Response of the mediastinal and thoracic viscera of the dog to intraoperative radiation therapy (IORT)

Companion Animals as a Key to Success for Translating Radiation Therapy Research into the Clinic

Many successful preclinical findings fail to be replicated during translation to human studies. This leads to significant resources being spent on large clinical trials, and in some cases, promising therapeutics not being pursued due to the high costs of clinical translation. These translational failures emphasize the need for improved preclinical models of human cancer so that there is a higher probability of successful clinical translation. Companion-animal cancers offer a potential solution. These cancers are more similar to human cancer than other preclinical models, with a natural evolution over time, genetic alterations, intact immune system, and a permanent adaptation to the microenvironment. These advantages have led pioneers in veterinary radiation oncology to aid human medicine by elucidating basic principles of radiation biology. More recently, the veterinary and human radiation oncology fields have increasingly collaborated to achieve advancements in education, radiotherapy techniques, and trial networks. This review describes these advancements, including significant prior research findings and the evolution of the veterinary radiation oncology discipline. It concludes by describing how companion-animal models can help shape the future of human radiotherapy. Taken as a whole, this review suggests companion-animal cancers may become widely used for preclinical radiotherapy research.

Clinical feasibility of combining intraoperative electron radiation therapy with minimally invasive surgery: a potential for electron-FLASH clinical development

BACKGROUND

Local cancer therapy by combining real-time surgical exploration and resection with delivery of a single dose of high-energy electron irradiation entails a very precise and effective local therapeutic approach. Integrating the benefits from minimally invasive surgical techniques with the very precise delivery of intraoperative electron irradiation results in an efficient combined modality therapy.

METHODS

Patients with locally advanced disease, who are candidates for laparoscopic and/or thoracoscopic surgery, received an integrated multimodal management. Preoperative treatment included induction chemotherapy and/or chemoradiation, followed by laparoscopic surgery and intraoperative electron radiation therapy.

RESULTS

In a period of 5 consecutive years, 125 rectal cancer patients were treated, of which 35% underwent a laparoscopic approach. We found no differences in cancer outcomes and tolerance between the open and laparoscopic groups. Two esophageal cancer patients were treated with IOeRT during thoracoscopic resection, with the resection specimens showing intense downstaging effects. Two oligo-recurrent prostatic cancer patients (isolated nodal progression) had a robotic-assisted surgical resection and post-lymphadenectomy electron boost on the vascular and lateral pelvic wall.

CONCLUSIONS

Minimally invasive and robotic-assisted surgery is feasible to combine with intraoperative electron radiation therapy and offers a new model explored with electron-FLASH beams.

Preclinical models of radiation-induced cardiac toxicity: Potential mechanisms and biomarkers

Radiation therapy (RT) is an important modality in cancer treatment with >50% of cancer patients undergoing RT for curative or palliative intent. In patients with breast, lung, and esophageal cancer, as well as mediastinal malignancies, incidental RT dose to heart or vascular structures has been linked to the development of Radiation-Induced Heart Disease (RIHD) which manifests as ischemic heart disease, cardiomyopathy, cardiac dysfunction, and heart failure. Despite the remarkable progress in the delivery of radiotherapy treatment, off-target cardiac toxicities are unavoidable. One of the best-studied pathological consequences of incidental exposure of the heart to RT is collagen deposition and fibrosis, leading to the development of radiation-induced myocardial fibrosis (RIMF). However, the pathogenesis of RIMF is still largely unknown. Moreover, there are no available clinical approaches to reverse RIMF once it occurs and it continues to impair the quality of life of long-term cancer survivors. Hence, there is an increasing need for more clinically relevant preclinical models to elucidate the molecular and cellular mechanisms involved in the development of RIMF. This review offers an insight into the existing preclinical models to study RIHD and the suggested mechanisms of RIMF, as well as available multi-modality treatments and outcomes. Moreover, we summarize the valuable detection methods of RIHD/RIMF, and the clinical use of sensitive radiographic and circulating biomarkers.

Advances in Preclinical Research Models of Radiation-Induced Cardiac Toxicity

Radiation therapy (RT) is an important component of cancer therapy, with >50% of cancer patients receiving RT. As the number of cancer survivors increases, the short- and long-term side effects of cancer therapy are of growing concern. Side effects of RT for thoracic tumors, notably cardiac and pulmonary toxicities, can cause morbidity and mortality in long-term cancer survivors. An understanding of the biological pathways and mechanisms involved in normal tissue toxicity from RT will improve future cancer treatments by reducing the risk of long-term side effects. Many of these mechanistic studies are performed in animal models of radiation exposure. In this area of research, the use of small animal image-guided RT with treatment planning systems that allow more accurate dose determination has the potential to revolutionize knowledge of clinically relevant tumor and normal tissue radiobiology. However, there are still a number of challenges to overcome to optimize such radiation delivery, including dose verification and calibration, determination of doses received by adjacent normal tissues that can affect outcomes, and motion management and identifying variation in doses due to animal heterogeneity. In addition, recent studies have begun to determine how animal strain and sex affect normal tissue radiation injuries. This review article discusses the known and potential benefits and caveats of newer technologies and methods used for small animal radiation delivery, as well as how the choice of animal models, including variables such as species, strain, and age, can alter the severity of cardiac radiation toxicities and impact their clinical relevance.

