When tumor repopulation starts? The onset time of prostate cancer during radiation therapy

Every-Other-Day Versus Once-a-Week Urethra-Sparing Prostate Stereotactic Body Radiation Therapy: 5-Year Results of a Randomized Phase 2 Trial

PURPOSE

The objective of this study was to present the 5-year results from a prospective, multicenter, phase 2 randomized trial of every-other-day (EOD) versus once-a-week (QW) urethra-sparing stereotactic body radiation therapy for localized prostate cancer.

METHODS AND MATERIALS

Between 2012 and 2015, 170 patients with cT1c-3aN0M0 prostate cancer from 9 European institutions were randomized to 36.25 Gy in 5 fractions (6.5 Gy/fraction to the urethra) delivered either EOD (arm A, n = 84) or QW (arm B, n = 86). The median follow-up was 78 months (interquartile range, 66-89 months) and 77 months (interquartile range, 66-82 months) for arms A and B, respectively.

RESULTS

Among the 165 patients treated and retained for the final analysis (arm A, n = 82; arm B, n = 83), acute toxicity (National Cancer Institute Common Terminology Criteria for Adverse Events version 4.03 scale) was mild or absent, with no differences between arms. The 5-year grade 2 or greater genitourinary toxicity-free survival was 75.9% and 76.1% for arms A and B, respectively (P = .945), whereas the 5-year grade 2 or greater gastrointestinal toxicity-free survival was 89% and 92% for arms A and B, respectively (P = .596). No changes in European Organisation for Research and Treatment of Cancer QLQ-PR25 scores were observed in both arms for genitourinary, gastrointestinal, and sexual domains at 5-year follow-up compared with baseline. At the last follow-up, biochemical failure was observed in 14 patients in the EOD arm and in 7 patients in the QW arm, with a 5-year biochemical relapse-free survival rate of 92.2% and 93% for arms A and B, respectively (P = .13).

CONCLUSIONS

Stereotactic body radiation therapy for prostate cancer with a 10% dose reduction to urethra was associated with a minimal effect on urinary function and quality of life regardless of an EOD or QW fractionation schedule. Biochemical control so far has been encouraging and much alike in both study arms, although longer follow-up is probably needed to assess the true value of overall treatment time on disease outcome.

Voxel-level biological optimisation of prostate IMRT using patient-specific tumour location and clonogen density derived from mpMRI

AIMS

This study aimed to develop a framework for optimising prostate intensity-modulated radiotherapy (IMRT) based on patient-specific tumour biology, derived from multiparametric MRI (mpMRI). The framework included a probabilistic treatment planning technique in the effort to yield dose distributions with an improved expected treatment outcome compared with uniform-dose planning approaches.

METHODS

IMRT plans were generated for five prostate cancer patients using two inverse planning methods: uniform-dose to the planning target volume and probabilistic biological optimisation for clinical target volume tumour control probability (TCP) maximisation. Patient-specific tumour location and clonogen density information were derived from mpMRI and geometric uncertainties were incorporated in the TCP calculation. Potential reduction in dose to sensitive structures was assessed by comparing dose metrics of uniform-dose plans with biologically-optimised plans of an equivalent level of expected tumour control.

RESULTS

The planning study demonstrated biological optimisation has the potential to reduce expected normal tissue toxicity without sacrificing local control by shaping the dose distribution to the spatial distribution of tumour characteristics. On average, biologically-optimised plans achieved 38.6% (p-value: < 0.01) and 51.2% (p-value: < 0.01) reduction in expected rectum and bladder equivalent uniform dose, respectively, when compared with uniform-dose planning.

CONCLUSIONS

It was concluded that varying the dose distribution within the prostate to take account for each patient's clonogen distribution was feasible. Lower doses to normal structures compared to uniform-dose plans was possible whilst providing robust plans against geometric uncertainties. Further validation in a larger cohort is warranted along with considerations for adaptive therapy and limiting urethral dose.

Applications of Nonlinear Programming to the Optimization of Fractionated Protocols in Cancer Radiotherapy

The present work of review collects and evidences the main results of our previous papers on the optimization of fractionated radiotherapy protocols. The problem under investigation is presented here in a unitary framework as a nonlinear programming application that aims to determine the optimal schemes of dose fractionation commonly used in external beam radiotherapy. The radiation responses of tumor and normal tissues are described by means of the linear quadratic model. We formulate a nonlinear, non-convex optimization problem including two quadratic constraints to limit the collateral normal tissue damages and linear box constraints on the fractional dose sizes. The general problem is decomposed into two subproblems: (1) analytical determination of the optimal fraction dose sizes as a function of the model parameters for arbitrarily fixed treatment lengths; and (2) numerical determination of the optimal fraction number, and of the optimal treatment time, in different parameter settings. After establishing the boundedness of the optimal number of fractions, we investigate by numerical simulation the optimal solution behavior for experimentally meaningful parameter ranges, recognizing the crucial role of some parameters, such as the radiosensitivity ratio, in determining the optimality of hypo- or equi-fractionated treatments. Our results agree with findings of the theoretical and clinical literature.

