Current status of clinical particle radiotherapy at Lawrence Berkeley Laboratory

A Practical Primer on Particle Therapy

PURPOSE

Particle therapy is a promising treatment technique that is becoming more commonly used. Although proton beam therapy remains the most commonly used particle therapy, multiple other heavier ions have been used in the preclinical and clinical settings, each with its own unique properties. This practical review aims to summarize the differences between the studied particles, discussing their radiobiological and physical properties with additional review of the available clinical data.

METHODS AND MATERIALS

A search was carried out on the PubMed databases with search terms related to each particle. Relevant radiobiology, physics, and clinical studies were included. The articles were summarized to provide a practical resource for practicing clinicians.

RESULTS

A total of 113 articles and texts were included in our narrative review. Currently, proton beam therapy has the most data and is the most widely used, followed by carbon, helium, and neutrons. Although oxygen, neon, silicon, and argon have been used clinically, their future use will likely remain limited as monotherapy.

CONCLUSIONS

This review summarizes the properties of each of the clinically relevant particles. Protons, helium, and carbon will likely remain the most commonly used, although multi-ion therapy is an emerging technique.

Quasi-real-time range monitoring by in-beam PET: a case for 15O

A fast and reliable range monitoring method is required to take full advantage of the high linear energy transfer provided by therapeutic ion beams like carbon and oxygen while minimizing damage to healthy tissue due to range uncertainties. Quasi-real-time range monitoring using in-beam positron emission tomography (PET) with therapeutic beams of positron-emitters of carbon and oxygen is a promising approach. The number of implanted ions and the time required for an unambiguous range verification are decisive factors for choosing a candidate isotope. An experimental study was performed at the FRS fragment-separator of GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany, to investigate the evolution of positron annihilation activity profiles during the implantation of [Formula: see text]O and [Formula: see text]O ion beams in a PMMA phantom. The positron activity profile was imaged by a dual-panel version of a Siemens Biograph mCT PET scanner. Results from a similar experiment using ion beams of carbon positron-emitters [Formula: see text]C and [Formula: see text]C performed at the same experimental setup were used for comparison. Owing to their shorter half-lives, the number of implanted ions required for a precise positron annihilation activity peak determination is lower for [Formula: see text]C compared to [Formula: see text]C and likewise for [Formula: see text]O compared to [Formula: see text]O, but their lower production cross-sections make it difficult to produce them at therapeutically relevant intensities. With a similar production cross-section and a 10 times shorter half-life than [Formula: see text]C, [Formula: see text]O provides a faster conclusive positron annihilation activity peak position determination for a lower number of implanted ions compared to [Formula: see text]C. A figure of merit formulation was developed for the quantitative comparison of therapy-relevant positron-emitting beams in the context of quasi-real-time beam monitoring. In conclusion, this study demonstrates that among the positron emitters of carbon and oxygen, [Formula: see text]O is the most feasible candidate for quasi-real-time range monitoring by in-beam PET that can be produced at therapeutically relevant intensities. Additionally, this study demonstrated that the in-flight production and separation method can produce beams of therapeutic quality, in terms of purity, energy, and energy spread.

Precision of the PET activity range during irradiation with10C,11C, and12C beams

Objective. Beams of stable ions have been a well-established tool for radiotherapy for many decades. In the case of ion beam therapy with stable¹²C ions, the positron emitters^10,11C are produced via projectile and target fragmentation, and their decays enable visualization of the beam via positron emission tomography (PET). However, the PET activity peak matches the Bragg peak only roughly and PET counting statistics is low. These issues can be mitigated by using a short-lived positron emitter as a therapeutic beam.Approach.An experiment studying the precision of the measurement of ranges of positron-emitting carbon isotopes by means of PET has been performed at the FRS fragment-separator facility of GSI Helmholtzzentrum für Schwerionenforschung GmbH, Germany. The PET scanner used in the experiment is a dual-panel version of a Siemens Biograph mCT PET scanner.Main results.High-quality in-beam PET images and activity distributions have been measured from the in-flight produced positron emitting isotopes¹¹C and¹⁰C implanted into homogeneous PMMA phantoms. Taking advantage of the high statistics obtained in this experiment, we investigated the time evolution of the uncertainty of the range determined by means of PET during the course of irradiation, and show that the uncertainty improves with the inverse square root of the number of PET counts. The uncertainty is thus fully determined by the PET counting statistics. During the delivery of 1.6 × 10⁷ions in 4 spills for a total duration of 19.2 s, the PET activity range uncertainty for¹⁰C,¹¹C and¹²C is 0.04 mm, 0.7 mm and 1.3 mm, respectively. The gain in precision related to the PET counting statistics is thus much larger when going from¹¹C to¹⁰C than when going from¹²C to¹¹C. The much better precision for¹⁰C is due to its much shorter half-life, which, contrary to the case of¹¹C, also enables to include the in-spill data in the image formation.Significance. Our results can be used to estimate the contribution from PET counting statistics to the precision of range determination in a particular carbon therapy situation, taking into account the irradiation scenario, the required dose and the PET scanner characteristics.

