What is Cutting Field IMRT (CFIMRT)
Three-dimensional conformal radiotherapy (3DCRT) and intensity-modulated radiotherapy (IMRT) have allowed considerably higher doses of radiation to be delivered to the malignant tumor with relatively lower doses to the organs at risk (such as lung, liver, bowel, etc.) . They enable dose escalation in order to increase tumor control, and the delivery of higher doses by decreasing side effects. The problems of both methods are that they require a long time for optimization and validation of treatment plan comparisons, and they need sever quality asualance, especially in IMRT.
Thus, we propose a method in which conventional techniques are combined by which the dose distribution corresponds to that in IMRT, that is, rectangular rotation irradiation is combined with fixed multiport irradiation which are collimated by multi-leaf collimator (MLC). Rotational irradiation techniques such as conformal irradiation show a relatively homogenous dose distribution, but there is a tendency for high dose irradiated area to be generated in the anterior part of tumor. On the other hand, fixed multiport irradiation shows a relatively inhomogeneous distribution and there is a tendency for high dose irradiated area to be generated within the surrounding of tumor, but it is easy to plan for various shape tumor. Then, we combined rectangular rotation irradiation for roughly uniform irradiation with fixed multiport irradiation in order to determine the morphology of tumor. A more homogenous dose distribution can be achieved by putting the weights of the doses or angles of fixedports on the posterior side. If a high dose area still occurs, MLC of a corresponding portion will be collimated ( Cutting Field). It is thought that this technique is a kind of IMRT since the intensity of rectangular rotational irradiation field is modulated by fixed multiport which are collimated by MLC, so we called this method Cutting Field IMRT ( CF-IMRT). If the concept is well understood, the plans can be made in a comparatively short time even by try and error. Furthermore, some cases which are difficult to plan by IMRT will become plannable.
Highly conformed plans were made in all cases while avoiding overdose exposure of important organs. Most plans were made within 30 minutes. Most of the over doses area will disappeare after adjusting dose weight and beam orientation. Typical cases are presented as follows.
Postoperative irradiation of breast.
There is a tendency which becomes inhomogenous distribution in tangential irradiation of the breast. CFIMRT can make homogenous distribution. This sample made by eight ports irradiation with two rectangular irradiation. Of corse, we did't use subsegments. And all fields covered for whole PTV. So this method is need not respiratory alignment.
Left fig. is tangential irradiation and right fig. is CFIMRT (eight port, no sub segments)
Cancer of the cervix of uterus (StageIII)
This patient refused RALS. So, we treat cervix and adnexal regions by high doses, and treat for pelvic lymphnodes by lower doses. This patient cured completely.
Inoperable gastric cancer
The operations of stomach cancer are also foundations now. A bypass operation or gastrostomy is foundations, when the patients who cannot receve an currative operation. This patient of the was the situation which condition of disease has reached an advanced stage, he has a metastasis for the left adrenal gland, and cannot eat a meal. Radiotherapy was performed on sufficient informed consent.
A meal can be taken in now out of a radiation treatment period, and body weight increased 5kg or more. The complete cure state also continues for the stomach now. However, I regard as wanting to understand that the radiotherapy in stomach cancer is very exceptional globally.
Discussion and conclusions
Because of the difficulty of QA, IMRT cannot be carried out at several facilities, and it takes a long time to plan IMRT because it involves many parameters. We combined conventional techniques to solve these problems, and designed a method of determining dose distribution resembling that in IMRT. The method may resemble a classical field-in-field method, but it is actually different in two points. That is, one rectangular rotational port is set, and the dose distribution is optimized by several dose weights and gantry angles. It may seem that this technique is complex, but it dose not require severe adjustment of the beam orientation. Because rectangular rotation irradiation guarantees some conformity, it is possible to concentrate planning on further conformity of tumor and the reduction of exposure to important organs by adjusting the dose weights and gantry angles of fixed ports. Rotational and fixed port irradiations have their own merits and demerits. The plans using CF-IMRT will not be inferior to that of IMRT if that in planed to supplement each other. One plan by this method can be made in about 30 minutes if planed according to a basic strategy. In addition, application will also be possible to inversed plans in any area because various templates such as that for the prostate can be easily fabricated.
<Although I wrote the above-mentioned text in 2003, changing until it continues up to now twists it, and it is true.>
last modification date: 2014/08/15