Tolerance of normal tissue to therapeutic irradiation

Cosmetic assessment in brachytherapy (interventional radiotherapy) for breast cancer: A multidisciplinary review

PURPOSE

This review was to focus on breast brachytherapy cosmetic assessment methods state of the art and to define the advantages and disadvantages related to.

METHODS AND MATERIALS

We conducted a literature review of the major experience on breast brachytherapy cosmetic assessment methods in several databases (PubMed, Scopus, and Google Scholar databases). To identify the relevant works, a task force screened citations at title and abstract level to identify potentially relevant paper. An expert board reviewed and approved the text. The assessment systems were classified into three main groups: (1) the Oncological Toxicity Scales, (2) the Independent Patients Perspective Measures, (3) the Patient-Related Outcome Measures. Each cosmetic assessment method was evaluated following six parameters: (1) anatomical site, (2) advantages, (3) disadvantages, (4) subjective/objective, (5) quantitative/qualitative, (6) computers or pictures needs.

RESULTS

Eleven assessment methods were selected. Three methods were classified as Oncological Toxicity Scale, six in the Independent Patients Perspective Measures classification, and two as Patient-Related Outcome Measures. Six methods are subjective, while eight are objective. Four systems are classified as quantitative, four as qualitative while three both. Five systems need informatics support. Moreover, each method was discussed individually reporting the main characteristics and peculiarities.

CONCLUSIONS

Cosmesis is one major end point for the patient who has a malignancy of low lethal potential. In modern personalized medicine, there is a need for standardized cosmetic outcome assessments to analyze and compare the results of treatments. No gold standard methods currently exist. The result of this review is to summarize the various cosmesis methods, defining the strengths and weaknesses of each one and giving a line in research and clinical practice.

Dosimetry and Gastrointestinal Toxicity Relationships in a Phase II Trial of Pelvic Lymph Node Radiotherapy in Advanced Localised Prostate Cancer

AIMS

Pelvic lymph node (PLN) radiotherapy for high-risk prostate cancer is limited by late gastrointestinal toxicity. Application of rectal and bowel constraints may reduce risks of side-effects. We evaluated associations between intensity-modulated radiotherapy (IMRT) dose-volume data and long-term gastrointestinal toxicity.

MATERIALS AND METHODS

Data from a single-centre dose-escalation trial of PLN-IMRT were analysed, including conventionally fractionated (CFRT) and hypofractionated (HFRT) radiotherapy schedules. Associations between volumes of rectum and bowel receiving specified doses and clinician- and patient-reported toxicity outcomes were investigated independently. A metric, δ median (δM), was defined as the difference in the medians of a volume between groups with and without toxicity at a specified dose and was used to test for statistically significant differences.

RESULTS

Constraints were respected in most patients and, when exceeded, led to higher rates of gastrointestinal toxicity. Biologically relevant associations between rectum dose-points and toxicity were more numerous with both mild and moderate toxicity thresholds, but statistical significance was limited after correction for false discovery rate. Rectal V50Gy (CFRT) associated with grade 2+ bleeding; bowel V43Gy and V47 (HFRT/4 days/week schedule) associated with patient-reported loose stools and diarrhoea, respectively. Further investigation showed that CFRT patients with rectal bleeding had a mean rectal V50Gy above the treatment planning constraint.

CONCLUSIONS

When dose-volume parameters are kept below tight constraints, toxicity is low. Residual dosimetry loses much of its predictive power for gastrointestinal toxicity in the setting of PLN-IMRT for prostate cancer. We have benchmarked dose-volume constraints for safely delivering PLN-IMRT using CFRT or HFRT.

Intracavitary radioimmunotherapy of high-grade gliomas: present status and future developments

There is a distinct need for new and second-line therapies to delay or prevent local tumor regrowth after current standard of care therapy. Intracavitary radioimmunotherapy, in combination with radiotherapy, is discussed in the present review as a therapeutic strategy of high potential. We performed a systematic literature search following the Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA). The available body of literature on intracavitary radioimmunotherapy (iRIT) in glioblastoma and anaplastic astrocytomas is presented. Several past and current phase I and II clinical trials, using mostly an anti-tenascin monoclonal antibody labeled with I-131, have shown median overall survival of 19-25 months in glioblastoma, while adverse events remain low. Tenascin, followed by EGFR and variants, or smaller peptides have been used as targets, and most clinical studies were performed with I-131 or Y-90 as radionuclides while only recently Re-188, I-125, and Bi-213 were applied. The pharmacokinetics of iRIT, as well as the challenges encountered with this therapy, is comprehensively discussed. This promising approach deserves further exploration in future studies by incorporating several innovative modifications.

Systematic review and meta-analysis of small bowel dose-volume and acute toxicity in conventionally-fractionated rectal cancer radiotherapy

INTRODUCTION

The limited radiation tolerance of the small-bowel causes toxicity for patients receiving conventionally-fractionated radiotherapy for rectal cancer. Safe radiotherapy dose-escalation will require a better understanding of such toxicity. We conducted a systematic review and meta-analysis using published datasets of small bowel dose-volume and outcomes to analyse the relationship with acute toxicity.

MATERIALS AND METHODS

SCOPUS, EMBASE & MEDLINE were searched to identify twelve publications reporting small-bowel dose-volumes and toxicity data or analysis. Where suitable data were available (mean absolute volume with parametric error measures), fixed-effects inverse-variance meta-analysis was used to compare cohorts of patients according to Grade ≥3 toxicity. For other data, non-parametric examinations of irradiated small-bowel dose-volume and incidence of toxicity were conducted, and a univariate logistic regression model was fitted.

RESULTS

On fixed-effects meta-analysis of three studies (203 patients), each of the dose-volume measures V_5Gy-V_40Gy were significantly greater (p < 0.00001) for patients with Grade ≥3 toxicity than for those without. Absolute difference was largest for the lowest dose-volume parameter; however relative difference increases with increasing dose. On logistic regression multiple small-bowel DVH parameters were predictive of toxicity risk (V_5Gy, V_10Gy, V_30Gy - V_45Gy), with V_10Gy the strongest (p = 0.004).

CONCLUSIONS

Analysis of published clinical cohort dose-volume data provides evidence for a significant dose-volume-toxicity response effect for a wide range of clinically-relevant doses in the treatment of rectal cancer. Both low dose and high dose are shown to predict toxicity risk, which has important implications for radiotherapy planning and consideration of dose escalation for these patients.

A machine-learning-based prediction model of fistula formation after interstitial brachytherapy for locally advanced gynecological malignancies

PURPOSE

External beam radiotherapy combined with interstitial brachytherapy is commonly used to treat patients with bulky, advanced gynecologic cancer. However, the high radiation dose needed to control the tumor may result in fistula development. There is a clinical need to identify patients at high risk for fistula formation such that treatment may be managed to prevent this toxic side effect. This work aims to develop a fistula prediction model framework using machine learning based on patient, tumor, and treatment features.

METHODS AND MATERIALS

This retrospective study included 35 patients treated at our institution using interstitial brachytherapy for various gynecological malignancies. Five patients developed rectovaginal fistula and two developed both rectovaginal and vesicovaginal fistula. For each patient, 31 clinical features of multiple data types were collected to develop a fistula prediction framework. A nonlinear support vector machine was used to build the prediction model. Sequential backward feature selection and sequential floating backward feature selection methods were used to determine optimal feature sets. To overcome data imbalance issues, the synthetic minority oversampling technique was used to generate synthetic fistula cases for model training.

RESULTS

Seven mixed data features were selected by both sequential backward selection and sequential floating backward selection methods. Our prediction model using these features achieved a high prediction accuracy, that is, 0.904 area under the curve, 97.1% sensitivity, and 88.5% specificity.

CONCLUSIONS

A machine-learning-based prediction model of fistula formation has been developed for patients with advanced gynecological malignancies treated using interstitial brachytherapy. This model may be clinically impactful pending refinement and validation in a larger series.

