142 Radiation Oncology ??Biology ??Physics November 1986,Volume 12, Sup. 1

99

CARCINOMAS OF THE ORAL TONGUE AND FLOOR OF MOUTH. RADIATION THERAPY RESULTS WITH EXTERNAL BEAM AND INTERSTITIAL IMPLANTATION.

Kathleen Kelly, M.D., Gabriela Boldman, M.D., Lily Lawn-Tsao, M.D., Andrew Wu, Ph.D., and Rupert Schmidt-Ullrich, M.D.

Dept. Therapeutic Radiology, New England Medical Center, Boston, MA and Tufts University School of Medicine, Boston, MA 02111

Between 1968 and 1983, 111 patients with carcinomas of the floor of mouth (FOM) and oral tongue (OT) were treated with irradiation, surgery or combined irradiation and surgery. The radiation therapy was standardized and consisted of 45-50 Gy external beam irradiation to the primary tumor and the draining lymphatics, followed by a boost to the primary tumor with interstitial implants that delivered an additional 20-30 Gy. Before 1977 predominantly Radium needles were used, thereafter we have employed the Ir-192 afterloading technique.

Assessment of the tumor volume, to be covered by the minimum isodose surface of the implant, was based on the tumor dimensions as assessed by inspection and palpation plus a minimum margin of 1.5 cm. The Quimby-type Ir-192 implants of the OT and FOM were constructed using commercially available angiocatheters that had been modified to facilitate a rapid and safe afterloading and removal of the radioactive sources. Based on computer-generated preplans, the angiocatheters were inserted perpendicularly through the submental area in parallel planes with a catheter spacing and plane separation of 1 cm each. The free ends of the catheters, after removal of the needles, were secured with crimped lead shots in the oral cavity. The Ir-192 ribbons were afterloaded from the submental area and held in place by magnets. To avoid the need of crossing needles for implantation of OT tumors, the most lateral plane was constructed such, that the lateral border of the tongue as well within the r?pr!-i?led minimum tumor dose of the implant. Delivery of the minimum tumor clij:je i*t, the tongue surface, without looping of the Ir-192 sources, was assured by placement of a minimum 3 mm high teflon spacer between the tongue surface and the lead shot. The Ir-192 ribbons were cut such that one Ir-192 seed was placed at the closed end of the catheter and protruded at least 3 mm above the tongue surface.

More than 80% of the patients were initially treated with irradiation alone and followed for local control of their primary tumors for a minimum of three years. For Tl carcinomas of the OT and FOM, irrespective of the nodal status, the three year local control rates were 90% and 60%, respectively. The local control rates for T2 tumors were in excess of 50% for both sites using irradiation alone. Between 25% and 50% of the patients with T3 and T4 carcinomas were found to have a three-year local control rate of their tumors.

100

TREATMENT PLANNING WITH IMAGES OF REGKEr.

S. Shalev, Ph.D., L. Bartel, B.Sc., P. Therrie", B.Sc., P. Hahn, M.D., Y. Carey, R.T.T.

Manitoba Cancer Treatment and Research Foundation, Winnipeg, Manitoba 3E OV9, Canada

The selection of one from a numher of alternative treabnent plans is often a difficult, subjective and frustrating experience. We have developed a method for assisting the dosimetrist or radiotherapist to identify undesirable characteristics in the plans, permitting the selective rejection of the most ""satisfactory plans

until one is chosen as the most suitable for treatment. Instead of the usual isodose plot, we display a diagram

of the patient contour, target and sensitive organs, with colour overlays indicating regions of regret. These

are either excessively high or low dose areas wlthin the target, or high doses in normal tissues or specific

sensitive organs.

Parameters defining the limits of regret are stored on file by radiotherapist, tumour site and stage. For

exaxlple, regions withl" the target with doses below 95% and 90% of the prescribed target dose may be coloured

light and dark blue respectively. Regions outside the target tith doses greater than 90% and 80% may be coloured dark and light red, while areas above a given critical dose In each sensitive organ are coloured purple. The result is a simple, llncluttered image in which areas of regret are clearly visible, and the can- parison of alternative plans is remarkably easy. The images of regret are viewed on the screen of the planning terminal, and recorded on instant colour film for the patient record.

The AECL Theraplan treatment planntng system has been modified to provide images of regret, in addition to or as a" alternative to isodose plots, and the modification is available 3s n fully documented software patch. Our experience shows that the capability of conparing plans easily leads to a greater willingness to compute more alternative beam sctttngs, and to consider more off-axis planes, than when only isodose plots are

available. Beam sizes, directiors and weights can be selected to minimize hot and cold spots in the target, to trim nornal tissue exposure, a"d to prevent unacceptable doses to critical organs.