Accumulated dose implications from systematic dose-rate transients in gated treatments with Viewray MRIdian accelerators.

The combination of magnetic resonance (MR) imaging and linear accelerators (linacs) into MR-Linacs enables continuous MR imaging and advanced gated treatments of patients. Previously, a dose-rate transient (∼8% reduced dose rate during the initial 0.5 s of each beam) was identified for a Viewray MRIdian MR-Linac (Klavsenet al2022Radiation Measurement106759). Here, the dose-rate transient is studied in more detail at four linacs of the same type at different hospitals. The implications of dose-rate transients were examined for gated treatments. The dose-rate transients were investigated using dose-per pulse measurements with organic plastic scintillators in three experiments: (i) A gated treatment with the scintillator placed in a moving target in a dynamic phantom, (ii) a gated treatment with the same dynamic conditions but with the scintillator placed in a stationary target, and (iii) measurements in a water-equivalent material to examine beam quality deviations at a dose-per-pulse basis. Gated treatments (i) compared with non-gated treatments with a static target in the same setup showed a broadening of accumulated dose profiles due to motion (dose smearing). The linac with the largest dose-rate transient had a reduced accumulated dose of up to (3.1 ± 0.65) % in the center of the PTV due to the combined dose smearing and dose-rate transient effect. Dose-rate transients were found to vary between different machines. Two MR-Linacs showed initial dose-rate transients that could not be identified from conventional linearity tests. The source of the transients includes an initial change in photon fluence rate and an initial change in x-ray beam quality. For gated treatments, this caused a reduction of more than 1% dose delivered at the central part of the beam for the studied, cyclic-motion treatment plan. Quality assurance of this effect should be considered when gated treatment with the Viewray MRIdian is implemented clinically.

Prediction of Radiation-induced Lymphopenia following Exposure of the Thoracic Region and Associated Risk of Infections and Mortality.

AIMS: Large blood volumes are irradiated when the heart is exposed to radiation. The mean heart dose (MHD) may be a good surrogate for circulating lymphocytes exposure. We investigated the association between MHD and radiation-induced lymphopenia and explored the impact of the end-of-radiation-therapy (EoRT) lymphocyte count on clinical outcomes. MATERIALS AND METHODS: In total, 915 patients were analysed: 303 patients with breast cancer and 612 with intrathoracic tumours: oesophageal cancer (291), non-small cell lung cancer (265) and small cell lung cancer (56). Heart contours were generated using an interactive deep learning delineation process and an individual dose volume histogram for each heart was obtained. A dose volume histogram for the body was extracted from the clinical systems. We compared different models analysing the effect of heart dosimetry on the EoRT lymphocyte count using multivariable linear regression and assessed goodness of fit. We published interactive nomograms for the best models. The association of the degree of EoRT lymphopenia with clinical outcomes (overall survival, cancer treatment failure and infection) was investigated. RESULTS: An increasing low dose bath to the body and MHD were associated with a low EoRT lymphocyte count. The best models for intrathoracic tumours included dosimetric parameters, age, gender, number of fractions, concomitant chemotherapy and pre-treatment lymphocyte count. Models for patients with breast cancer showed no improvement when adding dosimetric variables to the clinical predictors. EoRT lymphopenia grade ≥3 was associated with decreased survival and increased risk of infections among patients with intrathoracic tumours. CONCLUSION: Among patients with intrathoracic tumours, radiation exposure to the heart contributes to lymphopenia and low levels of peripheral lymphocytes after radiotherapy are associated with worse clinical outcomes.

Risk profiling based on p16 and HPV DNA more accurately predicts location of disease relapse in patients with oropharyngeal squamous cell carcinoma.

