Megavoltage Radiation Research Articles

Sclerosing Postirradiation Panniculitis

Sclerosing postirradiation panniculitis is an unusual variant of panniculitis that appears as a complication of megavoltage radiotherapy. Most patient are women with a history of breast cancer who develop nodular lesions on the anterior chest skin several months after receiving megavoltage therapy for breast carcinoma. Sclerosing postirradiation panniculitis is an unusual cutaneous complication of megavoltage radiotherapy that should be distinguished from subcutaneous metastatic disease, cellulitis, and connective tissue diseases involving the subcutaneous fat. The differential diagnosis can be established on the basis of the characteristic histopathologic features.

The Potential Clinical Advantages of Charged Particle Radiotherapy using Protons or Light Ions

The increasing use of charged particle radiotherapy (CPT) in many countries will require British oncologists to establish their personal viewpoints on this subject in order to advise their patients regarding the merits or otherwise of obtaining such treatment abroad. This paper covers the advantages and some disadvantages of CPT in many anatomical locations on the basis of the achievable dose distributions as a consequence of the Bragg peak effect. The advantages in terms of normal tissue effects should follow the reduction of tissue volumes exposed to low/moderate dose: significant reductions in acute tissue effects are expected and experienced. For late reacting tissues, the predicted benefits are in the reduction of chronic low-grade symptoms and so improving the quality of life. For tumour control, dose escalation beyond what is achievable with X-ray therapy is possible only for some tumour types. Also, some tumours not presently treated by X-rays can be treated by CPT instead of radical surgery. Many of the available publications about CPT are at ‘proof of principle’ stage, as the treatment technique continues to be optimised: this is a similar situation to mega-voltage radiotherapy around 50 years ago. Oncologists in the UK need to familiarise themselves with CPT dose distributions, continually educate themselves by following the results of clinical studies as these emerge with time and hopefully visit CPT centres for direct experience.

Visual sensations during megavoltage radiotherapy to the orbit attributable to Cherenkov radiation

During megavoltage photon and electron beam radiotherapy treatment involving the eye, patients commonly report visual sensations; "nerve stimulation" is the conventional explanation. We propose that the phenomenon can be attributed to Cherenkov radiation inside the eye. The threshold electron energy for Cherenkov radiation in water is 260 keV. The human retina is able to perceive approximately 5-14 visible photons in 0.001 s. A single 500 keV electron traversing 1 mm of water will induce nearly 15 Cherenkov visible range photons. We propose that a portal image involving the eye will produce sufficient Cherenkov radiation to be detected by the retina.

Local irradiation in combination with bevacizumab enhances radiation control of bone destruction and cancer‐induced pain in a model of bone metastases

Skeletal metastases are a major source of morbidity for cancer patients. The purpose of this study was to evaluate the effects of megavoltage irradiation and antiangiogenic therapy on metastatic bone cancer. A tumor xenograft model was prepared in C3H/Scid mice using 4T1 murine breast carcinoma cells. Twenty-eight mice bearing tumors were treated with either bevacizumab (15 mg/kg), local megavoltage irradiation (30 Gy in 1 fraction), combination of bevacizumab and local megavoltage irradiation or physiologic saline solution (control group). Tumor area, bone destruction, tumor microvessel density, pain-associated behaviors and expression of substance P were assessed. Combined modality treatment reduced the frequency of pain-associated behaviors, decreased levels of nociceptive protein expression in the spinal cord, maintained cortical integrity and decreased the density of microvessels as compared to single modality treatments. We conclude that concurrent antiangiogenic therapy and localized radiotherapy for the treatment of bone metastases warrants further evaluation in human clinical trials.

