Fast neutron radiotherapy for sarcomas of soft tissue, bone, and cartilage

Effects of tissue heterogeneity and comparisons of collapsed cone and Monte Carlo fast neutron patient dosimetry using the University of Washington clinical neutron therapy system (CNTS)

Fast neutron therapy is a high linear energy transfer (LET) radiation treatment modality offering advantages over low LET radiations. Multileaf collimator technology reduces normal-tissue dose (toxicity) and makes neutron therapy more comparable to MV x-ray treatments. Published clinical-trial and other experiences with fast neutron therapy are reported. Early comparative studies failed to consider differences in target-dose spatial conformality between x-ray and neutron treatments, which is especially important for organs-at-risk close to tumor targets. Treatments planning systems (TPS) for high-energy neutrons lag behind TPS tools for MV x-rays, creating challenges for comparative studies of clinical outcomes. A previously published Monte Carlo model of the University of Washington (UW) Clinical Neutron Therapy System (CNTS) is refined and integrated with the RayStation TPS as an external dose planning/verification tool. The collapsed cone (CC) dose calculations in the TPS are based on measured dose profiles and output factors in water, with the absolute dose determined using a tissue-equivalent ionization chamber. For comparison, independent (external) Monte Carlo simulation computes dose on a voxel-by-voxel basis using an atlas that maps Hounsfield Unit (HU) numbers to elemental composition and density. Although the CC algorithm in the TPS accurately computes neutron dose to water compared to Monte Carlo calculations, calculated dose to water differs from bone or tissue depending largely on hydrogen content. Therefore, the elemental composition of tissue and bone, rather than the material or electron density, affects fast neutron dose. While the CC algorithm suffices for reproducible patient dosimetry in fast neutron therapy, adopting methods that consider tissue heterogeneity would enhance patient-specific neutron dose accuracy relative to national standards for other types of ionizing radiation. Corrections for tissue composition have a significant impact on absolute dose and the relative biological effectiveness (RBE) of neutron treatments compared to other radiation types (MV x-rays, protons, and carbon ions).

Fast and Furious: Fast Neutron Therapy in Cancer Treatment

Fast neutron therapy has been used for decades. In conjunction with recent advances in photonic techniques, fast neutrons are no longer of much oncologic interest, which is not unequivocally positive, given their undoubted therapeutic value. This mini-review recalls the history of medical research on fast neutrons, considers their physical and radiobiological properties alongside their benefits for cancer treatment, and discusses their place in modern radiation oncology.

Predicted probabilities of brain injury after carbon ion radiotherapy for head and neck and skull base tumors in long-term survivors

BACKGROUND AND PURPOSE

We aimed to determine the risk factors for radiation-induced brain injury (RIBI¹) after carbon ion radiotherapy (CIRT) to predict their probabilities in long-term survivors.

MATERIALS AND METHODS

We evaluated 104 patients with head, neck, and skull base tumors who underwent CIRT in a regimen of 32 fractions and were followed up for at least 24 months. RIBI was assessed using the Common Terminology Criteria for Adverse Events.

RESULTS

The median follow-up period was 45.5 months; 19 (18.3 %) patients developed grade ≥2 RIBI. The maximal absolute dose covering 5 mL of the brain (D5ml) was the only significant risk factor for grade ≥2 RIBI in the multivariate logistic regression analysis (p = 0.001). The tolerance doses of D5ml for the 5% and 50% probabilities of developing grade ≥2 RIBI were estimated to be 55.4 Gy (relative biological effectiveness [RBE]) and 68.4 Gy (RBE) by a logistic model, respectively.

CONCLUSION

D5ml was most significantly associated with grade ≥2 RIBI and may enable the prediction of its probability.

