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Clinical Trials in BNCT at the MIT Research Reactor

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Clinical Trials in BNCT at the MIT Research Reactor

  1. 1. Journal of Neuro-Oncology 62: 111–121, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands. A critical examination of the results from the Harvard-MIT NCT program phase I clinical trial of neutron capture therapy for intracranial disease Paul M. Busse1 , Otto K. Harling3 , Matthew R. Palmer2 , W.S. Kiger III1 , Jody Kaplan1 , Irving Kaplan1 , Cynthia F. Chuang3 , J. Tim Goorley3 , Kent J. Riley3 , Thomas H. Newton3 , Gustavo A. Santa Cruz4 , Xing-Qi Lu1 and Robert G. Zamenhof2 1 Department of Radiation Oncology, 2 Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston; 3 Nuclear Reactor Laboratory, Massachusetts Institute of Technology, Cambridge, MA, USA; 4 Comisi´ n Nacional de Energ´a At´ mica, Buenos Aires, Argentina o ı o Key words: BNCT, glioblastoma, melanoma, clinical trial, boronophenylalanine-fructose (BPA-f) Summary A phase I trial was designed to evaluate normal tissue tolerance to neutron capture therapy (NCT); tumor response was also followed as a secondary endpoint. Between July 1996 and May 1999, 24 subjects were entered into a phase I trial evaluating cranial NCT in subjects with primary or metastatic brain tumors. Two subjects were excluded due to a decline in their performance status and 22 subjects were irradiated at the MIT Nuclear Reactor Laboratory. The median age was 56 years (range 24–78). All subjects had a pathologically confirmed diagnosis of either glioblastoma (20) or melanoma (2) and a Karnofsky of 70 or higher. Neutron irradiation was delivered with a 15 cm diameter epithermal beam. Treatment plans varied from 1 to 3 fields depending upon the size and location of the tumor. The 10 B carrier, l-p-boronophenylalanine-fructose (BPA-f), was infused through a central venous catheter at doses of 250 mg kg−1 over 1 h (10 subjects), 300 mg kg−1 over 1.5 h (two subjects), or 350 mg kg−1 over 1.5–2 h (10 subjects). The pharmacokinetic profile of 10 B in blood was very reproducible and permitted a predictive model to be developed. Cranial NCT can be delivered at doses high enough to exhibit a clinical response with an acceptable level of toxicity. Acute toxicity was primarily associated with increased intracranial pressure; late pulmonary effects were seen in two subjects. Factors such as average brain dose, tumor volume, and skin, mucosa, and lung dose may have a greater impact on tolerance than peak dose alone. Two subjects exhibited a complete radiographic response and 13 of 17 evaluable subjects had a measurable reduction in enhanced tumor volume following NCT. Introduction dose. Other important advances were made in beam dosimetry [1,2], 10 B quantification on macroscopic The modern clinical experience with neutron cap- [1,3] and microscopic levels [4], biologically tar- ture therapy (NCT) in the US began in 1994 with a geted boron-carrier compounds [5], three-dimensional series of clinical trials conducted at the Massachusetts Monte Carlo-based treatment planning programs [6], Institute of Technology (MIT) and the Brookhaven and the experimental derivation of relative biologi- National Laboratory (BNL), which represent the first cal effectiveness (RBE) and compound-specific rela- use of epithermal neutron radiation in human sub- tive biological effectiveness (C-RBE) values for the jects. These trials and the expansion of NCT to other radiation dose components associated with NCT [7]. international sites were made possible by a number of Under the sponsorship of the US Department of Energy important advances, most notably the shift from ther- (DOE), almost 80 human subjects were entered into mal to epithermal neutron sources. This was a major phase I and phase I/II trials at Harvard-MIT [8–11] step in improving the potential clinical utility of NCT and BNL [12–14] to evaluate the normal tissue toler- as it allowed for a greater penetration in tissue, skin ance and tumor response of epithermal neutron irra- sparing, and ultimately delivery of a higher tumor diation following the administration of 10 B via the
