Advancing Targeted Radionuclide Therapy Through the National Cancer Institute's Small Business Innovation Research Pathway

The Small Business Innovation Research (SBIR) and Small Business Technology Transfer (STTR) programs of the National Cancer Institute (NCI) are congressionally mandated set-aside programs that provide research funding to for-profit small businesses for the development of innovative technologies and treatments that serve the public good. These two programs have an annual budget of $159 million (in 2017) and serve as the NCI's main engine of innovation for developing and commercializing cancer technologies. In collaboration with the NCI's Radiation Research Program, the NCI SBIR Development Center published in 2015-2017 three separate requests for proposals from small businesses for the development of systemic targeted radionuclide therapy (TRT) technologies to treat cancer. TRT combines a cytotoxic radioactive isotope with a molecularly targeted agent to produce an anticancer therapy capable of treating local or systemic disease. This article summarizes the NCI SBIR funding solicitations for the development of TRTs and the research proposals funded through them.

Radiation-Induced Fibrosis: Mechanisms and Opportunities to Mitigate. Report of an NCI Workshop, September 19, 2016

A workshop entitled "Radiation-Induced Fibrosis: Mechanisms and Opportunities to Mitigate" (held in Rockville, MD, September 19, 2016) was organized by the Radiation Research Program and Radiation Oncology Branch of the Center for Cancer Research (CCR) of the National Cancer Institute (NCI), to identify critical research areas and directions that will advance the understanding of radiation-induced fibrosis (RIF) and accelerate the development of strategies to mitigate or treat it. Experts in radiation biology, radiation oncology and related fields met to identify and prioritize the key areas for future research and clinical translation. The consensus was that several known and newly identified targets can prevent or mitigate RIF in pre-clinical models. Further, basic and translational research and focused clinical trials are needed to identify optimal agents and strategies for therapeutic use. It was felt that optimally designed preclinical models are needed to better study biomarkers that predict for development of RIF, as well as to understand when effective therapies need to be initiated in relationship to manifestation of injury. Integrating appropriate endpoints and defining efficacy in clinical trials testing treatment of RIF were felt to be critical to demonstrating efficacy. The objective of this meeting report is to (a) highlight the significance of RIF in a global context, (b) summarize recent advances in our understanding of mechanisms of RIF,

Rapid RBE-Weighted Proton Radiation Dosimetry Risk Assessment

Proton therapy dose is affected by relative biological effectiveness differently than X-ray therapies. The current clinically accepted weighting factor is 1.1 at all positions along the depth-dose profile. However, the relative biological effectiveness correlates with the linear energy transfer, cell or tissue type, and the dose per fraction causing variation of relative biological effectiveness along the depth-dose profile. In this article, we present a simple relative biological effectiveness-weighted treatment planning risk assessment algorithm in 2-dimensions and compare the results with those derived using the standard relative biological effectiveness of 1.1. The isodose distribution profiles for beams were accomplished using matrices that represent coplanar intersecting beams. These matrices were combined and contoured using MATLAB to achieve the distribution of dose. There are some important differences in dose distribution between the dose profiles resulting from the use of relative biological effectiveness = 1.1 and the empirically derived depth-dependent values of relative biological effectiveness. Significant hot spots of up to twice the intended dose are indicated in some beam configurations. This simple and rapid risk analysis could quickly evaluate the safety of various dose delivery schema.

Radiation Necrosis in Pediatric Patients with Brain Tumors Treated with Proton Radiotherapy

BACKGROUND AND PURPOSE

Proton radiotherapy has been increasingly utilized to treat pediatric brain tumors, however, limited information exists regarding radiation necrosis among these patients. Our aim was to evaluate the incidence, timing, clinical significance, risk factors, and imaging patterns of radiation necrosis in pediatric patients with brain tumors treated with proton radiation therapy.

MATERIALS AND METHODS

A retrospective study was performed on 60 consecutive pediatric patients with primary brain tumors treated with proton radiation therapy. Radiation necrosis was assessed by examining serial MRIs and clinical records to determine the incidence, timing, risk factors, imaging patterns, and clinical significance associated with the development of radiation necrosis in these patients. Radiation necrosis was defined as areas of new enhancement within an anatomic region with previous exposure to proton beam therapy with subsequent decrease on follow-up imaging without changes in chemotherapy.

RESULTS

Thirty-one percent of patients developed radiation necrosis with a median time to development of 5.0 months (range, 3-11 months). Risk factors included multiple chemotherapy agents (>3 cytotoxic agents) and atypical teratoid rhabdoid tumor pathology (P = .03 and P = .03, respectively). The most common imaging patterns were small (median, 0.9 cm) and multifocal (63% of patients) areas of parenchymal enhancement remote from the surgical site. The median time to complete resolution on imaging was 5.3 months (range, 3-12 months). Among patients with imaging findings of radiation necrosis, 25% demonstrated severe symptoms with medical intervention indicated.