Hypofractionated external-beam radiotherapy for prostate cancer

There are radiobiological rationales supporting hypofractionated radiotherapy for prostate cancer. The recent advancements in treatment planning and delivery allow sophisticated radiation treatments to take advantage of the differences in radiobiology of prostate cancer and the surrounding normal tissues. The preliminary results from clinical studies indicate that abbreviated fractionation programs can result in successful treatment of localized prostate cancer without escalation of late toxicity.

Esophageal tolerance to high-dose stereotactic ablative radiotherapy

Dose-volume parameters are needed to guide the safe administration of stereotactic ablative radiotherapy (SABR). We report on esophageal tolerance to high-dose hypofractionated radiation in patients treated with SABR. Thirty-one patients with spine or lung tumors received single- or multiple-fraction SABR to targets less than 1 cm from the esophagus. End points evaluated include D(5cc) (minimum dose in Gy to 5 cm(3) of the esophagus receiving the highest dose), D(2cc) , D(1cc) , and D(max) (maximum dose to 0.01 cm(3) ). Multiple-fraction treatments were correlated using the linear quadratic and linear quadratic-linear/universal survival models. Three esophageal toxicity events occurred, including esophagitis (grade 2), tracheoesophageal fistula (grade 4-5), and esophageal perforation (grade 4-5). Chemotherapy was a cofactor in the high-grade events. The median time to development of esophageal toxicity was 4.1 months (range 0.6-6.1 months). Two of the three events occurred below a published D(5cc) threshold, all three were below a D(2cc) threshold, and one was below a D(max) threshold. We report a dosimetric analysis of incidental dose to the esophagus from SABR. High-dose hypofractionated radiotherapy led to a number of high-grade esophageal adverse events, suggesting that conservative parameters to protect the esophagus are necessary when SABR is used, especially in the setting of chemotherapy or prior radiotherapy.

Toward endobronchial Ir-192 high-dose-rate brachytherapy therapeutic optimization

A number of patients with lung cancer receive either palliative or curative high-dose-rate (HDR) endobronchial brachytherapy. Up to a third of patients treated with endobronchial HDR die from hemoptysis. Rather than accept hemoptysis as an expected potential consequence of HDR, we have calculated the radial dose distribution for an Ir-192 HDR source, rigorously examined the dose and prescription points recommended by the American Brachytherapy Society (ABS), and performed a radiobiological-based analysis. The radial dose rate of a commercially available Ir-192 source was calculated with a Monte Carlo simulation. Based on the linear quadratic model, the estimated palliative, curative and blood vessel rupture radii from the center of an Ir-192 source were obtained for the ABS recommendations and a series of customized HDR prescriptions. The estimated radius at risk for blood vessel perforation for the ABS recommendations ranges from 7 to 9 mm. An optimized prescription may in some situations reduce this radius to 4 mm. The estimated blood perforation radius is generally smaller than the palliative radius. Optimized and individualized endobronchial HDR prescriptions are currently feasible based on our current understanding of tumor and normal tissue radiobiology. Individualized prescriptions could minimize complications such as fatal hemoptysis without sacrificing efficacy. Fiducial stents, HDR catheter centering or spacers and the use of CT imaging to better assess the relationship between the catheter and blood vessels promise to be useful strategies for increasing the therapeutic index of this treatment modality. Prospective trials employing treatment optimization algorithms are needed.

IVUS-based dosimetry on patients with repeat-radiated coronary arteries to the same site

BACKGROUND AND PURPOSE

Intracoronary radiation reduces recurrent in-stent restenosis (ISR). Repeat radiation may become necessary due to recurrent ISR. This study reports outcome-related dose calculations for twice-radiated coronary artery segments.

MATERIALS AND METHODS

A total of 22 patients with angiographic evidence of ISR in a previously treated native coronary artery were assigned for repeat percutaneous coronary intervention and intravascular brachytherapy (IVBT). Intravascular brachytherapy was performed either with a 192Ir- or a 90Sr/Y-source (prescription dose: 14-18 and 23 Gy each at 2 mm from the center of the source), or a 32P-source (20 Gy 1-mm deep to the vessel wall). The mean time interval between the two IVBT treatments was 394+/-306 days. For each patient, angiograms and intravascular ultrasound cross sections were reviewed, on the basis of anatomical landmarks, matched, and the twice-radiated vessel segment identified.

RESULTS

Clinical follow-up at 379+/-146 days revealed a target vessel revascularization rate of 18.2% and a target lesion revascularization rate of 13.6%. One death was reported. Maximal dose and average dose at the endothelium were 261 and 124+/-72.3 Gy, and maximal dose and average dose at the adventitia-media border were 159 and 50.3+/-29.3 Gy. Fourteen patients had 1.71 times longer recurrence-free interval compared to the interval between both IVBT treatments.