BACKGROUND: In the era of precision medicine and HPV-related oropharyngeal squamous cell carcinoma (OPSCC), it is relevant to assess the risk of not only survival, but also the risk of local, regional, or distant treatment failure. The UICC 8th edition uses the surrogate marker p16 to stratify for HPV association but discordance between p16 status and HPV association has been shown. The purpose of this study was to develop a prognostic model to predict the risk of local, regional, and distant metastases and non-cancer-related death for patients with OPSCC, test the prognostic relevance of adding HPV DNA and p16 status, and validate the findings in an independent external dataset. PATIENTS AND METHODS: Consecutive patients diagnosed with OPSCC and treated with curative radiotherapy with or without cisplatin in eastern Denmark from 2000 to 2014 were included. Characteristics included age, gender, TNM stage, smoking habits, performance status, and HPV status assessed with p16 and HPV DNA. The information was used to develop a prognostic model for first site of failure with four competing events: recurrence in T-, N-, and M-site, and death with no evidence of disease. RESULTS: Overall 1243 patients were eligible for the analysis. A prognostic model with the four events was developed and externally validated in an independent dataset with a heterogeneously treated patient population from another institution. The individual prognostication from the competing risk analysis is displayed in a user friendly online tool (https://rasmussen.shinyapps.io/OPSCCmodelHPV_p16/). Replacing p16 status with the combined variable HPV/p16 status influenced the HR and patients with HPV-/p16+ had significantly higher HR of M-site recurrence than HPV+/p16+ with a HR = 2.56; CI [1.30; 5.02]; P = 0.006 (P = 0.013 in the validation cohort). CONCLUSION: Patients with HPV-/p16+ have significantly higher risk of M-site recurrence and could potentially be relevant candidates for clinical trials testing systemic treatments in combination with conventional treatments.

Testosterone deficiency in testicular cancer survivors - a systematic review and meta-analysis.

Results concerning treatment of Testicular Germ Cell Cancer (TGCC) and subsequent risk of testosterone deficiency are conflicting. To systematically evaluate and estimate the risk of testosterone deficiency (TD) in TGCC-patients according to treatment to optimize follow-up and for prevention of late effects related to hypogonadism. We performed a critical review of PubMed in January 2015 according to the Preferred Reporting Items for Systematic Review and Meta-analysis (PRISMA) statement. Twelve publications were selected for inclusion in this analysis. Eleven studies evaluated the risk of TD in TGCC-patients treated with standard chemotherapy (CT) and the odds ratio for TD was 1.8 (95% CI) (1.3-2.5), (p = 0.0007). Seven studies evaluated the risk of TD in TGCC-patients treated with non-conventional therapy and the odds ratio for TD was 3.1 (95% CI) (2.0-4.8), (p < 0.0001). Six studies evaluated the risk of TD in TGCC-patients treated with infradiaphragmatic radiotherapy (RT), and the odds ratio for TD was 1.6 (95% CI) (1.0-2.4), (p = 0.03). In all treatment groups the risk of TD was compared with TGCC-patients treated with orchiectomy alone. There was no indication of heterogeneity between studies in the three treatment groups. Strong evidence exists that standard CT, non-conventional therapy and infradiaphragmatic RT are associated with an increased risk of TD in TGCC-patients when compared with orchiectomy alone. The risk of testosterone defficiency appears to be highest in patients treated with non-conventional therapy.

Reproducibility of (18)F-FDG PET uptake measurements in head and neck squamous cell carcinoma on both PET/CT and PET/MR.

OBJECTIVE: To investigate reproducibility of fluorine-18 fludeoxyglucose ((18)F-FDG) uptake on (18)F-FDG positron emission tomography (PET)/CT and (18)F-FDG PET/MR scans in patients with head and neck squamous cell carcinoma (HNSCC). METHODS: 30 patients with HNSCC were included in this prospective study. The patients were scanned twice before radiotherapy treatment with both PET/CT and PET/MR. Patients were scanned on the same scanners, 3 days apart and according to the same protocol. Metabolic tumour activity was measured by the maximum and peak standardized uptake value (SUVmax and SUVpeak, respectively), and total lesion glycolysis from the metabolic tumour volume defined from ≥50% SUVmax. Bland-Altman analysis with limits of agreement, coefficient of variation (CV) from the two modalities were performed in order to test the reproducibility. Furthermore, CVs from SUVmax and SUVpeak were compared. The area under the curve from cumulative SUV-volume histograms were measured and tested for reproducibility of the distribution of (18)F-FDG uptake. RESULTS: 24 patients had two pre-treatment PET/CT scans and 21 patients had two pre-treatment PET/MR scans available for further analyses. Mean difference for SUVmax, peak and mean was approximately 4% for PET/CT and 3% for PET/MR, with 95% limits of agreement less than ±20%. CV was small (5-7%) for both modalities. There was no significant difference in CVs between PET/CT and PET/MR (p = 0.31). SUVmax was not more reproducible than SUVpeak (p = 0.09). CONCLUSION: (18)F-FDG uptake in PET/CT and PET/MR is highly reproducible and we found no difference in reproducibility between PET/CT and PET/MR. ADVANCES IN KNOWLEDGE: This is the first report to test reproducibility of PET/CT and PET/MR.