Dosimetric characteristics of the University of Washington Clinical Neutron Therapy System

The University of Washington (UW) Clinical Neutron Therapy System (CNTS), which generates high linear energy transfer fast neutrons through interactions of 50.5 MeV protons incident on a Be target, has depth-dose characteristics similar to 6 MV x-rays. In contrast to the fixed beam angles and primitive blocking used in early clinical trials of neutron therapy, the CNTS has a gantry with a full 360° of rotation, internal wedges, and a multi-leaf collimator (MLC). Since October of 1984, over 3178 patients have received conformal neutron therapy treatments using the UW CNTS. In this work, the physical and dosimetric characteristics of the CNTS are documented through comparisons of measurements and Monte Carlo simulations. A high resolution computed tomography scan of the model 17 ionization chamber (IC-17) has also been used to improve the accuracy of simulations of the absolute calibration geometry. The response of the IC-17 approximates well the kinetic energy released per unit mass (KERMA) in water for neutrons and photons for energies from a few tens of keV up to about 20 MeV. Above 20 MeV, the simulated model 17 ion chamber response is 20%-30% higher than the neutron KERMA in water. For CNTS neutrons, simulated on- and off-axis output factors in water match measured values within ~2%  ±  2% for rectangular and irregularly shaped field with equivalent square areas ranging in a side dimension from 2.8 cm to 30.7 cm. Wedge factors vary by less than 1.9% of the measured dose in water for clinically relevant field sizes. Simulated tissue maximum ratios in water match measured values within 3.3% at depths up to 20 cm. Although the absorbed dose for water and adipose tissue are within 2% at a depth of 1.7 cm, the absorbed dose in muscle and bone can be as much as 12 to 40% lower than the absorbed dose in water. The reported studies are significant from a historical perspective and as additional validation of a new tool for patient quality assurance and as an aid in ongoing efforts to clinically implement advanced treatment techniques, such as intensity modulated neutron therapy, at the UW.

Radiotherapy in the Treatment of Primary Osteosarcoma – a Single Center Experience

Purpose

To analyze our experiences concerning radiation treatment in patients with osteosarcoma.

Materials and methods

Since 1981, 40 patients with osteosarcoma have undergone radiotherapy in Heidelberg; 3 of them were immediately lost to follow-up. Twenty patients with metastases were treated palliatively and 17 patients were treated with a curative intent.

Results

Interestingly, 14 of the 17 patients treated with a curative intent were referred to our clinic during the last 8 years, whereas the number of patients referred for palliation decreased. The mean dose applied for palliation was 47 Gy (range, 26 Gy to >70 GyE), for cure was 59 Gy (range, 45 Gy to >70 GyE). Local control until death could be achieved in 15 of the 20 palliatively treated patients, with a mean survival of 7 months after radiation. Five patients experienced local failure with symptom recurrence, and 3 of them had received doses >60 Gy. At last follow-up, 3 of the 17 curatively treated patients had experienced local recurrence. Median follow-up was 32 months (range, 3-144). Estimated 5-year overall survival and local control rates were 38% and 68%, respectively. Local disease-free survival was shorter in patients treated for recurrent, inoperable or incompletely resected tumors and doses below 60 Gy.

Conclusions

With adequate doses, long-term local control is possible even in inoperable or incompletely resected tumors. Improvements of systemic therapy and modern radiation techniques have begun to bring the possibly curative role of radiation treatment back to the fore. However, in disseminated tumors, even doses beyond 60 Gy do not guarantee local control, suggesting an extremely low radiosensitivity of certain kinds of osteosarcoma.

Neutron radiation therapy for advanced thyroid cancers

PURPOSE

The aim of this study was to review institutional outcomes for advanced thyroid cancers treated with fast neutron radiation therapy (FNRT) and photon radiation therapy (RT).

METHODS AND MATERIALS

In all, 62 consecutive patients were analyzed. Fifty-nine had stage IV disease. Twenty-three were treated with FNRT and 39 with photon RT. Median follow-up was 14 months. The primary endpoint was overall survival (OS).

RESULTS

There was no significant difference in median OS between FNRT and photon RT (26 vs 16 months; P = .49). Patients with well-differentiated histologies had superior median OS with photon RT (17 vs 69 months; P = .04). There was a nonsignificant trend toward improved OS with FNRT for medullary and anaplastic histologies.

CONCLUSIONS

Outcomes in this study are in line with historical results. There is an apparent detriment in OS with FNRT for well-differentiated histologies and a trend toward improved OS with medullary and anaplastic histologies that warrants further investigation.