Nasopharyngeal Cancer: Advances in Radiotherapy

Nasopharyngeal Cancer: Advances in Radiotherapy

RESPONSE OF NINETEEN CATS WITH NASAL LYMPHOMA TO RADIATION THERAPY AND CHEMOTHERAPY

The records of 19 cats treated for stage I nasal lymphoma with radiation therapy and chemotherapy were reviewed to determine response to therapy, treatment outcome and possible prognostic indicators. All cats were treated with megavoltage radiation therapy to a total dose ranging from 22 to 48 Gy (median dose = 42 Gy). All cats were prescribed at least 6 months of multiagent chemotherapy. The median progression-free interval for all cats was 945 days (31 months). Two cats did not achieve clinical remission. Of 17 cats evaluable for relapse, 10 (58.8%) were progression free during the entire follow-up period. Four cats (23.5%) suffered local recurrence, while three (17.6%) experienced distant relapse. The median survival time was 955 days (31.4 months). The only variable found to have a significant negative impact on survival was destruction of the cribriform plate before therapy (P= 0.002). The long progression free and survival times reported here indicate that cats with stage I nasal lymphoma treated with aggressive local and systemic therapy can have a favorable outcome when compared with other anatomic forms of lymphoma. Despite strong clinical responses to the multimodality therapy used, the fact that three (17.6%) cats relapsed distantly supports the recommendation that treatment with radiation therapy alone is insufficient until further prospective studies can be performed.

Locoregional control significantly reduces the risk of subsequent distant metastases in patients with locally advanced breast cancer managed with radiotherapy as the primary locoregional treatment

11076 Background: The treatment results of patients with locally advanced breast cancer still remain far from satisfactory. Both lack of locoregional control and distant metastases remain the most common pattern of failuire. The aim of this study was to evaluate whether achieving locoregional control decreases the subsequent risk of distant metastases a large series of consecutive locally advanced breast cancer patients managed with radiotherapy as the primary locoregional treatment. Methods: The records of 261 primarily inoperable locally advanced breast cancer patients treated between 1991 and 1997 at two institutions: Medical University of Gdansk, Poland and Velindre NHS Trust, Cardiff, UK were analysed. All patients received megavoltage radiotherapy to the breast with two tangential fields, and the adjacent lymph node areas were irradiated using customised fields. In 241 patients radiotherapy constituted the only local treatment and the remaining 20 patients were subsequently subjected to mastectomy. Most patients received chemotherapy and/or endocrine therapy prior or after radiation therapy. Results: Follow-up ranged from 6 to 133 months (median 37 months). Five- year overall survival was 36% (95%CI: 28–43%) and 5-year loco-regional relapse-free survival was 48% (95%CI: 40–57%). Recurrence occurred in 167 patients (67%), including local recurence in 30 patients (12%), distant metastases - in 72 patients (27%) and both distant and local recurrence - in 65 patients (26%). Median time to distant metastases was significantly shorter among a subgroup of patients who presented locoregional failuire - 33 months as compared to patients who were free of locoregional recurrence or progression before presenting distant metastases-43 months (p<0.05) Conclusions: This study demonstrated that treatment results in patients with locally advanced breast cancer are still far from satisfactory. However it confirmed the importance of putting much effort in achieving locoregional control in that group of patients as it significantly reduces the risk of subsequent distant metastases. No significant financial relationships to disclose.

Évolution de la radiothérapie externe et intégration à l’hôpital Tenon (AP-HP) des innovations technologiques récentes dans la pratique de la radiothérapie externe des carcinomes bronchiques non à petites cellules

Much progress has been made in recent years in administration modalities for external radiotherapy of non-small-cell lung carcinoma. Three-dimensional conformal radiotherapy with or without intensity modulation, with respiratory gated radio-therapy (4D radiotherapy), and image-guided radiotherapy (IGRT) can be considered as a third revolution in radiation therapy after total dose fractionation and the development of megavoltage radiation therapy equipment. We describe progress in the three-dimensional radiotherapy technique and the integration of this technique in the department of Radiation Oncology at Tenon hospital (AP-HP).

SU‐FF‐T‐16: A Linear Programming Model and Solution for Radiation Shielding Design of Radiotherapy Treatment Vaults

Purpose: To optimize shielding material combinations and thicknesses for megavoltage radiotherapy accelerator vaults for any photon energy using linear programming by minimizing the costs of shielding materials while satisfying the constraints pertaining to regulatory doses and available space. Methods: Radiotherapy accelerator vault construction usually requires an experienced physicist to design the appropriate thicknesses of concrete, steel or lead to satisfy the regulatory limiting doses, available thicknesses for shielding and the budget allocated for the project. We have developed a model and solution using linear programming that minimizes the costs of the shielding materials while satisfying regulatory dose limits and space available for the project. The model considers primary, leakage and scatter x‐ray radiation and neutron contamination using calculation techniques as in NCRP 151. The optimization routine will insert the required tenth value layers (TVLs) of steel or lead depending on the demands and the cost of these materials. The optimization considers neutron contamination as well. We discuss a parameterized version of the model that is never infeasible and which allows the user to weight the space versus cost according user preference. Results: The results of the linear program can be easily checked for correctness using standard calculation techniques. If there is abundant space for the wall thickness, concrete only is the result of the optimization since it has the lowest cost. If the allowed wall thickness is too small for concrete only, the optimization will return combinations of concrete, steel or lead such that all constraints are satisfied and costs are minimized. Existing thicknesses of concrete, for example, are easily incorporated into the model as are special requirements for IMRT. Conclusion: The linear program returns reliable, viable and optimized shielding thicknesses of concrete, steel and lead for primary barriers as well as for leakage and scatter radiation barriers.