CONCLUSIONS

Pediatric patients with brain tumors treated with proton radiation therapy demonstrate a high incidence of radiation necrosis and a short time to development of necrosis. Multiple small areas of necrosis are frequently identified on imaging. Exposure to multiple chemotherapy agents was a significant risk factor associated with radiation necrosis in these patients.

Radiation therapy at end of life in children

OBJECTIVE

Few data exist on evaluating utilization patterns of radiotherapy (RT) at the end of life (EOL) in children. Metastatic disease in pediatric patients is not pathognomonic for palliative treatment intent; further complicating the issue are complexities surrounding the very select population of children receiving proton therapy (PrT). We compared data for RT and PrT in terms of death rate within 30 days.

METHODS

We performed chart reviews for patients receiving radiation therapy at age ≤21 years treated at Indiana University Health Proton Therapy Center (IUHPTC) between June 2008 and June 2013 and University of Miami Radiation Oncology Department (UM) between June 2000 and June 2013. Included were patients not completing prescribed courses of RT, and those dying within 30 days of therapy. Comparison was made of differences between practice data for PrT and conventional RT.

RESULTS

At IUHPTC, 2 children of 272 did not complete their courses and died within 30 days (0.7%). At UM, data are available for 425 children; 9 did not complete their courses and 7 died within 30 days (1.6%). Neither the number of patients who did not complete treatment nor the 30-day death rates (P=.21) for PrT and RT were significantly different.

CONCLUSIONS

Delivery of RT for children at EOL is complex. Frequency of RT at EOL in children occurs in is <2% of cases, and is not significantly less frequent in the proton milieu. This appears to be about an order of magnitude less than in adults.

Range modulation in proton therapy planning: a simple method for mitigating effects of increased relative biological effectiveness at the end-of-range of clinical proton beams

Background

The increase in relative biological effectiveness (RBE) of proton beams at the distal edge of the spread out Bragg peak (SOBP) is a well-known phenomenon that is difficult to quantify accurately in vivo. For purposes of treatment planning, disallowing the distal SOBP to fall within vulnerable tissues hampers sparing to the extent possible with proton beam therapy (PBT). We propose the distal RBE uncertainty may be straightforwardly mitigated with a technique we call “range modulation”. With range modulation, the distal falloff is smeared, reducing both the dose and average RBE over the terminal few millimeters of the SOBP.

Methods

One patient plan was selected to serve as an example for direct comparison of image-guided radiotherapy plans using non-range modulation PBT (NRMPBT), and range-modulation PBT (RMPBT). An additional plan using RMPBT was created to represent a re-treatment scenario (RMPBTrt) using a vertex beam. Planning statistics regarding dose, volume of the planning targets, and color images of the plans are shown.

Results

The three plans generated for this patient reveal that in all cases dosimetric and device manufacturing advantages are able to be achieved using RMPBT. Organ at risk (OAR) doses to critical structures such as the cochleae, optic apparatus, hypothalamus, and temporal lobes can be selectively spared using this method. Concerns about the location of the RBE that did significantly impact beam selection and treatment planning no longer have the same impact on the process, allowing these structures to be spared dose and subsequent associated issues.

Conclusions

This present study has illustrated that RMPBT can improve OAR sparing while giving equivalent coverage to target volumes relative to traditional PBT methods while avoiding the increased RBE at the end of the beam. It has proven easy to design and implement and robust in our planning process. The method underscores the need to optimize treatment plans in PBT for both traditional energy dose in gray (Gy) and biologic dose (RBE).

Definitive treatment of leptomeningeal spinal metastases in children

BACKGROUND

Uniquely in children, the existence of leptomeningeal spinal metastases does not confer a uniformly grave prognosis. Although the radiation tolerance of the spinal cord is of significant concern in these cases, the chemo- and radiosensitivity of these lesions argues for an aggressive approach where possible.

METHODS

The records of the Indiana University Health Proton Therapy Center were reviewed for patients undergoing proton beam therapy with curative intent for LSM between January 1, 2004 and July 7, 2012. Patients with microscopic disease only on LP were not included. Particulars of therapy, including dose, field sizes, toxicities, and outcomes were collated.

