Germline genetic biomarkers to stratify patients for personalized radiation treatment.

BACKGROUND: Precision medicine incorporating genetic profiling is becoming a standard of care in medical oncology. However, in the field of radiation oncology there is limited use of genetic profiling and the impact of germline genetic biomarkers on radiosensitivity, radioresistance, or patient outcomes after radiation therapy is poorly understood. In HNSCC, the toxicity associated with treatment can cause delays or early cessation which has been associated with worse outcomes. Identifying potential biomarkers which can help predict toxicity, as well as response to treatment, is of significant interest. METHODS: Patients with HNSCC who received RT and underwent next generation sequencing of somatic tumor samples, transcriptome RNA-seq with matched normal tissue samples were included. Patients were then grouped by propensity towards increased late vs. early toxicity (Group A) and those without (Group B), assessed by CTCAE v5.0. The groups were then analyzed for association of specific germline variants with toxicity and clinical outcomes. RESULTS: In this study we analyzed 37 patients for correlation between germline variants and toxicity. We observed that TSC2, HLA-A, TET2, GEN1, NCOR2 and other germline variants were significantly associated with long term toxicities. 34 HNSCC patients treated with curative intent were evaluated for clinical outcomes. Group A had significantly improved overall survival as well as improved rates of locoregional recurrence and metastatic disease. Specific variants associated with improved clinical outcomes included TSC2, FANCD2, and PPP1R15A, while the HLA-A and GEN1 variants were not correlated with survival or recurrence. A group of five HLA-DMA/HLA-DMB variants was only found in Group B and was associated with a higher risk of locoregional recurrence. CONCLUSIONS: This study indicates that germline genetic biomarkers may have utility in predicting toxicity and outcomes after radiation therapy and deserve further investigation in precision radiation medicine approaches.

Evaluating predictive factors for toxicities experienced by head & neck cancer patients undergoing radiotherapy.

PURPOSE: The purpose of this study was to evaluate if HPV status serves as an independent predictor of early and late dysphagia outcomes when considered alongside standard patient characteristics and dose metrics for head and neck cancer patients treated with radiotherapy. METHODS AND MATERIALS: The age, sex, smoking history, cancer type (oropharyngeal vs non-oropharyngeal), HPV status, and early and late dysphagia outcomes were obtained for 99 retrospective head and neck cancer patients treated at our clinic with radiotherapy. Additionally for each patient, the mean radiation dose to the pharynx, superior/middle/inferior pharyngeal constrictor muscles, and cricopharyngeus was calculated. The predictive power of these clinical characteristics and radiation metrics was evaluated using chi-square tests for categorical variables and t-tests for continuous variables. Then multi-variate logistic models were built for each outcome using a single dose metric at a time, and either HPV status, cancer type, or both. Multi-variate models were built using both top-down and bottom-up technique to establish the most predictive independent covariates. RESULTS: In the univariate analysis for early dysphagia, cancer type (p = 0.04) and four dose metrics (p ≤ 0.02) were significantly associated with outcome, while for late dysphagia, only cancer type (p = 0.04) was associated with outcome. In the multivariate analysis for early dysphagia, cancer type, smoking history, and mean dose to the five structures were consistently selected as covariates. For late dysphagia, either HPV status or cancer type was selected in each model and the mean dose to the cricopharyngeus was selected in one model. CONCLUSION: While HPV is a known contributing factor for tumor prognosis in oropharyngeal cancers, its role in normal tissue toxicities for head and neck cancers has not previously been evaluated. Our results indicate having an oropharyngeal cancer may increase a patient's risk of high-grade early and late dysphagia while HPV status was seldom selected.

Gene alterations as predictors of radiation-induced toxicity in head and neck squamous cell carcinoma.

