Impact of biological clearance on tumor radioresponsiveness

Comparison of tumor regression rate of uterine cervical squamous cell carcinoma during external beam and intracavitary radiotherapy

PURPOSE

We compared the radioresponse of cervical carcinoma that was closely related to local disease control by the tumor regression rate (RR) during intracavitary radiotherapy (ICRT) and external beam radiotherapy (EBRT) on the presumption that ICRT has a stronger treatment impact than EBRT because of its specific dose distribution.

MATERIALS AND METHODS

A total of 37 patients were treated by EBRT at 45.0 Gy over 5 weeks, followed by high-dose-rate ICRT at 6.0 Gy per weekly insertion at point A three to five times and by boost EBRT. RR was defined as the slope (day(-1)) of the tumor-volume shrinkage curve fit to an exponential regression equation. Assuming that the tumors were ellipsoid, the tumor volume was estimated using magnetic resonance (MR) images obtained before treatment, after 45.0 Gy of EBRT, and after the third ICRT insertion. RRs were compared based on the radiotherapy method.

RESULTS

RR ranged between -0.008 to 0.093 day(-1) (median 0.021 day(-1)) during EBRT and -0.001 to 0.097 day(-1) (median 0.018 day(-1)) during ICRT, showing no significant difference or correlation between treatments.

CONCLUSION

Contrary to expectations, RR did not directly relate to the impact of physical treatment. RR could be related to biological factors, such as the amount of tumor clearance and changes in tumor consistency during treatment.

Reduction rate of lymph node metastasis as a significant prognostic factor in esophageal cancer patients treated with neoadjuvant chemoradiation therapy

Tumor regression is used widely as a measure of tumor response following radiation therapy or chemoradiation therapy (CRT). In cases of esophageal cancer, a different pattern of tumor shrinkage is often observed between primary tumors and metastatic lymph nodes (MLNs). Regression of MLNs surrounded by normal tissue may be a more direct measure of the response to CRT than regression of a primary tumor as exfoliative mechanical clearance does not participate in shrinkage of MLNs. In this study we evaluated the significance of the reduction rate (RR) of MLNs as a prognostic factor in esophageal cancer patients treated with neoadjuvant CRT. Forty-two patients with marked MLNs were selected from 93 patients with esophageal carcinoma who had received neoadjuvant CRT. The RRs of the primary tumor and the MLNs were calculated from computed tomography scans. In 20 patients, surgical resection was carried out following CRT. Univariate analysis was used to determine which of the following variables were related to survival: size of the primary tumor and MLNs; RRs of both lesions; degree of lymph node (LN) metastasis; clinical stage; and surgical resection. Multivariate analysis was then performed to assess the prognostic relevance of each variable. The primary tumor was larger than the MLNs in 69% of patients before CRT and in 40% of patients after CRT. In 79% of the patients, the RR of the primary tumor was greater than the RR of the MLNs. The results of the univariate analyses showed that a high RR of the MLNs and surgical resection after CRT were associated with significantly improved survival. The multivariate analysis demonstrated that the RR of MLNs had the strongest influence on survival. The RR of LN metastasis should be evaluated as an important prognostic predictor in patients with marked LN metastasis of esophageal cancer treated with CRT.

Implications of quantitative tumor and nodal regression rates for nasopharyngeal carcinomas after 45 Gy of radiotherapy

PURPOSE

To quantitatively investigate the clinical implications of tumor regression rate (TRR-45) and nodal regression rate (NRR-45) of nasopharyngeal carcinomas (NPC) after receiving 45 Gy of radiotherapy (RT). The values, predictive values, and associated factors of TRR-45 and NRR-45 in NPC are analyzed.

METHODS AND MATERIALS

One hundred one patients with newly diagnosed NPC and who were curatively treated by RT alone were included in the study. Tumor volume and nodal volume before treatment and after 45 Gy were obtained from computed tomographic (CT) scans performed at those times and calculated with the assistance of a computer-based imaging analyzing system. TRR-45 (NRR-45) was defined as the ratio of reduced tumor (nodal) volume after 45 Gy to the initial tumor (nodal) volume. TRR-45 (NRR-45) values were stratified into three groups of slow (below 50%), moderate (between 50% and 75%), and rapid (above 75%) change. After conventional RT with 45 Gy, conformal RT for primary tumors was boosted to 70.2-72 Gy for T1-2 tumors, and 75.6-81 Gy for T3-T4 tumors. RT for residual neck masses was boosted by electron beam to 61-75 Gy.

