An analysis of clinical and treatment related prognostic factors on outcome using biochemical control as an end-point in patients with prostate cancer treated with external beam irradiation

Twice- vs. thrice-weekly moderate hypofractionated radiotherapy for prostate cancer: does overall treatment time matter?

PURPOSE

To evaluate the influence of overall treatment time (OTT) in disease control, acute, and long-term side effects with moderate hypofractionated external beam radiotherapy (RT) for prostate cancer (PCa) delivered either twice- or thrice-a-week.

METHODS

157 patients with localized PCa were treated consecutively with 56 Gy in 4 Gy/fraction delivered either twice (86 patients, from 2003 to 2010, group-1) or thrice a week (71 patients, from 2010 to 2017, group-2) using IMRT or VMAT techniques. Gastrointestinal (GI) and genitourinary (GU) toxicities were scored according to the CTCAE v3.0 grading scale. Median follow-up was 110 and 56 months for groups 1 and 2, respectively.

RESULTS

At 6 weeks, patients treated thrice-a-week experienced higher acute ≥ grade-2 GU toxicity compared to those treated twice a week (25.4% vs 5.8%, p = 0.001) even though none presented ≥ grade-3 GU or GI toxicity in the thrice-a-week group. The 5-year ≥ grade-2 late GU toxicity-free survival was higher in group-1 (95.9 ± 2.3%) than in group-2 (81.5 ± 4.9%, p = 0.003), while no differences in ≥ grade-2 late GI toxicity-free survival were observed between both groups (97.5 ± 1.7% vs. 97 ± 2.1% for groups 1 and 2, respectively). The 5-year biochemical relapse-free survival (bRFS) was not different for patients treated twice compared to those treated thrice-a-week (80.6 ± 4.5% vs. 85.3 ± 4.8%, respectively, p = 0.441), as much as for patients treated in > 5 weeks vs. those treated in ≤ 5 weeks (81.3 ± 4.4% vs. 84.4 ± 5.1%, respectively, p = 0.584).

CONCLUSIONS

In this retrospective hypothesis-generating analysis, less vs. more than 5 weeks OTT may increase acute and late GU toxicities without significantly improving bRFS in patients treated to high effective doses (> 80 Gy) with moderate hypofractionated RT. Prospective trials evaluating the impact of OTT on hypofractionated schedules for PCa are warranted.

Prostate alpha/beta revisited -- an analysis of clinical results from 14 168 patients

PURPOSE

To determine the dose response parameters and the fractionation sensitivity of prostate tumours from clinical results of patients treated with external beam radiotherapy.

MATERIAL AND METHODS

The study was based on five-year biochemical results from 14 168 patients treated with external beam radiotherapy. Treatment data from 11 330 patients treated with conventional fractionation have been corrected for overall treatment time and fitted with a logit equation. The results have been used to determine the optimum α/β values that minimise differences in predictions from 2838 patients treated with hypofractionated schedules.

RESULTS

Conventional fractionation data yielded logit dose response parameters for all risk groups and for all definitions of biochemical failures. The analysis of hypofractionation data led to very low α/β values (1-1.7 Gy) in all mentioned cases. Neglecting the correction for overall treatment time has little impact on the derivation of α/β values for prostate cancers.

CONCLUSIONS

These results indicate that the high fractionation sensitivity is an intrinsic property of prostate carcinomas and they support the use of hypofractionation to increase the therapeutic gain for these tumours.

Prolongation of total treatment time because of infrequently missed days of treatment is not associated with inferior biochemical outcome after dose-escalated radiation therapy for prostate cancer

PURPOSE

Prolongation of treatment time with radiation therapy (RT) is associated with inferior disease control for many rapidly proliferating tumors, but it is uncertain whether the same effect is seen in prostate cancer.

METHODS AND MATERIALS

596 patients underwent with curative-intent RT for adenocarcinoma of the prostate. By National Comprehensive Cancer Network criteria, men were classified as having low-risk (30%), medium-risk (40%), or high-risk (30%) disease. The median RT dose was 72 Gy. Androgen-deprivation therapy (ADT) was used in 45%. The idealized treatment time was defined as the total elapsed time (including weekends) to complete treatment if started on a Monday. Missed days of treatment, defined as the number of days beyond the idealized treatment time, was recorded for all patients. Missed days were added to the end of therapy resulting in a longer treatment time. Analysis was conducted for missed days and other standard prognostic variables against freedom from biochemical failure (FFBF).