RESULTS

Twenty-two children received therapy as described, of median age 5 years (range 1.1-17.1). Patients had medulloblastoma (n = 9), ATRT (n = 4), ependymoma, and PNET (n = 3 each). Five lesions (23%) were chemo-recurrent, though no patient had prior radiation to the spine. Median follow-up was 14 months (range 4-33) for all living patients. Fifteen (68%) children continued to have local control at last follow-up visit. Median dose was 37.8 Gy (range 21.6-54 Gy). Eight patients with chemo-recurrent disease or diffuse cord seeding did poorly, with local control and overall survival achieved in four. The 12-month overall survival was 68% with grade 1 skin erythema as the most frequent toxicity.

CONCLUSIONS

We describe a cohort of LSM patients treated with RT with definitive intent, and the only available data from the proton environment. Durable response is possible for these children in over two-thirds of cases. Significant toxicity was infrequent using proton radiotherapy and these fractionation schemes.

Dosimetric comparison between proton and photon beams in the moving gap region in cranio-spinal irradiation (CSI)

PURPOSE

To investigate the moving gap region dosimetry in proton beam cranio-spinal irradiation (CSI) to provide optimal dose uniformity across the treatment volume.

MATERIAL AND METHODS

Proton beams of ranges 11.6 cm and 16 cm are used for the spine and the brain fields, respectively. Beam profiles for a 30 cm snout are first matched at the 50% level (hot match) on the computer. Feathering is simulated by shifting the dose profiles by a known distance two successive times to simulate a 2 × feathering scheme. The process is repeated for 2 mm and 4 mm gaps. Similar procedures are used to determine the dose profiles in the moving gap for a series of gap widths, 0-10 mm, and feathering step sizes, 4-10 mm, for a Varian iX 6MV beam. The proton and photon dose profiles in the moving gap region are compared.

RESULTS

The dose profiles in the moving gap exhibit valleys and peaks in both proton and photon beam CSI. The dose in the moving gap for protons is around 100% or higher for 0 mm gap, for both 5 and 10 mm feathering step sizes. When the field gap is comparable or larger than the penumbra, dose minima as low as 66% is obtained. The dosimetric characteristics for 6 MV photon beams can be made similar to those of the protons by appropriately combining gap width and feathering step size.

CONCLUSION

The dose in the moving gap region is determined by the lateral penumbras, the width of the gap and the feathering step size. The dose decreases with increasing gap width or decreasing feathering step size. The dosimetric characteristics are similar for photon and proton beams. However, proton CSI has virtually no exit dose and is beneficial for pediatric patients, whereas with photon beams the whole lung and abdomen receive non-negligible exit dose.

Technique for sparing previously irradiated critical normal structures in salvage proton craniospinal irradiation

BACKGROUND

Cranial reirradiation is clinically appropriate in some cases but cumulative radiation dose to critical normal structures remains a practical concern. The authors developed a simple technique in 3D conformal proton craniospinal irradiation (CSI) to block organs at risk (OAR) while minimizing underdosing of adjacent target brain tissue.

METHODS

Two clinical cases illustrate the use of proton therapy to provide salvage CSI when a previously irradiated OAR required sparing from additional radiation dose. The prior radiation plan was coregistered to the treatment planning CT to create a planning organ at risk volume (PRV) around the OAR. Right and left lateral cranial whole brain proton apertures were created with a small block over the PRV. Then right and left lateral "inverse apertures" were generated, creating an aperture opening in the shape of the area previously blocked and blocking the area previously open. The inverse aperture opening was made one millimeter smaller than the original block to minimize the risk of dose overlap. The inverse apertures were used to irradiate the target volume lateral to the PRV, selecting a proton beam range to abut the 50% isodose line against either lateral edge of the PRV. Together, the 4 cranial proton fields created a region of complete dose avoidance around the OAR. Comparative photon treatment plans were generated with opposed lateral X-ray fields with custom blocks and coplanar intensity modulated radiation therapy optimized to avoid the PRV. Cumulative dose volume histograms were evaluated.

RESULTS

Treatment plans were developed and successfully implemented to provide sparing of previously irradiated critical normal structures while treating target brain lateral to these structures. The absence of dose overlapping during irradiation through the inverse apertures was confirmed by film. Compared to the lateral X-ray and IMRT treatment plans, the proton CSI technique improved coverage of target brain tissue while providing the least additional radiation dose to the previously irradiated OAR.

CONCLUSIONS

Proton craniospinal irradiation can be adapted to provide complete sparing of previously irradiated OARs. This technique may extend the option of reirradiation to patients otherwise deemed ineligible for further radiotherapy due to prior dose to critical normal structures.