BACKGROUND: Optimizing the therapeutic ratio for radiation therapy (RT) in head and neck squamous cell carcinoma (HNSCC) is uniquely challenging owing to high rates of early and late toxicity involving nearby organs at risk. These toxicities have a profound impact on treatment compliance and quality of life. Emerging evidence suggests that RT dose alone cannot fully account for the variable severity of RT-related adverse events (rtAEs) observed in HNSCC patients. Next-generation sequencing has become an increasingly valuable tool with widespread use in the oncology field and is being robustly explored for predicting rtAEs beyond dosimetric data. METHODS: Patients who had Foundation Medicine sequencing data and received RT for primary or locally recurrent HNSCC were selected for this study. Early and late toxicity data were collected and reported based on Common Terminology Criteria for Adverse Events version 5.0. Dosimetric parameters were collected for pertinent structures. RESULTS: A total of HNSCC 37 patients were analyzed in this study. Genetic alterations in BRCA2, ERBB3, NOTCH1 and CCND1 were all associated with higher mean grade of toxicity with BRCA2 alteration implicated in all toxicity parameters evaluated including mucositis, early dysphagia, xerostomia and to a lesser extent, late dysphagia. Interestingly, patients who exhibited alterations in both BRCA2 and ERBB3 experienced a twofold or greater increase in early dysphagia, early xerostomia and late dysphagia compared to ERBB3 alteration alone. Furthermore, several gene alterations were associated with improved toxicity outcomes. Within an RT supersensitive patient subset, alterations were found in TNFAIP3, HNF1A, SPTA1 and CASP8. All of these alterations were not found in the RT insensitive patient subset. We found 17 gene alterations in the RT insensitive patient subset that were not found in the RT supersensitive patient subset. CONCLUSION: Despite consistent RT dosimetric parameters, patients with HNSCC experience heterogeneous patterns of rtAEs. Identifying factors associated with toxicity outcomes offers a new avenue for personalized precision RT therapy and prophylactic management. Here, next-generation sequencing in a population of HNSCC patients correlates several genetic alterations with severity of rtAEs. Further analysis is urgently needed to identify genetic patterns associated with rtAEs in order to reduce harmful outcomes in this challenging population.

TG-51 reference dosimetry for the Halcyon™: A clinical experience.

Halcyon™ is a single-energy (6 MV-FFF), bore-enclosed linear accelerator. Patient setup is performed by first aligning to external lasers mounted to the front of the bore, and then loading to isocenter through pre-defined couch shifts. There is no light field, optical distance indicator or front pointer mechanism, so positioning is verified through MV imaging with kV imaging scheduled to become available in the future. TG-51 reference dosimetry was successfully performed for Halcyon™ in this imaging-based setup paradigm. The beam quality conversion factor, kQ , was determined by measuring %dd(10)x three ways: (a) using a Farmer chamber with lead filtering, (b) using a Farmer chamber without lead filtering, and (c) using a PinPoint chamber without lead filtering. Values of kQ were determined to be 0.995, 0.996, and 0.996 by each measurement technique, respectively. Halcyon™'s 6 MV-FFF beam was found to be broader than other FFF beams produced by Varian accelerators, and profile measurements at dmax showed the beam to vary less than 0.5% over the dimensions of our Farmer chamber's active volume. Reference dosimetry can be performed for the Halcyon™ accelerator simply, without specialized equipment or lead filtering with minimal dosimetric impact. This simplicity will prove advantageous in clinics with limited resources or physics support.

Spatial rectal dose/volume metrics predict patient-reported gastro-intestinal symptoms after radiotherapy for prostate cancer.

BACKGROUND: Gastro-intestinal (GI) toxicity after radiotherapy (RT) for prostate cancer reduces patient's quality of life. In this study, we explored associations between spatial rectal dose/volume metrics and patient-reported GI symptoms after RT for localized prostate cancer, and compared these with those of dose-surface/volume histogram (DSH/DVH) metrics. MATERIAL AND METHODS: Dose distributions and six GI symptoms (defecation urgency/emptying difficulties/fecal leakage, ≥Grade 2, median follow-up: 3.6 y) were extracted for 200 patients treated with image-guided RT in 2005-2007. Three hundred and nine metrics assessed from 2D rectal dose maps or DSHs/DVHs were subject to 50-times iterated five-fold cross-validated univariate and multivariate logistic regression analysis (UVA, MVA). Performance of the most frequently selected MVA models was evaluated by the area under the receiving-operating characteristics curve (AUC). RESULTS: The AUC increased for dose-map compared to DSH/DVH-based models (mean SD: 0.64 ± 0.03 vs. 0.61 ± 0.01), and significant relations were found for six versus four symptoms. Defecation urgency and faecal leakage were explained by high doses at the central/upper and central areas, respectively; while emptying difficulties were explained by longitudinal extensions of intermediate doses. CONCLUSIONS: Predictability of patient-reported GI toxicity increased using spatial metrics compared to DSH/DVH metrics. Novel associations were particularly identified for emptying difficulties using both approaches in which intermediate doses were emphasized.