The radiation response of sarcomas by histologic subtypes: a review with special emphasis given to results achieved with razoxane

Purpose. Relatively few results are available in the literature about the radiation response of unresectable sarcomas in relation to their histology. Therefore, an attempt was made to summarize the present situation. Materials and methods. This report is based on a review of the literature and the author's own experience. Adult-type soft tissue sarcomas, chondrosarcomas, and chordomas were analyzed. Radioresponse was mainly associated with the degree of tumor shrinkage, that is, objective responses. Histopathologic responses, that is, the degree of necrosis, are only discussed in relation to radiation treatment reports of soft tissue sarcomas as a group. Results. Radiation therapy alone leads to major responses in about 50% of lipo-, fibro-, leiomyo-, or chondrosarcomas. The response rate is less than 50% in malignant fibrous histiocytomas, synovial, neurogenic, and other rare soft tissue sarcomas. The response rates may increase up to 75% through the addition of radiosensitizers such as halogenated pyrimidines or razoxane, or by the use of high-LET irradiation. Angiosarcomas become clearly more responsive if biologicals, angiomodulating, and/or tubulin affinic substances are given together with radiation therapy. Razoxane is able to increase the duration and quality of responses even in difficult-to-treat tumors like chondrosarcomas or chordomas. Conclusions. The available data demonstrate that the radioresponsiveness of sarcomas is very variable and dependent on histology, kind of radiation, and various concomitantly given drugs. The rate of complete sustained remissions by radiation therapy alone or in combination with drugs is still far from satisfactory although progress has been made through the use of sensitizing agents.

Basics of particle therapy II biologic and dosimetric aspects of clinical hadron therapy

Besides photons and electrons, high-energy particles like protons, neutrons, ⁴He ions or heavier ions (C, Ne, etc) have been finding increasing applications in the treatment of radioresistant tumors and tumors located near critical structures. The main difference between photons and hadrons is their different biologic effect and depth-dose distribution. Generally speaking, protons are superior in dosimetric aspects whereas neutrons have advantages in biologic effectiveness because of the high linear energy transfer. In 1946 Robert Wilson first published the physical advantages in dose distribution of ion particles for cancer therapy. Since that time hadronic radiotherapy has been intensively studied in physics laboratories worldwide and clinical application have gradually come to fruition. Hadron therapy was made possible by the advances in accelerator technology, which increases the particles' energy high enough to place them at any depth within the patient's body. As a follow-up to the previous article Introduction to Hadrons, this review discusses certain biologic and dosimetric aspects of using protons, neutrons, and heavy charged particles for radiation therapy.

Radiotherapy for soft tissue sarcoma of the proximal lower extremity

Soft-tissue sarcoma (STS) is a histopathologically diverse group of tumors accounting for approximately 10,000 new malignancies in the US each year. The proximal lower extremity is the most common site for STS, accounting for approximately one-third of all cases. Coordinated multimodality management in the form of surgery and radiation is often critical to local control, limb preservation, and functional outcome. Based on a review of currently available Medline literature and professional experience, this paper provides an overview of the treatment of STS of the lower extremity with a particular focus on the modern role of radiotherapy.

Radiation techniques in neuro-oncology

Radiation therapy plays a critical role in the management of tumors of the brain. A variety of radiotherapy techniques have been used to treat these tumors. This review describes both classic and more recent and advanced techniques available to manage these tumors. Included is a discussion of standard two- and three-dimensional radiation, as well as intensity-modulated radiotherapy, image-guided radiation therapy, stereotactic radiosurgery, and heavy particles.

Radiation-induced pseudotumor following therapy for soft tissue sarcoma

PURPOSE

The purpose of this study was to describe the prevalence and imaging appearance of radiation induced pseudotumors in patients following radiation therapy for extremity soft tissue sarcomas.

MATERIALS AND METHODS

We retrospectively reviewed the serial magnetic resonance (MR) images of 24 patients following radiation therapy for extremity soft tissue sarcomas. A total of 208 exams were reviewed (mean, 8.7 exams per patient) and included all available studies following the start of radiation therapy. Exams were analyzed for the identification of focal signal abnormalities within the surgical bed suggesting local tumor recurrence. Histopathologic correlation was available in nine patients suspected of having local tumor recurrence. Additional information recorded included patient demographics, tumor type and location, radiation type, and dose.