RESULTS

The mean value of TRR-45 for all patients was lower than that of NRR-45 for the 78 patients with metastatic neck nodes (70% +/- 4.8% vs. 81% +/- 5%, p = 0.003). The 3-year actuarial neck control rate was better than the primary tumor control rate with statistical significance (98% vs. 85%, p = 0.009). No significant statistical differences concerning local control probability, nodal control probability, or survival rate were found among patients with slow, moderate, or rapid TRR-45 or NRR-45. T-stage was the only significant prognostic factor for locoregional control after multivariate analysis. Tumor volume and T-stage were found to have a statistically significant negative correlation with TRR-45. No associated factor was found to be significantly correlated with NRR-45.

CONCLUSION

Slow regression rates of the primary tumor or neck nodes in NPC after receiving 45 Gy of irradiation do not mean ultimately poor radiocurability, but may merely imply slow clearance of the cells damaged during irradiation. The different radiobiological behaviors of the regression rates during treatment, ultimate control probabilities, or associated factors for regression rates of NPC between primary tumors and neck nodes need to be further investigated.

Metastatic lymph-node clearance from head and neck epidermoid carcinomas following radiotherapy

Although tumor clearance is a common criterion in assessing the impact of radiotherapy (RT), it is not always reliable. Patterns of tumor clearance were determined using 91 metastatic lymph nodes (LNs) from 51 patients with head and neck tumors treated by definitive RT (61-80 Gy) or preoperative RT (43-65 Gy). Clearance rate (CR) was estimated as a daily volume decrement expressed as a ratio to the pre-RT LN volume. CR was greater for the so-called radioresponsive nasopharyngeal subgroups and more poorly differentiated than those of oral cavity and well-differentiated, respectively. Histologically, LNs that were removed following RT consisted mainly of fibrous tissues, necrotic tissues, and few cancer cells. There was no difference in CR between the cancer-cell-positive group (n = 21) and the cancer-cell-negative group (n = 31). Although the CR may reflect inherent radiosensitivity of tumor cells, tumor persistence predicts the amount of oncologically inactive materials rather than that of remaining cancer cells.

Radioresponse of thymomas verified with histologic response

Patterns of radiologic response of 10 thymomas treated by preoperative radiotherapy (RT) (18-20 Gy/2 weeks) were determined in conjunction with histologic response. Changes in tumor volume were evaluated with CT scans obtained 5 to 36 days before and 14 to 24 days after the initiation of RT and before surgery. The extent of tumor volume reduction (TR) varied widely (40-78%), while the mean daily volume decrement expressed as a percentage of the pre-RT tumor volume correlated significantly with the pre-RT tumor volume. Histologically, the tumors, all of which were resected 17 to 33 days after RT initiation, generally consisted of predominant fibrous tissues, rare necrotic foci, and few epithelial cells. The TR did not correlate with pre-RT tumor volume, observation period, histologic subtype, or quantity of remaining epithelial cells. The TR of thymomas does not predict RT impact on tumor cells but does reflect the quantity of inherent tumor stroma.

The predictive value of tumor regression rates during chemoradiation therapy in patients with advanced head and neck squamous cell carcinoma

OBJECTIVE

The value of tumor regression rates in predicting survival outcome during chemoradiation therapy was prospectively evaluated.

METHODS AND MATERIALS

Sixty-two patients diagnosed with locally advanced stage III/IV unresectable head and neck squamous cell carcinoma underwent weekly clinical and endoscopic serial assessment of primary and nodal tumor sizes during chemoradiation therapy between July 1993 and September 1995. Chemoradiation therapy consisted of protocol treatment using supradose intra-arterial targeted cisplatin (SIT-P) at 150 mg/m2 four times at weekly intervals along with intravenous sodium thiosulfate at 9 g/m2 and concurrent conventionally fractionated radiotherapy at 1.8 to 2.0 Gy/fraction (fx) to a total dose of 68 to 74 Gy. Tumor reduction was serially measured as a percentage of the original pretreatment size at weekly intervals by the same team of surgical and radiation oncologists. Correlations were then made between tumor regression rates and survival.