Considerations for Upright Particle Therapy Patient Positioning and Associated Image Guidance

Particle therapy is a rapidly growing field in cancer therapy. Worldwide, over 100 centers are in operation, and more are currently in construction phase. The interest in particle therapy is founded in the superior target dose conformity and healthy tissue sparing achievable through the particles’ inverse depth dose profile. This physical advantage is, however, opposed by increased complexity and cost of particle therapy facilities. Particle therapy, especially with heavier ions, requires large and costly equipment to accelerate the particles to the desired treatment energy and steer the beam to the patient. A significant portion of the cost for a treatment facility is attributed to the gantry, used to enable different beam angles around the patient for optimal healthy tissue sparing. Instead of a gantry, a rotating chair positioning system paired with a fixed horizontal beam line presents a suitable cost-efficient alternative. Chair systems have been used already at the advent of particle therapy, but were soon dismissed due to increased setup uncertainty associated with the upright position stemming from the lack of dedicated image guidance systems. Recently, treatment chairs gained renewed interest due to the improvement in beam delivery, commercial availability of vertical patient CT imaging and improved image guidance systems to mitigate the problem of anatomical motion in seated treatments. In this review, economical and clinical reasons for an upright patient positioning system are discussed. Existing designs targeted for particle therapy are reviewed, and conclusions are drawn on the design and construction of chair systems and associated image guidance. Finally, the different aspects from literature are channeled into recommendations for potential upright treatment layouts, both for retrofitting and new facilities.

Roadmap: helium ion therapy

Helium ion beam therapy for the treatment of cancer was one of several developed and studied particle treatments in the 1950s, leading to clinical trials beginning in 1975 at the Lawrence Berkeley National Laboratory. The trial shutdown was followed by decades of research and clinical silence on the topic while proton and carbon ion therapy made debuts at research facilities and academic hospitals worldwide. The lack of progression in understanding the principle facets of helium ion beam therapy in terms of physics, biological and clinical findings persists today, mainly attributable to its highly limited availability. Despite this major setback, there is an increasing focus on evaluating and establishing clinical and research programs using helium ion beams, with both therapy and imaging initiatives to supplement the clinical palette of radiotherapy in the treatment of aggressive disease and sensitive clinical cases. Moreover, due its intermediate physical and radio-biological properties between proton and carbon ion beams, helium ions may provide a streamlined economic steppingstone towards an era of widespread use of different particle species in light and heavy ion therapy. With respect to the clinical proton beams, helium ions exhibit superior physical properties such as reduced lateral scattering and range straggling with higher relative biological effectiveness (RBE) and dose-weighted linear energy transfer (LET_d) ranging from ∼4 keVμm^-1to ∼40 keVμm^-1. In the frame of heavy ion therapy using carbon, oxygen or neon ions, where LET_dincreases beyond 100 keVμm^-1, helium ions exhibit similar physical attributes such as a sharp lateral penumbra, however, with reduced radio-biological uncertainties and without potentially spoiling dose distributions due to excess fragmentation of heavier ion beams, particularly for higher penetration depths. This roadmap presents an overview of the current state-of-the-art and future directions of helium ion therapy: understanding physics and improving modeling, understanding biology and improving modeling, imaging techniques using helium ions and refining and establishing clinical approaches and aims from learned experience with protons. These topics are organized and presented into three main sections, outlining current and future tasks in establishing clinical and research programs using helium ion beams-A. Physics B. Biological and C. Clinical Perspectives.