CONCLUSIONS

Repeat IVBT to the same ISR site is safe without any adverse clinical events at an average 12 months' follow-up. A second IVBT treatment led to a prolonged ISR-free survival for the majority of patients. The choice of isotope did not influence outcome.

Intraoperative radiation therapy in the multimodality approach to upper aerodigestive tract cancer

The cure rate of operable lung cancer and locally advanced head and neck cancer remains suboptimal, with a limited rate of local control despite improvements in the surgical removal of primary tumors and in methods for mediastinal lymph node dissection, in particular. The efficacy of adjuvant therapy, such as EBRT, has improved, and the immediate efficacy of new chemotherapeutic drugs is increasingly significant, although local recurrences remain frequent. Locoregional failure is not uncommon in upper aerodigestive tract cancers. Factors limiting radiocurability for locally advanced (stage III) lung cancer include mediastinal intolerance of irradiation (high risk of mediastinal fibrosis, which increases exponentially when levels of much more than 50 Gy are administered to the whole mediastinum) and the very high radiosensitivity of the healthy lung, which can develop fibrosis with relatively small or moderate doses starting at 18 to 20 Gy, and even more frequently when larger volumes are irradiated. Head and neck neoplasms are less difficult sites in which to administer doses of up to 70 Gy of external beam radiotherapy initially, but, like locoregionally recurrent lung cancers, they are not easily reirradiated with tumoricidal doses of EBRT. For these reasons, IORT seems to be a good option for increasing local control, because areas of [figure: see text] residual microscopic disease may be irradiated using IOERT approaches without affecting critical organs to the same extent. In addition, careful patient selection is paramount. Combined modality treatment regimens incorporating IORT may benefit patients with locally advanced disease. The ability of IORT to sterilize microscopic residual disease can enhance the "completeness" of resection and thus, theoretically, improve local control. Although distant disease dissemination remains by far the overriding issue, as newer effective agents emerge, local failure will continue to be a problem. Preliminary studies have demonstrated that IORT can be administered to patients who have locally advanced NSCLC and head and neck cancer, in the context of aggressive combined modality therapy, and is generally well tolerated. Long-term efficacy and benefit can only be determined in the setting of carefully designed clinical trials. (See the article by Thomas and Merrick elsewhere in this issue for further discussion of this topic.) Several relatively small, single-institution pilot studies exploring the utility and benefit of IORT for locally advanced upper aerodigestive tract cancers have been conducted. Clear conclusions have been difficult to determine because of the mixing of disease stages, varying degrees and completeness of surgical resection, varying radiation doses, different schemas, and other factors. Yet, given the major morbidity and mortality associated with locally recurrent lung cancer, methods of improving local control need to be pursued and refined. Encouraging preliminary data suggest that IOERT can be safely administered and may benefit local control. Based on several centers' expertise in the combined modality treatment of locally advanced lung cancer and familiarity with IORT, the UCSF Thoracic Oncology Program has proposed a multicenter phase 2 study incorporating IORT in a combined multimodality treatment schema for patients who have completely resected locally advanced stage IIIA and IIIB NSCLC (nonpleural effusion, non-N3) (Fig. 1). It is hoped that this study will commence in the upcoming year.

Iatrogenic-induced dysfunction of the neuromuscular respiratory system

In the presence of respiratory symptoms that are associated with alveolar hypoventilation or a restrictive ventilatory defect and in the absence of parenchymal or pleural abnormalities on the chest radiograph, iatrogenic causes must be evoked, exactly as they are in the presence of interstitial lung disease. In most cases, the anamnestic and clinical contexts provide a strong diagnostic presumption. It is important to establish carefully the mechanism of the observed disorders, using the currently available arsenal of diagnostic tools for clinical and prognostic reasons and from a medicolegal standpoint. It is necessary to evaluate precisely the clinical repercussions of the respiratory neuromuscular abnormality to serve as a basis for follow-up and to discuss therapeutic options in certain cases (eg, nocturnal ventilation to correct nocturnal hypoventilation due to diaphragmatic dysfunction, diaphragm plication to alleviate dyspnea after complete phrenic nerve destruction, phrenic nerve pacing), again in the perspective of medicolegal actions.

Normal tissue tolerance to intraoperative radiotherapy

Much experimental evidence has been accumulated assessing the tolerance of various tissues to IORT, and much of the tolerance data have resulted from the use of canine models. Guidelines of IORT tissue tolerance established in experimental models have been used in the clinical application of IORT at numerous institutions. Although the radiotolerance of differing tissues can vary among species, sufficient clinical experience has accumulated to validate the canine tissue tolerance model as representative of human tissue responses to IORT. Cellular effects from radiation principally stem from direct damage to DNA, and thus proliferating tissues are among the most radiosensitive, with arrested or abnormal cell division. These tissues can manifest striking early toxicity, reflecting the rate of cell division that is affected by the radiation. Irradiation of nonproliferating or slowly proliferating tissues may show little or no early toxicity, but late effects can be manifested to considerable and varying degrees. In much of this late toxicity, pathologic changes develop from progressive ischemia, brought about by the gradual obliteration of small blood vessels. Irradiated endothelium often becomes replaced by a thickened fibrous layer, which, in small vessels, leads to occlusion and ischemic necrotic changes in the supplied tissue. In larger vessels, fibrosis can lead to wall weakening and aneurysmal dilatation, rupture, or thrombosis. The common denominator, then, of radiation damage to many tissues is related to vascular effects. Although the tolerance to IORT-induced toxicity can vary considerably among tissues, doses ranging to 25 Gy can generally be tolerated without significant toxicity. Vital areas where IORT dose must be carefully monitored include critical vasculature, gastrointestinal viscera, ureter, significant motor or sensory nerve trunks, and central nervous system structures. Higher doses can generally be delivered safely to anatomic areas at risk for tumor that are at a distance from sensitive organs or tissues. The general principle providing the rationale of IORT should always be practiced: maximize the radiation dose to the tumor and tumor-harboring tissues while minimizing dose exposure to surrounding normal tissues.

