Computed tomography in radiation therapy (report of the Committee on Radiation Oncology Studies Subcommittee on CT Scanning and Radiation Therapy)

High-dose conformal radiotherapy influenced the pattern of failure but did not improve survival in glioblastoma multiforme

BACKGROUND AND PURPOSE

Although glioblastoma multiforme is clearly radiation-resistant, there is evidence of a dose-dependent response relationship. The purpose of the study was to evaluate the impact of higher dose by rotational multileaf collimator (MLC) conformal radiation therapy.

MATERIALS AND METHODS

From 1984 to 1995, 38 consecutive cases with intracranial glioblastoma multiforme were treated using the rotational MLC conformal therapy. There were 25 men and 13 women with a median age of 47 years (12-73 years, mean 46.5 years). Median Karnofsky performance score was 80 (30-100, mean 78.2). Median tumor volume was 64 cc (8-800 cc, mean 110.3 cc). All underwent surgical intervention (only biopsy in 1, partial resection in 13, subtotal resection in 21, and gross total resection in 3). Radiation dose to was 60 to 80 Gy (median 68.5 Gy, mean 68.3 Gy) in 21 patients treated before 1990 and 90 Gy in the 17 patients thereafter. Biweekly i.v. chemotherapy was also administered for both arms.

RESULTS

The 1-year, 2-year, 5-year, and 10-year overall survival rates were 75%, 42%, 20%, and 15%, respectively. Univariate analysis showed the initial tumor volume, residual tumor volume, and Karnofsky performance score were statistically significant factors for survival. Only the residual tumor volume was statistically significant by multivariate analysis. The 5-year survival rate of patients with residual tumors of 5 cc or less in volume was as good as 37%. Survival of the 90-Gy Group appeared inferior to that of the Low-Dose Group, though no statistical difference was seen (the 3-year survival was 40% vs. 22%). Local failure was observed in 16 of the 19 recurrences in the Low-Dose Group, whereas it was observed in only 4 of the 13 recurrences in the 90-Gy Group. The difference in pattern of failure was statistically significant. Two patients of the High-Dose Group developed radiation necrosis and one died of it.

CONCLUSIONS

The high-dose conformal radiotherapy did not improve survival in the disease, but did change the pattern of failure.

Review of the curative role of radiotherapy in the treatment of non-small cell lung cancer

The present paper is a comprehensive review of available data concerning the role of radiotherapy as an intended curative treatment in patients with non-small cell lung cancer (NSCL). The following issues are reviewed (1) optimal dose, (2) optimal fractionation, (3) optimal treatment planning, (4) clinical results in terms of single treatment and combined treatment with either surgery or chemotherapy. In resectable NSCLC high dose radiotherapy to small localized tumours gives a 5-year survival rate of 7-38%. It is concluded that this treatment modality is appropriate for certain selected patients who refuse to have surgery, who have medical contradications for surgery, or who are of old age. It is discussed whether the treatment should be split course, continuous, hypo-og hyperfraction. A total dose of 55 Gy must be given. CT scanning should be mandatory for optimal planning and therapy. The literature does not give a conclusive answer to whether preoperative or postoperative radiotherapy is indicated. The data indicate that patients with Stage III NSCLC will benefit from a combined treatment modality in terms of chemotherapy based on high dose cisplatinum and radiotherapy. The main conclusion of the review is that many areas with randomized controlled trials are needed in order to answer the critical issue of the role of radiotherapy in the treatment of NSCLS.

Cost accounting in radiation oncology: a computer-based model for reimbursement

PURPOSE

The skyrocketing cost of medical care in the United States has resulted in multiple efforts in cost containment. The present work offers a rational computer-based cost accounting approach to determine the actual use of resources in providing a specific service in a radiation oncology center.