A Phase II Study to Prevent Radiation-induced Rectal Injury With Lovastatin

PURPOSE

Physician reported symptomatic late rectal injury occurs in about 5% to 25% of patients treated with radiation therapy for prostate cancer, depending on the treatment technique. Patients, however, report clinically meaningful declines in bowel/rectal function regardless of the technique used. Lovastatin has been shown to protect mice from late radiation injury. This study was designed to determine if lovastatin might reduce the incidence of late rectal injury in patients receiving radiation therapy for prostate cancer.

MATERIALS AND METHODS

Patients with adenocarcinoma of the prostate receiving radiotherapy with curative intent were eligible. A portion of the rectum had to receive at least 60 Gy. Gastrointestinal functioning was assessed using both physician-reported and patient-reported instruments at baseline and at prescribed intervals during and after treatment. Lovastatin (20 to 80 mg/d) was started on day 1 of radiation and continued for 12 months. Patients were followed for an additional 12 months. The primary endpoint was physician-reported rectal toxicity ≥grade 2 during the first 2 years after treatment.

RESULTS

A total of 20/53 (38%) patients developed grade 2 or higher toxicity during the 2-year follow-up period. Seventeen patients had 1 or more unresolved gastrointestinal symptom at the end of 2 years, 3 (6%) of which were grade 2 and none were of higher grade.

CONCLUSIONS

The primary endpoint of the study was not met. Lovastatin, as administered in this trial, did not reduce the incidence of grade 2 or higher rectal toxicity compared with historical controls.

Intravitreal aflibercept for the treatment of radiation-induced macular edema after ruthenium 106 plaque radiotherapy for choroidal melanoma

PURPOSE

To assess the efficacy of intravitreal aflibercept in patients suffering from post-radiation macular edema following plaque radiotherapy for choroidal melanoma.

METHODS

This prospective, interventional case series included patients affected by radiation maculopathy (RM) with macular edema secondary to ruthenium-106 plaque brachytherapy for choroidal melanoma. The effect of intravitreal aflibercept on best-corrected visual acuity (BCVA), central foveal thickness (CFT) detected by spectral domain optical coherence tomography (sd-OCT), and Horgan's grading scale of RM was evaluated throughout the 24-month follow-up. Intraocular pressure (IOP) and possible complications were also recorded.

RESULTS

Nine eyes of 9 patients were included. A mean of 4.4 ± 1.2 injections were given over the 24 months. At the end of follow-up, mean BCVA was significantly improved, from 0.9 ± 0.19 logMAR at baseline to 0.56 ± 0.3 logMAR (P = 0.028), and mean CFT was significantly decreased, from 546 ± 123 μm at baseline to 223 ± 34 μm (P < 0.001). Intravitreal aflibercept lowered baseline maculopathy stage as well. No significant change in IOP values and no complications, such as endophthalmitis, was recorded.

CONCLUSION

Intravitreal aflibercept is an effective treatment for patients with radiation-induced macular edema, allowing functional and anatomical improvements to be achieved with a relatively low number of injections.

Preclinical Evaluation of the Acute Radiotoxicity of the α-Emitting Molecular-Targeted Therapeutic Agent 211At-MABG for the Treatment of Malignant Pheochromocytoma in Normal Mice

The α-emitter ²¹¹At-labeled meta-astatobenzylguanidine (²¹¹At-MABG) has a strong antitumor effect on pheochromocytoma xenograft tumors and holds great promise as a new therapeutic option for malignant pheochromocytoma. To evaluate the acute radiation-related toxicity of ²¹¹At-MABG, we conducted biodistribution and dosimetry studies of ²¹¹At-MABG in ICR mice to estimate the doses absorbed by organs. We determined the maximum tolerated doses (MTD) of ²¹¹At-MABG on the basis of body weight loss and assessed the acute radiation-related toxicity induced by MTD administration on the basis of organ weights, histologic features, hematologic indices, and biochemical indices. The biodistribution and dosimetry studies of α-emitting ²¹¹At-MABG revealed high doses absorbed by most organs except the brain in ICR mice. The administration of 1.1, 2.2, and 3.3 MBq of ²¹¹At-MABG induced transient body weight loss, and 4.4 MBq of ²¹¹At-MABG induced unrecoverable body weight loss; thus, the MTD was 3.3 MBq for ICR mice. Although by day 5 the administration of 3.3 MBq had induced some radiation-related toxicity symptoms—such as body weight loss and leucopenia, which are generally observed in radiation therapy including β⁻-emitting radiopharmaceuticals—the mice had recovered by day 28. We observed no unexpected severe toxicity in ICR mice despite the high absorbed doses in most organs, especially the thyroid, heart, stomach, and adrenal glands. Our findings suggest that therapeutic treatments with appropriate doses of ²¹¹At-MABG estimated by dosimetry in each patient could be tolerated, although lower doses may initially be necessary to ensure patient safety in the first-in-human study.

Numerical Simulation Based on Individual Voxel Phantoms for a Sophisticated Evaluation of Internal Doses Mainly From 131I in Highly Exposed Workers Involved in the TEPCO Fukushima Daiichi NPP Accident

As a response to the Tokyo Electric Power Company's Fukushima Daiichi nuclear power plant accident in 2011, seven TEPCO workers whose exposure doses were expected to be >250 mSv (a tentative dose limit stipulated by the Japanese central authority) attended Japan's National Institute for Radiological Sciences for additional internal dose measurements. The National Institute for Radiological Sciences examination revealed that these workers' internal doses came mainly from their intake of the radionuclide I during emergency operations. In this study, we performed numerical simulations based on individual volume-pixel (voxel) phantoms of six of the seven workers for a more sophisticated evaluation of their internal doses, taking into account the individual thyroid size and other specific parameters. The voxel phantoms were created from magnetic resonance imaging scan images. As a result, the individual thyroid volumes ranged from 6.5 to 28.2 cm and were considerably smaller than the reference value (~20 cm) adopted in the International Commission on Radiation Protection's dosimetric model for four of the six subjects. Compared to the original estimates of the thyroid absorbed dose, our preliminary evaluation revealed values that were increased by approximately 3-fold or decreased by 30% at maximum. A wide difference in the individual thyroid size would be one of the significant modifiers in the current dose estimation of subjects of the ongoing epidemiological study project. The present simulations also provided evidence that the direct thyroid measurements by the National Institute for Radiological Sciences to determine the workers' I thyroid contents were sufficiently accurate.

Modulation indices and plan delivery accuracy of volumetric modulated arc therapy

PURPOSE

We evaluated the performance of various modulation indices (MI) for volumetric modulated arc therapy (VMAT) to predict plan delivery accuracy.

METHODS

The specific indices evaluated were MI quantifying the mechanical uncertainty (MI_t ), MI quantifying the mechanical and dose calculation uncertainties (MI_c ), MI for station parameter optimized radiation therapy (MI_SPORT ), modulation complexity score for VMAT (MCS_v ), leaf travel modulation complexity score (LTMCS), plan averaged beam area (PA), plan averaged beam irregularity (PI), plan averaged beam modulation (PM), and plan normalized monitor unit (PMU) to predict VMAT delivery accuracy. By utilizing 240 VMAT plans generated with the Trilogy and TrueBeam STx, Spearman's rank correlation coefficients (r) were calculated between the MIs and measures of conventional methods.

