The effect of dose on local control of prostate cancer

Carcinoma of the prostate: results of radical radiotherapy (1970-1985)

PURPOSE

To determine the outcome and prognostic factors in patients with localized carcinoma of the prostate treated with external beam radiation therapy.

METHODS AND MATERIALS

A retrospective review of 999 patients with histologically confirmed adenocarcinoma of the prostate treated radically with megavoltage irradiation at the Princess Margaret Hospital between 1970 and 1985. Prognostic factors were analyzed using recursive partitioning method.

RESULTS

Overall survival at 5 and 10 years were 69.8% and 40.1% for the whole group. The cause-specific survival rates were 78.9% and 53.5%, respectively. The cause-specific survival rates were significantly different at 10 years by T stage, T1 being 79.0%, T2 66.0%, T3 55% and T4 22%. The overall clinical local control rates was 77% in the first 5 years following treatment. There was no statistically significant difference in the local control rates of T1 and T2 stage disease at 5 years, the combined rate being 88%. Significant differences were observed between other stages, being 76% for T3 and 55% for T4. At 10 years the control rate for T1 tumours was maintained for T1 stage disease (92%) but was significantly reduced for other stages, T2 75%, T3 67% and for T4 37%. In the whole group 33.5% of patients had distant metastases in the first 5 years. The distant relapse rates at 10 years were significantly different by T stage, being 20% for T1, 33% for T2, 55% for T3 and 87% for T4. Multivariate analysis demonstrated that only T stage and histological grade were independent prognostic covariates for cause-specific survival. Age was the only other independent variate in terms of overall survival. The late radiation related morbidity was 2.3% overall; 1.3% affecting rectum and recto-sigmoid and 1.0% arising in the bladder.

CONCLUSION

In terms of survival the results of radiotherapy of intracapsular disease were excellent, but they were less satisfactory in patients with direct extracapsular extension. The assessment of local control was difficult and may have reflected more the lack of local disease progression rather than true local tumor control. The treatment was well tolerated and there were few serious late complications.

Potential improvement in the results of irradiation for prostate carcinoma using improved dose distribution

Results for radiation treatment of prostate carcinoma indicate that nearly one-third of Stage C patients fail locally. This number will likely increase as occult failures are discovered by monitoring serum prostate specific antigen levels. Thus, there is need for techniques that would increase the local control of prostatic carcinoma. Using cross-sectional imaging and 3-dimensional treatment planning, dose distributions for photon irradiation can be created that conform more closely to the shape of the prostate and seminal vesicles, sparing additional dose to portions of bladder and rectum. A dose escalation trial is underway to investigate whether these techniques will lead to increased local control without unacceptable increases in bladder and rectal complications. While zero local failures is probably an unattainable goal, reduction in local failure in prostate cancer would likely increase the overall cure rate in this disease.

Pions--the potential for therapeutic gain in locally advanced prostate cancer: dose escalation and toxicity studies

Since 1982, 49 patients with locally advanced carcinoma of the prostate have been treated with pion radiotherapy in tolerance and tumor response studies. The relative biological effectiveness (RBE) was confirmed as 1.5 for both acute and late effects, a figure expected on the basis of animal and human studies. The radiation dose has been safely escalated to tolerance, which is estimated to be 37.5 Gy pi in 15 fractions (volume less than 500 cc), and 36 Gy pi in 15 fractions (volume 500-800 cc). Severe acute toxicity occurred in 6% and severe chronic toxicity in 4%, figures comparable to those seen with conventional radiotherapy. The equivalent photon doses are approximately 78 Gy in 39 fractions and 73 Gy in 36 fractions, respectively. That this high dose can be delivered with no increase in toxicity is a reflection of smaller volume radiotherapy achieved by exploiting the dose distribution and biological characteristics of pions. Local response rates of 94% are reported. A Phase III study is now under way.

The effect of overall treatment time on the outcome of definitive radiotherapy for localized prostate carcinoma: the Radiation Therapy Oncology Group 75-06 and 77-06 experience

From 1976 to 1983, 1091 patients were entered into RTOG protocols 75-06 and 77-06. Of these, 780 patients complied with protocol requirements, received a minimum tumor dose of greater than or equal to 6500 cGy, and received no endocrine therapy. There were 78, 342, and 360 patients with localized prostate carcinoma, Stages T1b(A2), T2(B), and T3,4(C), respectively. The potential follow-up period ranges from 6 years 5 months to 13 years 3 months, with a median follow-up of 9 years. This study examines the influence of overall treatment time on the outcome of definitive radiotherapy for localized prostate carcinoma in this patient population. Within each stage, patients were divided into three groups according to the total number of elapsed days while on treatment: within 49 days (less than or equal to 7 weeks); 50 to 63 days (8 to 9 weeks); and greater than or equal to 64 days (greater than 9 weeks). Based on actuarial analysis, within each stage, the overall treatment time did not have any impact on the following: overall survival, NED survival, or local/regional control. When grouped under different histologic grades, that is, Gleason scores 2-5, 6-7, and 8-10, the actuarial local/regional control showed no statistical difference among the three groups. The actual local/regional failures were analyzed and stratified by stage and Gleason scores, and no statistical difference was noted among the three groups for each stratification. The range of local/regional failure rates among the three groups for T1b(A2), T2(B), and T3,4(C) disease were 0%-8%, 16%-23%, and 24%-27%, respectively. The corresponding range of local/regional failure rates for patients with Gleason scores of 2-5, 6-7, and 8-10 were 13%-14%, 18%-22%, and 22%-33%, respectively. The incidence of late complications was not related to the number of elapsed treatment days. Therefore, the overall treatment time does not have an impact on the outcome of definitive radiotherapy for localized prostate carcinoma. It is hypothesized that prostate carcinoma behaves as late-reacting tissue in which there is little, if any, accelerated repopulation of clonogenic tumor cells during the later half of a protracted course of radiotherapy. This observation is in direct contrast to that suggested for head and neck carcinoma and bears important implications in daily radiotherapeutic management of patients with prostate carcinoma.