RESULTS

The study group consisted of 12 men and 12 women, having an average age of 63 years (range, 39-88 years). Primary tumors were malignant fibrous histiocytoma (n = 13), leiomyosarcoma (n = 6), liposarcoma (n = 3), synovial sarcoma (n = 1), and extraskeletal chondrosarcoma (n = 1). All lesions were high-grade sarcomas, except for two myxoid liposarcomas. Average patient radiation dose was 5,658 cGy (range, 4,500-8,040 cGy). Average follow-up time was 63 months (range, 3-204 months). Focal signal abnormalities suggesting local recurrence were seen in nine (38%) patients. Three of the nine patients with these signal abnormalities were surgically proven to have radiation-induced pseudotumor. The pseudotumors developed between 11 and 61 months following the initiation of radiation therapy (mean, 38 months), with an average radiation dose of 5,527 cGy (range, 5,040-6,500 cGy). MR imaging demonstrated a relatively ill-defined ovoid focus of abnormal signal and intense heterogeneous enhancement with little or no associated mass effect.

CONCLUSION

MR imaging of radiation-induced pseudotumor typically demonstrates a relatively ill-defined ovoid mass-like focus of intense heterogeneous enhancement with little or no associated mass effect. Imaging follow-up or biopsy may be an alternative course of action to surgical re-exploration if this diagnosis is considered. The study revealed radiation-induced pseudotumor in 12.5% of patients in our extremity study group, suggesting that radiation-induced pseudotumor may be more prevalent than previously reported.

Modern radiation treatment planning and delivery--from Röntgen to real time

The field of radiation oncology has advanced exponentially since the discovery of X-rays just over 100 years ago. With the advent of three-dimensional treatment planning, the therapeutic index was increased by dose escalation and more accurate shielding of normal tissues. Now, even greater advances are under way with IMRT, image-guided radiation therapy, delineation and control of organ motion, and real-time imaging. Similarly, the use of particle therapies such as protons has the potential to effect even more accurate dose distributions. Clinical studies investigating these modalities will likely further increase the efficacy of radiation in years to come.

Radiotherapeutical innovations in pediatric solid tumors

There have been considerable technical improvements in radiation therapy for the past two decades. In children affected with cancer, these have been likely overshadowed by concommittant major chemotherapy-based advances, and at least in part ignored and misused. This article outlines principles, technological requirements, and clinical applications of innovations that aim at improving ballistical selectivity (such as conformal, intensity modulation, stereotactic photons, charged particles, and intraoperative therapies), as well as at influencing tumors and normal tissues sensitivity to radiations (such as high LET particles, and altered fractionations).

Le traitement par neutrons : hadronthérapie partie II : bases physiques et expérience clinique

Neutrons have radiobiological characteristics, which differ from those of conventional radiotherapy beams (photons) and which offer a theoretical advantage over photons to fight radioresistance by the differential relative biological effect of them between normal and tumour tissues. Neutron therapy beneficed of great interest between 1975 and 1985. Many of phase III trials were conducted and indications have been definitively deducted of them. After briefly describing the properties of neutron beams, this review discusses the indication of neutron therapy on the basis of the clinical results. Salivary, prostate tumours and sarcomas are the main indications of neutron therapy. In concern to the prostate cancers, other alternative treatments reduce the neutron therapy field. For sarcomas, the lack of randomised trials limits the impact of the interest of neutrons. For other tumours, the ratio benefice/risk of neutron therapy is inferior to these obtained with photons and they could not be considered like classical indications.

Fast neutron radiotherapy for soft tissue and cartilaginous sarcomas at high risk for local recurrence

PURPOSE

The practice policy at the University of Washington has been to employ fast neutron radiotherapy for soft tissue sarcoma lesions with prognostic features predictive for poor local control. These include gross residual disease/inoperable disease, recurrent disease, and contaminated surgical margins. Cartilaginous sarcomas have also been included in this high-risk group. This report updates and expands our previously described experience with this approach.

METHODS AND MATERIALS

Eighty-nine soft tissue sarcoma lesions in 72 patients were treated with neutron radiotherapy in our department between 1984 and 1996. Six patients, each with solitary lesions, were excluded from analysis due to lack of follow-up. Seventy-three percent were treated with fast neutron radiation alone, the rest with a combination of neutrons and photons. Median neutron dose was 18.3 nGy (range 4.8-22). Forty-two patients with solitary lesions were treated with curative intent. Thirty-one patients (including 7 previously treated with neutrons) with 41 lesions were treated with the goal of local palliation. Tumors were predominantly located in the extremity and torso. Thirty of 35 (85%) of curative group patients treated postoperatively had close or positive surgical margins. Thirty-four (82%) lesions treated for palliation were unresectable. Thirty-five patients (53%) were treated at the time of recurrence. Median tumor size at initial presentation was 8.0 cm (range 0.6-29), median treated gross disease size was 5.0 cm (range 1-22), and 46/69 evaluable lesions (67%) were judged to be of intermediate to high histologic grade. Fourteen patients (21%) had chondrosarcomas.

