and homogeneity index (HI) were compared for IMRT versus IMPT using student’s t-test. Results Target volume coverage was well achieved with both IMRT and IMPT. However, V100% of GTVp and GTVn and V95%, V98%, V99%, V100% of CTVPelvis and CTVTumourBoost were significantly better with IMPT. HI and CI of target volumes were also significantly improved with IMPT. There was a significant decrease in volume of OARs receiving doses <40 Gy. Volumes receiving higher doses (40-50 Gy) were very small and not significantly affected with use of IMPT. Conclusion IMPT offers improved target coverage with reduction in low-intermediate dose spill to OARs. Based on these results, dose constraints for IMPT planning have been generated for future clinical trial validation.
Respiratory motion management is essential in particle therapy because dose distributions are highly sensitive to motion. This study aimed to clarify the current implementation and technical trends of respiratory motion management in particle therapy in Japan. A questionnaire was distributed to all particle therapy facilities in Japan. Responses were received from 16 of the 26 institutions surveyed (61.5%). The survey investigated treatment sites requiring respiratory motion management, CT datasets used for treatment planning, irradiation techniques, respiratory monitoring devices, gating phase determination methods, dose evaluation approaches, and patient positioning techniques. The liver and pancreas were the treatment sites most frequently managed with respiratory motion mitigation, with 81.3% (13/16) of facilities implementing motion management for both sites. The most commonly used CT dataset for treatment planning was end-expiration phase CT (56.3%, 9/16). End-expiration respiratory-gated irradiation was the most commonly used irradiation method (87.5%, 14/16), while free-breathing and breath-hold irradiation were used less frequently. Laser-based respiratory monitoring systems were the most widely used devices for respiratory waveform acquisition (80.0%, 12/15). Determination of the irradiation phase based on tumor motion magnitude was the most commonly adopted approach (66.7%, 10/15), whereas some facilities used the same irradiation phase for all patients (20.0%, 3/15). Only a limited number of institutions explicitly evaluated dose variations associated with the interplay effect induced by respiratory motion. These findings provide an overview of current respiratory motion management practices in particle therapy facilities in Japan and may contribute to future technological development and standardization of respiratory motion management in particle therapy.
Background Radiotherapy with high linear energy transfer (LET) has shown promise for improving cancer outcomes. Carbon ion radiotherapy (CIRT) combines charged-particle dose conformality with enhanced biological effectiveness. However, clinical development remains constrained by limited center availability, modest trial accrual, and few randomized studies. We reviewed the global landscape of CIRT studies open to enrollment to identify current priorities and gaps. Methods This Particle Therapy Cooperative Group (PTCOG)-sanctioned project, conducted within the CIRT Guidelines Subcommittee, identified studies through registry review and institutional verification. ClinicalTrials.gov and the Japan Registry of Clinical Trials were searched from December 2025 through February 2026. We included interventional CIRT trials and prospective registries open to new enrollment and excluded studies not open to enrollment, retrospective cohorts, proton-only studies, and preclinical studies. Results Thirty-six studies were identified: 35 interventional trials in 6 countries and 1 North American registry-based comparative-effectiveness study. Japan had the largest share, followed by Germany, China, Italy, Austria, and France. Three centers (SPHIC, QST, and HIT) accounted for 21 of 36 studies. The portfolio included 7 phase I, 23 phase II, 5 phase III, and 1 registry study. Pancreatic cancer and sarcoma-related tumors each accounted for 7 studies; head and neck cancers, 5; prostate and breast cancers, 3 each; glioblastoma, lung cancer, and gynecologic malignancies, 2 each; and mucosal melanoma, mixed solid tumors, kidney cancer, esophageal cancer, and hepatocellular carcinoma, 1 each. Most studies were conducted at a single institution and emphasized feasibility, toxicity, local control, progression-free survival, or overall survival. Conclusions This expert-verified inventory shows that CIRT studies open to enrollment remain concentrated by center, disease site, and phase. Future progress may depend more on shared outcome definitions, transparent biological dose reporting, and registry-enabled or multicenter comparative designs than on additional isolated single-institution studies.