Radiation therapy for the management of localized prostate carcinoma

Radiation therapy has been reported as an effective modality for the curative management of localized prostate carcinoma. In a 6 year period (1982-87), 141 patients with localized prostate carcinoma were treated at Auckland Hospital. Most patients were given radiation to the prostate alone. The overall local failure rate was 14%, with 57 patients developing distant metastases at the time of analysis. Toxicity was generally acceptable but was clearly related to the size of the treatment volume. The 5 year actuarial survival for all patients was 69.5%. Relapse-free survival rate was 39% at 5 years. Clinical stage and histological differentiation were significant factors affecting survival. Histology was a significant factor in local control. Radiation therapy for localized prostate carcinoma is effective, with a high rate of local control and low morbidity.

The effect of local control on metastatic dissemination in carcinoma of the prostate: long-term results in patients treated with 125I implantation

The study evaluates the effect of the locally recurring tumor on the incidence of metastatic disease in early stage carcinoma of the prostate. The probability of distant metastases was studied in 679 patients with Stage B-C/N0 carcinoma of the prostate treated at MSKCC between 1970 and 1985 (median follow-up of 97 months). Patients were staged with pelvic lymph node dissection and treated with retropubic 125I implantation. The actuarial distant metastases free survival (DMFS) for patients at risk at 15 years after initial therapy was 37%. Cox proportional hazard regression analysis of covariates affecting the metastatic outcome showed that local failure, used in the model as a time dependent variable, was the most significant covariate, although stage, grade, and implant volume were also found to be independent variables. The relative risk of metastatic spread subsequent to local failure was 4-fold increased compared to the risk without evidence of local relapse. The 15-year actuarial DMFS in 351 patients with local control was 77% compared to 24% in 328 patients who developed local relapses (p less than 0.00001). The relation of distant spread to the local outcome was observed regardless of stage, grade, or implant dose. Even stage B1/N0-Grade I patient with local control showed a 15-year actuarial DMFS of 82%, compared to 22% in patients with local relapse; p less than 0.00001). The median local relapse-free survival (LRFS) in the 268 patients with local recurrences who did not receive hormonal therapy before distant metastases were detected was 51 months, compared to a median of 71 months for DMFS in the same patients (p less than 0.001), consistent with the possibility that distant dissemination may develop secondary to local failure. Furthermore, distant metastases in patients with local control, apparently already existing as micrometastases before treatment, were detected earlier (median DMFS of 37 months) than in patients with local relapse (median DMFS of 54 months; p = 0.009). These data suggest that the existence and re-growth of local residual disease in localized prostatic carcinoma promotes an enhanced spread of metastatic disease, and that early and complete eradication of the primary tumor is required if a long term cure is to be achieved, although the clinical expression of secondary metastases may not become apparent for 6.5 years or more in one-half of the patients.

Carcinoma of the prostate stage B and C: lack of influence of duration of radiotherapy on tumor control and treatment morbidity

Between 1966 and 1985, 542 of 585 patients with histologically confirmed carcinoma of the prostate, Stages B and C, were treated with definitive radiation therapy to a minimum of 6300 cGy. There were 191 Stage B patients and 351 Stage C patients. The median tumor dose for Stage B patients was 6957 cGy and for Stage C patients 7020 cGy. Daily fractions of 180 to 200 cGy were given 4 or 5 times per week with occasional rest periods of several days, usually because of side effects of radiation therapy. The minimum follow-up time was 3 years; maximum follow-up was 16.0 years, and the median was 4.8 years. In this analysis, within each stage, patients were divided into four groups based on the number of treatment days: less than or equal to 56 days (8 weeks), 57 to 63 days (9 weeks), 64 to 70 days (10 weeks), and greater than 70 days. The distribution of Stage B and Stage C patients by histologic grade and duration of therapy is fairly even within each group. The influence of duration of radiotherapy on actuarial survival, progression-free survival, pelvic control, and incidence of complications was analyzed, and no statistical difference among the four groups of patients was found. The scatterplots of pelvic failure by radiation dose and duration of radiotherapy for both Stage B and C prostate carcinoma patients did not show a correlation between failure rate and duration of radiotherapy. Tumor histologic grade did not influence the incidence of pelvic failure. In summary, within the dose range used in this analysis the overall length of radiation treatment time did not seem to affect the clinical outcome of patients with Stage B and C prostate carcinoma.