Estimating the second primary cancer risk due to proton therapy compared to hybrid IMRT for left sided breast cancer.

BACKGROUND AND PURPOSE: Proton therapy has been proposed as a technique to improve the long-term quality of life of breast cancer patients. This is due to its ability to reduce the dose to healthy tissue compared to conventional X-ray therapy. The aim of this study was to investigate the risk of secondary carcinogenesis due to proton therapy compared to hybrid IMRT for breast treatments. MATERIAL AND METHODS: In this study, the Pinnacle treatment planning system was used to simulate treatment plans for 15 female left-sided whole breast cancer patients with deep inspiration breath hold scans. Two treatment plans were generated for each patient: hybrid intensity modulated radiotherapy (h-IMRT) and intensity modulated proton therapy (IMPT). Using the dose-volume histograms (DVHs) from these plans, the mean lifetime attributed risk (LAR) for both lungs and the contralateral breast were evaluated using the BEIR VII and Schneider full risk models. RESULTS: The results from both risk models show lower LAR estimates for the IMPT treatment plan compared to the h-IMRT treatment plan. This result was observed for all organs of interest and was consistent amongst the two separate risk models. For both treatment plans, the organs from most to least at risk were: ipsilateral lung, contralateral breast, and contralateral lung. In all cases, the risk estimated via the BEIR VII model was higher that the Schneider full risk model. CONCLUSION: The use of proton therapy for breast treatments leads to reduced risk estimates for secondary carcinogenesis. Therefore, proton therapy shows promise in improving the long term treatment outcome of breast patients.

Dosimetric comparison of gantry and horizontal fixed-beam proton therapy treatment plans for base of skull chordoma.

INTRODUCTION: Australia's first proton beam therapy (PBT) centre will house a fixed-beam room and two gantry rooms. As the only PBT facility in Australia for at least the short term, there is a need to efficiently allocate treatment appointments between the gantry and fixed-beam rooms. This planning study assesses the dosimetric differences between fixed-beam and gantry-based treatment plans for base of skull chordoma, one of the core indications likely to be referred for PBT in Australia. METHODS: Retrospective gantry-based and fixed-beam treatment plans were generated for five patients with base of skull chordoma. Fixed-beam plans were generated with a conventional horizontal patient positioning system. Robust intensity modulated proton therapy (IMPT) optimisation and evaluation techniques were used for both delivery systems. Plans were designed to maximise target coverage while adhering to maximum dose constraints to neighbouring critical organs at risk. RESULTS: Robust target coverage and integral dose were found to be approximately equivalent for the gantry-based and fixed-beam plans. Doses to specific organs at risk could be reduced with the gantry-based geometry; however, the gantry-based plans did not exhibit a general decrease in doses to organs at risk. CONCLUSION: A fixed-beam treatment plan was found to be non-inferior to a gantry-based treatment plan for all base of skull patients included in the current study.

Single high-energy arc proton therapy with Bragg peak boost (SHARP).

INTRODUCTION: Because of the co-location of critical organs at risk, base of skull tumours require steep dose gradients to achieve the prescribed dosimetric criteria. When available, proton beam therapy (PBT) is often considered a desirable modality for these cases, but in many instances, compromises in target coverage are still required to achieve critical organ at risk (OAR) tolerance doses. A number of techniques have been proposed to further improve the penumbra of PBT. In the current study, we propose a novel, collimator-free treatment planning technique that combines high-energy shoot-through proton beams with conventional Bragg peak spot placement. The small spot size of the high-energy pencil beams provides a sharp penumbra at the target boundary, and the Bragg peak spots provide a higher linear energy transfer (LET) boost to the target centre. METHODS: Three base of skull chordoma patients were retrospectively planned with three different PBT treatment planning techniques: (1) conventional intensity-modulated proton therapy (IMPT); (2) high-energy proton arc therapy (HE-PAT); and (3) the novel technique combining HE-PAT and IMPT, referred to as single high-energy arc with Bragg peak boost (SHARP). The Monaco 6 treatment planning system was used. RESULTS: SHARP was found to improve the PBT penumbra in the plane perpendicular to the HE-PAT beams. Minimal penumbra differences were observed in the plane of the HE-PAT beams. SHARP reduced dose-averaged LET to surrounding organs at risk. CONCLUSION: A novel PBT treatment planning technique was successfully implemented. Initial results indicate the potential for SHARP to improve the penumbra of PBT treatments for base of skull tumours.

Dosimetric comparison of proton therapy and CyberKnife in stereotactic body radiation therapy for liver cancers.

