Beam Portals Research Articles

Which is the most suitable number of photon beam portals in coplanar radiation therapy?

Computer-controlled milling machines for compensator manufacture, dynamic multileaf collimators, and narrow scanned electron or bremsstrahlung photon beams have opened up new possibilities to shape nonuniform fluence profiles and have thus, paved the road for truly three dimensional (3D) dose delivery. The present paper investigates the number of beam portals required to optimize coplanar radiation therapy using uniform and nonuniform dose delivery. A recently developed algorithm has been used for optimization of the dose delivery in such a way that the probability of achieving tumor control without causing severe reactions in healthy normal tissues becomes as high as possible. This method has been used to optimize the delivered dose distribution for an increasing number of beam portals to determine how many coplanar beam portals are desirable to safely achieve a good treatment outcome. Target volumes in the head and neck, thorax, and abdomen have been investigated. Nonuniform dose delivery allows a considerable improvement in the treatment outcome compared to uniform dose delivery. This is evident both from the probability of achieving complication-free tumor control and the value of relevant properties of the dose distribution, such as the mean value and the standard deviation of the mean dose to target volume and organs at risk. The results also show a close relationship between the dose distribution parameters and the probability of achieving complication-free tumor control. The level of complication-free tumor control first increases rapidly when the number of beam portals is increased, but already reaches a level of saturation after three to five beam portals. When the saturation level has been reached, the standard deviation of the mean dose to the target volume is around 3%. To achieve optimal expectation value of the treatment outcome, within an accuracy of a few percent as measured by the probability of achieving complication-free tumor control, it is generally sufficient to use three nonuniform beam portals. A very large number of coplanar beams may only raise the probability of achieving complication-free tumor control by 1 to 2%. However, good treatment outcome with three beam portals requires that the directions of incidence of the coplanar nonuniform beams are optimally selected. If, on the other hand, the treatment is performed using uniform beams, it is not possible, even with an infinite number of fields, to obtain as high a level of complication-free tumor control as with a few nonuniform beams. From an optimization point of view, it is sufficient to reach a relative standard deviation of the mean dose to the target volume of around 3%. Improved dose homogeneity beyond this level will, in general, not significantly improve the complication-free tumor control.

Few‐field radiation therapy optimization in the phase space of complication‐free tumor control

AbstractThe phase space of P+, describing the probability of achieving tumor control without causing severe complications in normal tissues, has been investigated for three different clinically relevant treatment geometries. These include tumors in the head and neck region, thorax, and pelvis. Some general conclusions about the shape and properties of the P+ phase space are given for the selected target volumes. The use of three different radiation beam types‐strictly homogeneous, wedged, and generally nonuniform beams‐has been investigated and the considerable differences in the P+ phase space are shown. One conclusion is that the exact selection of beam entry direction becomes gradually less important as the number of beam portals becomes larger. One of the most important results is that use of appropriately selected nonuniform beam profiles reduces the number of necessary beam portals to such a low level that the treatment technique becomes simple and reliable at the same time as the probability of achieving tumor control without severe complications is almost as high as with an unlimited number of beams This means that most ordinary treatment units equipped with beam compensating filters can be used for closely optimal radiation therapy.

Concomitant boost radiotherapy for advanced squamous cell carcinoma of the head and neck

The concomitant boost technique is a variant of accelerated fractionation whereby the boost is delivered as a second daily fraction during the basic treatment course to reduce the total duration of treatment. From April 1972 through June 1983, 53 patients with advanced squamous cell carcinoma of various sites in the head and neck region were treated for cure at U.T. M. D. Anderson Hospital with this technique. In 12 patients, the concomitant boost was used because of rapid recurrence following surgical resection either before or after initiation of planned postoperative radiotherapy; the remaining patients had rapidly growing untreated or recurrent disease in the primary site, neck, or both. In most cases, the concomitant boost was delivered in fractions of 120-150 cGy, separated by 3-6 h from the basic daily treatment of 180-200 cGy. The boost treatments were given 2-3 times a week for 3-5 weeks, delivering an average of about 17 Gy in 12 fractions. Two different treatment techniques were used. Patients with predominantly neck disease (30) were treated with glancing AP and PA fields or with appositional electron beam portals to spare the mucous membranes, while those with advanced or rapidly progressive primary lesions, with or without nodal disease (23), received their concomitant boost through lateral photon or high energy electron beams to include the primary tumor site. As expected, the acute mucosal reactions were most severe in the latter group, but only three patients required interruption of treatment because of severe mucositis.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of adjuvant chemotherapy on cosmesis and complications in Stages I and II carcinoma of the breast treated by biopsy and radiation therapy