TU‐C‐AUD‐01: Visual Sensations During Megavoltage Radiotherapy to the Orbit Attributable to Cherenkov Radiation

Purpose: To compute and to verify experimentally Cherenkov radiation production inside the eye from direct and indirect high energy x‐ray irradiation of the orbit and that it exceeds detectability of Cherenkov radiation in scotopic vision. We show that the Cherenkov yield for direct and indirect irradiation exceeds the detection threshold of 6.4×107 photons/m2s. Methods: In photon and electron beam radiotherapy of intraorbital and periorbital tissues, patients commonly report having light sensations during treatment. The explanation usually offered is that ‘nerve stimulation’ is occurring. The radiotherapy literature reports the effect to be the result of ‘phosphenes’. Although phosphenes may play a role, we propose instead that patients are predominantly seeing Cherenkov radiation resulting from electrons inside the eye having kinetic energy exceeding the Cherenkov radiation threshold of 0.26 MeV. We consider calculations for direct irradiation of the eye from a portal image and indirect irradiation from treatment of peri‐orbital tissues and show that it exceeds threshold detection. Results: We calculate the Cherenkov yield using analytic methods and the measurements were in good agreement with our calculations. The Cherenkov radiation from a distilled water phantom, a square plastic phantom and an anthropomorphic plastic phantom were readily visible with a high quality CCD video camera. A digital camera captures the images from the console monitor. Threshold detection of Cherenkov radiation emanating from the water phantom through the video camera was determined and compared to a measurable source. The calculations for the water phantom match reasonably well with measurements and are roughly 1 lux and 3 lux respectively. Conclusion: We show images of Cherenkov radiation emanating from routine radiotherapy treatments and demonstrate that measurements corresponding to these images match well with calculations. We show that the Cherenkov component generated inside ocular media is sufficient to be detected by the patient.

SU‐FF‐T‐03: 3D Characterization of Small Megavoltage Radiation Fields Using An Optical CT Scanner with Ferrous Xylenol Orange Gels

Purpose: To investigate the feasibility of using a 3D dosimetry system consisting of a radiochromic ferrous xylenol orange (FX) gel and a prototype commercial cone beam optical‐CT scanning system (Vista™, Modus Medical Devices, Inc., London, ON) to dosimetrially characterize small megavoltage photon fields. Method and Materials: An FXG gel was irradiated using 6MV x‐ray fields (30, 10 and 5mm diameter) produced via custom stereotactic collimators mounted on a Varian Clinac 2100EX accelerator. Measurements were also completed using radiochromic (Gafchromic EBT) and radiographic (Kodak EDR2) film, and a Exradin #a1SL ion chamber for comparison purposes. The gel was optically CT scanned 10, 20, 30 and 40 minutes post‐irradiation to assess the effects of xylenol orange/ferric ion complex diffusion in gel. Lateral dose profiles and percentage depth dose (PDD) curves were extracted from the 3D image data sets for analysis. Results: FX gels together with fast optical CT scanning allows for the measurement of all dosimetric parameters required as pencil beam input for treatment planning systems in a single irradiation. The experimental set‐up is simple, and the gel allows for dose measurements in a tissue‐equivalent and energy‐independent medium. Lateral beam profiles as measured in the FXG gel matched those measured using both types of film within 2 mm. PDD curves measured with gel and ion chamber were also in good agreement (within 3 mm) up to 65mm depth. Conclusion: The radiochromic FX gel and fast optical CT scanner is a promising dosimetry system for the characterization of small x‐ray fields for the purposes of commissioning treatment planning systems. The advantage is that a full 3D data set can be acquired quickly and efficiently. Conflict of Interest: Two of the authors (KJ and JB) have a licensing agreement with Modus Medical Devices, Inc. for the commercialization of the Vista™ scanner.