Associations between volume changes and spatial dose metrics for the urinary bladder during local versus pelvic irradiation for prostate cancer.

BACKGROUND: Inter-fractional variation in urinary bladder volumes during the course of radiotherapy (RT) for prostate cancer causes deviations between planned and delivered doses. This study compared planned versus daily cone-beam CT (CBCT)-based spatial bladder dose distributions, for prostate cancer patients receiving local prostate treatment (local treatment) versus prostate including pelvic lymph node irradiation (pelvic treatment). MATERIAL AND METHODS: Twenty-seven patients (N = 15 local treatment; N = 12 pelvic treatment) were treated using daily image-guided RT (1.8 Gy@43-45 fx), adhering to a full bladder/empty rectum protocol. For each patient, 9-10 CBCTs were registered to the planning CT, using the clinically applied translations. The urinary bladder was manually segmented on each CBCT, 3 mm inner shells were generated, and semi and quadrant sectors were created using axial/coronal cuts. Planned and delivered DVH metrics were compared across patients and between the two groups of treatment (t-test, p < .05; Holm-Bonferroni correction). Associations between bladder volume variations and the dose-volume histograms (DVH) of the bladder and its sectors were evaluated (Spearman's rank correlation coefficient, rs). RESULTS: Bladder volumes varied considerably during RT (coefficient of variation: 16-58%). The population-averaged planned and delivered DVH metrics were not significantly different at any dose level. Larger treatment bladder volumes resulted in increased absolute volume of the posterior/inferior bladder sector receiving intermediate-high doses, in both groups. The superior bladder sector received less dose with larger bladder volumes for local treatments (rs ± SD: -0.47 ± 0.32), but larger doses for pelvic treatments (rs ± SD: 0.74 ± 0.24). CONCLUSIONS: Substantial bladder volume changes during the treatment course occurred even though patients were treated under a full bladder/daily image-guided protocol. Larger bladder volumes resulted in less bladder wall spared at the posterior-inferior sector, regardless the treatment received. Contrary, larger bladder volumes meant larger delivered doses to the superior bladder sector for pelvic RT but smaller doses for local treatments.

Aspiration pneumonia after concurrent chemoradiotherapy for head and neck cancer.

BACKGROUND: Aspiration pneumonia represents an under-reported complication of chemoradiotherapy in patient with head and neck cancer. The objective of the current study was to evaluate the incidence, risk factors, and mortality of aspiration pneumonia in a large cohort of patients with head and neck cancer who received concurrent chemoradiotherapy. METHODS: Patients who had head and neck cancer diagnosed between 2000 and 2009 were identified from the Surveillance, Epidemiology, and End Results-Medicare database. Aspiration pneumonia was identified from Medicare billing claims. The cumulative incidence, risk factors, and survival after aspiration pneumonia were estimated and compared with a noncancer population. RESULTS: Of 3513 patients with head and neck cancer, 801 developed aspiration pneumonia at a median of 5 months after initiating treatment. The 1-year and 5-year cumulative incidence of aspiration pneumonia was 15.8% and 23.8%, respectively, for patients with head and neck cancer and 3.6% and 8.7%, respectively, for noncancer controls. Among the patients with cancer, multivariate analysis identified independent risk factors (P < .05) for aspiration pneumonia, including hypopharyngeal and nasopharyngeal tumors, male gender, older age, increased comorbidity, no surgery before radiation, and care received at a teaching hospital. Among the patients with cancer who experienced aspiration pneumonia, 674 (84%) were hospitalized; and, of these, 301 (45%) were admitted to an intensive care unit. The 30-day mortality rate after hospitalization for aspiration pneumonia was 32.5%. Aspiration pneumonia was associated with a 42% increased risk of death (hazard ratio, 1.42; P < .001) after controlling for confounders. CONCLUSIONS: The current results indicated that nearly 25% of elderly patients will develop aspiration pneumonia within 5 years after receiving chemoradiotherapy for head and neck cancer. A better understanding of mitigating factors will help identify patients who are at risk for this potentially lethal complication.

