The accuracy of absorbed dose calculations for external photon beam therapy depends on the computational algorithms being used: the acquisition of basic beam data, the patient's anatomical information, the spacing of the points in the matrices, the interpolation routine, inhomogeneity corrections, etc. At present, the dose calculation algorithms employed in most commercially available treatment planning systems for absorbed dose calculation are two-dimensional methods for photon fluence and do not take electronic equilibrium into account. Therefore, their use for radiation treatment planning is limited. In particular, the problem of inhomogeneity correction for lung is the most significant. The inhomogeneity correction methods most commonly used are ratio of TAR (RTAR), power law TAR (PTAR) and equivalent TAR (ETAR) methods. One JASTRO task group has compared the three correction methods mentioned above with measured values using the same JARP level dosimeter and lung model phantom. The photon energies were ⁶⁰Co y rays, 4, 6, 10 and 18 MV x rays, and field sizes were 5×5, 10×10 and 20×20cm² at SSD 100cm. RTAR lead to errors (%) of 2.5 to 12.6, 1.7 to 10.9, 2.7 to 8.5, 3.1 to 9.9, and 1.0 to 19.1; PTAR errors were-0.7 to 2.3, -2.1 to 1.6, -1.1 to 2.2, -0.3 to 3.9, and-2.0 to 6.6; and ETAR errors were 0.7 to 2.5, o to 3.1, -0.1 to 6.8, 3.4 to 9.2, and 1.0 to 18.6 for ⁶⁰Co γ rays, 4, 6, 10 and 18 MV x rays, respectively. Survey results showed that about 50% of the institutions used measured data obtained by themselves. Basic beam data acquisition should be self-contained.

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Total-skin electron-beam irradiation is suitable for the treatment of widespread skin lesions. To degrade electron-beam energy, a degrader is widely used for total skinelectron-beam irradiation. The effects of the source-degrader distance on dose distribution in total-skin electron beam-irradiation were investigated. Measurements include percentage depth dose, photon contamination, dose rate at surface and surface, beam intensity for various source-degrader distances. From the results, the main advantages of the large source-degrader distance are: a) decrease in X-ray contamination; b) higher dose rate at skin surfece. For example: with a 5 mm thick degrader: a) the X-ray contamination was 15% at a source-degrader distance of 100 cm and 8% at 350 cm; and b) the dose rate at the skin surface for a source-degrader distance of 350 cm is 2 times that for 100 cm. It is concluded that the degrader should be placed closer to the patients.

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Factors influencing local progression-free rate and prognosis in forty-nine patients with stage I non-small cell lung cancer who were treated by radiation therapy from 1968 to 1991 were analysed by univariate and multivariate methods. No siginificant factor influencing the local progression-free rate was identified by univariate analysis and also by multivariate analysis. Significant association was found between survival rates and serum albumin, serum LDH, pulmonary function test and mediastinal irradiation by univariate analysis. In multivariable analysis using Cox's proportional hazard model, serum albumin, serum LDH and age were significant factors for survival. Serum albumin was especially considered to have the strongest correlation with survival.

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Between 1967 and 1988, 102 patients with Stage T1-2N0 squamous cell carcinoma of the tongue were treated with uneven fractional irradiation therapy (intra-oral electron beam irradiation with and without prophylactic ipsilateral upper neck irradiation at the Dept). of Radiology, Nihon University School of Medicine. Of 102 primary lesions, 89 cases were controlled with this therapy. In this study, these 89 cases were investigated in order to analyze the prophylactic effect of upper neck irradiation. Of the 89 patients, 42 received only intra-oral electron beam irradiation, while the remaining 47 received a combination of intra-oral electron beam irradiation and prophylactic irradiation to the ipsilateral upper neck. Twenty three of the 89 (25.8%) developed metastasis to the neck after the radiotherapy. A breakdown of these 23 cases reveals that 3/21 (14.3%) received 40-50 Gy to the neck, 9/26 (34.6%) received 20-40 Gy to the neck, and 11/42 (26.2%) received no irradiation to the neck (p<0.05 between first and second groups, and between first and third groups). The neck metastasis was classified into one of three categories based on the region in which it first appeared (ipsilateral upper neck, ipsilaeral lower neck or contralateral neck). The first metastasis was seen in the ipsilateral upper neck, in the ipsilateral lower neck and in the contralateral neck in 17, 4 and 2 patients, respectively. In 1/19 who had received 40-50 Gy, in 5/21 who had received 20-40 Gy and in 11/42 who had not received neck irradiation the first metastasis appeared in the ipsilateral upper neck. The fi ve year survival rate was 94%, 75% and 85% in the patients receiving 40-50 Gy, 20-40 Gy and no neck irradiation, respectively. These results suggest that prophylactic irradiation of 40-50 Gy to the ipsilateral upper neck might decrease the incidence of neck metastasis and slightly prolong survival time.