RESULTS

Complete or near complete regression of disease during chemoradiation therapy as compared with nonresponsive/partially responsive disease was associated with better survival outcome (P = 0.001 and P = 0.013, respectively). Among patients exhibiting complete or near complete regression of disease, rapid tumor reduction (median = 4.2 weeks) was associated with inferior survival outcome when compared with slower disease regression (median = 6.4 weeks, P = 0.007).

CONCLUSIONS

Our findings fail to support the "traditional" hypothesis that rapid tumor regression during treatment is predictive of an improved survival outcome. Treatment strategies that alter ongoing therapy based upon initial tumor regression rates should be avoided.

The response of tumours with Gompertzian growth characteristics to fractionated radiotherapy

Proliferation of tumour cells during radiotherapy may be a significant factor determining response to treatment. In previous work based on the linear-quadratic (LQ) model, tumour cell proliferation was assumed to be independent of both tumour size and the temporal structure of treatment. This paper examines a form of tumour cell proliferation that is exponential at small tumour sizes and Gompertzian at larger sizes. This is integrated with the LQ description of tumour cell sterilization. It is assumed that exposure to therapeutic radiation changes the state of tumour cells from viable to doomed. Doomed cells are assumed to be lost from the tumour mass with exponential kinetics. Six parameters are used to describe tumour response. Three of these are the standard 'LQ+time' (alpha, beta, Tpot) parameters. Two additional parameters are required to describe the shape of the tumour growth/regrowth curve (VG, Vmax). The sixth parameter (Ts) represents the rate of loss of doomed cells from the tumour. The model may be used to describe the effects of radiation therapy, both in terms of cure response (clonogenic cell sterilization) and also remission response (tumour regression and regrowth). An important feature of the model is that it enables the effects of temporally non-uniform treatments to be described. Preliminary modelling studies suggest that it may be possible to manipulate the temporal structures of fractionation schedules to increase the duration of remission at the expense of the probability of cure.

Clearance of parenchymal tumors following radiotherapy: analysis of hepatocellular carcinomas treated by proton beams

Clearance of a parenchymal tumor following radiotherapy was determined by using follow-up CT scans of 18 hepatocellular carcinoma tumors treated with focused proton beams. Regression analysis of the daily decrement (DD) and the diameter (D) of a tumor mass in each CT observation interval, DD = a*Db, showed that the exponent b was 3.0 or larger in early periods and 2.0 or smaller in late periods. This suggests that the clearance depends initially on the tumor volume, subsequently on the tumor surface area, and then it becomes much more moderate, possibly due to radiation damage to the parenchymal tissues.

Cell kinetics and tumor regression during radiotherapy in head and neck squamous-cell carcinomas

Head and neck squamous-cell carcinoma (HN-SCC) patient management is mainly based on TNM classification and needs be improved by considering other potentially useful prognostic factors. We examined the pre-radiotherapy tumor potential doubling time (Tpot) evaluated after in vivo infusion of bromodeoxyuridine and flow-cytometric analysis and the early clinical tumor regression after 40 Gy (40 Gy-TR). Tpot values and clinical 40 Gy-TR classes (minor and major) were available for 82 HN-SCC patients. Radiation therapy completion was done either with 1 dose per day (conventional regimen) or 2 doses per day (accelerated regimen). Local control was also available for follow-up times above 4 years. We found that major 40 Gy-TR was strongly correlated with fast tumor growth, characterized by Tpot values below 5 days, and that patients with major 40 Gy-TR showed better local control than those with minor 40 Gy-TR, independently from the radiotherapy regimen type. We also found that treatment completion with accelerated radiotherapy gave better local control for patients with major 40 Gy-TR and fast tumor growth than conventional radiotherapy. Multivariate analysis, performed on all patients, assigned an independent prognostic value to Tpot, tumor classification and 40 Gy-TR.