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.

Long-term results of a phase II study of hypofractionated proton therapy for prostate cancer: moderate versus extreme hypofractionation

Background

We performed a prospective phase II study to compare acute toxicity among five different hypofractionated schedules using proton therapy. This study was an exploratory analysis to investigate the secondary end-point of biochemical failure-free survival (BCFFS) of patients with long-term follow-up.

Methods

Eighty-two patients with T1-3bN0M0 prostate cancer who had not received androgen-deprivation therapy were randomized to one of five arms: Arm 1, 60 cobalt gray equivalent (CGE)/20 fractions/5 weeks; Arm 2, 54 CGE/15 fractions/5 weeks; Arm 3, 47 CGE/10 fractions/5 weeks; Arm 4, 35 CGE/5 fractions/2.5 weeks; and Arm 5, 35 CGE/5 fractions/4 weeks. In the current exploratory analysis, these ardms were categorized into the moderate hypofractionated (MHF) group (52 patients in Arms 1–3) and the extreme hypofractionated (EHF) group (30 patients in Arms 4–5).

Results

At a median follow-up of 7.5 years (range, 1.3–9.6 years), 7-year BCFFS was 76.2% for the MHF group and 46.2% for the EHF group (p = 0.005). The 7-year BCFFS of the MHF and EHF groups were 90.5 and 57.1% in the low-risk group (p = 0.154); 83.5 and 42.9% in the intermediate risk group (p = 0.018); and 41.7 and 40.0% in the high risk group (p = 0.786), respectively. Biochemical failure tended to be a late event with a median time to occurrence of 5 years. Acute GU toxicities were more common in the MHF than the EHF group (85 vs. 57%, p = 0.009), but late GI and GU toxicities did not differ between groups.

Conclusions

Our results suggest that the efficacy of EHF is potentially inferior to that of MHF and that further studies are warranted, therefore, to confirm these findings.

Trial registration

This study is registered at ClinicalTrials.gov, no. NCT01709253; registered October 18, 2012; retrospectively registered).

Relating the proton relative biological effectiveness to tumor control and normal tissue complication probabilities assuming interpatient variability in α/β

BACKGROUND

Proton therapy uses a constant relative biological effectiveness (RBE) of 1.1. The use of variable RBE values has been suggested but is currently not feasible due to uncertainties. The impact of variable RBE has solely been studied using dosimetric indices. This work elucidates the impact of RBE variations on tumor control and normal tissue complication probabilities (TCP/NTCP).

METHODS

Models to estimate TCP and NTCP were used in combination with an empirical proton RBE model. Variations in outcome as a function of linear-quadratic model parameters for cellular radiosensitivity were determined for TCP in prostate and ependymoma. In addition, NTCP analysis was done for brainstem necrosis.

RESULTS

Considering a variable proton RBE as a dose-modifying factor for prescription doses and dose constraints is misleading, as TCP/NTCP do not simply scale with RBE. The dependency of RBE on α/β cannot be interpreted independent of TCP/NTCP because variations in radiosensitivity affect both photon and proton treatments. Assuming interpatient variability in radiosensitivity results in lower TCP for patients with low α/β. In proton therapy, the magnitude of TCP variations is reduced due to an RBE increase as α/β decreases. The TCP in proton therapy is less affected by interpatient variability in α/β. On the other hand, patients with a lower α/β would have a lower complication probability, which is counteracted by an increase in RBE as α/β decreases. Toxicities in proton therapy would be more affected by α/β variations compared to photon therapy.

CONCLUSIONS

Assessment of variable RBE in proton therapy should be based on TCP and NTCP. Potential interpatient variability in radiosensitivity causes a smaller variance in TCP but a larger variance in NTCP for proton patients. The relative TCP as a function of α/β was found to be higher than the RBE, whereas the relative NTCP was lower than a calculated RBE.

Conventional Versus Hypofractionated Radiation Therapy for Localized or Locally Advanced Prostate Cancer: A Systematic Review and Meta-analysis along with Therapeutic Implications

PURPOSE

A systematic review and meta-analysis were conducted to evaluate the therapeutic outcomes of conventional radiation therapy (CRT) and hypofractionated radiation therapy (HRT) for localized or locally advanced prostate cancer (LLPCa).

METHODS AND MATERIALS

A total of 599 abstracts were extracted from 5 databases and screened in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Only phase III trials randomized between CRT and HRT in LLPCa with a minimum of 5 years of follow-up data were considered. The evaluated endpoints were biochemical failure, biochemical and/or clinical failure, overall mortality, prostate cancer-specific mortality, and both acute and late gastrointestinal (GI) and genitourinary (GU) (grade ≥2) toxicity.