An image-based method to quantify biomechanical properties of the rectum in radiotherapy of prostate cancer.

BACKGROUND: Gastrointestinal morbidity after radiotherapy (RT) for prostate cancer may be related to the biomechanical properties of the rectum. In this study we present a magnetic resonance imaging (MRI)-based method to quantitate the thickness and elasticity of the rectal wall in prostate cancer patients treated with RT. MATERIAL AND METHODS: Four patients previously treated with RT for prostate cancer underwent an MRI session with stepwise rectal bag deflation (from a maximum tolerable volume to 0 ml, in 50 ml steps), with a probe inserted inside the bag to monitor the internal rectal pressure. MRIs were acquired using Dixon sequences (4 mm axial slice thickness) at each deflation step. Rectal walls were defined from the recto-sigmoid junction to 3 cm above the anal canal as the space between the inner and outer wall surfaces. The wall thickness was determined and biomechanical properties (strain and stress) were calculated from the pressure measurements and the MRI-segmented rectal walls. RESULTS: The integral rectal pressure varied for the maximum tolerable volume (range 150-250 ml) across patients and ranged from 1.3 to 4.0 kPa (SD = 1.2 kPa). Wall thickness was found to vary between patients and also across different rectum segments, with a mean (SD) thickness for the different segments at the 50 ml distension volume of 1.8-4.0 (0.6) mm. Stress showed larger variation than strain, with mean (SD) values for the different segments ranging between 1.5 and 7.0 (1.5) kPa. CONCLUSION: We have developed a method to quantify biomechanical properties of the rectal wall. The resulting rectal wall thickness, strain and stress differed between patients, as well as across different rectal wall sections. These findings could provide guidance in future predictive outcome modelling in order to better understand the rectal dose-volume response relationship.

Chest wall pain after single-fraction thoracic stereotactic ablative Radiotherapy: Dosimetric analysis from the iSABR trial.

BACKGROUND AND PURPOSE: Concerns over chest wall toxicity has led to debates on treating tumors adjacent to the chest wall with single-fraction stereotactic ablative radiotherapy (SABR). We performed a secondary analysis of patients treated on the prospective iSABR trial to determine the incidence and grade of chest wall pain and modeled dose-response to guide radiation planning and estimate risk. MATERIALS AND METHODS: This analysis included 99 tumors in 92 patients that were treated with 25 Gy in one fraction on the iSABR trial which individualized dose by tumor size and location. Toxicity events were prospectively collected and graded based on the CTCAE version 4. Dose-response modeling was performed using a logistic model with maximum likelihood method utilized for parameter fitting. RESULTS: There were 22 grade 1 or higher chest wall pain events, including five grade 2 events and zero grade 3 or higher events. The volume receiving at least 11 Gy (V11Gy) and the minimum dose to the hottest 2 cc (D2cc) were most highly correlated with toxicity. When dichotomized by an estimated incidence of ≥ 20 % toxicity, the D2cc > 17 Gy (36.6 % vs. 3.7 %, p < 0.01) and V11Gy > 28 cc (40.0 % vs. 8.1 %, p < 0.01) constraints were predictive of chest wall pain, including among a subset of patients with tumors abutting or adjacent to the chest wall. CONCLUSION: For small, peripheral tumors, single-fraction SABR is associated with modest rates of low-grade chest wall pain. Proximity to the chest wall may not contraindicate single fractionation when using highly conformal, image-guided techniques with sharp dose gradients.

Is individual perfusion dose-response different than ventilation dose-response for lung cancer patients treated with radiotherapy?