RESULTS

The median number of missed days was 2 (range, -3 to 22). With a median follow-up of 51 months, men with 5 or more missed days had similar 4-year FFBF rates (79% vs. 83% in men with <5 missed days, p = 0.0809), especially in the subset of men receiving 74 Gy or greater (89% for both groups, p = 0.8008). Analysis of missed days was performed for the subsets of dose, ADT, and risk category. Men without ADT had a lower FFBF rate with more missed days (p = 0.0030), but this association was not seen in men treated to a dose of 74 Gy or greater (p = 0.7425). On multivariate analysis, dose (p = 0.0010), T stage (p = 0.0145), and prostate-specific antigen level (p < 0.0001) were associated with FFBF, but Gleason score (p = 0.1351) and missed days (p = 0.3767) were not.

CONCLUSIONS

Slight prolongation of treatment time (e.g., ≤7 days) was not associated with inferior FFBF, especially in men receiving an RT dose of 74 Gy or greater.

Dual radiobiological interpretations of retrospective clinical data: the time factor

Dual interpretations are different radiobiological mechanisms that explain theoretically the same observed results. Radiobiological interpretations of the time factor are most frequently based on changes in total dose that produce a given effect. If this dose is increased by different mechanisms (e.g. increasing overall time and decreasing dose per fraction) at the same time, proposals for altered fractionation schemes based on the choice of one or the other mechanism, in principle, can lead to erroneous predictions of outcome. This is especially the case when the analyses are based on retrospective clinical data, where the influence of patient selection is unknown. Examples of dual interpretations taken from the literature on head and neck, melanoma and prostate cancer are discussed.

Does treatment duration affect outcome after radiotherapy for prostate cancer?

PURPOSE

The protraction of external beam radiotherapy (RT) time is detrimental in several disease sites. In prostate cancer, the overall treatment time can be considerable, as can the potential for treatment breaks. We evaluated the effect of elapsed treatment time on outcome after RT for prostate cancer.

METHODS AND MATERIALS

Between April 1989 and November 2004, 1,796 men with prostate cancer were treated with RT alone. The nontreatment day ratio (NTDR) was defined as the number of nontreatment days divided by the total elapsed days of RT. This ratio was used to account for the relationship between treatment duration and total RT dose. Men were stratified into low risk (n = 789), intermediate risk (n = 798), and high risk (n = 209) using a single-factor model.

RESULTS

The 10-year freedom from biochemical failure (FFBF) rate was 68% for a NTDR <33% vs. 58% for NTDR >/=33% (p = 0.02; BF was defined as a prostate-specific antigen nadir + 2 ng/mL). In the low-risk group, the 10-year FFBF rate was 82% for NTDR <33% vs. 57% for NTDR >/=33% (p = 0.0019). The NTDR was independently predictive for FFBF (p = 0.03), in addition to T stage (p = 0.005) and initial prostate-specific antigen level (p < 0.0001) on multivariate analysis, including Gleason score and radiation dose. The NTDR was not a significant predictor of FFBF when examined in the intermediate-risk group, high-risk group, or all risk groups combined.

CONCLUSIONS

A proportionally longer treatment duration was identified as an adverse factor in low-risk patients. Treatment breaks resulting in a NTDR of >/=33% (e.g., four or more breaks during a 40-fraction treatment, 5 d/wk) should be avoided.

What does postradiotherapy PSA nadir tell us about freedom from PSA failure and progression-free survival in patients with low and intermediate-risk localized prostate cancer?

OBJECTIVES

To determine whether the post-external beam radiotherapy (RT) prostate-specific antigen nadir (nPSA) improves our ability to predict freedom from PSA failure, progression-free survival (PFS), and overall survival. Controversy regarding the importance of nPSA after external beam RT as a prognostic indicator for patients with localized prostate cancer has continued.

METHODS

This analysis was based on the data from 748 patients with low and intermediate-risk localized prostate cancer treated with external beam RT alone. Patients were categorized by nPSA quartile groups with cutpoints of less than 0.3, 0.3 to less than 0.6, 0.6 to less than 1.2, and 1.2 ng/mL or greater. Both univariate and multivariate analyses were used to determine the significance of nPSA on PSA failure (American Society for Therapeutic Radiology Oncology consensus definition), PFS (death after PSA failure), and overall survival (death from any cause).