RESULTS

Median follow-up was 6 months (range 2-47) and 38 months (range 2-175) for the palliative and curative groups, respectively. Kaplan-Meier estimates were obtained for probability of local relapse-free survival (68%), distant disease-free survival (59%), cause-specific survival (68%), and overall survival (66%) at 4 years for the curatively treated group. For the palliatively treated group, estimated local relapse-free survival at 1 year was 62%. Log-rank analysis of the curative group revealed recurrent disease to be the only risk factor predictive for significantly worse local and distant disease-free survival. Intermediate-/high-grade histology was predictive for inferior overall survival. Effective clinical response was documented for 21/27 (78%) lesions treated palliatively. Ten patients (15%) experienced serious chronic radiation-related complications. All of these patients had clinical situations requiring delivery of high neutron doses and/or large radiotherapy fields.

CONCLUSION

Fast neutron radiotherapy is locally effective for soft tissue and cartilaginous sarcomas having well-recognized high-risk features. Results in the palliative setting appear to be particularly encouraging, with neutrons frequently providing significant symptomatic response for gross disease, with minimal serious chronic sequelae. Fast neutron radiotherapy should be considered in patients at high risk for local recurrence in both the curative and palliative settings.

A comparison of the potential therapeutic gain of p(66)/Be neutrons and d(14)/Be neutrons

PURPOSE

To determine the relationship between photon sensitivity and neutron sensitivity and between neutron RBE and photon resistance for two neutron modalities (with mean energies of 6 and 29 MeV) using human tumor cell lines spanning a wide range of radiosensitivities, the principal objective being whether or not a neutron advantage can be demonstrated.

METHODS AND MATERIALS

Eleven human tumor cell lines with mean photon inactivation doses of 1.65-4. 35 Gy were irradiated with 0-5.0 Gy of p(66)/Be neutrons (mean energy of 29 MeV) at Faure, S.A. and the same plating was irradiated on the same day with 0-10.0 Gy of Cobalt-gamma-rays. Twelve human tumor cell lines, many of which were identical with the above selection, and spanning mean photon inactivation doses of 1.75-4.08 Gy, were irradiated with 0-4 Gy of d(14)/Be neutrons (mean energy of 6 MeV) and with 0-10 Gy of 240 kVp X-rays at the Essen Klinikum. Cell survival was determined by the clonogenic assay, and data were fitted to the linear quadratic equation.

RESULTS

1. Using the mean inactivation dose, a significant correlation was found to exist between neutron sensitivity and photon sensitivity. However, this correlation was more pronounced in the Faure beam (r(2) = 0.89, p </= 0.0001) than in the Essen beam (r(2) = 0.65, p = 0.0027). 2. No significant relationship could be established between neutron RBE and photon resistance for both modalities (p = 0.69 and p = 0.07, respectively). 3. Using alpha-coefficients as a criterion, the neutron sensitivity for the Faure beam correlated with photon sensitivity (p = 0.001), but this did not apply to the Essen beam (p = 0.27). 4. The neutron RBE for the Essen beam derived from alpha-coefficients showed a steep increase with photon resistance (p = 0.003). In the Faure beam there was no increase of RBE with photon resistance (p = 0.494).

CONCLUSION

Radiobiological differences between high-energy and low-energy neutrons are particularly apparent in the dependence of the neutron RBE on photon sensitivity. The increase of RBE with photon resistance is more pronounced in the low-energy Essen neutrons than in the high-energy Faure neutrons. An RBE advantage is indicated for photon-resistant cell lines and this is particularly apparent in the low-dose range using alpha-coefficients as compared to the mean inactivation dose. The clinical application of low-energy neutrons may be more restricted because of poor penetration and lack of skin sparing. However, these neutrons discriminate better between photon-sensitive and photon-resistant cells giving an RBE range of 2-6 and a mean RBE of 4.1, than high-energy neutrons where the RBE range is 1.6-3.5 and the mean RBE is 2.4. From the radiobiological point of view it, therefore, appears that the clinical potential of low-energy neutrons is considerably underrated.