  2. 2. 112 boron-carrier compound l-para-boronophenylalanine- Table 1. RBE values for radiation components in glioblastoma, fructose (BPA-f). These trials demonstrated the fea- brain, and melanoma sibility of NCT for intracranial tumors, specifically Tissue 10 B1 Fast Thermal Gamma3 glioblastoma multiforme and metastatic melanoma, at neutron neutron an acceptable level of tolerance of the central nervous GBM2 3.8 3.2 3.2 0.5 system and other normal tissues, and demonstrated a Brain 1.3 3.2 3.2 0.5 favorable tumor response in some instances. The results Melanoma 4.0 3.2 3.2 0.5 of the Harvard-MIT phase I trial are presented and 1 RBE value for 10 B accounts for microdistribution in cells and is include a complete description of all adverse reactions referred to as C-RBE. 2 GBM: Glioblastoma multiforme. 3 RBE as well as observations of tumor response. The last sub- is adjusted to account for prolonged irradiation duration and two ject was irradiated in 1999 and follow-up is complete. fractions. was amended to allow two irradiations when neces- Methods and clinical material sary. The 10 B carrier, BPA-f, was infused through a central venous catheter at doses of 250 mg kg−1 over A phase I clinical trial conducted at Harvard-MIT 1 h (10 subjects), 300 mg kg−1 over 1.5 h (two subjects), was designed primarily to determine a maximum and 350 mg kg−1 over 1.5 h (10 subjects). Neutron irra- tolerated dose (MTD) and secondarily to evaluate diation was scheduled to begin 45 min after the end of tumor response following cranial NCT. The protocol the BPA-f infusion. The radiation dose is expressed in and informed consent documents underwent critical photon equivalent RBE-Gy, which is the sum of the review and were approved by the respective com- physical dose for each component in the beam weighted mittees on clinical investigation at the Beth Israel by its RBE [7]. The RBE for 10 B is expressed as the Deaconess Medical Center and MIT. Separate but sim- C-RBE, a value that also takes into account the distribu- ilarly worded informed consent documents were used tion of the boron-carrier molecule in tissue at the micro- to obtain consent for each institution. Patient eligi- scopic level. The RBE and C-RBE values that were bility was restricted to a biopsy-proven diagnosis of used for the dose calculations are shown in Table 1. The either glioblastoma multiforme or radiologic evidence dose was prescribed to the normal tissue Dmax , a 1-ml of melanoma metastatic to the CNS, age greater than volume that was assigned the RBE and C-RBE values 18, a Karnofsky performance status of 70 or greater, of normal brain. The initial dose of 8.8 RBE-Gy was no prior history of cranial irradiation, and a projected considered a conservative starting point. Escalation life expectancy of at least 3 months. Subjects with a was carried out in a stepwise fashion and was increased diagnosis of phenylketonuria (PKU) were excluded. by 10% every 3–5 subjects. The interval between the Following an initial evaluation, subjects underwent a first subjects of any two dose cohorts was at least CT and an MRI with and without contrast for treatment 3 months. planning purposes. These also served as baseline stud- Vital signs, EKG tracing, and blood oxygenation ies for follow-up. Each subject had an individualized were continuously monitored from the initiation of treatment plan developed with MacNCTPlan [6,15–17] infusion of BPA-f to when subjects were transported and computed using the MCNP 4B Monte Carlo radi- back to the hospital, where they continued to be moni- ation transport code. This software system allows tored overnight. With rare exception, discharge was the normal tissue and tumor volumes to be assigned, and following day. Follow-up was scheduled monthly with generates two-dimensional isodose contours for nor- MRI scans whenever possible. mal tissue as well as tumor. Depending upon the loca- tion and volume of disease, treatment plans varied from one to three separate fields. Subjects were simulated in Results the appropriate position for each beam entry position and immobilized with commercially available systems. The first subject was entered in 1996 and the trial was All irradiations were performed at the MIT Nuclear completed in 1999. Twenty-four subjects were entered Reactor Laboratory with the M67 epithermal neutron and 22 were irradiated; 2 subjects were excluded due beam [2]. The initial plan of the trial was to deliver to decline in performance status. The median age was the irradiation for each subject in one fraction; how- 56 (range 24–78). Of the irradiated subjects, two had ever, due to protracted irradiation times the protocol metastatic melanoma and the remainder glioblastoma