OBJECTIVE: Current ventilation and perfusion dose-response studies focus on single-modalities (ventilation or perfusion) and perform pulmonary-toxicity assessment related to radiotherapy on a population-based basis. This study aims at quantitative and clinical evaluation of intrapatient differences between ventilation and perfusion dose-responses among lung cancer patients treated with radiotherapy. METHODS: 20 patients enrolled on a prospective functional avoidance protocol underwent single photon emission computed tomography-CT ventilation and perfusion scans pre- and post-radiotherapy. Relative changes in pre- to post-treatment ventilation and perfusion in lung regions receiving ≥20 Gy were calculated. In addition, the slopes of the linear fit to the relative ventilation and perfusion changes in regions receiving 0-60 Gy were calculated. A radiologist read and assigned a functional defect score to pre- and post-treatment ventilation/perfusion scans. RESULTS: 25% of patients had a difference >35% between ventilation and perfusion pre- to post-treatment changes and 20-30% of patients had opposite directions for ventilation and perfusion pre- to post-treatment changes. Using a semi-quantitative scale, radiologist assessment showed that 20% of patients had different pre- to post-treatment ventilation changes when compared to pre- to post-treatment perfusion changes. CONCLUSION: Our data showed that ventilation dose-response can differ from perfusion dose-response for 20-30% of patients. Therefore, when performing thoracic dose-response in cancer patients, it is insufficient to look at ventilation or perfusion alone; but rather both modes of functional imaging may be needed when predicting for clinical outcomes. ADVANCES IN KNOWLEDGE: The significance of this study can be highlighted by the differences between the intrapatient dose-response assessments of this analysis compared to existing population-based dose-response analyses. Elucidating intrapatient ventilation and perfusion dose-response differences may be valuable in predicting pulmonary toxicity in lung cancer patients post-radiotherapy.

The relationship between radiation dose and bevacizumab-related imaging abnormality in patients with brain tumors: A voxel-wise normal tissue complication probability (NTCP) analysis.

PURPOSE: Bevacizumab-related imaging abnormality (BRIA), appearing as areas of restricted diffusion on magnetic resonance imaging (MRI) and representing atypical coagulative necrosis pathologically, has been observed in patients with brain tumors receiving radiotherapy and bevacizumab. We investigated the role of cumulative radiation dose in BRIA development in a voxel-wise analysis. METHODS: Patients (n = 18) with BRIA were identified. All had high-grade gliomas or brain metastases treated with radiotherapy and bevacizumab. Areas of BRIA were segmented semi-automatically on diffusion-weighted MRI with apparent diffusion coefficient (ADC) images. To avoid confounding by possible tumor, hypoperfusion was confirmed with perfusion imaging. ADC images and radiation dose maps were co-registered to a high-resolution T1-weighted MRI and registration accuracy was verified. Voxel-wise normal tissue complication probability analyses were performed using a logistic model analyzing the relationship between cumulative voxel equivalent total dose in 2 Gy fractions (EQD2) and BRIA development at each voxel. Confidence intervals for regression model predictions were estimated with bootstrapping. RESULTS: Among 18 patients, 39 brain tumors were treated. Patients received a median of 4.5 cycles of bevacizumab and 1-4 radiation courses prior to BRIA appearance. Most (64%) treated tumors overlapped with areas of BRIA. The median proportion of each BRIA region of interest volume overlapping with tumor was 98%. We found a dose-dependent association between cumulative voxel EQD2 and the relative probability of BRIA (ß0 = -5.1, ß1 = 0.03 Gy-1, γ = 1.3). CONCLUSIONS: BRIA is likely a radiation dose-dependent phenomenon in patients with brain tumors receiving bevacizumab and radiotherapy. The combination of radiation effects and tumor microenvironmental factors in potentiating BRIA in this population should be further investigated.

Fine Motor Skill Decline After Brain Radiation Therapy-A Multivariate Normal Tissue Complication Probability Study of a Prospective Trial.

PURPOSE: Brain radiation therapy can impair fine motor skills (FMS). Fine motor skills are essential for activities of daily living, enabling hand-eye coordination for manipulative movements. We developed normal tissue complication probability (NTCP) models for the decline in FMS after fractionated brain radiation therapy (RT). METHODS AND MATERIALS: On a prospective trial, 44 patients with primary brain tumors received fractioned RT; underwent high-resolution volumetric magnetic resonance imaging, diffusion tensor imaging, and comprehensive FMS assessments (Delis-Kaplan Executive Function System Trail Making Test Motor Speed [DKEFS-MS]; and Grooved Pegboard dominant/nondominant hands) at baseline and 6 months postRT. Regions of interest subserving motor function (including cortex, superficial white matter, thalamus, basal ganglia, cerebellum, and white matter tracts) were autosegmented using validated methods and manually verified. Dosimetric and clinical variables were included in multivariate NTCP models using automated bootstrapped logistic regression, least absolute shrinkage and selection operator logistic regression, and random forests with nested cross-validation. RESULTS: Half of the patients showed a decline on grooved pegboard test of nondominant hands, 17 of 42 (40.4%) on grooved pegboard test of -dominant hands, and 11 of 44 (25%) on DKEFS-MS. Automated bootstrapped logistic regression selected a 1-term model including maximum dose to dominant postcentral white matter. The least absolute shrinkage and selection operator logistic regression selected this term and steroid use. The top 5 variables in the random forest were all dosimetric: maximum dose to dominant thalamus, mean dose to dominant caudate, mean and maximum dose to the dominant corticospinal tract, and maximum dose to dominant postcentral white matter. This technique performed best with an area under the curve of 0.69 (95% CI, 0.68-0.70) on nested cross-validation. CONCLUSIONS: We present the first NTCP models for FMS impairment after brain RT. Dose to several supratentorial motor-associated regions of interest correlated with a decline in dominant-hand fine motor dexterity in patients with primary brain tumors in multivariate models, outperforming clinical variables. These data can guide prospective fine motor-sparing strategies for brain RT.