METHODS AND MATERIALS

A procedure-level cost accounting system was developed by using recorded information on actual time and effort spent by individual staff members performing various radiation oncology procedures, and analyzing direct and indirect costs related to staffing (labor), facilities and equipment, supplies, etc. Expenditures were classified as direct or indirect and fixed or variable. A relative value unit was generated to allocate specific cost factors to each procedure.

RESULTS

Different costs per procedure were identified according to complexity. Whereas there was no significant difference in the treatment time between low-energy (4 and 6 MV) or high-energy (18 MV) accelerators, there were significantly higher costs identified in the operation of a high-energy linear accelerator, a reflection of initial equipment investment, quality assurance and calibration procedures, maintenance costs, service contract, and replacement parts. Utilization of resources was related to the complexity of the procedures performed and whether the treatments were delivered to inpatients or outpatients. In analyzing time motion for physicians and other staff, it was apparent that a greater effort must be made to train the staff to accurately record all times involved in a given procedure, and it is strongly recommended that each institution perform its own time motion studies to more accurately determine operating costs. Sixty-six percent of our facility's global costs were for labor, 20% for other operating expenses, 10% for space, and 4% for equipment. Significant differences were noted in the cost allocation for professional or technical functions, as labor, space, and equipment costs are higher in the latter. External beam treatment-related procedures accounted for more than 50% of all technical and professional revenues, simulation for 8% to 10%, and other physics/dosimetry procedures for 11% to 14% of revenues. Some discrepancies were identified between the actual cost and level of reimbursement of various procedures. Details are described in the manuscript.

CONCLUSION

It is imperative to develop an equitable reimbursement system for radiation oncology services, based on cost accounting and other measures that may enhance productivity and reduce the cost per procedure unit, while at the same time preserving the highest quality of service provided to patients.

A simple method for use in QC of CT for radiation therapy treatment planning

A simple procedure for monitoring constancy of spatial measurement and CT number determination from CT images used in radiation therapy treatment planning is described. The procedure uses low-Z material rods glued to the underside of the CT table insert and does not require a special phantom. Measurements are made on the same patient images used for treatment planning. Deviations from predetermined baseline values outside quality control limits of +/- 2 mm in spatial resolution and +/- 20 CT numbers in density can be detected with a confidence level of 97% or better.

MRI treatment planning for CNS neoplasm: graphic display of target volume using boxed cursor

Treatment planning systems are now capable of interfacing with MRI units, however, reconstructing images in multiple planes remains a laborious process. We have described the construction of contrast markers used with MRI imaging to determine the isocenter coordinates of preplanned CNS treatment fields. Currently existing software was then used to reconstruct the patients target volume by centering a box cursor of appropriate size over the predetermined coordinate representing isocenter. Off axis views of the target volume were easily reconstructed, as were images in the coronal and axial planes. The box cursor technique was useful in making modifications to field placement and field size.

Dose to the cardiac vascular and conduction systems in primary breast irradiation

Using computerized tomography (CT) in which cardiac anatomy was defined, doses delivered to the cardiac compartments, vascular and conduction systems were assessed for various standard techniques of primary breast irradiation. Included in the analysis were 6 MV photon tangents (T) alone, or in conjunction with a separate internal mammary field (IMF). Beams evaluated in the IMF were 6 MV photons, 12 MeV electron beam, and mixed photon/electron beam; Cobalt 60 was also analyzed as an alternate photon beam. Treatment of the IMF with photons, either alone or in combination with electron beam, delivered doses ranging between 30 Gy to 50 Gy to all chambers of the heart, coronary arteries and branches of the conduction system. Complete sparing of the posterior cardiac structures and volume is accomplished with treatment plans using tangents alone or in combination with 12 MeV electron beam irradiation to the IMF. Sparing of the anterior wall of the left ventricle, Bundle of His and left anterior descending coronary artery is also achieved in treatment with tangents and 12 MeV electron beam IMF. Doses to this region with tangents alone ranged from 20 Gy to 45 Gy compared to 0 to 30 Gy with tangents and 12 MeV electron beam IMF. Clinical significance of these findings will be discussed.