The short and long term effects of intraoperative electron beam radiotherapy (IORT) on thoracic organs after pneumonectomy an experimental study in the canine model

PURPOSE

The tolerance of mediastinal structures and thoracic organs to intraoperative radiotherapy (IORT) was investigated in the canine model.

METHODS AND MATERIALS

Twenty-two adult beagles divided into three groups were subjected to a left pneumonectomy and IORT (10 MeV electrons) at doses of 20 Gy (n = 9), 25 Gy (n = 4), or 30 Gy (n = 9). Intraoperative electron beam radiotherapy was delivered through a 5 cm circular lucite cone encompassing a mediastinal field including the bronchial stump, aorta, esophagus, heart, phrenic nerve, contralateral hilar structures, and lung. Clinical monitoring was performed with regular chest X-ray, ECG, bronchoscopy, esofagoscopy, and fluoroscopy. From the different treatment dose groups, dogs were electively sacrificed at 1.5, 6, 12, and 72 months with complete autopsies.

RESULTS

There was no bronchial stump dehiscence or acute morbidity. Four dogs developed radiation induced esophagitis (18%), one in the 20 Gy IORT group (11%) and three in the 30 Gy IORT group (33%). There were six IORT related mortalities (27.5%), one esophagoaortic fistula (4.5%) and five bronchovascular fistulas (23%): two in the 20 Gy IORT group (22%), two in the 25 Gy IORT group (50%) and two in the 30 Gy IORT group (22%). Histopathological findings in uncomplicated follow-up showed marked myointimal fibrosis in the muscular arteries, submucosal fibrosis of the esophagus, and interstitial fibrosis of bronchial and lung tissue, especially in the higher dose group.

CONCLUSION

The mediastinal vascular, bronchial and esophageal structures are relatively sensitive to doses > 20Gy IORT. The IORT related morbidity found in this study may be lower when the current clinically used IORT doses of 10-15 Gy are applied. Further clinical application of IORT in the future treatment strategies for resectable nonsmall cell lung cancer may be worthwhile to investigate.

[Late effects of intraoperative radiotherapy]

Several experimental studies on animals have yielded to the tolerance single doses for different critical organs. Anatomical alterations are located essentially in the intima of the arteries with oedema, histio-lymphoplasmocytoïd infiltration in a first time leading to arterial obstructions and necrosis after the 6th week. These radiation injuries are related to the IORT dose, the target volume and the time interval between the IORT treatment and the apparition of the side-effects. Moreover, some radiation induced sarcomas have been observed in animals after the 5th year which suggest that the follow-up period after IORT must be prolonged enough to appreciate the exact complications rate of IORT. If we exclude the usual post-operative complications, the complications observed in human IORT treatments may be either early side effects on small bowel, esophagus or late effects: peripheral neuropathies, osseous complications, and microvascular obstructions. A more precise clinical description and an improved knowledge of the relationships with different treatment characteristics should allow us to prevent more efficiently the IORT complications.

Tumors in dogs exposed to experimental intraoperative radiotherapy

PURPOSE

The frequency of radiation-induced neoplasms was determined in dogs enrolled in the National Cancer Institute canine trials of intraoperative radiotherapy (IORT).

METHODS AND MATERIALS

Twelve protocols assessing normal tissue response to IORT involved 238 dogs in a 15-year trial. Eighty-one dogs were followed for > 24 months postoperatively and were assessed for tumor development; 59 of these animals received IORT.

RESULTS

Twelve tumors occurred in the 59 dogs receiving IORT. Nine were in the IORT portals and were considered to be radiation induced. No tumors occurred in 13 sham animals or in 9 animals treated with external beam radiotherapy alone. The frequency of radiation-induced malignancies in dogs receiving IORT was 15%, and was 25% in animals receiving > or = 25 Gy IORT. Frequency of all tumors, including spontaneous lesions, was 20%.

CONCLUSIONS

Intraoperative radiotherapy contributed to a high frequency of sarcoma induction in these dogs. Unknown to date in humans involved in clinical trials of IORT, this potential complication should be looked for as long-term survivors are followed.

Tolerance of the bladder to intraoperative radiation in a canine model: a five-year follow-up

PURPOSE

Late effects of intraoperative radiation therapy (IORT) on bladder were investigated in a canine model.