Stereotactic body radiation therapy (SBRT) has been increasingly used for the ablation of liver tumours. CyberKnife and proton beam therapy (PBT) are two advanced treatment technologies suitable to deliver SBRT with high dose conformity and steep dose gradients. However, there is very limited data comparing the dosimetric characteristics of CyberKnife to PBT for liver SBRT. PBT and CyberKnife plans were retrospectively generated using 4DCT datasets of ten patients who were previously treated for hepatocellular carcinoma (HCC, N = 5) and liver metastasis (N = 5). Dose volume histogram data was assessed and compared against selected criteria; given a dose prescription of 54 Gy in 3 fractions for liver metastases and 45 Gy in 3 fractions for HCC, with previously published consensus-based normal tissue dose constraints. Comparison of evaluation parameters showed a statistically significant difference for target volume coverage and liver, lungs and spinal cord (p < 0.05) dose, while chest wall and skin did not indicate a significant difference between the two modalities. A number of optimal normal tissue constraints was violated by both the CyberKnife and proton plans for the same patients due to proximity of tumour to chest wall. PBT resulted in greater organ sparing, the extent of which was mainly dependent on tumour location. Tumours located on the liver periphery experienced the largest increase in organ sparing. Organ sparing for CyberKnife was comparable with PBT for small target volumes.

Point-of-care ultrasound as a diagnostic tool in respiratory assessment in awake paediatric patients: a comparative study.

BACKGROUND: Chest X-ray (CXR) has typically been the main investigation in children with suspected respiratory pathology. Recent advances in lung point-of-care ultrasound (POCUS) have shown the potential for it to be comparative, if not better, than CXR. The objective of this study was to compare CXR with lung POCUS in children with respiratory illness in a ward-based setting at a paediatric teaching hospital. METHODS: Any child <18 years of age presenting to Southampton Children's Hospital requiring a CXR for clinical reasons also had lung POCUS performed. CXR was reported by a consultant paediatric radiologist and lung POCUS was reviewed retrospectively by a blinded POCUS clinician, with only the clinical information provided on the CXR request. Comparisons were made between the CXR and lung POCUS findings. RESULTS: 100 paired lung POCUS and CXR were included in the study. 30% of lung POCUS were normal with 97% of these having a normal CXR. 70% of cases had POCUS abnormalities with 96% of POCUS cases identifying comparative lung pathology. Lung POCUS therefore had a sensitivity of 98.51% and a specificity of 87.9% with a diagnostic accuracy of 95% when compared with the CXR report. CONCLUSIONS: Lung POCUS has excellent diagnostic accuracy. The diagnosis of normal lung on POCUS when performed by a trained practitioner can reliably reduce the need for a CXR, thus reducing CXR use and radiation exposure in children. An abnormal lung POCUS could then either give the diagnosis or lead to a CXR with the expectation of clinically relevant findings.

A systematic review of volumetric image guidance in proton therapy.

In recent years, proton therapy centres have begun to shift from conventional 2D-kV imaging to volumetric imaging systems for image guided proton therapy (IGPT). This is likely due to the increased commercial interest and availability of volumetric imaging systems, as well as the shift from passively scattered proton therapy to intensity modulated proton therapy. Currently, there is no standard modality for volumetric IGPT, leading to variation between different proton therapy centres. This article reviews the reported clinical use of volumetric IGPT, as available in published literature, and summarises their utilisation and workflow where possible. In addition, novel volumetric imaging systems are also briefly summarised highlighting their potential benefits for IGPT and the challenges that need to be overcome before they can be used clinically.

Volumetric modulated arc therapy (VMAT) comparison to 3D-conformal technique in lung stereotactic ablative radiotherapy (SABR).