Cardiac Disease in Childhood Cancer Survivors Treated With Radiation Therapy: A PENTEC Comprehensive Review.

PURPOSE: Radiation therapy (RT) is an essential component in the treatment of many pediatric malignancies. Thoracic RT may expose the heart to radiation dose and thereby increase the risk of late cardiac disease. This comprehensive review from the Pediatric Normal Tissue Effects in the Clinic (PENTEC) initiative focused on late cardiac disease in survivors of childhood cancer treated with RT. METHODS AND MATERIALS: This systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) methodology. We identified 1496 articles; 4 were included for dose-response modeling between mean cardiac radiation dose and risk of late coronary artery disease, heart failure (HF), valvular disease, and any cardiac disease. RESULTS: For each 10-Gy increase in corrected mean cardiac radiation dose in 1.8- to 2.0-Gy fractions, we estimated a hazard ratio of 2.01 (95% confidence interval [CI], 1.79-2.25) for coronary artery disease, of 1.87 (95% CI, 1.70-2.06) for HF, of 1.87 (95% CI, 1.78-1.96) for valvular disease, and of 1.88 (95% CI, 1.75-2.03) for any cardiac disease. From the same model, for each 100-mg/m2 increase in cumulative anthracycline dose, the hazard ratio for the development of HF was 1.93 (95% CI, 1.58-2.36), equivalent to an increase in mean heart dose of approximately 10.5 Gy. Other nontreatment factors were inconsistently reported in the analyzed articles. CONCLUSIONS: Radiation dose to the heart increases the risk of late cardiac disease, but survivors of childhood cancer who receive a mean dose <10 Gy at standard fractionation are at low absolute risk (<∼2% approximately 30 years after exposure) of late cardiac disease in the absence of anthracycline exposure. Minimizing cardiac radiation dose is especially relevant in children receiving anthracyclines. When cardiac sparing is not possible, we recommend prioritizing target coverage. It is likely that individual cardiac substructure doses will be a better predictor of specific cardiac diseases than mean dose, and we urge the pediatric oncology community to further study these relationships.

Biological consequences of MLC calibration errors in IMRT delivery and QA.