METHODS AND MATERIALS

After laporatomy and cystotomy in adult female foxhounds weighing 25-35 kg, 12 MeV electrons were delivered intraoperatively to a 5 cm circular bladder field which included the trigone and both uretero-vesicle junctions. Each animal received doses of 0, 20, 25, 30, 35, or 40 Gy. All the dogs were followed 5 years postoperatively. An unoperated dog receiving no surgery or radiation treatment was followed as a control. Close clinical monitoring was performed with regular cystometrics and intravenous pyelography. Animals were killed as scheduled with complete necropsies, including histopathology, with special attention to genitourinary structures.

RESULTS

There were no acute or late bladder complications detected clinically in any animal. The dog receiving 30 Gy IORT developed rhabdomyosarcoma in the treatment field at 58 months. On follow-up testing over 5 years, there was no loss of bladder contractility on cystometry, and mild changes in the ureters on intravenous pyleography when animals receiving IORT were compared with baseline pretreatment values or with control animals. Histologically, a difference was evident between irradiated and unirradiated animals, but the changes were not clearly dose-related.

CONCLUSION

Intraoperative radiation therapy may by safely delivered to the canine bladder with few acute or chronic complications. It is an approach which has potential for clinical use and should continue to be explored in human clinical trials.

Experimental and clinical studies of intraoperative radiation therapy

Intraoperative radiation therapy (IORT) is an innovative treatment modality that has recently been given considerable attention as an approach toward controlling various locally advanced cancers. IORT involves surgical extirpation or debulking of the malignant lesion and the delivery of a large single dose of radiation to the tumor bed or to residual disease. This strategy allows for a theoretical enhancement of the therapeutic effect of radiation for three reasons: (1) the biologic effectiveness of a single large radiation dose is higher than for the same dose given in a fractionated regimen; (2) the dose of radiation is precisely given to the area at greatest risk of tumor recurrence (or persistence); and (3) irradiation of dose-limiting normal tissues may be avoided by operative mobilization of the tissues from the treatment volume by customized lead shielding of anatomically fixed structures or by judicious choice of electron beam energies or use of a bolus to limit dose to deep structures. Electrons are generally used for IORT because of sharp dose falloff. This avoids potential toxic effects to normal structures that may lie deep to the treatment volume. Conventional external beam photon radiation therapy (EBRT) allows less accurate tumor volume delineation (even with sophisticated treatment planning technique) and dose limitations necessitated by normal tissues incidentally in the treatment volume. A considerable amount of experimental and clinical data are available on the acute and late effects of IORT on normal tissues. Dose tolerances of many organs have been described in large animal models, and clinical toxicities are evident in several trials. Clinical IORT treatments are provided in more than 250 U.S. and foreign centers at the present time. Given the current interest in IORT, this monograph will review IORT methods and experimental and clinical results with emphasis on its present and future role for locally advanced cancers.

Effects of intraoperative radiotherapy on vascular grafts in a canine model

PURPOSE

The effects of intraoperative radiotherapy +/- external beam radiotherapy on prosthetic vascular grafts were investigated in a canine model.

METHODS AND MATERIALS

In 1986 and 1987, 30 adult beagles underwent laparotomy with transection and segmental resection of the infrarenal aorta followed by immediate reconstruction with a prosthetic graft. Intraoperative radiotherapy at varying doses from 0-30 Gy was then administered to all animals. Half of the dogs received 36 Gy external beam radiotherapy in 10 fractions postoperatively. Animals were sacrificed and necropsied at predetermined intervals and as clinically indicated to assess early (< or = 6 months) and late (> 6 months) effects to the vascular graft and surrounding normal tissue.

RESULTS

Histopathologic analyses of irradiated vascular structures were performed and correlations were made with the clinical outcome. The most frequent early clinical toxicity was graft thrombosis, occurring in 7 of 10 animals followed for < or = 6 months. Early graft thrombus formation appeared unrelated to radiotherapy dose and probably represented a technical surgical complication. Anastomotic stenosis of varying severity occurred in most animals followed > 6 months. Late (> 6 months) graft stenosis was correlated with intraoperative radiotherapy dose. At < or = 20 Gy of intraoperative irradiation, 3 of 14 animals developed late graft occlusion; at > 25 Gy, five of six animals developed late occlusion. On histopathologic review, increasing intraoperative dose and increasing total radiotherapy dose (intraoperative+external beam) appeared to correspond with increasing severity of graft changes seen after 6 months of follow-up.

CONCLUSIONS

Thrombus formation is a frequent early complication of vascular graft placement of the infrarenal aorta in our beagle dog model. Intraoperative doses up to 20 Gy appear to contribute minimally to late graft occlusion, while doses > or = 25 Gy contribute to late occlusion with high likelihood. Both intraoperative dose and total radiotherapy dose correlated with late graft occlusion, and with histopathologic changes in the graft and anastomoses.