RESULTS

For the Trilogy system, MI_c showed the highest r values with gamma passing rates (GPRs) (r = -0.624 with P < 0.001 for MapCHECK2 and r = -0.655 with P < 0.001 for ArcCHECK). For TrueBeam STx, MI_c also showed the highest r values with GPRs (r = -0.625 with P < 0.001 for the MapCHECK2 and r = -0.561 with P < 0.001 for the ArcCHECK). The MI_t and MI_c showed the highest r values to the MLC position errors for the Trilogy and TrueBeam STx systems (r = 0.770 with P < 0.001 and r = 0.712 with P < 0.001, respectively). The PA showed the highest percent of r values (P < 0.05) to differences in the dose-volume parameters between original VMAT plans and actual deliveries for the Trilogy systems (30.9%). Both the MI_t and MI_c showed the highest percent of r values (P < 0.05) to differences in the dose-volume parameters between original VMAT plans and actual deliveries for the TrueBeam STx systems (31.8%).

CONCLUSION

To comprehensively review the results, the MI_c showed the best performance to predict the VMAT delivery accuracy.

What Neuroradiologists Need to Know About Radiation Treatment for Neural Tumors

Radiation oncologists and radiologists have a unique and mutually dependent relationship. Radiation oncologists rely on diagnostic imaging to locate the tumor and define the treatment target volume, evaluation of response to therapy, and follow-up. Accurate interpretation of post-treatment imaging requires diagnostic radiologists to have a basic understanding of radiation treatment planning and delivery. There are various radiation treatment modalities such as 3D conformal radiation therapy, intensity modulated radiation therapy and stereotactic radiosurgery as well as different radiation modalities such as photons and protons that can be used for treatment. All of these have subtle differences in how the treatment is planned and how the imaging findings might be affected. This paper provides an overview of the basic principles of radiation oncology, different radiation treatment modalities, how radiation therapy is planned and delivered, how knowledge of this process can help interpretation of images, and how the radiologist can contribute to this process.

Radiation-Associated Cardiac Disease: From Molecular Mechanisms to Clinical Management

PURPOSE OF REVIEW

Radiation-associated cardiac disease (RACD) is an increasingly recognized latent manifestation of chest and mediastinal radiation therapy. The delayed presentation reflects increased survival rates from malignancies successfully treated decades previously. However, individuals are now presenting with multiple coexistent manifestations of RACD and pulmonary disease as a consequence of high-dose radiation administered prior to the routine institution of modern dose-modulating regimens. Increased awareness of RACD is critical for implementation of appropriate screening algorithms and for specific management strategies involving the timing and strategies of intervention in these patients.

RECENT FINDINGS

Recent advances in multimodality cardiac imaging have demonstrated pathognomonic findings of RACD, which can predict outcomes including mortality. Accurate diagnosis of these typically concurrent manifestations is critical and should prompt referral to a center experienced in managing RACD as surgical risk is significantly increased for this patient cohort, particularly for those undergoing redo operation. The latent effect of RACD and its unique combination of manifestations means that these patients will increasingly present with challenging management issues, resulting in increased rates of morbidity and mortality. Timing of treatment intervention must be carefully considered, although percutaneous options may provide alternative future strategies for this higher risk cohort.

Improved prognosis of extranodal NK/T cell lymphoma, nasal type of nasal origin but not extranasal origin

Extranodal NK/T cell lymphoma (NKTCL), nasal type (ENKL) that shows no apparent nasal involvement, is termed extranasal NKTCL or non-nasal NKTCL. In this study, we aimed to explore therapeutic approaches and outcomes in patients with extranasal NKTCL in current clinical practice. A data set of patients with newly diagnosed NKTCL who were diagnosed at 31 institutes in Japan between 2000 and 2013 was used for analysis. The patients' fitness for steroid, methotrexate, ifosfamide, L-asparaginase, and etoposide (SMILE) chemotherapy was assessed using the major inclusion criteria of the SMILE phase 2 study. Of 358 patients, 47 (13%) had extranasal NKTCL. The most frequent extranodal sites of involvement in extranasal NKTCL were skin/subcutaneous tissue (n = 18). Six (13%) of the patients with extranasal NKTCL had localized disease and were diagnosed before 2010. With a median follow-up of 5.8 years, the 2-year overall survival (OS) in patients with nasal and extranasal NKTCL was 70% (95% confidence interval [CI], 65-75%) and 34% (95% CI, 21-47%), respectively. OS in patients with nasal NKTCL had a trend toward better according to treatment era (P = 0.063). In contrast, no obvious improvement of OS was observed in extranasal NKTCL (P = 0.43). The major inclusion criteria of the SMILE-P2 were met in 21% (10/47) of patients with extranasal NKTCL and 60% (188/311) of those with nasal NKTCL (P < 0.001). Despite the advent of new treatments for ENKL, OS remains unfavorable in extranasal NKTCL. A more effective therapy is needed for extranasal NKTCL.

Genomics of radiation sensitivity in squamous cell carcinomas

Radiotherapy is an important modality in the management of squamous cell cancers with 50% of patients receiving radiotherapy at some point. Despite technological advances, the risk of severe toxicity in a proportion of radiosensitive patients limits radiation doses that can be safely prescribed affecting the potential for cure. While comorbidities, lifestyle and treatment factors can influence interindividual variations, genetic factors are thought to play a major role, accounting for approximately 80% of the variance observed. Over the last decade, substantial progress has been made in the field of radiogenomics, with compelling associations for SNPs identified in genes involved in DNA-damage response, cell-cycle control, apoptosis, antioxidant defenses and cytokine production. Future research efforts should be collaborative, focused on validating and broadening their clinical applicability. Numerous obstacles exist to the clinical application of this knowledge, which need to be overcome before personalized radiation therapy becomes a routine component of oncologic care.

Consolidative mediastinal irradiation of malignant lymphoma using active scanning proton beams: clinical outcome and dosimetric comparison

PURPOSE

Current research approaches in lymphoma focus on reduction of therapy-associated long-term side effects. Especially in mediastinal lymphoma, proton beam radiotherapy (PT) may be a promising approach for reducing the dose to organs at risk (OAR).

PATIENTS

In total, 20 patients were irradiated with active scanning PT at Heidelberg Ion Beam Therapy Center (HIT) between September 2014 and February 2017. For comparative analysis, additional photon irradiation plans with helical intensity-modulated radiotherapy (IMRT) were calculated and quantitative and qualitative dose evaluations were made for both treatment modalities. Toxicity and survival outcomes were evaluated.

RESULTS

Clinical target volume coverage was comparable in both treatment modalities and did not significantly differ between IMRT and PT. Nevertheless, PT showed superiority regarding the homogeneity index (HI_PT = 1.041 vs. HI_IMRT = 1.075, p < 0.001). For all OAR, PT showed significantly higher dose reductions compared with IMRT. In particular, the dose to the heart was reduced in PT (absolute dose reduction of D_mean of 3.3 Gy [all patients] and 4.2 Gy [patients with pericardial involvement]). Likewise, the subgroup analysis of female patients, who were expected to receive higher doses to the breast, showed a higher dose reduction in D_mean of 1.2 Gy (right side) and 2.2 Gy (left side). After a median follow-up of 32 months (range 21-48 months), local and distant progression free survival (LPFS and DPFS) were 95.5% and 95.0%, respectively. Radiotherapy was tolerated well with only mild (grade 1-2) radiation-induced acute and chronic side effects.

CONCLUSION

A significant reduction in the dose to the surrounding OAR was achieved with PT compared with photon irradiation, without compromising target volume coverage. Dosimetric advantages may have the potential to translate into a reduction of long-term radiation-induced toxicity in young patients with malignant lymphoma of the mediastinum.

Treatment Outcome after Fractionated Conformal Radiotherapy for Hepatocellular Carcinoma in Patients with Child-Pugh Classification B in Korea (KROG 16-05)

Purpose

There is limited data on radiotherapy (RT) for hepatocellular carcinoma (HCC) in patients with Child-Pugh classification B (CP-B). This study aimed to evaluate the treatment outcomes of fractionated conformal RT in HCC patients with CP-B.