PURPOSE: The purpose of this work is threefold: (1) to explore biological consequences of the multileaf collimator (MLC) calibration errors in intensity modulated radiotherapy (IMRT) of prostate and head and neck cancers, (2) to determine levels of planning target volume (PTV) and normal tissue under- or overdose flagged with clinically used QA action limits, and (3) to provide biologically based input for MLC QA and IMRT QA action limits. METHODS: Ten consecutive prostate IMRT cases and ten consecutive head and neck IMRT cases were used. Systematic MLC offsets (i.e., calibration error) were introduced for each control point of the plan separately for X1 and X2 leaf banks. Offsets were from - 2 to 2 mm with a 0.5 mm increment. The modified files were imported into the planning system for forward dose recalculation. The original plan served as the reference. The generalized equivalent uniform dose (gEUD) was used as the biological index for the targets, rectum, parotid glands, brainstem, and spinal cord. Each plan was recalculated on a CT scan of a 27 cm diameter cylindrical phantom with a contoured 0.6 cc ion chamber. Dose to ion chamber and 3D gamma analysis were compared to the reference plan. QA pass criteria: (1) at least 95% of voxels with a dose cutoff of 50% of maximum dose have to pass at 3 mm/3% and (2) dose to chamber within 2% of the reference dose. RESULTS: For prostate cases, differences in PTV and rectum gEUD greater than 2% were identified. However, a larger proportion of plans leading to greater than 2% difference in prostate PTV gEUD passed the ion chamber QA but not 3D gamma QA. A similar trend was found for the rectum gEUD. For head and neck IMRT, the QA pass criteria flagged plans leading to greater than 4% differences in PTV gEUD and greater than 5% differences in the maximum dose to brainstem. If pass criteria were relaxed to 90% for gamma and 3% for ion chamber QA, plans leading to a 5% difference in PTV gEUD and a 5%-8% difference in brainstem maximum dose would likely pass IMRT QA. A larger proportion of head and neck plans with greater than 2% PTV gEUD difference passed 3D gamma QA compared to ion chamber QA. CONCLUSIONS: For low modulation plans, there is a better chance to catch MLC calibration errors with 3D gamma QA rather than ion chamber QA. Conversely, for high modulation plans, there is a better chance to catch MLC calibration errors with ion chamber QA rather than with 3D gamma QA. Ion chamber and 3D gamma analysis IMRT QA can detect greater than 2% change in gEUD for PTVs and critical structures for low modulation treatment plans. For high modulation treatment plans, ion chamber and 3D gamma analysis can detect greater than 2% change in gEUD for PTVs and a 5% change in critical structure gEUD since either QA methods passes the QA criteria. For gEUD changes less than those listed above, either QA method has the same proportion of passing rate.

The use and QA of biologically related models for treatment planning: short report of the TG-166 of the therapy physics committee of the AAPM.

Treatment planning tools that use biologically related models for plan optimization and/or evaluation are being introduced for clinical use. A variety of dose-response models and quantities along with a series of organ-specific model parameters are included in these tools. However, due to various limitations, such as the limitations of models and available model parameters, the incomplete understanding of dose responses, and the inadequate clinical data, the use of biologically based treatment planning system (BBTPS) represents a paradigm shift and can be potentially dangerous. There will be a steep learning curve for most planners. The purpose of this task group is to address some of these relevant issues before the use of BBTPS becomes widely spread. In this report, the authors (1) discuss strategies, limitations, conditions, and cautions for using biologically based models and parameters in clinical treatment planning; (2) demonstrate the practical use of the three most commonly used commercially available BBTPS and potential dosimetric differences between biologically model based and dose-volume based treatment plan optimization and evaluation; (3) identify the desirable features and future directions in developing BBTPS; and (4) provide general guidelines and methodology for the acceptance testing, commissioning, and routine quality assurance (QA) of BBTPS.

Automated segmentation of multiparametric magnetic resonance images for cerebral AVM radiosurgery planning: a deep learning approach.

Stereotactic radiosurgery planning for cerebral arteriovenous malformations (AVM) is complicated by the variability in appearance of an AVM nidus across different imaging modalities. We developed a deep learning approach to automatically segment cerebrovascular-anatomical maps from multiple high-resolution magnetic resonance imaging/angiography (MRI/MRA) sequences in AVM patients, with the goal of facilitating target delineation. Twenty-three AVM patients who were evaluated for radiosurgery and underwent multi-parametric MRI/MRA were included. A hybrid semi-automated and manual approach was used to label MRI/MRAs with arteries, veins, brain parenchyma, cerebral spinal fluid (CSF), and embolized vessels. Next, these labels were used to train a convolutional neural network to perform this task. Imaging from 17 patients (6362 image slices) was used for training, and 6 patients (1224 slices) for validation. Performance was evaluated by Dice Similarity Coefficient (DSC). Classification performance was good for arteries, veins, brain parenchyma, and CSF, with DSCs of 0.86, 0.91, 0.98, and 0.91, respectively in the validation image set. Performance was lower for embolized vessels, with a DSC of 0.75. This demonstrates the proof of principle that accurate, high-resolution cerebrovascular-anatomical maps can be generated from multiparametric MRI/MRA. Clinical validation of their utility in radiosurgery planning is warranted.

Risk of Cerebrovascular Events Among Childhood and Adolescent Patients Receiving Cranial Radiation Therapy: A Pediatric Normal Tissue Effects in the Clinic Normal Tissue Outcomes Comprehensive Review.