TU‐EE‐A3‐03: Performing Concurrent Kilovoltage Imaging While Delivering Megavoltage Treatment Beams

Purpose: To investigate the clinical feasibility of performing concurrent kilovoltage (kV) x‐ray imaging while the patient at the treatment position was irradiated by megavoltage (MV) beams. Method and Materials: Anatomical visibility and contrast details in kV images acquired with and without concurrent MV irradiations were compared. An on‐board imager (OBI) mounted to the gantry of a Varian 21EX Linac with an electronic portal imager (EPI) was used in this study. A pelvis (Rando) and a contrast (Vegas) phantoms were placed near the treatment isocenter with a detector‐to‐isocenter distance of 50 cm. The effect of MV beam and its dose rate on noise‐to‐signal ratio (NSR), defined as the ratio of the standard deviation to the mean pixel value in a region‐of‐interest (ROI), and relative contrast, defined as the ratio of mean pixel values between the signal ROI and the background ROI, were studied based on Vegas phantom. Results: Scattering MV beams and electronic noises due to kV detector scanning rate and MV beam pulse rate are two major factors affect the concurrent kV image quality. The calculated NSR increases as dose rate increases. Compared to kV images without concurrent MV irradiation, the NSRs of the contrast phantom were increased by a factor of 2.6 with 300MU/min MV beams and 4.5 with 600MU/min MV beams. However, the relative contrasts were increased by a factor of 1.02 with 300MU/min MV beam and 1.06 with 600MU/min MV beam. Conclusion: It is clinically feasible to acquire concurrent kV images during treatment with MV beams. The kV image quality may be improved by minimizing MV scattering effect and by correcting electronic noises. The ability to take kV images with concurrent MV irradiation allows real‐time verification and tracking of moving target during the gated treatment.Partially supported by a research grant from Varian Medical Systems.

Retrospective analysis of role of interstitial brachytherapy using template (MUPIT) in locally advanced gynecological malignancies

The aim of this retrospective study was to assess treatment outcomes for patients with locally advanced gynecological malignancies being treated with interstitial brachytherapy using Martinez universal perineal interstitial template (MUPIT) and to study the acute and late sequelae and survival after treatment by this technique. Ninety seven patients untreated with histopathological confirmation of carcinoma of cervix (37) vault (40) and vagina (20) were treated by combination of external beam RT (EBRT) using megavoltage irradiation to pelvis to dose of 4000-5000 cGy followed by interstitial brachytherapy using MUPIT between September 2001 to March 2005. Median age was 46 years. Only those patients who were found unsuitable for conventional brachytherapy or in whom intracavitatory radiotherapy was found to be unlikely to encompass a proper dose distribution were treated by interstitial template brachytherapy using MUPIT application and were enrolled in this study. The dose of MUPIT was 1600-2400 cGy in 4-6# with 400 cGy/# and two fractions a day with minimum gap of six hours in between two fractions on micro-HDR. Criteria for inclusion of patients were as follows: Hb minimum 10 gm/dl, performance status--70% or more (Karnofsy scale), histopathological confirmation FIGO stage IIB-IIIB (excluding frozen pelvis). Among the 97 patients studied, 12 patients lost to follow-up and hence they were excluded from the study. Follow-up of rest of the patients was then done up to September 2006. The duration of follow-up was in the range of 20-60 months. Parameters studied were local control rate, complication rate, mortality rate and number of patients developing systemic metastasis. Local control was achieved in 56/85 (64.7%) and complication rate was 15/85 (17.6%). Local control was better for nonbulky tumors compared bulky tumors irrespective of stage of disease. Local control was better in patients with good regression of disease after external beam radiotherapy. Time of gap between EBRT and implant also had an impact on the outcome. Interstitial template brachytherapy by MUPIT is a good alternative to deliver high dose radiation in locally advanced gynecological malignancies where conventional brachytherapy application is either not feasible or likely to give optimal dose distribution. Loco regional control obtained is definitely better than EBRT alone and within the accepted range of complications.

