Computed tomography in planning radiation therapy for bronchogenic carcinoma

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.

Beams eye view-based photon radiotherapy I

Geographic miss, dosimetric miss (underdosing), and proximity of the tumor to sensitive normal tissues are some of the causes of inadequate radiation dose delivery; this is one of many causes of failure after radiotherapy. In the past decade, computerized tomography (CT)-based treatment planning has helped to overcome some of these problems. Beam's eye view (BEV)-based radiotherapy planning is an improvement over CT-based treatment planning that may further increase the therapeutic ratio. Since January 1988, we have treated 198 patients with BEV-based photon radiotherapy. About 40% of our patients treated with radical radiotherapy undergo BEV-based treatment, and about 70% of patients who undergo planning CT in the treatment position receive BEV-based radiotherapy. Our findings are as follows: (a) routine use of BEV-based RT (BEVRT) is possible in a busy radiation oncology department; (b) BEVRT improves geometric coverage of tumors; (c) BEVRT is extremely useful in the design of oblique portals; (d) time commitments for various members of the RT treatment-planning team are reasonable; (e) BEVRT helps individualize RT technique; (f) preliminary data suggest decreased acute toxicity with the use of BEVRT for prostate cancer patients. Whether these advantages will help to improve the outcome (i.e., improve local control and survival) and/or decrease the long-term toxicity is not yet known.

Analysis of movement of intrathoracic neoplasms using ultrafast computerized tomography

Twenty patients with intrathoracic neoplasms were evaluated with ultrafast (cine) computerized tomography to determine the contribution of tumor motion to geographic errors. The treatment portals were setup with conventional simulation techniques and then scanned with cine computerized tomography. Eight tomographic levels were studied, 10 images per level over 7 seconds time. Major geographic misses were detected in three patients (15%), and minor geographic misses in an additional three (15%). The greatest tumor movement was noted in lesions located adjacent to the heart or aorta or near the diaphragm. Five of six hilar lesions showed significant lateral motion (average = 9.2 mm) with cardiac contraction, and three of four lower lobe lesions showed significant craniocaudal movement with respiration. Mediastinal lesions moved an average of 8.7 mm laterally. Lesions in the upper lobes showed minimal movement (average = 2.2 mm), and tumors attached to the chest wall showed no measurable movement.

The development of distant pulmonary infiltrates following thoracic irradiation: the role of computed tomography with dosimetric reconstruction in diagnosis

High doses of external beam radiotherapy are required to obtain local control of many intrathoracic neoplasms. Because spinal cord tolerance limits the radiation dose that can be given through anterior and posterior fields, it is often necessary to increase the dose to the primary tumor site using oblique or lateral fields. When pulmonary infiltrates develop following treatment in these patients, it is frequently difficult to distinguish between infection, recurrent tumor, and radiation pneumonitis. In nine patients in whom acute pulmonary infiltrates occurred following a course of thoracic irradiation, computed tomography (CT) with computed dosimetric reconstruction (CDR) were studied in an attempt to correlate the treatment volumes with the location and configuration of the infiltrates and in this way establish the source for the pulmonary abnormalities. In seven of these patients, the diagnosis was changed, and the resulting post-irradiation clinical therapy was altered as a consequence of this retrospective study.

Computed tomography in radiotherapy planning of the axillary region

Computed tomography was used in the pretreatment evaluation of three patients with neoplasms involving the axillary region. Radiation therapy treatment fields were more accurately defined using the computed tomography data. Computed tomography has a valuable role in radiotherapy planning in patients with tumors involving the axillary region.

Reassessment of radiation therapy for the management of lung cancer in patients with chronic pulmonary disease

Surgery has remained the mainstay of definitive treatment for lung cancer. Radiation therapy has been advocated when the location of the lung cancer precludes resection or the severity or the cardiopulmonary impairment indicates that the patient cannot withstand the proposed resection. Extended field irradiation has been shown to improve tumor control and survival. However, in patients with chronic pulmonary disease, extended field irradiation may exacerbate pulmonary insufficiency and compromise survival. Between 1975 and 1980, 29 patients with lung cancer and chronic pulmonary disease were treated by involved field irradiation (IFR). This was compared to the experience of 41 patients who had been treated prior to 1975 by extended field irradiation (EFR). The frequency of subjective response and tumor control were comparable in each group. One patient treated by IFR developed a marginal recurrence. Radiation pneumonitis was observed in 7/41 (17%) EFR patients versus 2/29 (7%) IFR. Treatment related death occurred in 2/41 (5%) EFR versus 1/29 (3.3%) IFR. One year disease free survival was 8/41 (19%) EFR versus 12/29 (41%) IFR. Two of 14 (14%) IFR patients at risk five years are alive without evidence of disease.

User requirements on CT-based computed dose planning systems in radiation therapy. Presentation of 'check lists'

The expanding use of computers in radiation therapy procedures, especially the rapidly increasing use of digital CT-information, necessitates the coordination of the different systems in order to facilitate their developments. In order to define necessary demands for tomorrow a Nordic cooperation was initiated 1981 by NORDFORSK (Nordic co-operative organization for applied research), and a group of physicians and physicists having their daily work in this field of medicine and physics was invited to produce a report on 'User requirements on CT-based computed dose planning systems on radiation therapy'. The work has been done within the frame of NORDFORSK's activities and has been independent of the existing commissions and associations in the radiology field, but it has taken into consideration recommendations that have been given by or are being produced by other organizations. This report is a short summary of the complete paper which will be published in Acta Radiologica. The aim of this short version is to get an early presentation of the 'requirement lists' (see Appendix) which we think are of immediate importance.

Evaluation of computed tomography numbers for treatment planning of lung cancer

Computerized tomography numbers (CTN) were evaluated in 32 computerized tomography scans performed on patients with carcinoma of the lung, with the aim of evaluating CTN in normal (lung, blood, muscle, etc) and pathologic tissues (tumor, atelectasis, effusion, post-radiation fibrosis). Our main findings are: 1. Large individual CTN variations are encountered in both normal and pathologic tissues, above and below mean values. Hence, absolute numbers are meaningless. Measurements of any abnormal intrathoracic structure should be compared in relation to normal tissue CTN values in the same scan. 2. Tumor and complete atelectasis have CTN basically similar to soft tissue. Hence, these numbers are not useful for differential diagnosis. 3. Effusions usually have lower CTN and can be distinguished from previous situations. 4. Dosimetry based on uniform lung density assumptions (i.e., 300 mg/cm3) might produce substantial dose errors as lung CTN exhibit very large variations indicating densities well above and below this value. 5. Preliminary information indicates that partial atelectasis and incipient post-radiation fibrosis can have very low CTN. Hence, they can be differentiated from solid tumors in certain cases, and help in differential diagnosis of post radiation recurrence within the radiotherapy field versus fibrosis.

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.