  3. 3. 113 multiforme. Surgery was performed on all subjects with the exception of the two melanomas, including gross total resection in four, subtotal resection in 12, and biopsy only in four. The volume of tumor at the time of NCT was variable and ranged from a small vol- ume of enhancement on MRI (<10 cm3 ) to 121 cm3 of gross disease with central necrosis. Twelve subjects received corticosteroids before, during, and after NCT irradiation. Six dose cohorts were completed: 8.8, 9.7, 10.6, 11.7, 12.9, and 14.2 RBE-Gy. The number of fields ranged from 1 to 3, and the orientations var- ied over the course of the trial in order to optimize dose to the tumor within the normal tissue dose con- straints. An example of a typical normal tissue iso- dose distribution from a two-field beam arrangement is shown in Figure 1. In this arrangement, the dose distribution is highly lateralized. The dose to normal structures such as the eye, optic nerve, and optic chi- asm were kept below 8 RBE-Gy (Figure 1A), a sin- gle fraction dose shown to be within the tolerance of these structures [18]. While the peak dose was esca- lated in a systematic fashion, a second normal tissue dose parameter, the volume average brain dose, varied primarily as a function of the number of fields, and sec- ondarily by tumor size and location and the prescribed peak dose (Figure 2). The mean volume average brain doses were 3.0, 4.5, and 6.5 RBE-Gy for 1–3 fields, respectively. 10 B was delivered as BPA-f through an intravenous infusion that lasted between 60 and 90 min. The amount of BPA-f was increased during the trial from 250 to 350 mg kg−1 , and no untoward effects were observed from the infusion (Figure 3). A detailed pharmacoki- netic curve for blood was generated for each subject. These demonstrated a peak infusion 10 B concentra- tion of approximately 32 µg g−1 followed by a bipha- sic washout due to redistribution and renal excretion [19,20]. Because of the protracted irradiation times with the M67 epithermal beam, it was necessary to fol- low the blood 10 B concentration throughout the irradi- ation so that the appropriate neutron fluence could be delivered in order to reach the target dose for each field. Figure 1. (A) Normal tissue isodose distribution for a subject The final dosimetry for each subject was determined with multiple ipsilateral unresected melanoma nodules. Dose is through a retrospective analysis based upon the mea- expressed as RBE-Gy using normal brain RBE and C-RBE val- sured blood 10 B concentration and the delivered fluence ues. (B) Tumor isodose distribution for the same subject. Dose is for each field. expressed as RBE-Gy using tumor values for RBE and C-RBE. All adverse events, irrespective of cause, were tab- ulated and assigned severity scores between 1 and shown in Table 2. Overall, there were 16 grade 3 events, 5 according to the Common Toxicity Criteria of the 1 grade 4 events and 3 grade 5 events. Almost all National Cancer Institute’s Cancer Therapy Evaluation subjects experienced alopecia within the area of skin Program (NCI-CTEP CTC, v. 2.0). These data are exposed directly to the radiation. This was permanent