Radiation-induced heart disease: review of experimental data on dose response and pathogenesis

Clinical and experimental heart irradiation can cause a variety of sequelae. A single dose of greater than or equal to 15 Gy leads to a reversible exudative pericarditis, occurring in dogs, rabbits or rats at around 100 days. Its time-course is very similar in all species investigated, but there are considerable species and strain differences in severity and incidence. After longer, dose-dependent latency times chronic congestive myocardial failure develops. At histological examination myocardial degeneration and necrosis is observed, which in some species is accompanied by a variable degree of interstitial fibrosis. In rabbits and rats, myocardial degeneration becomes apparent at around 70 days after 20 Gy and is preceded by a marked reduction in capillary density as well as ultrastructural endothelial cell degeneration. Simultaneously to structural capillary damage, a focal loss of the endothelial marker enzyme alkaline phosphatase was observed in rats in areas with subsequent myocardial degeneration. Cell kinetic studies in rabbits and rats revealed a radiation-induced wave of increased endothelial cell proliferation at 30-100 days postirradiation. In the rat it is exclusively seen in conjunction with alteration of endothelial cell marker enzymes. The temporal and spatial pattern of proliferative response exludes endothelial cell death in mitosis as the sole pathogenetic mechanism causing capillary loss and myocardial degeneration. Parallel to development of morphological damage, haemodynamic studies in various rats strains revealed a drop in cardiac output and left ventricular ejection fraction to about 64% of normal values after 20 Gy. In vivo, this slightly reduced cardiac function was then maintained in a steady state for many weeks, probably due to a compensatory up-regulation of cardiac beta-adrenergic receptors. In denervated working heart preparations in vitro, however, these compensatory mechanisms are not effective and stroke volume as well as cardiac contractility show a rapid and steady deterioration. In many respects radiation-induced heart disease conforms to radiobiological concepts of late-responding tissues, showing a chronic progressive time-course and a very pronounced fractionation effect. However, pathogenesis cannot be understood in terms of target cell depletion alone, and experimental evidence indicates the importance of alterations of regulatory mechanisms.

Late radiation response of canine mediastinal tissues

The mediastinal tissues which included heart, lung, trachea and esophagus of 70 adult beagle dogs were irradiated to a range of total radiation doses between 24 and 68 Gy given in 2, 3 and 4 Gy fractions. The purpose of the study was the calculation of alpha/beta ratios for morphologic and functional changes of the mediastinal tissues. Functional assays including echocardiography, electrocardiography, right heart hemodynamics and cardiac output were performed. Histomorphometric analyses of all tissues included in the field were done 2 years after treatment. Euthanasia was performed on 7 of 70 dogs prior to 2 years due to congestive heart failure and seven other dogs had signs of heart failure 2 years after treatment. Heart failure was thought to be caused by either pericardial effusions or constrictive pericarditis in these dogs. Heart failure occurred at doses of 62 and 68 Gy given in 2 Gy fractions, 60 Gy given in 3 Gy fractions and 52 Gy given in 4 Gy fractions. The ED50 values for pericardial fibrosis for 2, 3 and 4 Gy fractions were 46.1, 43.9 and 26.6 Gy, respectively. An alpha/beta ratio of 2.5 Gy was calculated by direct quantal response analysis. Small foci of myocytolytic lesions were detected in 11 dogs. Calculated ED50 values for myocytolysis were 70.4 Gy given in 2 Gy fractions and 50.8 Gy given in 4 Gy fractions. The estimated alpha/beta ratio was 3.2 Gy. Heart rates determined from physical examination and frequency of S-T segment changes increased with increasing dose. No other dose related changes were found in any of the other functional parameters. Functional changes were detected in the 14 dogs with clinical signs of heart failure. Focal consolidation and subpleural fibrosis were present in the irradiated lung volume. These late changes had no detectable physiologic effect in these dogs because of the small volume of lung irradiated. The ED50 values for lung consolidation were 54.3, 45.8 and 26.6 Gy after 2, 3 or 4 Gy fractions, respectively. The estimated alpha/beta ratio was 3.4 Gy. No dose-related changes could be detected in the trachea or esophagus at 2 years after treatment. These results demonstrate that lung and pericardium are the most responsive tissues in the mediastinum within the first 2 years after treatment. Myocardial lesions were present with high ED50 values, but were not found to be functionally significant at 2 years after irradiation. Human clinical data indicate that longer observation periods are needed for development of these lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

Long term tolerance of thoracic organs to intraoperative radiotherapy

The tolerance of mediastinal structures to intraoperative radiotherapy (IORT) was investigated in 3 separate animals trials using 49 adult foxhounds and one limited Phase I trial in 4 patients with Stage II or III non-small cell lung cancer (NSCLC). The 1- to 2-year results of these trials have been previously reported with significant toxicity found at dose levels over 20 Gy. We now report the results of five dogs reserved for long term studies and one Stage II NSCLC patient alive at 5 years. Two dogs received 20 Gy IORT and one received 30 Gy IORT to the esophagus, all three to a single 6 cm field with 9 MeV electrons. One control dog underwent surgery without irradiation. One dog received 20 Gy IORT to a single 5 cm mediastinal field with 13 MeV electrons following left pneumonectomy. At 5 years, all five dogs reserved for a long term evaluation were alive and evaluable with minimal endoscopic and radiographic abnormalities. The one patient alive at 5 years for evaluation received 25 Gy IORT to two matched 6 cm fields with 13 MeV electrons. She has stable dyspnea on exertion and there is no evidence of cancer by endoscopy. We conclude, based on these limited data, that IORT in the mediastinum may be safe at dose levels that do not exceed 20 Gy, and further careful evaluation at these lower treatment doses is warranted to determine efficacy.