Materials and Methods

We retrospectively reviewed the data of HCC patients with CP-B treated with RT between 2009 and 2014 at 13 institutions in Korea. HCC was diagnosed by the Korea guideline of 2009, and modern RT techniques were applied. Fraction size was ≤ 5 Gy and the biologically effective dose (BED) ≥ 40 Gy₁₀ (α/β = 10 Gy). A total of 184 patients were included in this study.

Results

Initial CP score was seven in 62.0% of patients, eight in 31.0%, and nine in 7.0%. Portal vein tumor thrombosis was present in 66.3% of patients. The BED ranged from 40.4 to 89.6 Gy₁₀ (median, 56.0 Gy₁₀). After RT completion, 48.4% of patients underwent additional treatment. The median overall survival (OS) was 9.4 months. The local progression-free survival and OS rates at 1 year were 58.9% and 39.8%, respectively. In the multivariate analysis, non-classic radiation-induced liver disease (RILD) (p < 0.001) and additional treatment (p < 0.001) were the most significant prognostic factors of OS. Among 132 evaluable patients without progressive disease, 19.7% experienced non-classic RILD. Normal liver volume was the most predictive dosimetric parameter of non-classic RILD.

Conclusion

Fractionated conformal RT showed favorable OS with a moderate risk non-classic RILD. The individual radiotherapy for CP-B could be cautiously applied weighing the survival benefits and the RILD risks.

A systematic review of dose-volume predictors and constraints for late bowel toxicity following pelvic radiotherapy

BACKGROUND

Advanced pelvic radiotherapy techniques aim to reduce late bowel toxicity which can severely impact the lives of pelvic cancer survivors. Although advanced techniques have been largely adopted worldwide, to achieve their aim, knowledge of which dose-volume parameters of which components of bowel predict late bowel toxicity is crucial to make best use of these techniques. The rectum is an extensively studied organ at risk (OAR), and dose-volume predictors of late toxicity for the rectum are established. However, for other components of bowel, there is a significant paucity of knowledge. The Quantitative Analyses of Normal Tissue Effects in the Clinic (QUANTEC) reviews recommend dose-volume constraints for acute bowel toxicity for peritoneal cavity and bowel loops, although no constraints are recommended for late toxicity, despite its relevance to our increasing number of survivors. This systematic review aims to examine the published literature to seek dose-volume predictors and constraints of late bowel toxicity for OARs (apart from the rectum) for use in clinical practice.

METHODS

A systematic literature search was performed using Medline, Embase, Cochrane Library, Web of Science, Cinahl and Pubmed. Studies were screened and included according to specific pre-defined criteria. Included studies were assessed for quality against QUANTEC-defined assessment criteria.

RESULTS

101 studies were screened to find 30 relevant studies. Eight studies related to whole bowel, 11 to small bowel, and 21 to large bowel (including 16 of the anal canal). The anal canal is an important OAR for the development of late toxicity, and we recommend an anal canal Dmean <40Gy as a constraint to reduce late incontinence. For other components of bowel (sigmoid, large bowel, intestinal cavity, bowel loops), although individual studies found statistically significant parameters and constraints these findings were not corroborated in other studies.

CONCLUSIONS

The anal canal is an important OAR for the development of late bowel toxicity symptoms. Further validation of the constraints found for other components of bowel is needed. Studies that were more conclusive included those with patient-reported data, where individual symptom scores were assessed rather than an overall score, and those that followed statistical and endpoint criteria as defined by QUANTEC.

The value of a bladder-filling protocol for patients with prostate cancer who receive post-operative radiation: results from a prospective clinical trial

BACKGROUND AND PURPOSE

This study compares two different strategies for maintaining a constant bladder volume during a course of postoperative radiotherapy in prostate cancer. In addition, we studied how changes in bladder filling affect the clinical target volume (CTV) and the coverage hereof.

MATERIAL AND METHODS

Twenty-nine patients with PSA-relapse after radical prostatectomy were divided into two groups: voiding and drinking 300 ml 1 hour before treatment (Group 1); and maintained a comfortably filled bladder (Group 2). The bladder volumes were calculated based on the planning CT (pCT) and a weekly Cone Beam CT (CBCT) during the treatment period. Furthermore, the variability of bladder extension was analyzed and correlated to the volume of the bladder covered with the 95% of the dose (V_95%,bladder).

RESULTS

The estimated median bladder volumes were 120 ml (95% CI: (93, 154)) and 123 ml (95% CI: (98, 155)) in groups 1 and 2, respectively. The intra-individual variation in bladder volume, assessed as the standard deviation, was 64 ml (95% CI: (46, 105)) in Group 1 and 61 (95% CI: (45, 94)) ml in Group 2. Increasing the bladder volume extended the bladder cranially while the caudal extension was almost constant. The correlation between bladder volume and V_95%,bladder was 3.5 ml per 100 ml in group 1 and 1.2 ml per 100 ml in group 2 with no significant difference.

CONCLUSIONS

The intention to maintain a constant volume for the bladder is not fulfilled with either of the protocols in this study, and changes in bladder volumes does not seem to affect the position, or the coverage of the CTV.

Transient Inhibition of mTORC1 Signaling Ameliorates Irradiation-Induced Liver Damage

Recurrent liver cancer after surgery is often treated with radiotherapy, which induces liver damage. It has been documented that activation of the TGF-β and NF-κB signaling pathways plays important roles in irradiation-induced liver pathologies. However, the significance of mTOR signaling remains undefined after irradiation exposure. In the present study, we investigated the effects of inhibiting mTORC1 signaling on irradiated livers. Male C57BL/6J mice were acutely exposed to 8.0 Gy of X-ray total body irradiation and subsequently treated with rapamycin. The effects of rapamycin treatment on irradiated livers were examined at days 1, 3, and 7 after exposure. The results showed that 8.0 Gy of irradiation resulted in hepatocyte edema, hemorrhage, and sinusoidal congestion along with a decrease of ALB expression. Exposure of mice to irradiation significantly activated the mTORC1 signaling pathway determined by pS6 and p-mTOR expression via western blot and immunostaining. Transient inhibition of mTORC1 signaling by rapamycin treatment consistently accelerated liver recovery from irradiation, which was evidenced by decreasing sinusoidal congestion and increasing ALB expression after irradiation. The protective role of rapamycin on irradiated livers might be mediated by decreasing cellular apoptosis and increasing autophagy. These data suggest that transient inhibition of mTORC1 signaling by rapamycin protects livers against irradiation-induced damage.

[Medical prevention and treatment of radiation-induced urological and nephrological complications]

Abdominal and pelvic irradiations play a major place in the management of patients with cancer and present a risk of acute and late side effects. Radiation-induced lesions can affect kidney or urological structures. These side effects can have an impact in the quality of life of patients. The aim of this article is to describe the physiopathology, the symptomatology, and the principles of management of radiation-induced nephropathy, uretheritis, cystitis, and urethritis.