Multicentric epithelioid angiosarcoma of the spine: a case report of a rare bone tumor

Background context Epithelioid angiosarcoma (EA) is a high-grade sarcoma of vascular origin. EA is a rare variant of angiosarcoma. It is characterized by large cells with an epethelioid morphology. EA has been reported in sites like skin thyroid, adrenal gland, soft tissue, and rarely in bone. Purpose The current article describes a case of multicentric EA of the spine that presented simultaneously at T4 spine and the posterior one third of the left fourth rib. Study design/settings This study included a patient with a rare spinal tumor, which presented insidiously. Radiologically, the lesions were osteolytic with erosion of cortices. The tumor was composed of nests and cords of malignant cells with epithelioid morphology with areas of vascular differentiation, necrosis, and hemorrhage. Anastomosing vascular spaces lined by epithelioid endothelial cells suggested focal endotheliod differentiation. Methods Histopathological evaluation of the tumor obtained from en bloc resection of the fourth rib and specimen from decompression of the fourth thoracic vertebra was done. Immunohistochemistry showed positivity for endothelioid cell markers like CD31 and factor VIII related antigen. The authors point out the need for immunohistochemical evaluation after careful histological analysis for vascular differentiation for an accurate diagnosis of vascular bone tumors with epithelioid features so that an erroneous diagnosis of metastatic carcinoma can be avoided. EA occurs rarely in bone. EA is marked by the presence of large polygonal epithelioid malignant cells with marked cellular atypia and pleomorphism. The arrangement of the cells may mimic epithelial neoplasm. These types of lesions are a definite diagnostic challenge in bone biopsy. The tumor was treated with en bloc resection of the rib and decompression of the body of T4 spine, followed by megavoltage radiotherapy. Follow-up X-rays showed regression of the tumor at 2 years. CD31 is the most sensitive marker for EA. Even in the absence of obvious vascular differentiation, abundant intratumoral hemorrhage and intratumoral neutrophils are definite morphologic changes that should suggest a vascular origin. Results The patient was followed up for 2 years. A conservative surgical approach with a radical course of megavoltage radiotherapy could yield a good result in EA of bone. At the time of writing this report, there is no evidence of tumor recurrence. Conclusion It is important to differentiate EA from other tumors because the clinical course and treatment are specific for these conditions. Careful histologic and immunohistochemical analysis will clinch the diagnosis. Even though rare, we stress the importance to be aware of the existence of this tumor, which is essential for correct diagnosis.

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Dosimetric characteristics of a newly designed GRID block for megavoltage radiotherapy were investigated using TLD, film, and ionization chamber. Therapeutic advantage for this treatment modality was calculated using a linear quadratic model. Efficacy was assessed for three different GRID designs of aperture size, pattern, and spacing and tissue radiosensitiviy.

External-beam radiotherapy for localized extrahepatic cholangiocarcinoma

The role of radiation therapy (RT) in extrahepatic cholangiocarcinoma (EHCC) is not clear and only limited reports exist on the use of this modality. We have reviewed our institutional experience to determine the pattern of failure in patients after potentially curative resection and the expected outcomes after adjuvant RT and in unresectable patients. After institutional review board approval, 81 patients diagnosed with EHCC (gallbladder 28, distal bile duct 24, hilar 29) between June 1986 and December 2004 were identified and their records reviewed. Twenty-eight patients (35%) underwent potentially curative resection with R0/R1 margins. Fifty-two patients (64%) were unresectable or underwent resection with macroscopic residual disease (R2). All patients received three-dimensional planned megavoltage RT. The dose for each patient was converted to the equivalent total dose in a 2 Gy/fraction, using the linear-quadratic formalism and alpha/beta ratio of 10. The median dose delivered was 58.4 Gy (range, 23-88.2 Gy). 54% received concomitant chemotherapy. With a median follow-up time of 1.2 years (range, 0.1-9.8 years) 75 patients (93%) have died. Median overall survival (OS) and progression-free survival (PFS) were 14.7 (95% CI, 13.1-16.3) and 11 (95% CI, 7.6-13.2) months, respectively. There was no difference among the three disease sites in OS (p = 0.70) or PFS (p = 0.80). Complete resection (R0) was the only predictive factor significantly associated with increase in both OS and PFS (p = 0.002), and there was no difference in outcomes between R1 and R2 resections. The first site of failure was predominantly locoregional (68.8% of all failures). Local failure is a major problem in EHCC, suggesting the need for more intense radiation schedules and better radiosensitizing strategies. Because R1 resection appears to convey no benefit, it appears that surgery should be contemplated only when an R0 resection is likely. Borderline-resectable patients might be better served by neoadjuvant therapy.