PURPOSE: Radiation-induced cerebrovascular toxicity is a well-documented sequelae that can be both life-altering and potentially fatal. We performed a meta-analysis of the relevant literature to create practical models for predicting the risk of cerebral vasculopathy after cranial irradiation. METHODS AND MATERIALS: A literature search was performed for studies reporting pediatric radiation therapy (RT) associated cerebral vasculopathy. When available, we used individual patient RT doses delivered to the Circle of Willis (CW) or optic chiasm (as a surrogate), as reported or digitized from original publications, to formulate a dose-response. A logistic fit and a Normal Tissue Complication Probability (NTCP) model was developed to predict future risk of cerebrovascular toxicity and stroke, respectively. This NTCP risk was assessed as a function of prescribed dose. RESULTS: The search identified 766 abstracts, 5 of which were used for modeling. We identified 101 of 3989 pediatric patients who experienced at least one cerebrovascular toxicity: transient ischemic attack, stroke, moyamoya, or arteriopathy. For a range of shorter follow-ups, as specified in the original publications (approximate attained ages of 17 years), our logistic fit model predicted the incidence of any cerebrovascular toxicity as a function of dose to the CW, or surrogate structure: 0.2% at 30 Gy, 1.3% at 45 Gy, and 4.4% at 54 Gy. At an attained age of 35 years, our NTCP model predicted a stroke incidence of 0.9% to 1.3%, 1.8% to 2.7%, and 2.8% to 4.1%, respectively at prescribed doses of 30 Gy, 45 Gy, and 54 Gy (compared with a baseline risk of 0.2%-0.3%). At an attained age of 45 years, the predicted incidence of stroke was 2.1% to 4.2%, 4.5% to 8.6%, and 6.7% to 13.0%, respectively at prescribed doses of 30 Gy, 45 Gy, and 54 Gy (compared with a baseline risk of 0.5%-1.0%). CONCLUSIONS: Risk of cerebrovascular toxicity continues to increase with longer follow-up. NTCP stroke predictions are very sensitive to model variables (baseline stroke risk and proportional stroke hazard), both of which found in the literature may be systematically erring on minimization of true risk. We hope this information will assist practitioners in counseling, screening, surveilling, and facilitating risk reduction of RT-related cerebrovascular late effects in this highly sensitive population.

A radiotherapy planning study of RapidArc, intensity modulated radiotherapy, three-dimensional conformal radiotherapy, and parallel opposed beams in the treatment of pediatric retroperitoneal tumors.

BACKGROUND: This planning study compared RapidArc, fixed-field IMRT (cIMRT), 3D conformal radiotherapy (3D-CRT), and a parallel-opposed pair (POP) for children with retroperitoneal tumors. PROCEDURE: Plans were generated in eight patients to treat the PTV (dose range 19.8-45 Gy) while limiting kidney and liver doses. In selected patients, vertebral body (VB) dose heterogeneity was minimized. Cumulative DVH parameters, monitor units (MU), and treatment times were compared for the four techniques using the Wilcoxon matched pairs test. RESULTS: RapidArc and cIMRT covered target volumes more conformally than 3D-CRT and POP (P = 0.012). There was no difference in the ability to meet kidney dose constraints. A significantly lower volume of the liver received 12 Gy with cIMRT or RapidArc compared with 3D-CRT (P = 0.028). Where VB was included in PTV, VB dose homogeneity was generally within 94-104% of the prescription dose. Time to deliver a single fraction with RapidArc, POP, 3D-CRT, and cIMRT was 1.25 ± 0.01, 1.38 ± 0.10, 2.6 ± 0.45, and 4.02 ± 1.12 min, respectively (P = 0.012). Monitor units for a single fraction with POP, 3D-CRT, RapidArc, and cIMRT were 203 ± 26, 235 ± 32, 325 ± 71, and 665 ± 215, respectively (P < 0.05). CONCLUSIONS: POP resulted in favorable MU, treatment time and dosimetry but had poor conformality. 3D-CRT was more conformal but had higher MU and treatment time. RapidArc and cIMRT were generally no better dosimetrically than conformal techniques. RapidArc was dosimetrically very similar to cIMRT, but resulted in a major reduction in time and MU used to deliver the radiation.