Voxel-Based Dosimetry of Iron Oxide Nanoparticle-Conjugated 177Lu-Labeled Folic Acid Using SPECT/CT Imaging of Mice

Several radiolabeled folic acid conjugates have been developed for targeted imaging and therapy. However, the therapeutic concept with radiolabeled folate conjugates has not yet been applied to clinical applications owing to the high renal absorbed dose. The effectiveness of targeted radionuclide therapy (TRT) depends primarily on the absorbed dose rate and on the total absorbed dose delivered to the tumor and to normal tissue. Owing to various limitations associated with organ level dosimetry, voxel-based dosimetry has become essential for the assessment of a more  accurate absorbed dose during TRT. In this study, we synthesized iron oxide nanoparticle (IONP)-conjugated radiolabeled folate (¹⁷⁷Lu-IONP-Folate) and performed voxel-based dosimetry using SPECT/CT images of normal mice through direct Geant4 application for emission tomography (GATE) Monte Carlo (MC) simulation. We also prepared ¹⁷⁷Lu-Folate and ¹⁷⁷Lu-IONPs for the comparison of absorbed doses with that of ¹⁷⁷Lu-IONP-Folate. In addition, we calculated the mean absorbed dose at the organ-level using the medical internal radiation dose (MIRD) schema. The radioactivities of all three radiotracers were mainly accumulated in the liver and kidneys immediately after injection. For the kidneys, the voxel-based absorbed doses obtained with ¹⁷⁷Lu-IONP-Folate, ¹⁷⁷Lu-Folate, and ¹⁷⁷Lu-IONPs were 1.01 ± 0.17, 2.46 ± 0.50, and 0.52 ± 0.08 Gy/MBq, respectively. The renal absorbed dose decreased significantly (∼half) when ¹⁷⁷Lu-IONP-Folate was used compared with when the ¹⁷⁷Lu-Folate only was used. The mean absorbed dose values obtained at organ-level using the MIRD schema were comparable to voxel-based absorbed doses estimated with GATE MC. The voxel-based absorbed dose values obtained in this study of individualized activity show that the renal absorbed dose could be reduced to almost half with ¹⁷⁷Lu-IONP-Folate. Therefore, ¹⁷⁷Lu-IONP-Folate could be clinically applicable in the TRT of folate receptor-positive cancers in a personalized manner when using the voxel-based dosimetry method.

Salvage Carbon-Ion Radiation Therapy For Locoregionally Recurrent Head and Neck Malignancies

To investigate the safety and efficacy of salvage carbon-ion radiation therapy (CIRT) in patients with locoregionally recurrent head and neck malignancies. One hundred and forty-one patients with locally recurrent head and neck malignancies previously treated with radiotherapy were salvaged using intensity-modulated carbon-ion radiation therapy (CIRT). The median dose was 60 Gray-Equivalent (GyE) (range 50–69 GyE, 2.0~3.5 GyE/daily fraction). All patients completed planned CIRT except for one. With a median follow-up time of 14.7 (range 1.6–36.4) months, the 1-year overall survival rate was 95.9%. Local, regional, and distant progression free survival rates were 84.9% and 97.7%, and 96%, respectively. Grade 3 or higher acute and late toxicities were observed in 7.1% of the patients. Ten patients developed mucosal necrosis and 4 of these patients deceased. Due to its physical and biological characteristics, CIRT appeared to be an acceptable treatment option for patients with locoregionally recurrent head and neck malignancies after previous radiotherapy. Treatment-induced adverse effects and early response to CIRT were both favorable. Longer follow-up is needed to evaluate the long-term outcome in terms of disease control, survival, as well as potential late effects.

Therapeutic efficacy evaluation of radioimmunotherapy with 90 Y-labeled anti-podoplanin antibody NZ-12 for mesothelioma

Podoplanin is a type I transmembrane sialomucin‐like glycoprotein that is highly expressed in malignant mesothelioma. The rat‐human chimeric antibody NZ‐12 has high affinity for human podoplanin and antibody‐dependent cellular cytotoxicity and is applicable for radioimmunotherapy (RIT) to enhance the antitumor effect. In the present study, we evaluated the in vivo and in vitro properties of radiolabeled NZ‐12 and the antitumor effect of RIT with ⁹⁰Y‐labeled NZ‐12 in an NCI‐H226 (H226) malignant mesothelioma xenograft mouse model. ¹¹¹In‐labeled NZ‐12 bound specifically to H226 cells with high affinity, and accumulation was high in H226 tumors but low in major organs. RIT with ⁹⁰Y‐labeled NZ‐12 significantly suppressed tumor growth and prolonged survival without body weight loss and obvious adverse effects. Higher podoplanin expression levels were observed in human mesothelioma specimens, suggesting higher tumor accumulation of ⁹⁰Y‐labeled NZ‐12 in patients compared with the H226 tumor xenografts. Our findings suggest that ⁹⁰Y‐labeled NZ‐12 is a promising RIT agent as a new therapeutic option for malignant mesothelioma that warrants further clinical studies to evaluate the dosimetry and efficacy in patients.

Technical Note: Simplified and practical pretherapy tumor dosimetry - A feasibility study for 131 I-MIBG therapy of neuroblastoma using 124 I-MIBG PET/CT

PURPOSE

Radiation dose calculated on tumors for radiopharmaceutical therapy varies significantly from tumor to tumor and from patient to patient. Accurate estimation of radiation dose requires multiple time point measurements using radionuclide imaging modalities such as SPECT or PET. In this report, we show our technical development of reducing the number of scans needed for reasonable estimation of tumor and normal organ dose in our pretherapy imaging and dosimetry platform of ¹²⁴ I-metaiodobenzylguanidine (MIBG) positron emission tomography/computed tomography (PET/CT) for ¹³¹ I-MIBG therapy of neuroblastoma.

METHODS

We analyzed the simplest kinetic data, areas of two-time point data for five patients with neuroblastoma who underwent 3 or 4 times of ¹²⁴ I-MIBG PET/CT scan prior to ¹³¹ I-MIBG therapy. The data for which we derived areas were percent of injected activity (%IA) and standardized uptake value of tumors. These areas were correlated with time-integrated activity coefficients (TIACs) from full data (3 or 4 time points). TIACs are direct correlates with radiation dose as long as the volume and the radionuclide are known.

RESULTS

The areas of %IAs between data obtained from all the two-time points with time points 1 and 2 (day 0 and day 1), time points 2 and 3 (day 1 and day 2), and time points 1 and 3 (day 0 and day 2) showed reasonable correlation (Pearson's correlation coefficient |r| > 0.5) with not only tumor and organ TIACs but also tumor and organ absorbed doses. The tumor and organ doses calculated using %IA areas of time point 1 and time point 2 were our best fits at about 20% individual percent difference compared to doses calculated using 3 or 4 time points.

CONCLUSIONS

We could achieve reasonable accuracy of estimating tumor doses for subsequent radiopharmaceutical therapy using only the two-time point imaging sessions. Images obtained from these time points (within the 48-h after administration of radiopharmaceutical) were also viewed as useful for diagnostic reading. Although our analysis was specific to ¹²⁴ I-MIBG PET/CT pretherapy imaging data for ¹³¹ I-MIBG therapy of neuroblastoma and the number of imaging datasets was not large, this feasible methodology would generally be applicable to other imaging and therapeutic radionuclides with an appropriate data analysis similar to our analysis to other imaging and therapeutic radiopharmaceuticals.

Volumetric modulated arc therapy with robust optimization for larynx cancer

PURPOSE

The aim of this study was to perform a comparison between robust optimization and planning target volume (PTV)-based optimization plans using volumetric modulated arc-therapy (VMAT) by evaluating perturbed doses induced by localization offsets for setup uncertainties in larynx cancer radiation therapy.

METHODS

Ten patients with early-stage (T1-2N0) glottis carcinoma were selected. The clinical target volume (CTV), carotid arteries, and spinal cord were contoured by a radiation oncologist. PTV-based and robust optimization plans were normalized at D_50% to the PTV and D_98% to the CTV, respectively. Both optimization plans were evaluated using perturbed doses by specifying user defined shifted values from the isocenter. CTV dose (D_98%, D_50%, and D_2%), homogeneity index (HI) and conformity index (CI_95%, CI_80%, and CI_50%), as well as doses to the carotid arteries and spinal cord were compared between PTV-based and robust optimization plans.

RESULTS

The robust optimization plans exhibited superior CTV coverage and a reduced dose to the carotid arteries compared to the PTV-based optimization plans (p < 0.05). HI, CI_95% and the dose to the spinal cord did not significantly differ between the PTV-based and robust optimization plans (p > 0.05). The robust optimization plans showed better CI_80% and CI_50% compared to the PTV-based optimization plans (p < 0.05). Plan perturbed evaluations showed that the robust optimization plan has small variations in the doses to the CTV, carotid arteries, and spinal cord compared to the PTV-based optimization plan.