The impact of involved node, involved field and mantle field radiotherapy on estimated radiation doses and risk of late effects for pediatric patients with Hodgkin lymphoma.

BACKGROUND: The use of radiotherapy (RT) is debated for pediatric patients with Hodgkin lymphoma (HL) due to the late effects of treatment. Radiation doses to the thyroid, heart, lungs, and breasts are compared with the extensive mantle field (MF), Involved Field RT(IFRT), Modified IFRT (mIFRT), and Involved Node RT (INRT) and the risk of radiation-induced cardiovascular disease, secondary cancers, and the corresponding Life Years Lost (LYL) is estimated with each technique. PROCEDURE: INRT, mIFRT, IFRT, and MF plans (20 and 30 Gy) were simulated for 10 supradiaphragmatic, clinical stage I­II classical HL patients <18 years old, total of 4 x 2 plans for each patient. The lifetime excess risks of cardiac morbidity, cardiac mortality, lung, breast, and thyroid cancer with each technique were estimated. The estimated excess risks attributable to RT were based on HL series with long-term follow-up, treating death from other causes as competing risks. The corresponding LYL were derived from the estimated excess risks. Statistical analyses were performed with repeated measures ANOVA. RESULTS: Both a reduction in field size and in prescribed radiation dose significantly lowered the estimated dose to the heart, lungs, breasts, and thyroid compared to past,extended fields, even for patients with mediastinal disease. This translated into a significantly reduced estimated risk of cardiovascular disease, secondary cancers, and LYL. CONCLUSIONS: Involved Node Radiotherapy should be considered for pediatric patients with Hodgkin lymphoma since it is estimated to substantially lower the risk of severe long-term complications.

Doses to head and neck normal tissues for early stage Hodgkin lymphoma after involved node radiotherapy.

PURPOSE: To evaluate dose plans for head and neck organs at risk (OARs) for classical Hodgkin lymphoma (HL) patients using involved node radiotherapy (INRT) delivered as 3D conformal radiotherapy (3DCRT), volumetric modulated arc therapy (VMAT), and intensity modulated proton therapy (PT), in comparison to the past mantle field (MF). MATERIALS AND METHODS: Data from 37 patients with cervical lymph node involvement were used. All patients originally received chemotherapy followed by 3DCRT-INRT (30.6 Gy). A VMAT-INRT, PT-INRT (both 30.6 Gy), and a MF plan (36 Gy) were simulated. Doses to head and neck OARs were compared with cumulative DVHs and repeated measures ANOVA. RESULTS: The estimated median mean doses were 15.3, 19.3, 15.4, and 37.3 Gy (thyroid), 10.9, 12.0, 7.9, and 34.5 Gy (neck muscles), 2.3, 11.1, 1.8, and 37.1 Gy (larynx), 1.7, 5.1, 1.3, and 23.8 Gy (pharynx), 0.5, 0.8, 0.01, and 32.3 Gy (ipsilateral parotid), and 2.4, 3.8, 0.7, and 34.7 Gy (ipsilateral submandibular) with 3DCRT, VMAT, PT, and MF (all p<0.0001), respectively. CONCLUSION: The use of INRT significantly lowered the estimated radiation dose to the head and neck OARs. VMAT appeared suboptimal compared to 3DCRT and PT, and for some patients, PT offered an additional gain.

Estimated risk of cardiovascular disease and secondary cancers with modern highly conformal radiotherapy for early-stage mediastinal Hodgkin lymphoma.