Radiation Therapy for Chronic Vesicular Hand Dermatitis

Chronic vesicular hand dermatitis is a chronic disease that can be debilitating for patients, and many treatment options do not provide lasting remission. We attempted to determine the efficacy of megavoltage irradiation in the treatment of this disease. Between July 2001 and March 2005, 9 patients with severe chronic vesicular hand dermatitis had megavoltage radiation therapy to their sites of disease. Eight pairs of hands and seven pairs of feet were irradiated (15 total sites). All patients had an improvement in their disease during the course of radiation therapy. Patients were followed after radiation therapy for a median follow-up time of 20.2 months (range, 1 to 45 months). The disease completely resolved in 7 of the 15 (47%) sites irradiated. There was a decrease in the severity or frequency of flare-ups at the other 8 sites (53%). Megavoltage radiation therapy may be effective in the treatment of chronic vesicular hand dermatitis and may provide durable remissions in some patients.

Giant Cell Tumor of the Petrous Temporal Bone with Direct Invasion into the Middle Ear

Giant cell tumor (GCT) is an uncommon primary bone tumor. The GCT mostly involves the extremity long bones. Rare is a GCT with tumoral growth in the cranium, especially other than the sphenoid bone. We herein report a 31-year-old male patient presenting with ipsilateral hearing loss and episodes of vertigo due to a large lobulated GCT of the right petrous temporal bone extending into the contiguous middle cranial fossa, infratemporal space, middle ear and external ear canal. He was treated with a macroscopically radical tumor excision followed by conventional megavoltage radiotherapy. The patient remains free of clinical and radiological evidences of tumoral recurrence six years after treatment. This experience supports the rationale for the combined treatment with radical excision plus irradiation toward this rare neoplasm when vigorous invasion of the skull base is encountered.

SU‐FF‐T‐357: Physical and Biological Characteristics of Megavoltage Grid Radiation Therapy

Purpose: Dosimetric characteristics of a newly designed GRID block for megavoltage radiotherapy were investigated using TLD, film, and ionization chamber. Therapeutic advantage of this treatment modality was determined using a linear quadratic model in terms of treatment dose, GRID hole size, center‐to‐center spacing between the holes, and sensitivity of tissues to radiation. Method and Materials: Recently a newly redesigned GRID block has been introduced by Radiation Product Design, Inc. for different linear accelerators. Dosimetric characteristics (i.e. GRID output, dose profiles, and %DD) of three GRID blocks with different hole size and spacing were experimentally investigated. These GRID blocks were designed for a Varian 21EX linear accelerator. The measurements were performed using radiographic films and thermoluminescent dosimeters (TLDs) in Solid Water™ phantom materials and an ionization chamber in water. The measured dose profiles were then utilized to evaluate the therapeutic advantage of the GRID therapy as a function of dose, grid hole size and spacing, and also radiosensitivity of tissues with a linear‐quadratic (LQ) model. Therapeutic advantage of these GRID blocks was determined for a single fraction dose of up to 30 Gy. Results: Dosimetric characteristics of the GRID field were determined as a function of field size, beam energy, and Grid geometry. The results had shown that the therapeutic advantage of GRID increases by increasing the hole size, decreasing the spacing between the holes, and increasing the treatment dose. Moreover, the advantage of the GRID therapy was more pronounced for the radioresistant cells than radiosensitive cells. Conclusion: GRID radiotherapy exhibited a significant therapeutic advantage over the open field radiotherapy when the tumor cells were more radioresistant than normal cells. In addition, the therapeutic advantage of the GRID therapy is dependent on the treatment dose, GRID hole size and spacing between the holes.

The Changing Structure of Radiation Oncology: Implications for the Era of Managed Care.

This report presents results from the facilities surveys that are useful for radiation oncology practices facing the challenges of managed care. Facilities surveys collect data from the entire census of facilities practicing megavoltage radiation therapy. Data include equipment, personnel, and patient load. The data presented show that most, but not all, facilities throughout the United States are adequately equipped in terms of highest energy treatment machine, type of treatment planning computer, simulation, and quality assurance programs. The data also present the variation in percentage of new cancer cases receiving radiation therapy and repeat patients as a percentage of new radiation therapy cases by census region. The data show trends in patient load per type of personnel for academic, hospital-based, and freestanding facilities in 1994 show that academic facilities are larger and treat more patients per treatment machine. Academic facilities used more therapists per machine than other facilities.