CONCLUSIONS

The robust optimization plan may be a suitable treatment method in radiotherapy for larynx cancer patient.

Selection criteria for 3D conformal radiotherapy versus volumetric-modulated arc therapy in high-grade glioma based on normal tissue complication probability of brain

There are no quantitative selection criteria for identifying high-grade glioma (HGG) patients who are suited for volumetric-modulated arc therapy (VMAT). This study aimed to develop selection criteria that can be used for the selection of the optimal treatment modality in HGG. We analyzed 20 patients with HGG treated by 3D conformal radiotherapy (3DCRT). First, VMAT plans were created for each patient retrospectively. For each plan, the normal tissue complication probability (NTCP) for normal brain was calculated. We then divided the patients based on the NTCPs of the 3DCRT plans for normal brain, using the threshold of 5%. We compared the NTCPs of the two plans and the gross tumor volumes (GTVs) of the two groups. For the GTVs, we used receiver operating characteristic curves to identify the cut-off value for predicting NTCP < 5%. We determined the respective correlations between the GTV and the GTV's largest cross-sectional diameter and largest cross-sectional area. In the NTCP ≥ 5% group, the NTCPs for the VMAT plans were significantly lower than those for the 3DCRT plans (P = 0.0011). The NTCP ≥ 5% group's GTV was significantly larger than that of the NTCP < 5% group (P = 0.0016), and the cut-off value of the GTV was 130.5 cm3. The GTV was strongly correlated with the GTV's largest cross-sectional diameter (R2 = 0.82) and largest cross-sectional area (R2 = 0.94), which produced the cut-off values of 7.5 cm and 41 cm2, respectively. It was concluded that VMAT is more appropriate than 3DCRT in cases in which the GTV is ≥130.5 cm3.

Hybrid Therapy for Metastatic Epidural Spinal Cord Compression: Technique for Separation Surgery and Spine Radiosurgery

BACKGROUND

Despite major advances in radiation and systemic treatments, surgery remains a critical step in the multidisciplinary treatment of metastatic spinal cord tumors.

OBJECTIVE

To describe the indications, rationale, and technique of "hybrid therapy" (separation surgery and concomitant spine stereotactic radiosurgery [SRS]) along with practical nuances.

METHODS

Separation surgery describes a posterolateral approach for circumferential epidural decompression and stabilization. The goal is to decompress the spinal cord, stabilize the spine, and create adequate separation between the neural elements and the tumor for SRS to achieve durable tumor control.

RESULTS

A transpedicular route to achieve ventrolateral access and limited resection of the tumorous vertebral body is carried out. In the setting of high-grade cord compression, caution must be taken when performing the tumor decompression. "Separation" of the ventral epidural tumor component anteriorly creates space for concomitant SRS while a simple laminectomy would not adequately achieve this goal. Dissection of the posterior longitudinal ligament allows maximal ventral decompression. Gross total tumor resection is not crucial for durable tumor control using the "hybrid therapy" model. Thus, attempts at ventral tumor resection may unnecessarily increase operative morbidity. Cement augmentation of the construct or vertebral body may improve construct stability. CT myelogram is the preferred exam for postoperative SRS planning. Radiosurgical planning constitutes a multidisciplinary effort and guidelines for contouring in the postoperative setting have recently become available.

CONCLUSION

Separation surgery is an effective, well-tolerated, and reproducible surgery. It provides safe margins for concomitant SRS. Combined, this "Hybrid Therapy" allows durable local control, maintenance of spinal stability, and palliation of symptoms, while minimizing operative morbidity.

Pre-Operative Versus Post-Operative Radiosurgery of Brain Metastases-Volumetric and Dosimetric Impact of Treatment Sequence and Margin Concept

BACKGROUND

Pre-operative radiosurgery (SRS) preceding the resection of brain metastases promises to circumvent limitations of post-operative cavity SRS. It minimizes uncertainties regarding delineation and safety margins and could reduce dose exposure of the healthy brain (HB).

METHODS

We performed a systematic treatment plan comparison on 24 patients who received post-operative radiosurgery of the resection cavity at our institution. Comparative treatment plans were calculated for hypofractionated stereotactic radiotherapy (7 × 5 Gray (Gy)) in a hypothetical pre-operative (pre-op) and two post-operative scenarios, either with (extended field, post-op-E) or without the surgical tract (involved field, post-op-I). Detailed volumetric comparison of the resulting target volumes was performed, as well as dosimetric comparison focusing on targets and the HB.

RESULTS

The resection cavity was significantly smaller and different in morphology from the pre-operative lesion, yielding a low Dice Similarity Coefficient (DSC) of 53% (p = 0.019). Post-op-I and post-op-E targets showed high similarity (DSC = 93%), and including the surgical tract moderately enlarged resulting median target size (18.58 ccm vs. 22.89 ccm, p < 0.001). Dosimetric analysis favored the pre-operative treatment setting since it significantly decreased relevant dose exposure of the HB (Median volume receiving 28 Gy: 6.79 vs. 10.79 for pre-op vs. post-op-E, p < 0.001). Dosimetrically, pre-operative SRS is a promising alternative to post-operative cavity irradiation that could furthermore offer practical benefits regarding delineation and treatment planning. Comparative trials are required to evaluate potential clinical advantages of this approach.

Radiation-induced optic neuropathy after stereotactic and image guided intensity-modulated radiation therapy (IMRT)

BACKGROUND/PURPOSE

To quantify the risk of radiation-induced optic neuropathy (RION) after stereotactic/image-guided positioning and intensity-modulated radiotherapy (IMRT) with ≥50 Gy to the anterior visual pathway (AVP).

METHODS

Patients irradiated with ≥50 Gy to the AVP using stereotactic/image-guided positioning between 2002 and 2011 in Mannheim were identified. Detailed dosimetric data were collected and patients or family members were retrospectively asked to rate visual acuity and visual disorders.

RESULTS

125 patients fulfilled the eligibility criteria. Average maximum equivalent point dose (D_max-EQD-2_[α/β=1.6]) to the AVP was 53.1 ± 3.9 Gy. 99 patients received ≥50 Gy bilaterally (chiasm or both optic nerves), resulting in 224 (99x2 bilateral plus 26 unilateral) visual-fields-at-risk (VFAR) for RION. Eighty-two patients provided pre/post-IMRT visual status information (n = 151 VFARs). Permanent visual deterioration occurred in 18 (22%) patients. In seven, visual deterioration was possibly related to radiotherapy (two-sided deterioration in one patient) for a crude incidence of 8.5% (7/82 patients) and 5.3% (8/151 VFARs). Two cases were caused by chronic keratitis/conjunctivitis; in five patients RION could not be excluded (one two-sided). In one of 13 patients with D_max-EQD-2 > 58 Gy, RION could not be excluded. In all affected patients, visual acuity post-IMRT had decreased only mildly (1-2 points on the 5-point-scale). One patient with relevant baseline visual impairment (3/5) developed unilateral blindness (crude incidence of blindness on patient-/VFAR-level: 1.2% and 0.66%; competing risk-adjusted/actuarial 24-month incidence: patient/VFAR-level: 1.8% and 0.95%).

CONCLUSION

Risk of RION was low in this cohort with accurate positioning and precise dosimetric information. Less conservative tolerance doses may be considered in patients with high risk of recurrence.