  4. 4. 114 and complete in all subjects. Additional dermal effects responded to medical management. A grade 4 included erythema that was self-limiting. One subject event related to increased ICP (decreased level in the 14.2 RBE-Gy dose cohort was irradiated for a of consciousness/somnolence) occurred in a young temporal lobe GBM and experienced moist desquama- woman with a large tumor (84 cm3 ) who was given tion on the temporal area of the scalp six weeks fol- high-dose intravenous steroids starting 12 h before and lowing NCT, which eventually completely healed. This during NCT. After the second fraction, she became subject also experienced mucositis of the oral cavity increasingly somnolent and unresponsive and after sev- and oropharynx two weeks after NCT. eral days developed the syndrome of inappropriate Many adverse events, especially those of grade 3 anti-diuretic hormone secretion (SIADH). Aggressive severity, were associated with a temporary increase medical management was successful and a debulk- in intracranial pressure (ICP) following NCT and ing resection was performed. The resected tumor dis- played extensive tumor cell cytoplasmic vacuolization, fibrinoid vascular necrosis, and an extreme paucity of mitotic figures, a histologic appearance very dif- ferent from her initial surgery. One subject experi- enced a treatment-related death 5 days after NCT. This was a 58-year-old woman with a large central tumor (121 cm3 ) who received only the first of two planned fractions. After the first fraction, she experienced men- tal status changes and had an increase in peritumoral edema as seen on CT and MRI. A new ipsilateral thalamic infarct was also found. Two subjects experienced respiratory compromise Figure 2. Volume average brain doses as a function of the number of radiation fields; mean dose and standard deviation. and ultimately adult respiratory distress syndrome (ARDS). Both were women in their mid-seventies who required high-dose steroids for management of tumor- associated edema, and both were irradiated with three fields. The initial pattern of pulmonary infiltrate was diffuse and not restricted to the lung apices as one might expect if the infiltrate was related to a cranial irradiation. A rapid clinical progression from dyspnea and mild pulmonary infiltrates to ventilator dependency and the clinical diagnosis of ARDS was observed. A postmortem examination of one of these subjects showed classic pulmonary changes associated with ARDS, but no characteristic radiation changes to the lung parenchyma. Later subjects who received irradia- tions at a higher dose level and longer in duration did not experience this adverse event. Table 3 shows preliminary information on some of the clinical factors that may be associated with the development of grade 3 or above adverse events thought to be related to increased ICP. Sixty-seven percent of the subjects with gross disease exceeding 60 cm3 at the time of NCT and 50% of the subjects irradiated on two successive days experienced some Figure 3. 10 B concentration in blood during and after infusion form of CNS symptom that required medical interven- of 250 mg kg−1 of BPA-f. Open symbols represent 10 B measure- ments using PGNAA or ICP-AES; the line is the fit of a two- tion. Subjects not on steroids at the time of entry onto compartment pharmacokinetic model to the measurements. The the protocol, who typically had small tumor volumes shaded area under the curve shows the irradiation time for a single and no edema, were irradiated without steroids. These field. subjects had a low incidence of developing an acute
  5. 5. 115 Table 2. NCI CTEP common toxicity criteria: NCT, all dose groups Category Grade 1 Grade 2 Grade 3 Grade 4 Grade 5 Alopecia 21 — — — Radiation dermatitis 6 7 1 Headache 1 2 3 Nausea 7 — — Vomiting 1 3 2 Mucositis 2 2 Dysphagia – pharyngeal 1 1 Dehydration 2 Xerostomia 1 Taste disturbance 1 Auditory – middle ear 2 Auditory – inner ear 2 Fatigue 1 3 Weight loss 2 ↓ LOC1 /somnolence 3 1 Seizure — 1 1 Neurological – cranial n. 1 Neurological – motor n. 1 Neurological – sensory n. 1 New L thalamic infarct 1 Decreased LTM2 1 SIADH3 1 ARDS4 2 Singultus 1 Pulmonary – other 1 2 Renal calculus 1 FUO5 1 1 Pleuritic chest pain 1 1 LOC = Level of consciousness. 2 LTM = Long-term memory. 3 SIADH = Syndrome of inappropriate anti- diuretic hormone secretion. 4 ARDS = Adult respiratory distress syndrome. 