RESULTS

Freedom from PSA failure was strongly associated with nadir quartile groups (P <0.0001). PFS was also significantly different statistically among nadir quartile groups (P = 0.02). No statistically significant difference was found in overall survival associated with nPSA at this point.

CONCLUSIONS

nPSA is a strong independent predictor of freedom from PSA failure and PFS in patients with low and intermediate-risk localized prostate cancer treated with RT alone. Longer follow-up and larger patient numbers are required to confirm these observations.

Chemical disease-free survival in localized carcinoma of prostate treated with external beam irradiation: comparison of American Society of Therapeutic Radiology and Oncology Consensus or 1 ng/mL as endpoint

PURPOSE

To compare postirradiation biochemical disease-free survival using the American Society of Therapeutic Radiology and Oncology (ASTRO) Consensus or elevation of postirradiation prostate-specific antigen (PSA) level beyond 1 ng/mL as an endpoint and correlate chemical failure with subsequent appearance of clinically detected local recurrence or distant metastasis.

METHODS AND MATERIALS

Records of 466 patients with histologically confirmed adenocarcinoma of the prostate treated with irradiation alone between January 1987 and December 1995 were analyzed; 339 patients were treated with bilateral 120 degrees arc rotation and, starting in 1992, 117 with three-dimensional conformal irradiation. Doses were 68--77 Gy in 1.8 to 2 Gy daily fractions. Minimum follow-up is 4 years (mean, 5.5 years; maximum, 9.6 years). A chemical failure was recorded using the ASTRO Consensus or when postirradiation PSA level exceeded 1 ng/mL at any time. Clinical failures were determined by rectal examination, radiographic studies, and, when clinically indicated, biopsy.

RESULTS

Six-year chemical disease-free survival rates using the ASTRO Consensus according to pretreatment PSA level for T1 tumors were: < or = 4 ng/mL, 100%; 4.1--20 ng/mL, 80%; and > 20 ng/mL, 50%. For T2 tumors the rates were: < or = 4 ng/mL, 91%; 4.1--10 ng/mL, 81%; 10.1--20 ng/mL, 55%; 20.1--40 ng/mL, 63%; and > 40 ng/mL, 46%. When postirradiation PSA levels higher than 1 ng/mL were used, the corresponding 6-year chemical disease-free survival rates for T1 tumors were 92% for pretreatment PSA levels of < or = 4 ng/mL, 58--60% for levels of 4.1--20 ng/mL, and 30% for levels > 20 ng/mL. For T2 tumors, the 6-year chemical disease-free survival rates were 78% in patients with pretreatment PSA levels of 4--10 ng/mL, 45% for 10.1--40 ng/mL, and 25% for > 40 ng/mL. Of 167 patients with T1 tumors, 30 (18%) developed a chemical failure, 97% within 5 years from completion of radiation therapy; no patient has developed a local recurrence or distant metastasis. In patients with T2 tumors, overall 45 of 236 (19%) had chemical failure, 94% within 5 years of completion of radiation therapy; 4% have developed a local recurrence, and 10%, distant metastasis. In patients with T3 tumors, overall, 24 of 65 (37%) developed a chemical failure, 100% within 3.5 years from completion of radiation therapy; 4% of these patients developed a local recurrence within 2 years, and 12% developed distant metastasis within 4 years of completion of irradiation. The average time to clinical appearance of local recurrence or distant metastasis after a chemical failure was detected was 5 years and 3 years, respectively.

CONCLUSION

There was a close correlation between the postirradiation nadir PSA and subsequent development of a chemical failure. Except for patients with T1 tumors and pretreatment PSA of 4.1--20 ng/mL, there is good agreement in 6-year chemical disease-free survival using the ASTRO Consensus or PSA elevations above 1 ng/mL as an endpoint. Although the ASTRO Consensus tends to give a higher percentage of chemical disease-free survival in most groups, the differences with longer follow-up are not statistically significant (p > 0.05). It is important to follow these patients for at least 10 years to better assess the significance of and the relationship between chemical and clinical failures.