Enteral Activation of WR-2721 Mediates Radioprotection and Improved Survival from Lethal Fractionated Radiation

Unresectable pancreatic cancer is almost universally lethal because chemotherapy and radiation cannot completely stop the growth of the cancer. The major problem with using radiation to approximate surgery in unresectable disease is that the radiation dose required to ablate pancreatic cancer exceeds the tolerance of the nearby duodenum. WR-2721, also known as amifostine, is a well-known radioprotector, but has significant clinical toxicities when given systemically. WR-2721 is a prodrug and is converted to its active metabolite, WR-1065, by alkaline phosphatases in normal tissues. The small intestine is highly enriched in these activating enzymes, and thus we reasoned that oral administration of WR-2721 just before radiation would result in localized production of the radioprotective WR-1065 in the small intestine, providing protective benefits without the significant systemic side effects. Here, we show that oral WR-2721 is as effective as intraperitoneal WR-2721 in promoting survival of intestinal crypt clonogens after morbid irradiation. Furthermore, oral WR-2721 confers full radioprotection and survival after lethal upper abdominal irradiation of 12.5 Gy × 5 fractions (total of 62.5 Gy, EQD2 = 140.6 Gy). This radioprotection enables ablative radiation therapy in a mouse model of pancreatic cancer and nearly triples the median survival compared to controls. We find that the efficacy of oral WR-2721 stems from its selective accumulation in the intestine, but not in tumors or other normal tissues, as determined by in vivo mass spectrometry analysis. Thus, we demonstrate that oral WR-2721 is a well-tolerated, and quantitatively selective, radioprotector of the intestinal tract that is capable of enabling clinically relevant ablative doses of radiation to the upper abdomen without unacceptable gastrointestinal toxicity.

Dosimetric predictors of temporal lobe injury after intensity-modulated radiotherapy for T4 nasopharyngeal carcinoma: a competing risk study

BACKGROUND

In patients with T4 nasopharyngeal carcinoma (NPC), death may occur prior to the occurrence of temporal lobe injury (TLI). Because such competing risk death precludes the occurrence of TLI and thus the competing risk analysis should be applied to TLI research. The aim was to investigate the incidence and predictive factors of TLI after intensity-modulated radiotherapy (IMRT) among T4 NPC patients.

METHODS

From March 2008 to December 2014, T4 NPC patients treated with full-course radical IMRT at our center were reviewed retrospectively. A nested case-control study was designed for this cohort of patients. The cases were patients with TLI diagnosed by MRI during the follow-up period, and the controls were patients without TLI after IMRT matched 1:1 to each case by gender, age at diagnosis, intercranial involvement, and follow-up time. The end point was time to TLI or death without prior TLI. We analyzed the cumulative incidence function (CIF) and performed a competing risk regression model to identify the predictors of TLI.

RESULTS

With a median follow-up of 40.1 months, 63 patients (63/506, 12.5%) developed TLI as diagnosed by MRI, and 136 deaths occurred during the period. The cumulative incidence of TLI at 5 years was 13.2%, while 26.7% died without prior TLI. The univariate analysis showed that all selected dosimetric parameters were associated with the occurrence of TLI. On multivariate analysis, D1cc and V20 remained statistically significant. Based on the area-under-the-curve (AUC) values, D1cc was considered the most predictive. The patients with D1cc > 71.14 Gy had a 7.920-fold increased risk of TLI compared with those with D1cc ≤71.14 Gy (P < 0.05). Similarly, V20 > 42.22 cc was found to result in a statistically significant higher risk of TLI (subdistribution hazard ratio [sHR] =3.123, P < 0.05).

CONCLUSIONS

TL D1cc and V20 were predictive of TLI after IMRT for T4 NPC. They should be considered as first and second priorities of dose constraints of the TL. D1cc ≤71.14 Gy and V20 ≤ 42.22 cc could be useful dose-volume constraints for reducing the occurrence of TLI during IMRT treatment planning without obviously compromising the tumor coverage.

Targeted Radionuclide Therapy of Painful Bone Metastases: Past Developments, Current Status, Recent Advances and Future Directions

Bone pain arising from secondary skeletal malignancy constitutes one of the most common types of chronic pain among patients with cancer which can lead to rapid deterioration of the quality of life. Radionuclide therapy using bone-seeking radiopharmaceuticals based on the concept of localization of the agent at bone metastases sites to deliver focal cytotoxic levels of radiation emerged as an effective treatment modality for the palliation of symptomatic bone metastases. Bone-seeking radiopharmaceuticals not only provide palliative benefit but also improve clinical outcomes in terms of overall and progression-free survival. There is a steadily expanding list of therapeutic radionuclides which are used or can potentially be used in either ionic form or in combination with carrier molecules for the management of bone metastases. This article offers a narrative review of the armamentarium of bone-targeting radiopharmaceuticals based on currently approved investigational and potentially useful radionuclides and examines their efficacy for the treatment of painful skeletal metastases. In addition, the article also highlights the processes, opportunities, and challenges involved in the development of bone-seeking radiopharmaceuticals. Radium-223 is the first agent in this class to show an overall survival advantage in Castration-Resistant Prostate Cancer (CRPC) patients with bone metastases. This review summarizes recent advances, current clinical practice using radiopharmaceuticals for bone pain palliation, and the expected future prospects in this field.

Animal models of radiation retinopathy - From teletherapy to brachytherapy

Radiation retinopathy is a serious vision-impairing complication of radiation therapy used to treat ocular tumors. Characterized by retinal vasculopathy and subsequent retinal damage, the first sign of radiation retinopathy is the preferential loss of vascular endothelial cells. Ensuing ischemia leads to retinal degradation and late stage neovascularization. Despite the established disease progression, the pathophysiology and cellular mechanisms contributing to radiation retinopathy remain unclear. Clinical experience and basic research for other retinal vasculopathies, such as diabetic retinopathy and retinopathy of prematurity, can inform our understanding of radiation retinopathy; however, the literature investigating the fundamental mechanisms in radiation retinopathy is limited. Treatment trials have shown modest success but, ultimately, fail to address the cellular events that initiate radiation retinopathy. Animal models of radiation retinopathy could provide means to identify effective therapies. Here, we review the literature for all animal models of radiation retinopathy, summarize anatomical highlights pertaining to animal models, identify additional physiological factors to consider when investigating radiation retinopathy, and explore the use of clinically relevant tests for studying in vivo models of radiation retinopathy. We encourage further investigation into the mechanistic characterization of radiation retinopathy in the hope of discovering novel treatments.

Efficacy of stereotactic body radiotherapy for unresectable or recurrent cholangiocarcinoma: a meta-analysis and systematic review

PURPOSE

Non-surgical treatment including stereotactic body radiation therapy (SBRT) have been used practically as alternative modalities for unresectable or recurrent cholangiocarcinoma (CC). We performed a systematic review and meta-analysis to examine the efficacy of SBRT for such patients.

METHODS

Embase, PubMed, MEDLINE, and Cochrane library databases were searched systematically until October 2017. Primary endpoint was 1‑year local control (LC) rate; 1‑year overall survival (OS), response rates, and grade ≥3 toxicities were assessed as secondary endpoints.

RESULTS

Eleven studies (226 patients) were included. The prescribed median SBRT dose was 45 (range 30-55) Gy in 3-5 fractions. The pooled 1‑year LC rate was 81.8% (95% confidence interval [CI] 69.4-89.9%) in the studies using an equivalent dose in 2 Gy per fraction (EQD2) ≥71.3 Gy2 and 74.7% (95% CI 57.1-86.7%) in the studies using an EQD2 <71.3 Gy2. The median OS was 13.6 (range 10-35.5) months. The pooled 1‑year OS rate was 53.8% (95% CI 44.9-62.5%) and the pooled 1‑year LC rate was 78.6% (95% CI 69.0-85.8%). Most common toxicity was duodenal ulcer and gastric ulcer in available studies, with the acute incidence of grade ≥3 of less than 10% and the late incidence of 10-20%.

CONCLUSIONS

SBRT was a feasible treatment option with respect to achieving a high LC for unresectable or recurrent CC. Gastrointestinal toxicity is acceptable, but remains an obstacle related to dose escalation.