5 FUO = Fever of unknown origin. Table 3. Treatment parameters and the development of grade 3 incomplete, as subjects in this study lived throughout or above CNS adverse events related to increased ICP the US and Europe and often had difficulty in obtaining Subject/treatment Percent of subjects MRI exams on a monthly schedule, or failed to com- parameter developing CNS ply with the planned course of follow-up. However, adverse event data on 17 subjects were sufficient for a quantitative ≥ grade 3 assessment of changes in the volume of disease fol- Tumor volume <60 cm3 19 lowing NCT. Transverse images of the gadolinium- Tumor volume >60 cm3 67 enhanced baseline MRI and all available follow-up Dmax < 12 RBE-Gy 31 MRIs were scanned on a high-resolution scanner and Dmax > 12 RBE-Gy 43 1 Fraction 20 the region of interest outlined. Tumor volume was then 2 Fractions 50 measured using software developed in our laboratory 1 Field 33 (G. Santa Cruz). These data are shown in Figure 4. 2 Fields 29 For each of the evaluable subjects, the volume of 3 Fields 33 gross (enhancing) disease is indicated at baseline (just No steroids at evaluation 10 prior to NCT) and at successive time points during the or during NCT follow-up period. It can be seen that subjects in this clinical trial presented with a range of tumor volumes, increase in ICP. The number of fields does not appear from <10 to 120 cm3 . Two subjects with tumor vol- to be related to CNS events. umes of 84 and 121 cm3 were not evaluable, as one The tumor response following NCT was monitored expired and the other underwent post-NCT debulking with serial MRI studies. These data are inherently surgery (subjects described above). A trend toward a
  6. 6. 116 Figure 4. Contrast-enhanced tumor volumes in evaluable sub- Figure 5. Contrast-enhanced tumor volumes normalized to the jects at the time of NCT and in follow-up. initial tumor volume at the time of NCT. reduction in volume post-NCT is evident, particularly was evident. This response was durable until the subject in smaller tumors. developed widespread metastatic disease. No chronic The response to NCT becomes clearer when the changes to the normal brain were observed at the site tumor volumes are normalized to the initial tumor vol- of the original lesion. ume, as shown in Figure 5. It can be seen that the majority of subjects, 13 of 17 (76%), experienced a Discussion sizable and progressive reduction in enhancing vol- ume over the first several months, followed by a period These data represent a comprehensive analysis of the of disease stability or regrowth (five subjects). When results of a phase I trial designed to evaluate the tumor volumes are grouped by size, 6/7 with initial feasibility, safety, normal tissue tolerance, and tumor volumes <10 cm3 , 4/4 with volumes between 10 and response following cranial NCT, a novel form of radi- 30 cm3 , and 3/6 with volumes >30 cm3 responded. Two ation therapy. An additional phase I trial for subjects subjects experienced a complete radiographic response with melanoma of the extremities was open con- (CR). One example of a complete response is shown currently. Preliminary evaluations of each have been in Figure 6. This subject underwent NCT for an unre- reported [8,10,11,21]. These trials, along with similarly sected occipital melanoma metastasis. Serial contrast- designed NCT phase I/II trials at BNL [12–14] served enhanced MRI studies were obtained once a month and as clinical validation of a considerable amount of pre- progressive volume reduction was noted, until a CR clinical work in NCT, from in vitro experiments to large
  7. 7. 117 Figure 6. Demonstration of a complete radiographic response following NCT for a metastatic melanoma in the occipital lobe. Images are from enhanced MRI studies obtained monthly. A frontal craniotomy, evident in saggital views, is from a previously resected solitary melanoma metastasis. (A) Pre-NCT MRI, saggital view. (B) Pre-NCT MRI, axial view. (C) Increased enhancement at the site of original tumor one month following NCT, saggital view. (D) Increased enhancement at the site of original tumor one month following NCT, axial view. (E) Loss of enhanced signal and mass effect 7 months following NCT, saggital view. (F) Loss of enhanced signal and mass effect 7 months following NCT, axial view.