Progress in 3-D treatment planning for photon beam therapy

The purpose of this report is to study the feasibility of improving dose distributions using non-coplanar photon beams from a linear accelerator. Non-coplanar beams may enter the patient in any arbitrary configuration. This type of treatment technique requires a three-dimensional (3-D) planning system. Clinical examples are used to illustrate the general problems in 3-D treatment planning, and the potential improvement over coplanar beam treatments. Features of a treatment planning system for 3-D planning are discussed.

Locate: An application of computed tomography in radiation therapy treatment planning with emphasis on tumor localization

Computed tomography can provide precise information for radiation therapy treatment planning. However, inaccuracies in radiation field design may occur when the radiation oncologist attempts to transfer information about tumor location from the transverse plane of the CT scan to the longitudinal plane of the simulation film. This report describes a new computer program, LOCATE, which addresses this problem. The program uses operator generated information from the cross sectional CT images to draw an outline of tumor on AP and lateral longitudinal scanned projection radiographs. The resultant images are useful because they are in the same plane as radiographs obtained on a therapy simulator. The impact of LOCATE on radiation treatment planning for 26 patients is discussed along with several cases in which LOCATE was particularly helpful.

Advantages and limitations of computed tomography scans for treatment planning of lung cancer

Forty-five Chest computed tomography (CT) scans performed on patients with lung carcinoma (LC) were evaluated in an attempt to understand the pattern of intrathoracic tumor spread and the advantages and limitations this technique offers for treatment planning when compared to planning done by conventional X rays. The following findings can help treatment planning. (1) When regular X rays do not show tumor location (i.e., hemithorax opacification), CT scan will show it in 68% of patients. If regular X rays show a well localized mass, unsuspected tumor extensions were disclosed in 78% of these patients. Hence, CT scans should be done in all LC patients prior to treatment planning; (2) Mediastinal masses frequently spread anteriorly toward the sternum and posteriorly around the vertebral bodies toward the cord and costal pleura. This should be considered for radiotherapy boost techniques; (3) Lung masses spread in one third of cases toward the lateral costal pleura. Thus, the usual 1-2cm of safety margin around the LC are not sufficient in some cases; (4) Tumor size can appear much smaller in regular X rays than in CT scans. Hence, CT scans are necessary for accurate staging and evaluation of tumor response. Some CT scan limitations are: (1) Atelectasis blends with tumor in approximately half of the patients, thus obscuring tumor boundaries; (2) CT numbers and contrast enhancement did not help to differentiate between these two structures; and (3) Limited definition of CT scan prevents investigation of suspected microscopic spread around tumor masses.

Prospects of computed tomography in radiation therapy

Computerized tomography has become an essential element in the staging of tumors and in the localization of the tumor and neighboring normal tissues for treatment planning. It offers the potential for more accurate delivery of higher doses with improved therapeutic ratio, for the identification of and correction for tissue inhomogeneities, and for three-dimensional treatment planning. For treatment planning purposes only minor changes are required in the current generation of scanners. Possibilities for the future include dynamic radiation treatment, combined CT scanners, simulators, and treatment planning computers, and a potential for significant cost saving through improvements in the results of cancer therapy.

The utility of computed tomography in evaluation of extracranial diseases

The application of CT to the extracranial portions of the body has only been possible since 1975, when technological advances made scanning in less than 20 seconds available to radiologists. Our experience during the first 5 years with body CT have been rewarding and we have demonstrated several significant contributions in the radiologic diagnosis of disease entities that have changed the ideal approach to the evaluation of many patients. The introduction and development of body CT has also been controversial on several issues, primarily related to cost. Increasing clinical experience will improve our definition of the strengths and limitations of CT and allow a more precise definition of the efficient utilization of this new technology. Improvements continue to be reported and it is safe to predict that CT will have further applications to clinical diagnosis in the near future.