A scoring system predicting acute radiation dermatitis in patients with head and neck cancer treated with intensity-modulated radiotherapy

Background and purpose

We created a scoring system incorporating dosimetric and clinical factors to assess the risk of severe, acute skin reactions in patients undergoing intensity-modulated radiation therapy (IMRT) to treat head and neck cancer (HNC).

Materials and methods

A total of 101 consecutive patients who received definitive IMRT or volumetric modulated arc therapy (VMAT) with a prescription dose of 70 Gy to treat HNC between 2013 and 2017 in our hospital were enrolled. Skin V_5Gy, V_10Gy, V_20Gy, V_30Gy, V_40Gy, V_50Gy, and V_60Gy values delivered 5 mm within the body contour were compared between patients with Grades 1–2 and Grade 3 dermatitis. A scoring system was created based on logistic regression analysis (LRA) that identified the most significant dosimetric and clinical factors.

Results

The V_60Gy was significantly associated with radiation dermatitis grade in both LRA and recursive partitioning analysis (RPA). A scoring system incorporating the V_60Gy, concurrent chemotherapy status, age, and body mass index was used to divide all patients into three subgroups (0–1, 2–3, and 4–6 points) in the RPA. The incidence of Grade 3 dermatitis significantly differed among the subgroups (0, 20.5, and 58.6%, respectively, P < 0.01).

Conclusions

A risk analysis model incorporating dose-volume parameters successfully predicted acute skin reactions and will aid in the appropriate management of radiation dermatitis.

Leveraging Bioorthogonal Click Chemistry to Improve 225Ac-Radioimmunotherapy of Pancreatic Ductal Adenocarcinoma

PURPOSE

Interest in targeted alpha-therapy has surged due to α-particles' high cytotoxicity. However, the widespread clinical use of this approach could be limited by on-/off-target toxicities. Here, we investigated the inverse electron-demand Diels-Alder ligation between an 225Ac-labeled tetrazine radioligand and a trans-cyclooctene-bearing anti-CA19.9 antibody (5B1) for pretargeted α-radioimmunotherapy (PRIT) of pancreatic ductal adenocarcinoma (PDAC). This alternative strategy is expected to reduce nonspecific toxicities as compared with conventional radioimmunotherapy (RIT).Experimental Design: A side-by-side comparison of 225Ac-PRIT and conventional RIT using a directly 225Ac-radiolabeled immunoconjugate evaluates the therapeutic efficacy and toxicity of both methodologies in PDAC murine models.

RESULTS

A comparative biodistribution study of the PRIT versus RIT methodology underscored the improved pharmacokinetic properties (e.g., prolonged tumor uptake and increased tumor-to-tissue ratios) of the PRIT approach. Cerenkov imaging coupled to PRIT confirmed the in vivo biodistribution of 225Ac-radioimmunoconjugate but-importantly-further allowed for the ex vivo monitoring of 225Ac's radioactive daughters' redistribution. Human dosimetry was extrapolated from the mouse biodistribution and confirms the clinical translatability of 225Ac-PRIT. Furthermore, longitudinal therapy studies performed in subcutaneous and orthotopic PDAC models confirm the therapeutic efficacy of 225Ac-PRIT with the observation of prolonged median survival compared with control cohorts. Finally, a comparison with conventional RIT highlighted the potential of 225Ac-PRIT to reduce hematotoxicity while maintaining therapeutic effectiveness.

CONCLUSIONS

The ability of 225Ac-PRIT to deliver a radiotherapeutic payload while simultaneously reducing the off-target toxicity normally associated with RIT suggests that the clinical translation of this approach will have a profound impact on PDAC therapy.

Radioimmunotherapy of PANC-1 Human Pancreatic Cancer Xenografts in NRG Mice with Panitumumab Modified with Metal-Chelating Polymers Complexed to 177Lu

Our aim was to evaluate the effectiveness and normal tissue toxicity of radioimmunotherapy (RIT) of s.c. PANC-1 human pancreatic cancer (PnCa) xenografts in NRG mice using anti-EGFR panitumumab linked to metal-chelating polymers (MCPs) that present 13 DOTA chelators to complex the β-emitter, ¹⁷⁷Lu. The clonogenic survival (CS) of PANC-1 cells treated in vitro with panitumumab-MCP-¹⁷⁷Lu (0.3-1.2 MBq) and DNA double-strand breaks (DSBs) in the nucleus of these cells were measured by confocal immunofluorescence microscopy for γ-H2AX. Subcellular distribution of radioactivity for panitumumab-MCP-¹⁷⁷Lu was measured, and absorbed doses to the cell nucleus were calculated. Normal tissue toxicity was assessed in non tumor-bearing NRG mice by monitoring body weight, complete blood cell counts (CBC), serum alanine aminotransferase (ALT), and creatinine (Cr) after i.v. injection of 6 MBq (10 μg) of panitumumab-MCP-¹⁷⁷Lu. RIT was performed in NRG mice with s.c. PANC-1 tumors injected i.v. with 6 MBq (10 μg) of panitumumab-MCP-¹⁷⁷Lu. Control mice received nonspecific human IgG-MCP-¹⁷⁷Lu (6 MBq; 10 μg), unlabeled panitumumab (10 μg), or normal saline. The tumor growth index (TGI) was compared. Tumor and normal organ doses were estimated based on biodistribution studies. Panitumumab-MCP-¹⁷⁷Lu reduced the CS of PANC-1 cells in vitro by 7.7-fold at the highest amount tested (1.2 MBq). Unlabeled panitumumab had no effect on the CS of PANC-1 cells. γ-H2AX foci were increased by 3.8-fold by panitumumab-MCP-¹⁷⁷Lu. Panitumumab-MCP-¹⁷⁷Lu deposited 3.84 Gy in the nucleus of PANC-1 cells. Administration of panitumumab-MCP-¹⁷⁷Lu (6 MBq; 10 μg) to NRG mice caused no change in body weight, CBC, or ALT and only a slight increase in Cr compared to NRG mice treated with normal saline. Panitumumab-MCP-¹⁷⁷Lu strongly inhibited tumor growth in NRG mice (TGI = 2.3 ± 0.2) compared to normal saline-treated mice (TGI = 5.8 ± 0.5; P < 0.01). Unlabeled panitumumab had no effect on tumor growth (TGI = 6.0 ± 1.6; P > 0.05). The absorbed dose of PANC-1 tumors was 12.3 Gy. The highest normal organ doses were absorbed by the pancreas, liver, spleen, and kidneys. We conclude that EGFR-targeted RIT with panitumumab-MCP-¹⁷⁷Lu was able to overcome resistance to panitumumab in KRAS mutant PANC-1 tumors in NRG mice and may be a promising approach to treatment of PnCa in humans.

Discovery of Metabolic Biomarkers Predicting Radiation Therapy Late Effects in Prostate Cancer Patients

Patients presenting with prostate cancers undergo clinical staging evaluations to determine the extent of disease to guide therapeutic recommendations. Management options may include watchful waiting, surgery, or radiation therapy. Thus, initial risk stratification of prostate cancer patients is important for achieving optimal therapeutic results or cancer cure and preservation of quality of life. Predictive biomarkers for risks of complications or late effects of treatment are needed to inform clinical decisions for treatment selection. Here, we analyzed pre-treatment plasma metabolites in a cohort of prostate cancer patients (N = 99) treated with Stereotactic Body Radiation Therapy (SBRT) at Medstar-Georgetown University Hospital in a longitudinal, quality-of-life study to determine if individuals experiencing radiation toxicities can be identified by a molecular profile in plasma prior to treatment. We used a multiple reaction mass spectrometry-based molecular phenotyping of clinically annotated plasma samples in a retrospective outcome analysis to identify candidate biomarker panels correlating with adverse clinical outcomes following radiation therapy. We describe the discovery of candidate biomarkers, based on small molecule metabolite panels, showing high correlations (AUCs ≥ 95%) with radiation toxicities, suitable for validation studies in an expanded cohort of patients.