BACKGROUND: Hodgkin lymphoma (HL) survivors have an increased morbidity and mortality from secondary cancers and cardiovascular disease (CD). We evaluate doses with involved node radiotherapy (INRT) delivered as 3D conformal radiotherapy (3D CRT), volumetric modulated arc therapy (VMAT), or proton therapy (PT), compared with the extensive Mantle Field (MF). PATIENTS AND METHODS: For 27 patients with early-stage, mediastinal HL, treated with chemotherapy and INRT delivered as 3D CRT (30 Gy), we simulated an MF (36 Gy), INRT-VMAT and INRT-PT (30 Gy). Dose to the heart, lungs, and breasts, estimated risks of CD, lung (LC) and breast cancer (BC), and corresponding life years lost (LYL) were compared. RESULTS: 3D CRT, VMAT or PT significantly lower the dose to the heart, lungs and breasts and provide lower risk estimates compared with MF, but with substantial patient variability. The risk of CD is not significantly different for 3D CRT versus VMAT. The risk of LC and BC is highest with VMAT. For LYL, PT is the superior modern technique. CONCLUSIONS: In early-stage, mediastinal HL modern radiotherapy provides superior results compared with MF. However, there is no single best radiotherapy technique for HL-the decision should be made at the individual patient level.

Modern hypofractionation schedules for tangential whole breast irradiation decrease the fraction size-corrected dose to the heart.

AIMS: Hypofractionation of postoperative radiotherapy for breast cancer has been evaluated in a number of large randomised clinical trials, but concerns remain over the late cardiac toxicity. In this study, we examined the predictions of the linear quadratic model on the estimated fraction size-corrected dose to the heart for four evidence-based hypofractionation regimens. MATERIALS AND METHODS: Dose plans for 60 left-sided breast cancer patients were analysed. All patients were planned with tangential fields for whole breast irradiation. Dose distributions were corrected to the equivalent dose in 2 Gy fractions (EQD(2)) using the linear quadratic model for five different fractionation schedules (50 Gy/25 fractions and four hypofractionation regimens) and for a range of α/ß values (0-5 Gy). The mean EQD(2) to the heart ( [Formula: see text] ) and the volume receiving 40 Gy ( [Formula: see text] ), both as calculated from the EQD(2) dose distributions, were compared between schedules. RESULTS: For α/ß = 3 Gy, [Formula: see text] favours hypofractionation for 40 Gy/15 fractions, 39 Gy/13 fractions and 42.5 Gy/16 fractions, but not for 41.6 Gy/13 fractions. All of the hypofractionation schedules result in lower [Formula: see text] compared with normofractionation. These results hold as long as α/ߠ≳ 1.5 Gy. If the heart is blocked from the treatment beam, the fraction size-corrected dose is lower for the first three hypofractionation schedules, compared with normofractionation, even for α/ß = âˆ¼1 Gy. CONCLUSION: For standard tangential field whole breast irradiation, most of the examined hypofractionation schedules are estimated to spare the heart when compared with normofractionation. The dose to the heart, adjusted for fraction size using the linear quadratic model, will generally be lower after hypofractionated compared with normofractionated schedules, even for very low values of α/ß.

Methods for estimating the site of origin of locoregional recurrence in head and neck squamous cell carcinoma.

PURPOSE: Methods to estimate the likely origin of recurrences after radiation therapy for head and neck squamous cell carcinoma are compared. METHODS AND MATERIALS: A total of 25 patients meeting the following inclusion criteria were randomly selected: curatively intended intensity-modulated radiotherapy planned on a positron emission tomography-computed tomography (PET/CT) scan during the period 2005-2009; squamous cell carcinoma in the oral cavity, pharynx or larynx; complete clinical response followed by locoregional recurrence; and a CT scan at recurrence before any salvage therapy. Exclusion criteria were previous cancer in the area, surgery prior to radiotherapy, or a synchronous cancer. Three methods of estimating focal points of recurrence origin and two volume overlap methods assigning the recurrences to the most central target volumes encompassing at least 50% or 95% of the recurrence volumes were tested. Treatment planning and recurrence scans were rigid and deformable co-registered in order to transfer focal points to the treatment planning scan. Double determinations of all volumes, points, and co-registrations were made. RESULTS: The volume overlap methods assigned the recurrences to significantly more peripheral target volumes than focal methods (p < 0.0001 for all comparisons of 95% overlap vs. focal methods, p < 0.028 for all comparisons of 50% overlap vs. focal methods). Repeated registrations of the same point had higher reproducibility with deformable registration than with rigid registration (median distance 0.31 vs. 0.35 cm, p = 0.015). No significant differences were observed among the focal methods. CONCLUSION: Significant differences between methods were found which may affect strategies to improve radiotherapy based on pattern of failure analyses.