Clustered DNA Double-Strand Breaks: Biological Effects and Relevance to Cancer Radiotherapy

Cells manage to survive, thrive, and divide with high accuracy despite the constant threat of DNA damage. Cells have evolved with several systems that efficiently repair spontaneous, isolated DNA lesions with a high degree of accuracy. Ionizing radiation and a few radiomimetic chemicals can produce clustered DNA damage comprising complex arrangements of single-strand damage and DNA double-strand breaks (DSBs). There is substantial evidence that clustered DNA damage is more mutagenic and cytotoxic than isolated damage. Radiation-induced clustered DNA damage has proven difficult to study because the spectrum of induced lesions is very complex, and lesions are randomly distributed throughout the genome. Nonetheless, it is fairly well-established that radiation-induced clustered DNA damage, including non-DSB and DSB clustered lesions, are poorly repaired or fail to repair, accounting for the greater mutagenic and cytotoxic effects of clustered lesions compared to isolated lesions. High linear energy transfer (LET) charged particle radiation is more cytotoxic per unit dose than low LET radiation because high LET radiation produces more clustered DNA damage. Studies with I-SceI nuclease demonstrate that nuclease-induced DSB clusters are also cytotoxic, indicating that this cytotoxicity is independent of radiogenic lesions, including single-strand lesions and chemically "dirty" DSB ends. The poor repair of clustered DSBs at least in part reflects inhibition of canonical NHEJ by short DNA fragments. This shifts repair toward HR and perhaps alternative NHEJ, and can result in chromothripsis-mediated genome instability or cell death. These principals are important for cancer treatment by low and high LET radiation.

Overview of hadron therapy: rationales, present status and future prospects

The rationales for hadron therapy are based on the physical selectivity and biological effects of the respective beams. Fastneutron therapy began as long ago as 1938 and subsequently proton, alpha particle, heavy ion, pion and neutron capture therapy have beenused. To date it is estimated that in excess of 50000 peoplehave undergone some form of hadron therapy. In the future it isexpected that fast neutron therapy will be used for selected tumourtypes for which neutrons are known to show improved cure rates. Thefuture trends in charged particle therapy will be driven by increasingcommercialization. The future of neutron capture therapy will dependon current clinical trials with epithermal neutron beams and thedevelopment of new tumour-seeking drugs.

Two cases of orbital adenocarcinoma treated with heavy charged carbon particle irradiation

BACKGROUND

Orbital adenocarcinoma is a relatively rare, primary orbital malignant epithelial tumor, and shares the poor prognosis of orbital adenoid cystic carcinoma. We report the cases of two patients with orbital adenocarcinoma who were treated with heavy charged carbon particle irradiation and followed up for more 6 years.

METHOD

Two patients with orbital adenocarcinoma, 62 and 74 years old, received 57.6 GyE of heavy charged particle irradiation therapy.

RESULTS

In both cases, the size of the tumor gradually decreased after carbon ion irradiation therapy. No recurrences or metastasis of the tumor were found for more than 6 years.

CONCLUSION

Orbital adenocarcinoma has a poor prognosis in general. Two patients with orbital adenocarcinoma were treated with heavy charged carbon particle irradiation therapy and had a relatively good outcome and good prognosis. We believe that heavy charged carbon particle irradiation therapy is a promising therapy for orbital adenoid cystic carcinoma and adenocarcinoma.

Measurements of neutron effective doses and attenuation lengths for shielding materials at the heavy-ion medical accelerator in Chiba

The effective doses and attenuation lengths for concrete and iron were measured for the design of heavy ion facilities. Neutrons were produced through the reaction of copper, carbon, and lead bombarded by carbon ions at 230 and 400 MeV.A, neon ions at 400 and 600 MeV.A, and silicon ions at 600 and 800 MeV.A. The detectors used were a Linus and a Andersson-Braun-type rem counter and a detector based on the activation of a plastic scintillator. Representative effective dose rates (in units of 10(-8) microSv h(-1) pps(-1) at 1 m from the incident target surface, where pps means particles per second) and the attenuation lengths (in units of m) were 9.4 x 10(4), 0.46 for carbon ions at 230 MeV.A; 8.9 x 10(5), 0.48 for carbon ions at 400 MeV.A; 9.3 x 10(5), 0.48 for neon ions at 400 MeV.A; 3.8 x 10(6), 0.50 for neon ions at 600 MeV.A; 3.9 x 10(6), 0.50 for silicon ions at 600 MeV.A; and 1.1 x 10(7), 0.51 for silicon ions at 800 MeV.A. The attenuation provided by an iron plate approximately 20 cm thick (nearly equal to the attenuation length) corresponded to that of a 50-cm block of concrete in the present energy range. Miscellaneous results, such as the angular distributions of the neutron effective dose, narrow beam attenuation experiments, decay of gamma-ray doses after the bombardment of targets, doses around an irradiation room, order effects in the multi-layer (concrete and iron) shielding, the doses from different targets, the doses measured with a scintillator activation detector, the gamma-ray doses out of walls and the ratio of the response between the Andersson-Braun-type and the Linus rem counters are also reported.