Cosmesis and complication rates were examined in patients with early stage carcinoma of the breast treated by biopsy and radiation therapy with and without adjuvant chemotherapy in an attempt to determine the effect of chemotherapy upon these parameters. Between April 1, 1975 and June 1, 1980, 51 patients were treated with radiation therapy and adjuvant chemotherapy (XRT + ACT) and 83 patients with radiotherapy alone (XRT). Chemotherapy usually consisted of cytoxan, methotrexate and 5-fluorouracil for 6 or 12 cycles. Minimum follow-up was 36 months. Cosmetic results deteriorated with time in both groups but to a greater extent in the XRT + ACT group. At 36 months, excellent cosmetic results were obtained in 73 of the 83 patients (88%) in the XRT group compared to 37 of 51 patients (73%) in the XRT + ACT group ( p = <.05). Comparison of the two treatment groups revealed that complication rates were significantly increased in the XRT + ACT group. Of the 51 patients in the XRT + ACT group, 21 patients (41%) suffered complications compared to 8 (10%) of the 83 patients in the XRT group ( p = <.001). This difference in complication rates resulted primarily from an increased incidence in the XRT + ACT group of wet desquamation in the electron beam portal used to treat the internal mammary lymph nodes and a trend towards a higher incidence of spontaneous nonpathologic rib fractures, myositis and arm edema. An increased incidence of nonbreast primary cancers was not seen. Our preliminary conclusions are that adjuvant chemotherapy has a negative impact upon cosmesis and complication rates in patients being treated with definitive radiotherapy. However, cosmetic results remain satisfactory and complication rates are maintained at an acceptable level. Continued close follow-up will be required before definitive conclusions can be reached as to the overall incidence and severity of the changes noted.

Parametrial implant in Stage III B cancer of the cervix. III. A five-year study.

Since 1975, the Department of Radiation Therapy, University of Maryland Hospital initiated a policy of supplementing the dose to the affected parametrium by using radium needles implants in conjunction with a protruding tandem preferably, or Manchester ovoid in the case of absence of the lower segment of the uterus. The authors have noted a remarkable improvement in local control as well as an improved three-year survival rate with minimal immediate complications. Additional Stage IIIB (FIGO) cases were collected and they were treated by the same technique and have a close follow-up since 1975. Forty-nine cases studied, 32 (65%) survived with disease-free status for a minimum of five years with no loss to follow-up. Local control was excellent, as expected, at the level of 84% (41/49). There were 8% major complications as a consequence of radiation treatment and the majority of them required surgical intervention with excellent success. Paraaortic metastasis remains a major problem and requires further study. The current plan will include retroperitoneal exploratory laparotomy and para-aortic node sampling with extension of the external beam portals to include the positive node region and followed by interstitial and intracavitary brachytherapy.

Hyperbaric oxygen as a radiotherapeutic adjuvant in advanced cancer of the uterine cervix.Preliminary results of a randomized trial

From September 1968 to March 1974, a randomized clinical trial was carried out, using conventional fractionation, i.e., five treatments per week, in 233 patients with advanced cancers of the uterine cervix--Stages IIB, IIA, IIIB and IVA. The age limit was 70 years and all patients had medical clearance. Lymphangiography and, in some patients, an exploratory laparotomy with selective lymphadenectomy, were done prior to treatment to determine the extent of nodal disease. The staging has not been changed either by lymphangiogram or lymphadenectomy findings. A few patients with bulky Stage I and IIA lesions were entered into the trial because of extensive nodal disease demonstrated either by lymphangiogram and/or lymphadenectomy. First, the patients were grouped according to the clinical stage. The secondary stratification was according to the lymphangiogram and/or selective lymphadenectomy findings. The patients were then randomized to air or hyperbaric oxygen within each group. The patients were pressurized in a Vickers chamber at 3 atmosphere absolute, using a 20-minute soak time prior to the irradition. The size of the external beam portal was determined by the status of the nodes. The difference in absolute NED (no evidence of disease) survival rates for both groups as a whole and by stages is not statistically significant. There is no difference in the incidence of failures in the irradiated area between the HPO and air patients. There is no increase in distant metastases in the HP group. It does not seem that the HPO has had an effect on the major complications. However, there was an increase in the incidence of complications with extended fields. The addition of lymphadenectomy had increased the incidence of fatal complications, even with routine pelvic portals. The negative results of this trial with conventional fractioantion should not lead to the conclusion that HPO could not be useful with schemes using a few high dose fractions.