Intraoperative plus external beam irradiation in nonresectable lung cancer: assessment of local response and therapy-related side effects

Since 1987, 24 patients with inoperable non-small-cell lung cancer (NSCLC), stage T1-3 N0-2 M0, have undergone lymph node dissection and intraoperative radiation therapy (IORT) to the primary with 10-20 Gy. Patient selection criteria were nonresectability based on severe cardiorespiratory impairment, no radiological evidence of distant metastases and a Karnofsky performance status of greater than 80. In 18 patients the IORT procedure was followed by an external beam radiation series (EBR) including the tumor with 46 Gy and the regional lymph nodes with 46/56 Gy. The tumor response was assessed by CAT-scan volumetry before the institution of IORT, 4 weeks later, before the onset of EBR, 8 weeks after the combined treatment course and on a 3 months basis thereafter. Prospectively, MRI of the thorax with/without Gadolinium-DTPA was performed to examine contrast enhancement and signal behavior of the tumor, in an attempt to differentiate residual disease compared to therapy-related collateral damage. So far, 18 patients have completed the combined treatment course with a median follow-up of 11 months (range 4.5 to 25 months). The overall local response rate (CR and PR) was 88.2%. In detail, 11 complete responses, 6 partial responses and one minimal response were observed. The overall and recurrence-free survival at 25 months was 49.6% and 83.3%, respectively.

Tumor induction following intraoperative radiotherapy: late results of the National Cancer Institute canine trials

Intraoperative radiotherapy has been employed in human cancer research for over a decade. Since 1979, trials to assess the acute and late toxicity of IORT have been carried out at the National Cancer Institute in an adult dog model in an attempt to establish dose tolerance guidelines for a variety of organs. Of the 170 animals entered on 12 studies with a minimum follow-up of 2 years, 148 dogs received IORT; 22 control animals received only surgery. Animals were sacrificed at designated intervals following IORT, usually at 1, 6, 12, 24, and 60 month intervals. 102 of 148 irradiated dogs were sacrificed less than 24 months; 46 dogs were followed greater than or equal to 24 months after IORT. To date, 34 of the 46 animals have been sacrificed; the 12 remaining animals are to be followed to 5 years. These 12 animals have minimum follow-up of 30 months. In the irradiated group followed for greater than or equal to 24 months, 10 tumors have arisen in 9 animals. One animal developed an incidental spontaneous breast carcinoma outside the IORT port, discovered only at scheduled post-mortem exam. The remaining nine tumors arose within IORT ports. Two tumors were benign neural tumors--a neuroma and a neurofibroma. One animal had a "collision" tumor comprised of grade I chondrosarcoma adjacent to grade III osteosarcoma arising in lumbar vertebrae. Two other grade III osteosarcomas, one grade III fibrosarcoma, and one grade III malignant fibrous histiocytoma arose in retroperitoneal/paravertebral sites. An embryonal rhabdomyosarcoma (sarcoma botryoides) arose within the irradiated urinary bladder of one animal. No sham irradiated controls nor IORT animals sacrificed less than 24 months have developed any spontaneous or radiation-induced tumors. The time range of diagnoses of tumors was 24-58 months (median 40 months). The IORT dose range associated with tumor development was 20-35 Gy (median 30 Gy). The carcinogenesis capability of single fraction, high dose radiation in animals is discussed, as are the implications of these data for continued research and clinical usage of IORT in the treatment of humans.

Intraoperative radiotherapy during lung cancer surgery: technical description and early clinical results

A phase I-II study of intraoperative radiotherapy (IORT) for Stage III lung cancer was performed in 34 patients during a period of 58 months. Loco-regional treatment included tumor resection if technically feasible, IORT boost of electron beams using moderate single doses (10-15 Gy) to tumor bearing areas and external photon beam irradiation (46-50 Gy in 5 weeks) using conventional fields. Indications for this study were unresectable hiliar tumors (14, 41%), and mediastinal, hiliar and/or chest wall residual disease following resection (20, 59%). Thirty-four procedures, with 40 IORT fields, have been analyzed to describe the relevant technical aspects and the toxicity. IORT was delivered using acrylic transparent cones of different diameters. Surgical approach consisted in a lateral thoracotomy in all patients (21 right side and 13 left side). Tissues included within the IORT field were: tumor or residual tumor tissues (34, 100%), collapsed lung parenchyma and main bronchus not surgically manipulated (14, 41%), bronchial stump and vascular suture following resection (19, 55%), mediastinal structures (20, 58%), and brachial plexus (1, 3%). The bronchial suture was covered with pleural or pericardial flap after IORT in 10 cases (29%). Life threatening toxicity related to IORT consisted in broncho-pleural fistula (1, 3%) and massive hemoptysis (1, 3%). Other reversible toxic events were acute pneumonitis (12, 85%) and esophagitis (10, 50%). Long term asymptomatic lung fibrosis was detected in 11 cases (32%). Median survival time for the entire group has been 12 months. With a median follow-up time of 12 months the freedom from thoracic recurrence rate is 30% (65% in cases with tumor resection). Projected actuarial survival rates at 4 years were 28% for resected group and 7% for unresected cases. This experience supports IORT as a feasible alternative modality to be used in the management of locally advanced lung cancer. Tolerance of thoracic organs to moderate doses of IORT appeared to be adequate and local control is achieved in certain patients. These results deserve further investigation and confirmation trials.