Circadian rhythm modulated 5-FUdR infusion with Megace in the treatment of advanced pancreatic cancer

Thirteen patients with advanced pancreatic carcinoma were treated with circadian rhythm modulated infusion of 5-FUdR and Megace. Treatment was initiated at a dose of 0.15 mg/kg/day for 14 days every 28 days and was increased or decreased by 0.025 mg/kg/day with each subsequent cycle until maximum tolerated dose (MTD) was achieved. Megace (200 mg) was administered daily in divided doses. One-third of the patients were able to complete > or = 6 cycles of treatment, one-half could only complete < or = 2 cycles, and the remainder managed 3-4 cycles. No patients had regression of disease, but a small number, who were able to receive 6-7 months of treatment, achieved stable disease in the short term. In conclusion, treatment was fairly well tolerated. However, increased dose intensity by this method did not significantly increase response rate. In only a few patients was disease stabilized for a brief period. Megace did not materially improve nutritional status. CA-19-9 levels did not correlate well with disease activity.

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.

Reoxygenation in a rat rhabdomyosarcoma tumor following X-irradiation

The paired survival curve technique was used to characterize the rate at which the fraction of hypoxic cells in rat rhabdomyosarcoma R-1 tumors returns to the preirradiation value of 37% following a single dose of 225-kVp X rays. Tumors were administered a conditioning x-ray dose of 15-Gy, followed at 0, 3, 6, 12, 24, or 48 hr by a 5-Gy, 10-Gy, or 15-Gy dose of X rays under air-breathing conditions or under hypoxic conditions produced by nitrogen-gas asphyxiation 5 min prior to irradiation. Cellular surviving fractions were determined by the tumor excision assay following in vivo irradiation. From the ratio of the survival fractions measured for tumor cells from air-breathing and hypoxic animals, the fraction of hypoxic cells was determined as a function of time postirradiation. These results indicated that immediately following a 15-Gy dose of X rays, essentially 100% of the viable cells remaining were hypoxic. The tumors reoxygenated rapidly, returning to the preirradiation level of 37% during the first 6 hr postirradiation.

Response of rat rhabdomyosarcoma tumors to split doses of mixed high- and low-let radiation

Radiation-induced growth delay was measured in rat rhabdomyosarcoma tumors exposed to split doses of high-LET (linear energy transfer) neon ions in the extended-peak ionization region and low-LET X rays. Top-off doses of 7.5, 15, and 25 Gy of 225-kVp X rays were administered to the tumors at 0.5, 4.0, and 24.0 hr following priming doses of either peak neon ions or X rays. The priming doses used were 7 Gy of peak neon ions and 20 Gy of X rays, both of which produced a 10 day delay in tumor regrowth to a volume twice that measured on the day of irradiation. The tumor response to split doses of X rays indicated rapid repair of sublethal damage, with significant recovery occurring at 0.5 hr and complete recovery by 4 hr after the initial 20-Gy X ray dose. The top-off doses of X rays required to produce an additional 10 or 20 days of tumor growth delay were 18 and 7% larger, respectively, when the priming dose was 20 Gy of X rays as compared to 7 Gy of peak neon ions. This result indicates that relatively little interaction of the neon-ion and X ray radiations occurred, even when the time interval between split-dose irradiations was as short as 0.5 hr. Our data indicate that the interaction of high- and low-LET radiation modalities is small, and approaches a simple additivity of effects when the tumors repair a major portion of the sublethal radiation injury imparted by a priming dose before the second dose is administered.