INTRODUCTION: Stereotactic ablative radiotherapy (SABR) can be a curative option for non-small cell lung cancer (NSCLC) and oligometastatic lung disease. Volumetric modulated arc therapy (VMAT) has offered further advancements in terms of radiation dose shaping without compromising treatment times however there is potential for greater low-dose exposure to the lung. This study was to assess whether VMAT lung SABR would result in any increase to the dosimetry parameters compared with three-dimensional conformal radiotherapy (3D-CRT) that could confer increased risk of radiation pneumonitis. METHODS: A total of 53 and 30 3D-CRT treatment plans of patients treated with 48 Gy in 4 fractions were compared. RESULTS: No statistically significant difference in planning target volumes between the VMAT 29.9 cc (range 12.4-58.5 cc) and 3D-CRT 31.2 cc (range 12.3-58.3 cc) P = 0.79. The mean of total lung V5, ipsilateral lung V5 and contralateral lung V5 all showed a trend of being smaller in the VMAT treatment group- 14% versus 15.8%, 25.6% versus 30.4% and 1.6% versus 2.2%, respectively, but all were not statistically significant differences. Mean of the mean lung dose MLD, again showed a trend of being lower in the VMAT treatments but was also non-significant, 2.6 Gy versus 3.0 Gy, P = 1.0. Mean V20 was the same in both cohorts, 3.3%. CONCLUSIONS: The dosimetry for 3D-CRT and VMAT plans were not significantly different including V5, and therefore we conclude that VMAT treatment is unlikely to be associated with an increased risk of radiation pneumonitis.

If we build it, will they come? Modeling of public hospital care requirements for the Australian Bragg Centre for Proton Therapy and Research.

INTRODUCTION: The Australian Bragg Centre for Proton Therapy and Research (ABCPTR) will be Australia's first proton beam therapy (PBT) facility. A model was developed to predict associated public hospital care requirements for patients during PBT, to facilitate resource planning for pediatric, adolescent and young adult (AYA), and adult public hospitals in South Australia. METHODS: National incidence rates for specific cancer indications were obtained from the Australian Childhood Cancer Registry, Australian Institute of Health and Welfare and published data. Australian Bureau of Statistics national population projections were used to estimate new cases in 2025 and beyond. Radiation oncologists and pediatric oncologists from the Central Adelaide Local and Women's and Children's Health Network, along with international colleagues, provided guidance on chemotherapy utilization and inpatient admission estimates. RESULTS: It was estimated 180 patients (40.4%) within the adult population (≥25 years) and 265 patients (59.6%) within the pediatric/AYA population (<25 years) would be eligible for PBT in 2025. There was no indication adult cancers would require concurrent outpatient/inpatient chemotherapy, in contrast with pediatric and AYA patients (59.5% and 62.8% outpatient and 18.9% and 41.9% inpatient, respectively). It was estimated 53% and 29% of pediatric and AYA patients could require inpatient admission for toxicity related to disease, concurrent chemotherapy or PBT. CONCLUSION: Associated public hospital care requirements related to the delivery of a national PBT service were estimated. This has particular implications for planning of the new Women's and Children's hospital, co-located with the ABCPTR. True data accuracy will be determined on future data generation and analysis.

Proton-to-photon comparative treatment planning guidelines for the Australian context.

Proton-to-photon comparative treatment planning is a current requirement of Australian Government funding for patients to receive proton beam therapy (PBT) overseas, and a future requirement for Medicare funding of PBT in Australia. Because of the fundamental differences in treatment plan creation and evaluation between PBT and conventional radiation therapy with x-rays (XRT), there is the potential for a lack of consistency in the process of comparing PBT and XRT treatment plans. This may have an impact on patient eligibility assessment for PBT. The objective of these guidelines is to provide a practical reference document for centres performing proton-to-photon comparative planning and thereby facilitate national uniformity.

Development of a randomized 3D cell model for Monte Carlo microdosimetry simulations.

PURPOSE: The objective of the current work was to develop an algorithm for growing a macroscopic tumor volume from individual randomized quasi-realistic cells. The major physical and chemical components of the cell need to be modeled. It is intended to import the tumor volume into GEANT4 (and potentially other Monte Carlo packages) to simulate ionization events within the cell regions. METHODS: A MATLAB© code was developed to produce a tumor coordinate system consisting of individual ellipsoidal cells randomized in their spatial coordinates, sizes, and rotations. An eigenvalue method using a mathematical equation to represent individual cells was used to detect overlapping cells. GEANT4 code was then developed to import the coordinate system into GEANT4 and populate it with individual cells of varying sizes and composed of the membrane, cytoplasm, reticulum, nucleus, and nucleolus. Each region is composed of chemically realistic materials. RESULTS: The in-house developed MATLAB© code was able to grow semi-realistic cell distributions (~2 × 10(8) cells in 1 cm(3)) in under 36 h. The cell distribution can be used in any number of Monte Carlo particle tracking toolkits including GEANT4, which has been demonstrated in this work. CONCLUSIONS: Using the cell distribution and GEANT4, the authors were able to simulate ionization events in the individual cell components resulting from 80 keV gamma radiation (the code is applicable to other particles and a wide range of energies). This virtual microdosimetry tool will allow for a more complete picture of cell damage to be developed.