Hypothalamic obesity syndrome: rare presentation of CNS+ B-cell lymphoblastic lymphoma

Hypothalamic obesity syndrome can affect brain tumor patients following surgical intervention and irradiation. This syndrome is rare at diagnosis in childhood cancer, but has been reported with relapse of acute lymphoblastic leukemia. Here we present a case of hypothalamic obesity syndrome as the primary presentation of a toddler found to have CNS+ B-cell lymphoblastic lymphoma. Cytogenetic studies on diagnostic cerebrospinal fluid revealed MLL gene rearrangement (11q23). Hyperphagia and obesity dramatically improved following induction and consolidation chemotherapy. We describe a novel presentation of hypothalamic obesity syndrome in CNS B-cell lymphoblastic lymphoma, responsive to chemotherapy.

Crystallographic and NMR Analyses of UvsW and UvsW.1 from Bacteriophage T4

The uvsWXY system is implicated in the replication and repair of the bacteriophage T4 genome. Whereas the roles of the recombinase (UvsX) and the recombination mediator protein (UvsY) are known, the precise role of UvsW is unclear. Sequence analysis identifies UvsW as a member of the monomeric SF2 helicase superfamily that translocates nucleic acid substrates via the action of two RecA-like motor domains. Functional homologies to Escherichia coli RecG and biochemical analyses have shown that UvsW interacts with branched nucleic acid substrates, suggesting roles in recombination and the rescue of stalled replication forks. A sequencing error at the 3'-end of the uvsW gene has revealed a second, short open reading frame that encodes a protein of unknown function called UvsW.1. We have determined the crystal structure of UvsW to 2.7A and the NMR solution structure of UvsW.1. UvsW has a four-domain architecture with structural homology to the eukaryotic SF2 helicase, Rad54. A model of the UvsW-ssDNA complex identifies structural elements and conserved residues that may interact with nucleic acid substrates. The NMR solution structure of UvsW.1 reveals a dynamic four-helix bundle with homology to the structure-specific nucleic acid binding module of RecQ helicases.

Improvement in relapse-free survival throughout the PSA era in patients with localized prostate cancer treated with definitive radiotherapy: Year of treatment an independent predictor of outcome

PURPOSE

In patients treated with radical prostatectomy in the prostate-specific antigen (PSA) era, it has been demonstrated that the year of treatment in the PSA era is associated with better pathologic parameters and outcomes, independently of other well-recognized parameters such as clinical stage, pretreatment PSA level, or Gleason score. The purpose of the present study was to study a similar phenomenon with definitive radiotherapy (RT).

METHODS AND MATERIALS

The inclusion criteria were as follows: clinical Stage T1-T2, available pretreatment PSA level and biopsy Gleason score, treatment delivered before January 2000 with standard fractionation external beam radiotherapy to at least 70 Gy, no adjuvant androgen deprivation (AD), all neoadjuvant AD limited to < or =6 months, and a minimum of 3 years of PSA follow-up. A total of 467 cases treated between January 1986 and December 1999 were included. Short-course AD in the adjuvant or neoadjuvant setting for < or =6 months was given in 124 cases (27%). The median radiation dose was 74 Gy (range 70.0-78.0). A conformal technique was used in 293 cases (63%). The median follow-up was 62 months (range 37-189). A total of 4931 follow-up PSA levels were available for analysis (average 11 per patient). A multivariate analysis for factors affecting biochemical relapse-free survival rates using the proportional hazards model was performed for all cases using the following variables: age (continuous variable), race (black vs. white), clinical T stage (T1-T2a vs. T2b-T2c), pretreatment PSA (continuous variable), biopsy Gleason score (continuous variable), use of AD (yes vs. no), radiation dose (continuous variable), and year of treatment (continuous variable: 1986-1999).

RESULTS

The projected 8-year biochemical relapse-free survival rate was 74%. The projected 5-year biochemical relapse-free survival rate for the 143 patients treated in the 1986-1995 period was 58% vs. 82% for the 324 patients treated in the 1996-1999 period (p <0.001). The difference was attributable to a multitude of factors (earlier stage cancer, higher radiation doses, shorter follow-up). To study the confounding effects of these factors on the year of therapy, a multivariate analysis was performed. The multivariate analysis revealed the initial PSA level (p <0.001), Gleason score (p <0.001), RT dose (p = 0.045), and year of treatment (p <0.001) to be independent predictors of outcome. Age (p = 0.41), race (p = 0.14), T stage (p = 0.10), and use of AD (p = 0.58) were not.

CONCLUSION

When controlling for tumor, treatment, and follow-up parameters, the year in which RT was performed was still an independent predictor of outcome, consistent with observations made for radical prostatectomy patients. This indicates a more favorable presentation of localized prostate in current years probably related to a combination of factors such as screening and increased patient awareness leading to earlier diagnosis. Outcome predictions should be based on contemporaneous series.