Proton Pencil Beam Scanning Facilitates the Safe Treatment of Extended Radiation Targets for Hodgkin Lymphoma: A Report from the Proton Collaborative Group Registry
Because proton beam therapy (PBT) can lower the dose of radiation to the heart, lungs, and breast, it is an established radiation modality for patients with Hodgkin lymphoma (HL). Pencil beam scanning (PBS) PBT facilitates the treatment of more extensive targets. This may be especially of value for lymphoma patients who require RT to both mediastinal and axillary targets, defined here as extended target RT (ETRT), given the target distribution and need to minimize the lung, heart, and breast dose. Using the Proton Collaborative Group registry, we identified patients with HL treated with PBT to both their mediastinum and axilla, for which DICOM-RT was available. All patients were treated with PBS. To evaluate the dosimetric impact of PBS, we compared delivered PBS plans with VMAT butterfly photon plans optimized to have the same target volume coverage, when feasible. Between 2016 and 2021, twelve patients (median 26 years) received PBS ETRT (median 30.6 Gy (RBE)). Despite the large superior/inferior (SI, median 22.2 cm) and left/right (LR, median 22.8 cm) extent of the ETRT targets, all patients were treated with one isocenter except for two patients (both with SI and LR > 30 cm). Most commonly, anterior beams, with or without posterior beams, were used. Compared to photons, PBS had greater target coverage, better conformity, and lower dose heterogeneity while achieving lower doses to the lungs and heart, but not to the breast. No acute grade 3+ toxicities were reported, including pneumonitis. Proton ETRT in this small cohort was safely delivered with PBS and was associated with an improved sparing of the heart and lungs compared to VMAT.
Building a precise machine-specific time structure of the spot and energy delivery model for a cyclotron-based proton therapy system
Abstract Objective . We proposed an experimental approach to build a precise machine-specific beam delivery time (BDT) prediction and delivery sequence model for standard, volumetric, and layer repainting delivery based on a cyclotron accelerator system. Approach . Test fields and clinical treatment plans’ log files were used to experimentally derive three main beam delivery parameters that impacted BDT: energy layer switching time (ELST), spot switching time, and spot drill time. This derived machine-specific model includes standard, volumetric, and layer repainting delivery sequences. A total of 103 clinical treatment fields were used to validate the model. Main results . The study found that ELST is not stochastic in this specific machine. Instead, it is actually the data transmission time or energy selection time, whichever takes longer. The validation showed that the accuracy of each component of the BDT matches well between machine log files and the model’s prediction. The average total BDT was about (−0.74 ± 3.33)% difference compared to the actual treatment log files, which is improved from the current commercial proton therapy system’s prediction (67.22%±26.19%). Significance . An accurate BDT prediction and delivery sequence model was established for an cyclotron-based proton therapy system IBA ProteusPLUS ® . Most institutions could adopt this method to build a machine-specific model for their own proton system.
Selection of Mediastinal Lymphoma Patients for Proton Therapy Within the Proton Collaborative Group Registry
Purpose: As patients with mediastinal lymphoma are typically young with curable disease, advanced radiation techniques such as proton therapy are often considered to minimize subacute and late toxicity. However, it is unclear which mediastinal lymphoma patients are treated with proton therapy. Within a prospective, multi-institutional proton registry, we characterized mediastinal lymphoma patients treated with proton therapy and assessed concordance with consensus recommendations published in 2018 by the International Lymphoma Radiation Oncology Group (ILROG). Methods: Eligible patients included those with lymphoma of the mediastinum treated exclusively with proton therapy for whom digital imaging and communications in medicine (DICOM) treatment data were available for review. Given the challenge with reliably visualizing the left mainstem coronary artery, the inferior-most aspect of the left pulmonary artery (PA) was used as a surrogate. Extent of disease was characterized as upper mediastinum (above level of left PA), middle mediastinum (below left PA but at or above level of T8), or low mediastinum (below T8). Results: Between November 2012 and April 2019, 56 patients were treated and met inclusion criteria. Patients treated with proton therapy were young (median, 24 y; range: 12 to 88), with over half being female (55%). Patients were most commonly treated at initial diagnosis (86%) and had Hodgkin lymphoma (79%). Most patients (96%) had mediastinal disease that extended down to the level of the heart: 48% had middle and 48% had low mediastinal involvement. Nearly all patients (96%) met the ILROG consensus recommendations: 95% had lower mediastinal disease, 46% were young females, and 9% were heavily pretreated. Heart (mean) and lung dose (mean, V5, V20) were significantly associated with lowest extent of mediastinal disease. Conclusions: Mediastinal lymphoma patients treated with proton therapy are typically young with lower mediastinal involvement. Within a prospective, multi-institutional proton registry, nearly all treated patients fit the ILROG consensus recommendations regarding which mediastinal lymphoma patients may most benefit from proton therapy.
Guidelines for the use and interpretation of assays for monitoring autophagy (4th edition)
1