Boron neutron capture enhanced fast neutron radiotherapy for malignant gliomas and other tumors

Both fast neutron radiotherapy and boron neutron capture therapy have been investigated as new radiation treatment techniques for patients with malignant gliomas. While each of these techniques individually has shown the potential for pathological eradication of malignant glioma, to date neither has evolved into an accepted, improved method of treatment. We have recently begun a research program investigating the feasibility of combining the benefits of both types of therapy. As a fast neutron beam penetrates tissue some of the particles are degraded to thermal energies. These can be captured by 10B or other suitable isotopes resulting in a highly-localized release of additional energy during a course of fast neutron radiotherapy. In this article we will review the rationale for such an approach, and review the underlying physics as well as in vitro, in vivo, and early human studies testing its feasibility. If appropriate carrier agents can be found that preferentially-localize in tumor cells, this approach ena be applied to many different tumor systems.

Hip stiffness following mixed conformal neutron and photon radiotherapy: a dose-volume relationship

PURPOSE

To determine the relationship between dose, volume, and the incidence of hip stiffness in patients who received conformal neutron irradiation for prostate cancer.

METHODS AND MATERIALS

A series of dose-searching studies using neutron irradiation for prostate cancer were performed to determine the optimal dose, fraction size, field size, technique, and proportions of photon and neutron dose. Neutron doses ranged from 9 to 20 Gy and photon doses ranged from 0 to 38 Gy. Data were analyzed by using a hip stiffness grading scale.

RESULTS

Hip stiffness was recorded on follow-up examination in 30% of patients (40 out of 132) treated with fast neutrons or mixtures of fast neutron and photon radiation for prostate cancer. Hip stiffness was categorized as none (Grade 0, 92 patients), mild (Grade 1, 24 patients), moderate (Grade 2, 10 patients), or severe (Grade 3, 6 patients). The incidence of hip stiffness differed significantly by dose and volume in the five dose levels studied (p < 0.001).

CONCLUSIONS

By using a mixture of conformal neutron and photon irradiation and limiting the total neutron dose to less than 13 Gy, hip stiffness toxicity could be reduced to acceptable levels.

Fast neutron radiotherapy and boron neutron capture therapy: application to a human melanoma test system

Fast neutron radiotherapy has proven to be an effective form of treatment in a selected subset of tumors (salivary gland tumors, sarcomas, and locally-advanced prostate cancer), but has not proven to be more beneficial than conventional photon irradiation for the majority of tumor types upon which it has been tested. Normal tissue tolerance limits preclude simply further escalating the neutron dose. Boron neutron capture (BNC) provides a way of selectively augmenting the radiation dose to the tumor. This process is described, and cell culture and animal model data reviewed. An irradiation configuration was developed where an enhancement of 2.10(-3) for 1 microgram of 10B per gram of tissue was achieved. This is similar to the enhancement achievable in the center of a 20 x 20 cm field envisioned for future applications such as metastases in the brain. A boron concentration of 50 micrograms per gram of tumor tissue leads to a 10% increase in the delivered physical dose in this scenario. The first human test of BNC enhancement of a fast neutron radiotherapy beam using pharmacologically-acceptable doses of orally-administered, 10B-enriched, L-paraboronophenylalanine is reported. An enhancement of tumor response was demonstrated for a melanoma skin nodule test system. Boron levels achieved in blood, skin, and tumors are presented. Future research plans are discussed.

Boron neutron capture therapy: a mechanism for achieving a concomitant tumor boost in fast neutron radiotherapy

PURPOSE

For many years neutron radiation has been used to treat malignant disease both as fast neutron radiotherapy and as thermal neutron induced boron neutron capture therapy (BNCT). To date, these two approaches have been used independently of one another due to the large difference in neutron energies each employs. In this paper we discuss the potential application of BNCT to enhance the therapeutic effectiveness of a fast neutron radiotherapy beam.

METHODS AND MATERIALS

Measurements are presented for the thermal neutron component that is spontaneously developed as the University of Washington fast neutron radiotherapy beam penetrates a water phantom. The biological effect of this thermalized component on cells "tagged" with boron-10 (10B) is modeled mathematically and the expected change in cell survival calculated. The model is then extended to estimate the effect this enhanced cell killing would have for increased tumor control.