Intraoperative radiation therapy combined with external irradiation in nonresectable non-small-cell lung cancer: preliminary report

Twenty-one patients with nonresectable non-small-cell lung cancer (15 squamous-cell, 4 adeno, 2 large-cell; T1-T3, N0-N2, all M0) underwent lymph node dissection and intraoperative irradiation of the tumor (IORT) with doses between 10 and 20 Gy (energies: 7 to 20 MeV electron beam). Postoperatively, 46-56 Gy external beam irradiation (8 or 23 MeV photon beam) were delivered to the mediastinum and 46 Gy to the tumor bearing area. Fifteen patients were available for follow-up investigations. The CT-scan tumor volumetry 4 weeks postoperatively showed a significant overall decrease (Wilcoxon test: p less than 0.05) with eight minor responses (MR) (tumor regressions between 4 and 45%) and six partial responses (PR) (between 50 and 84%). One case was not evaluable. A second volumetry after external irradiation was done in 14 patients, 18 weeks after IORT, showing 3 complete responses, 10 partial responses (62 to 84%), and 1 minor response (28%). The recent volumetries (10 patients) between 4.5 and 16.5 months after IORT showed 7 complete responses and 3 partial responses (63 to 94%). One patient died from intrabronchial hemorrhage at 7 weeks. Three others died from unrelated causes, 6, 12 and 14 months, respectively, after IORT and in one further case the cause of death at 15 months was local tumor regrowth. Within the median time elapsed since IORT (12 months) only this one case of local regrowth and one further case of distant spread were observed.

Response of canine esophagus to intraoperative electron beam radiotherapy

Tolerance of esophagus to intraoperative radiotherapy (IORT) was investigated in dogs. Thirteen adult foxhounds were subjected to right thoractomy, mobilization of the intrathoracic esophagus, and IORT to a 6 cm full-thickness esophageal segment using 9 MeV electrons at doses of 0, 2,000, or 3,000 cGy. Dogs were followed clinically and were evaluated at regular intervals after treatment with fiberoptic esophagoscopy, barium swallows, and postmortem histologic evaluations. One sham-irradiated control dog showed no abnormalities during follow-up of 24 months. Seven dogs receiving 2,000 cGy IORT showed transient mild dysphagia and mild esophagitis, but no clinically or pathologically significant complications. Five dogs receiving 3,000 cGy demonstrated severe ulcerative esophagitis within 6 weeks of treatment which progressed to chronic ulcerative esophagitis with stricture formation by 9 months following IORT. One 3,000 cGy dog died at 13 months from an esophageal perforation. On the basis of a pilot experience using 13 experimental animals, it was concluded that intact canine esophagus tolerates IORT well to doses of 2,000 cGy, but doses of 3,000 cGy pose serious and potentially lethal risks. The clinical application of IORT to the treatment of human intrathoracic neoplasms requiring esophageal irradiation should be approached with caution, particularly at doses exceeding 2,000 cGy.

Delivery of intraoperative radiation therapy after pneumonectomy: experimental observations and early clinical results

Intraoperative radiation therapy (IORT) is capable of delivering high doses of radiation to mediastinal structures while sparing lung parenchyma, heart, and other locoregional tissues. A canine model of pulmonary resection and IORT was investigated by performing a pneumonectomy in 15 adult foxhounds followed by 0 cGy, 2,000 cGy, 3,000 cGy, 4,000 cGy. No clinical complications developed in 4 animals in the 2,000-cGy group. However, 2 of the 8 animals given a high dose died of esophageal hemorrhage or carinal necrosis. Esophagitis occurred in 10 of 12 animals, and none of the animals experienced bronchial stump dehiscence. In a limited Phase I protocol, 4 patients with non-small cell lung cancer were treated with resection and 2,500 cGy of IORT to two separate ports encompassing the superior and inferior mediastinum. Two patients experienced life-threatening bronchopleural fistulas, and 2 patients died as a consequence of esophageal problems. One patients had recurrence with brain metastases, and the 1 long-term survivor is free from disease. As opposed to the animal model of thoracic IORT, the clinical study demonstrated major toxicity with respiratory and esophageal morbidity. The therapeutic usefulness of thoracic IORT in the management of lung cancer must be questioned in view of this small but consistent series of patients. Further carefully designed clinical studies using lower doses of IORT are needed.