  8. 8. 118 animal studies. Although much attention and hope for group of subjects, increased ICP was successfully a quick clinical success has been placed in NCT, espe- treated with steroids and IV mannitol as indicated. cially as a potential therapy for high grade astrocytic Non-neurological acute reactions were seen in the tumors, the results presented here need to be interpreted parotid gland and the mucosal lining of the oral cav- within the context of an exploratory, dose-seeking clin- ity and oropharynx. These were all self-limiting and ical study of a nascent form of experimental radiation required only symptomatic intervention. One subject therapy. at the highest dose level was irradiated for a tumor in As originally designed, this trial sought to determine the anterior temporal lobe and experienced a dermal an MTD for brain by systematic dose escalation using (moist desquamation) and mucosal reaction (confluent parallel-opposed fields for all subjects. This is an opti- mucositis of the tongue and oropharynx) that required mal field arrangement for a deep-seated midline tumor. close observation and management. It appears from However, the limited penetration of epithermal neu- both clinical observation and studies in experimental trons in tissue results in a steep dose gradient in the animal systems that BPA concentrates not only in tumor brain and suboptimal tumor doses for lesions in loca- but also in the parotid gland and in rapidly dividing nor- tions other than the midline when this arrangement is mal tissue such as the basal layer of the skin and mucosa used. It was therefore decided early in the trial that of the oral cavity [22,23]. As with conventional radia- treatment planning would be optimized for each sub- tion therapy, acute and painful normal tissue reactions ject such that the highest possible dose would be given may be a potential dose-limiting factor to NCT. to the tumor while not exceeding the normal tissue and Chronic effects were also tabulated and are pre- dose escalation constraints of the protocol. A mini- sented in Table 2; however, a limitation of these data mum dose to the tumor was not formally specified, a is the variability in the length and quality of follow-up. distinction between this study and the BNL trials. As The geographic dispersion of the study population a result, subjects received 1, 2, or 3 fields depending and the understandable tendency of subjects to pur- upon the size and location of the tumor. This resulted sue additional forms of therapy or to stop obtaining in a greater degree of variation in the volume average scans once disease progression had become obvious brain dose (Figure 2), as opposed to a uniform, step- make the long-term data variable in quality and quan- wise increase with each dose cohort. This normal tissue tity. However, all follow-up radiographic studies were dose parameter may have important clinical implica- reviewed and examined for evidence of MRI changes. tions. It is well-recognized in clinical radiation therapy One of the primary radiographic endpoints for toxi- that the volume of irradiated tissue, in this case CNS, city in this trial was the development of white mat- is directly related to the development of side effects. ter changes following irradiation; this effect preceded This relationship most likely holds true for NCT as the manifestation of clinically apparent neurological well as for conventional radiation. Preliminary evi- changes and was typically seen 6 months following dence for this comes from a comparison of the inci- NCT in dogs [24,25]. Within the scope of this study, dence of grade 3 somnolence in this series (4/20) with any MRI changes following NCT have been attribut- the incidence seen in the last group of subjects irradi- able to disease progression (as seen in one subject with ated at BNL (Protocol #5) [14]. In BNL Protocol #5 multifocal metastatic melanoma) and not to injury to the average brain dose was increased to 9 RBE-Gy, and the brain parenchyma. 7/7 subjects experienced somnolence. The threshold The data presented on the type and severity of for its development may reside in an average brain dose observed adverse events are not atypical for a diverse between 7 and 9 RBE-Gy. The somnolence observed population of patients undergoing combined modality in both NCT experiences is a known CNS reaction fol- therapy for glioblastoma multiforme or intracranial lowing cranial irradiation and was similar to that expe- metastatic melanoma. The majority of the reactions rienced by many patients treated with standard external were acute, self-limiting, and related to a temporal beam photon therapy. increase in ICP, and responded to standard measures A number of anticipated and unanticipated acute such as dexamethasone, anticonvulsants, antiemetics, effects have been noted following NCT. Acute effects and occasionally intravenous mannitol. An increase secondary to increased ICP such as severe headache, in ICP is often multifactorial; however, in this trial it nausea, vomiting, change in consciousness, and appears to be related to enhancing tumor volume at seizures were seen during hospitalization and occa- the time of NCT irradiation. A comparison of the fre- sionally reached grade 3 in terms of severity. In this quency with which increased ICP was seen and tumor