RESULTS

The basic predictions of the model on changes in cell survival are verified with in vitro measurements using the V-79 cell line. An additional factor of 10-100 in tumor cell killing appears achievable with currently available 10B carriers using our present neutron beam. A Poisson model is then used to estimate the change in tumor control this enhanced cell killing would produce in various clinical situations and the effect is sufficiently large so as to be clinically relevant. It is also demonstrated that the magnitude of the thermalized component can be increased by a factor of 2-3 with relatively simple changes in the beam generating conditions.

CONCLUSION

BNCT may provide a means of enhancing the therapeutic effectiveness of fast neutron radiotherapy in a wide variety of clinical situations and is an area of research that should be aggressively pursued.

Present results of neutron therapy. The German experience

Results of fast neutron therapy are reviewed with special reference to the main indications for this type of treatment and the experience of five German centers. Neutron therapy seems beneficial compared to conventional radiotherapy in advanced salivary gland tumors, inoperable or unresectable soft tissue sarcomas, some bone tumors, prostate cancer stage C and some rare low-grade tumors. About 3,000 patients with malignancies have been treated with neutrons at the German centers Berlin/Rossendorf, Essen, Hamburg, Heidelberg and Münster. Treatment results and treatment-related morbidity depend on the treatment techniques and the physical selectivity of the neutron machines. A critical appraisal suggests that fast neutrons are of advantage in about 5% of all radiotherapy patients.

Development of fast neutron therapy worldwide. Radiobiological, clinical and technical aspects

Radiobiological data indicate that fast neutrons could bring a benefit in the treatment of some tumour types, and suggest mechanisms through which this benefit could be achieved. However, radiobiology also clearly indicates that there is a need for patient selection as well as for a high-physical selectivity. The main difficulty when interpreting the results of neutron therapy are the poor technical conditions in which the first treatments were applied. This explains why the value and the place of neutron therapy are not universally recognized, although more than 15,000 patients have been treated so far worldwide. There are, however, clinical indications of fast neutrons bringing a benefit for the following tumour sites: salivary glands, paranasal sinuses, soft tissue sarcomas, prostatic adenocarcinomas, palliative treatment of melanoma and rectum. These tumours represent about 10-15% of all patients currently referred to the radiation therapy departments.

Enhancement of fast neutron beams with boron neutron capture therapy. A mechanism for achieving a selective, concomitant tumor boost

Both fast neutron radiotherapy and boron neutron capture therapy (BNCT) have been utilized to treat malignant disease. Herein we discuss the potential of combining these treatments to enhance the effectiveness of fast neutron therapy through a concomitant BNCT boost. Using a fast neutron beam generated from a 50 MeV proton on beryllium reaction, we have determined that 0.1% of the beam per microgram of boron-10 per gram of tissue (microgram/g) can be deposited via BNCT. Our mathematical modeling predicts that BNCT enhancement of our beam will lead to an additional 1-2 logs of tumor cell kill for boron-10 concentrations of 30-50 micrograms/g. We have validated this via V-79 cell line in vitro measurements. A Poisson model estimation of how this additional cell kill will influence local tumor control, predicts that BNCT enhancement of fast neutron radiation will lead to a clinically significant improvement in outcome.

The role of fast neutron therapy in unresectable pelvic osteosarcoma: preliminary report

Primary osteosarcoma of the pelvic bones represents less than 10% of all osteosarcoma. Despite mutilating surgical procedures or high-dose radiotherapy and neoadjuvant chemotherapy, local failures and distant metastases remain common. The 2-year actuarial survival rate is less than 50% and the disease-free survival is under 20% at 2 years. We report 4 cases of pelvic osteosarcoma treated by a combination of chemotherapy, photon beam and neutron beam radiotherapy. After a median follow-up of 24 months, all 4 patients are alive and disease free.

Osteosarcomas and adult soft tissue sarcomas: is there a place for high LET radiation therapy?