Phase II trial of 5-fluorouracil, adriamycin and cisplatin (FAP) followed by radiation and 5-fluorouracil in locally advanced pancreatic cancer

A total of 19 patients (7 men, 12 women) with locally advanced pancreatic adenocarcinoma were treated with six cycles of FAP (5-fluorouracil, 300 mg/m2 i.v. on days 1-5; Adriamycin, 50 mg/m2 i.v. on day 1; cisplatin, 20 mg/m2 i.v. on days 1-5). Each course was repeated every 28 days. After six cycles, the treatment was followed by irradiation amounting to 4,000 cGy (split course) in combination with 5-FU (500 mg/m2) on days 1-3 of the two irradiation periods. The median age of our patients was 55 years (range, 40-64 years). The median WHO performance status was 1, with a range of 0-2. Three (16%) complete (CR) and six (31%) partial responses (PR) were observed, as were six cases of stable disease (SD) and four of progressive disease (PD). The median duration of response was 11 months, with a range of 4-24 months, and the median survival was 14 months (range, 5-27 + months). FAP toxicity was tolerated fairly poorly. The dose-limiting toxic effect was myelosuppression, with a mean WBC nadir of WHO grade 1.6 (range, 0-3) and a mean platelet count of WHO grade 1.1 (range, 0-4). Nausea and vomiting were not dose-limiting. Complete alopecia was seen in 14/19 patients. Neuropathy was mild (WHO grade 1) in seven and moderate (grade 2) in four. Irradiation in combination with 5-FU was generally well tolerated. Due to several reasons, only ten patients could be treated with all six cycles of FAP. We conclude that in future combined modality studies, irradiation should be given after three cycles of chemotherapy, and that combined modality treatment for locally advanced pancreatic cancer is feasible and warrants further testing.

Treatment of unresectable pancreatic carcinoma using irradiation with concurrent intravenous 5-FU infusion therapy

Ten patients with unresectable carcinoma of the pancreas who had only bypass surgery to relieve biliary obstruction were treated with radiation therapy to the pancreas and liver with concurrent 5-fluorouracil (5-FU) intravenous infusion therapy. Treatment regimen was three cycles of chemoradiotherapy with a two week rest period between cycles. 5-FU (1,000 mg/m2 per day) was administered by continuous infusion for the first five days of each cycle. In the first cycle radiotherapy was given to the pancreas to 2,000 cGy/10 fractions using 6 to 10 mV x-rays. In the second cycle 2,400 cGy/160 rads/fraction radiation was delivered to the pancreas and whole liver. In the third cycle, 1,600 cGy/160 rads/fraction to a total dose of 6,000 rads, was administered to the pancreatic tumor. All ten patients completed the treatments without interruption. No major side effects were noticed during the course of treatment. Survival ranged from 9 to 16 months and median survival was 11 months. Symptomatic relief was obtained in all 10 patients. One patient who lived for 16 months developed duodenal stenosis and underwent gastrojejunostomy.

Dose volume histogram analysis of liver radiation tolerance

Eleven patients with carcinoma of the pancreas or biliary system received heavy charged particle radiation treatments and whole liver heavy charged particle radiation at Lawrence Berkeley Laboratory. Doses to the whole liver ranged from 10 to 24 Gray-equivalent (the biological equivalent of 10 to 24 Gray of low-LET photon radiation), whereas the dose to the primary lesion ranged from 53.5 to 70 Gray-equivalent (GyE). The fraction size was 2 to 3 GyE. The liver received partial as well as whole organ irradiation. Integral dose volume histograms for the liver were obtained in all 11 patients. An integral dose volume histogram displays on the ordinate the percentage of liver that was irradiated in excess of the dose specified on the abcissa. In this study, the clinical liver radiation tolerance of these patients is correlated with the information contained in an integral dose volume histogram. One patient developed radiation hepatitis. The integral dose volume histogram of this patient differed from the dose volume histograms of the other 10 patients. This difference was greatest in the range of doses between 30 and 40 GyE. Our results suggest that liver doses in excess of 30 to 35 GyE should be limited to 30% of the liver or less when 18 GyE of whole liver radiation is delivered at 2 GyE per fraction in addition to primary radiation of the pancreas or biliary system.

Interstitial irradiation of skull base tumours

The rationale for interstitial irradiation of tumours in and around the skull base is reviewed, and the experience accumulated with pituitary adenomas, meningiomas, and chordomas is summarized. Intracystic irradiation for craniopharyngiomas is also reviewed.