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We retrospectively evaluated factors associated with the development of late bowel complications in 147 patients with cervical cancer treated by external and high dose-rate intracavitary irradiation (ICI). The patients were treated with 20-50 Gy by whole pelvis irradiation (WPI) followed by ICI at a total dose at Point A of 22.5-36 Gy/5-8 F/ 3-4 W. Stage IIb-IV patients were boosted with 10 Gy by split field irradiation. The actuarial incidence of overall late bowel complications was 26.4% at 5 year. Multivariate proportionalhazard analysis showed such significant correlations that the complications were higher with a high WPI fraction dose, a high ICI fraction dose at the anterior rectal wall (R), a high ICI total dose at R, as well as a combined total dose of WPI + ICI at R. Significant risk factors were: advanced age (≥60 years), the presence or history of hypertension, a long duration of symptoms of cervical cancer before treatment, and previous abdomino-pelvic inflammation associated with a higher complication rate.

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Recently, stereotactic radiosurgery using a linear accelerator is becoming the center of interest. To perform stereotactic radiosurgery using a linear accelerator, it is necessary to study the fundamental examinations; these include making the collimators for high energy X-ray narrow beams, measurement of dose profiles of narrow beams, and irradiation methods for stereotactic radiosurgery. Field sizes of narrow beams were measured; they were 9 mm, 18 mm and 27 mm in diameter. TPR (Tissue Peak Ratio) and dose profiles of high energy X-ray narrow beams were also measured. The high energy X-ray narrow beams obtained with these collimators satisfy clinical requirements for stereotactic radiosurgery, as indicated by measurement of TPR and dose profiles. The main irradiation methods for stereotactic radiosurgery include dynamic rotation, precessional convergent irradiation, and multiple non-coplanar converging arcs method. Considering the dose profiles, isodose curves, and locus maps constructed by three dimentional culculation using computers; dynamic spiral irradiation, combined dynamic rotation and precessional convergent irradiation, is superior method for stereotactic radiosurgery. However, if this method is performed clinically, a particular treatment table is necessary. On the other hand, the multiple non-coplanar converging arcs method needs no drastic linear accelerator reconstruction, nor treatment table; and dose profiles, isodose curves and locus maps for this method are relatively satisfactory. Thus, the multiple non-coplanar converging arcs method is the most appropriate irradiation method for stereotactic radiosurgery usin r accelerator.

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To study the relative risk of second cancer after radiotherapy, we reviewed 2465 cases of uterine cervical cancer who were treated in our institute from 1962 to 1986 and were followed up for more than 5 years. Among them, 1502 cases were treated by radiotherapy with or without surgery (radiotherapy group), and the remainder were treated by surgery only (surgery only group). We defined second cancer as malignancy that occurred in another organ after an interval of 5 years or more from the end of treatment of the first cancer. The relative risk of second cancer was computed by the person-year method advocated by Schoenberg. Second cancer was observed among 8 cases of the surgery group, whereas 43 cases were observed among the radiotherapy group. The cases were: rectal cancer, 6 cases; bladder cancer, 4 cases. The observed and expected ratio (O/E ratio) was 4.02 in rectal cancer and 7.98 in bladder cancer. This incidence of the both cancers was significantly high in the radiotherapy group. Three of the 6 cases with rectal cancer underwent operation in our institute. The incubation periods between the first and second cancers were from 9 to 21 years. Each case exhibited symptoms of chronic radiation proctitis after radiotherapy for uterine cervical cancer. It is thought necessary to follow up such cases carefully to detect radiation induced cancer.

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Two hundred fifty-three patients with clinical stage III non-small cell lung carcinoma treated by radiation therapy alone at Seoul National University Hospital between 1979 and 1987 were retrospectively analysed. Median follow-up period was 52 months, ranged from 44 to 100 months. One hundred twenty-four patients were stage IIIA and 103 patients were stage IIIB. The overall survival at 2 and 5 years for all patients was 14.8% and 4.3%, respectively with median survival of 9 months. No difference was observed in median survival time between stage IIIA and IIIB (10 vs 9 months p = 0.29), in 2-year survival rate (18.4% vs 10.5%) or in 5-year survival rate (4.9% vs 3.5%). In a multivariate analysis, N-stage was related to survival. For stage IIIA patients, the 2-year survival rate with NO-1 and N2 was 32.5% and 12.8%(p=0.0056), respectively. For stage IIIB patients, the 2-year survival rate for N0-2 and N3 was 12.8% and 6.4%, respectively (p=0.05). A total of 198 patients had failed after treatment. Of 178 patients who were evaluable for the failure sites, local failure alone and as a component of overall failures occurred in 100 patients (56%) and 28 patients (16%), respectively. Distant metastasis was noted in 44% of the overall failures.
As local failure is a major component of overall failure, new therapeutic strategies should be considered in the management of stage III non-small cell lung carcinoma.

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