The treatment policy for non-operable or unresectable osteosarcoma and adult soft tissue sarcoma remains unclear or controversial, despite the progress achieved in multimodality treatments. The poor results obtained by radiotherapy alone led to consider these tumours as radioresistant and to use high Linear Energy Transfer (LET) particles, such as neutrons. These particles benefit from a higher Relative Biological Efficiency (RBE) and other biological properties tending to decrease radioresistance phenomenas. From the non randomized studies previously published, neutron-therapy seems to give better local control rates, compared to photons and/or electrons. But these results are not strongly convincing, due to the large heterogeneities in patient recruitment, histological types, sizes, sites and moreover to the high complication rates encountered in some studies, even if they are mainly imputable to the use of low energy machines. The use of high-energy hospital-based accelerators combined to the possibilities of accurate dose distribution offered by conformal therapy, the potential value of light ion beam therapy combining the dose distribution advantages of protons to the biological properties of high LET particles, represent the directions in which progresses might be made for further improvement of non-operable or unresectable osteosarcoma and soft tissue sarcomas treatment results.

Preliminary results in heavy charged particle irradiation of bone sarcoma

Between 1979 and 1989, 17 patients with unfavorable bone sarcoma were treated wholly or in part with heavy charged particle irradiation (helium and/or neon ions) at the University of California Lawrence Berkeley Laboratory. The majority of tumors were located near critical structures such as the spinal cord or brain. Gross tumor was present in all but two patients at the time of irradiation. Six patients were treated for recurrent disease. Histologies included osteosarcoma, Ewing's sarcoma, and recurrent osteoblastoma. Four of the osteosarcomata were believed to have been induced by previous therapeutic irradiation for various tumors. Follow-up time since initiation of radiation ranged from 7 to 118 months (median 40 months). The 5-year Kaplan-Maier local control rate was 48%; the corresponding survival rate was 41%. Over half the patients succumbed to distant metastases despite the majority of patients receiving chemotherapy. In this preliminary study, we have shown that heavy charged particle irradiation can be effectively used for control of bone sarcoma. A Phase II trial is warranted to determine optimal treatment for unresectable or gross residual disease.

Neutron therapy in Saudi Arabia: an overview and results of dose searching study in head and neck cancer

The King Faisal Specialist Hospital and Research Centre is the only center in the Middle East that incorporates a neutron therapy facility. The neutron beam is produced by a cyclotron, which produces a beam by either a (d(15)+Be) or (p(26)+Be) reaction. The beam from the proton reaction is selected for therapy because of its superior physical characteristics. These were verified by an intercomparison conducted by the European Organization for Research on Treatment of Cancer (EORTC) Heavy Particle Therapy Group. Full beam data are presented. The first study in the neutron therapy Program is on the treatment of squamous cancers of the head and neck. This consists of two parts. Part I is a dose searching phase and Part II is a comparison of our current photon treatment versus neutrons using the neutron dose selected by Part I of the study. Results of the dose searching phase (Part I) are presented.

Neon ion radiotherapy: results of the phase I/II clinical trial

Neon ion radiotherapy possesses biologic and physical advantages over megavoltage X rays. Biologically, the neon beam reduces the oxygen enhancement ratio and increases relative biological effectiveness. Cells irradiated by neon ions show less variation in cell-cycle related radiosensitivity and decreased repair of radiation injury. The physical behavior of heavy charged particles allows precise delivery of high radiation doses to tumors while minimizing irradiation of normal tissues. In 1979 a Phase I-II clinical trial was started at Lawrence Berkeley Laboratory using neon ions to irradiate patients for whom conventional treatment modalities were ineffective. By the end of 1988 a total of 239 patients had received a minimum neon physical dose of 1000 cGy (median follow-up for survivors 32 months). Compared with historical results, the 5-year actuarial disease-specific survival (DSS5) and local control (LC5) rates suggest that neon treatment improves outcome for several types of tumors: a) advanced or recurrent macroscopic salivary gland carcinomas (DSS5 59%; LC5 61%); b) paranasal sinus tumors (DSS5 69%; LC5 69% for macroscopic disease); c) advanced soft tissue sarcomas (DSS5 56%, LC5 56% for macroscopic disease); d) macroscopic sarcomas of bone (DSS5 45%; LC5 59%); e) locally advanced prostate carcinomas (DSS5 90%; LC5 75%); and f) biliary tract carcinomas (DSS5 28%; LC5 44%). Treatment of malignant gliomas, pancreatic, gastric, esophageal, lung, and advanced or recurrent head and neck cancer has been less successful; results for these tumors appear no better than those achieved with conventional x-ray therapy. These findings suggest that Phase III trials using the neon beam should be implemented for selected malignancies.