Multimodality therapy of localized unresectable pancreatic adenocarcinoma

Eighty-eight patients with localized unresectable carcinoma of the pancreas were treated at Thomas Jefferson University Hospital between 1974 and 1981. Four treatment regimens were used which were sequential modifications of the technique based on the experience in the preceding group of patients. Each treatment changed the course of the disease, and as patterns of failure were identified, the treatment was altered to deal with them. Initially, all patients were treated with external beam radiation. Subsequently, Iodine-125 implantation was added to improve local control; low-dose preoperative radiotherapy to reduce the risk of peritoneal seeding; and adjuvant chemotherapy to reduce the risks of distant metastases. The addition of 125I implantation increased the local control from 22% to 81%, but did not increase the median survival, which was unchanged from 7 months. The addition of adjuvant chemotherapy increased the median survival from 7 months to 14 months, but had no impact on the control of the pancreatic tumor. Adjunctive chemotherapy and low-dose preoperative radiotherapy appear synergistic in reducing the risk of peritoneal seeding. The combination of 125I implantation, external beam radiation, and adjunctive chemotherapy is safe and effective. This regimen produces excellent local control with acceptable morbidity. This regimen produced a 30% survival at 18 months. The patterns of failure among these patients suggest future modifications of the technique.

Imaging by injection of accelerated radioactive particle beams

The process of imaging by detection of the annihilation gamma rays generated from positron emitters which have been injected into a patient by a particle accelerator has been studied in detail. The relationships between patient dose and injected activity have been calculated for C-11, N-13, C-15, F-17, and Ne-19 and measured for C-11 and Ne-19 with good agreement with the calculations. The requirements for imaging of the small amounts of activity that can be injected safely have been analyzed in terms of one specific application of the radioactive beam injection technique, that of Bragg peak localization in support of radiotherapy by heavy ions. The characteristics of an existing camera with sufficient sensitivity and spatial accuracy for that task are described. Results of the calculations of radioactive beam flux requirements are shown.

Interstitial iodine-125 implant in the management of unresectable pancreatic carcinoma

Eighteen patients with locally advanced adenocarcinoma of the head, body and tail of the pancreas were treated by a combination of biliary bypass, external and interstitial irradiation at Southern California Cancer Center of California Hospital Medical Center, Los Angeles, and Memorial Hospital Medical Center of Long Beach, Long Beach, CA, from July 31, 1975 to December 31, 1980. A dose of 3000 to 5000 rad was delivered to the pancreas and regional lymph nodes by external irradiation utilizing megavoltage units and 10,000 to 15,000 rad to the pancreas and metastatic lymph nodes by permanent Iodine-125 implants. In this group of 18 patients with unresectable carcinoma of the pancreas, excellent palliation of pain, jaundice and vomiting was achieved, with a median survival of 14 months.

Energy of proton accelerator necessary for treatment of choroidal melanomas

We have reviewed 94 patients with choroidal melanoma treated by proton beam therapy at the Harvard Cyclotron Laboratory. A beam penetration of f27 mm would be required to treat 90% of the lesions. We conclude that a machine energy of at least 55 and, preferably, 60 MeV would be necessary for a clinically viable therapy unit for the treatment of choroidal melanomas. An extracted beam current of 10(-9) A would be more than sufficient.

Treatment of cancer with heavy charged particles

A clinical radiotherapeutic trial using heavy charged particles in the treatment of human cancers has accrued over 400 patients since 1975, 378 of whom were treated with particles and 28 with low LET photons as control patients. Heavy charged particle radiotherapy offers the potential advantages of improved dose localization and/or enhanced biologic effect, depending on particle selected for treatment. Target sites have included selected head and neck tumors, ocular melanomata, malignant gliomata of the brain, carcinoma of the esophagus, carcinoma of the stomach, carcinoma of the pancreas, selected juxtaspinal tumors and other locally advanced, unresectable tumors. A Phase III prospective clinical trial has been started in carcinoma of the pancreas using helium ions. Phase I-II studies are underway with heavier particles such as carbon, neon and argon ions in order to prepare for prospective Phase III trials. Silicon ions are also under consideration for clinical trial. These studies are supported by the United States Department of Energy and National Institutes of Health.