  9. 9. 119 volume shows that tumors with volumes >60 cm3 were Some of the smaller enhancing volumes (<10 cm3 ) in associated with a 67% incidence of developing grade 3 subjects who have undergone resection may represent or higher symptoms, while tumors <60 cm3 had a post-operative changes to the brain, and the data from 19% incidence. In addition, the two subjects with the this group must be interpreted with caution; neverthe- most severe CNS adverse events, grades 4 and 5, had less, as an aggregate these responses are very encour- volumes of 84 cm3 and 121 cm3 , respectively. aging, particularly at such an early stage in the NCT The 10 B carrier chosen for this study was BPA-f. clinical trials. The median survival for the subjects Experimental and early clinical work in Japan showed in this series was 13 months, a duration not unlike BPA to have promise [26] as a therapy for melanoma. that seen with resection and standard radiation. An Human tumor biodistribution studies on GBM demon- important caveat however is, some subjects underwent strated a sufficient intracellular concentration of BPA-f second surgeries as well as reirradiation for recurrent could be achieved to allow the delivery of a clinically disease so 13 months is not a survival value for NCT meaningful dose of NCT [27,28]. The limitation of sol- alone. It does indicate that no untoward reaction was ubility of BPA-f to approximately 30 mg ml−1 at phys- experienced by the group as a whole that led to a reduc- iological pH at room temperature meant that infused tion in median survival. volumes were hypertonic and frequently approached or A true MTD for CNS tolerance was not reached exceeded 1 liter. These factors, along with an increase in this study. There were a number of adverse events of the BPA-f dose, led to the use of a central venous observed but not with a consistent pattern or clear catheter for drug delivery and an increase in the dura- etiology. One reason is the heterogeneity of the patient tion of the infusion from 60 to 90 min. The blood population and the finding that acute tolerance may pharmacokinetic profiles are characteristic and repro- be more related to gross residual intracranial dis- ducible and have allowed the development of a highly ease than to normal tissue brain dose. Another factor predictive model [19,20]. is that the irradiation times became increasingly long While the primary endpoint of a phase I trial is with the M67 epithermal beam and further dose esca- normal tissue tolerance, evidence of tumor response lation became impractical. The M67 beam was also is not without interest. The two subjects who expe- scheduled to be replaced by a new medical neutron rienced a CR following NCT, one with a small vol- source, the fission converter beam (FCB) [29–31], for ume residual GBM and the other with an unresected which additional phase I studies were planned. These melanoma nodule, were dramatic examples of a ther- trials using the FCB, a phase I/II for GBM and intracra- apeutic potential for NCT in two disease settings that nial melanoma and a phase II for peripheral melanoma, have limited success with conventional radiation ther- have been funded by the NIH and are in progress. While apy. In order to evaluate response or intervals of dis- the FCB will allow an irradiation to be completed in ease stability in the subjects who experienced less a matter of minutes with a higher therapeutic ratio, than a CR, a program was developed in our labora- that alone may not be sufficient for NCT to realize its tory where regions of interest could be identified on full utility. Newer compounds demonstrating a higher axial MRI images for measurement of tumor volume. tumor uptake of 10 B and prolonged retention or a more All available baseline and post-NCT imaging studies rapid normal tissue washout could hold potential, as were evaluated and tumor volumes quantified. Once could novel methods for selective delivery of already normalized to the tumor volume at the time of NCT, available 10 B-containing compounds [32,33]. 13 of 17 subjects displayed strikingly similar degrees and rates of tumor volume reduction for the first sev- eral months, after which the disease either stabilized or Acknowledgements grew, sometimes rapidly. Larger tumor volumes were less likely to show a measurable reduction in volume; The authors would like to thank Dr. John Bernard and these subjects either had stable disease or significant the MIT Nuclear Reactor Laboratory for reactor time side effects such as an increase in peritumoral edema, and support provided by the reactor-sharing program. which is suggestive of a high dose to the tumor. This This work was supported by a grant from the United trend in response is consistent with response following States Department of Energy: DE-FG02-96ER62193. conventional radiation therapy, i.e., the likelihood or Human subject transportation was provided by magnitude of a clinical response is inversely related to American Medical Response and the Fallon the amount of disease present at the time of treatment. Ambulance Service.
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