RESULTS

Ten trials from 9 studies, with a total of 8146 patients (CRT, 3520; HRT, 4626; 1 study compared 2 HRT schedules with a common CRT regimen), were included in the evaluation. No significant differences were found in the patient characteristics between the 2 arms. However, the RT parameters differed significantly between CRT and HRT (P<.001 for all). The use of androgen deprivation therapy varied from 0% to 100% in both groups (mean ± standard deviation 43.3% ± 43.6% for CRT vs HRT; P=NS). The odds ratio, risk ratio, and risk difference (RD) between CRT and HRT for biochemical failure, biochemical and/or clinical failure, overall mortality, prostate cancer-specific mortality, acute GU toxicity, and late GU and GI toxicities were all nonsignificant. Nevertheless, the incidence of acute GI toxicity was 9.1% less with CRT (RD 0.091; odds ratio 1.687; risk ratio 1.470; P<.001 for all). On subgroup analysis, the patient groups with ≤66.8% versus >66.8% androgen deprivation therapy (RD 0.052 vs 0.136; P=.008) and <76% versus ≥76% full seminal vesicles in the clinical target volume (RD 0.034 vs 0.108; P<.001) were found to significantly influence the incidence of acute GI toxicity with HRT.

CONCLUSIONS

HRT provides similar therapeutic outcomes to CRT in LLPCa, except for a significantly greater risk of acute GI toxicity. HRT enables a reduction in the overall treatment time and offers patient convenience. However, the variables contributing to an increased risk of acute GI toxicity require careful consideration.

A validated tumor control probability model based on a meta-analysis of low, intermediate, and high-risk prostate cancer patients treated by photon, proton, or carbon-ion radiotherapy

PURPOSE

A fully heterogeneous population averaged mechanistic tumor control probability (TCP) model is appropriate for the analysis of external beam radiotherapy (EBRT). This has been accomplished for EBRT photon treatment of intermediate-risk prostate cancer. Extending the TCP model for low and high-risk patients would be beneficial in terms of overall decision making. Furthermore, different radiation treatment modalities such as protons and carbon-ions are becoming increasingly available. Consequently, there is a need for a complete TCP model.

METHODS

A TCP model was fitted and validated to a primary endpoint of 5-year biological no evidence of disease clinical outcome data obtained from a review of the literature for low, intermediate, and high-risk prostate cancer patients (5218 patients fitted, 1088 patients validated), treated by photons, protons, or carbon-ions. The review followed the preferred reporting item for systematic reviews and meta-analyses statement. Treatment regimens include standard fractionation and hypofractionation treatments. Residual analysis and goodness of fit statistics were applied.

RESULTS

The TCP model achieves a good level of fit overall, linear regression results in a p-value of <0.000 01 with an adjusted-weighted-R(2) value of 0.77 and a weighted root mean squared error (wRMSE) of 1.2%, to the fitted clinical outcome data. Validation of the model utilizing three independent datasets obtained from the literature resulted in an adjusted-weighted-R(2) value of 0.78 and a wRMSE of less than 1.8%, to the validation clinical outcome data. The weighted mean absolute residual across the entire dataset is found to be 5.4%.

CONCLUSIONS

This TCP model fitted and validated to clinical outcome data, appears to be an appropriate model for the inclusion of all clinical prostate cancer risk categories, and allows evaluation of current EBRT modalities with regard to tumor control prediction.

Moderate Hypofractionated Protracted Radiation Therapy and Dose Escalation for Prostate Cancer: Do Dose and Overall Treatment Time Matter?

PURPOSE

This was a retrospective study of 2 sequential dose escalation regimens of twice-weekly 4 Gy/fractions hypofractionated intensity modulated radiation therapy (IMRT): 56 Gy and 60 Gy delivered within a protracted overall treatment time (OTT) of 6.5 and 7 weeks, respectively.

METHODS AND MATERIALS

163 prostate cancer patients with cT1c-T3a disease and nodal involvement risk ≤20% (Roach index) were treated twice weekly to the prostate ± seminal vesicles with 2 sequential dose-escalated IMRT schedules: 56 Gy (14 × 4 Gy, n=81) from 2003 to 2007 and 60 Gy (15 × 4 Gy, n=82) from 2006 to 2010. Patient repositioning was made with bone matching on portal images. Gastrointestinal (GI) and genitourinary (GU) toxicities were scored according to the Common Terminology Criteria for Adverse Events version 3.0 grading scale.

RESULTS

There were no significant differences regarding the acute GU and GI toxicities in the 2 dose groups. The median follow-up times were 80.2 months (range, 4.5-121 months) and 56.5 months (range, 1.4-91.2 months) for patients treated to 56 and 60 Gy, respectively. The 5-year grade ≥2 late GU toxicity-free survivals with 56 Gy and 60 Gy were 96 ± 2.3% and 78.2 ± 5.1% (P=.001), respectively. The 5-year grade ≥2 late GI toxicity-free survivals with 56 Gy and 60 Gy were 98.6 ± 1.3% and 85.1 ± 4.5% (P=.005), respectively. Patients treated with 56 Gy showed a 5-year biochemical progression-free survival (bPFS) of 80.8 ± 4.7%, worse than patients treated with 60 Gy (93.2 ± 3.9%, P=.007). A trend for a better 5-year distant metastasis-free survival was observed among patients treated in the high-dose group (95.3 ± 2.7% vs 100%, P=.073, respectively). On multivariate analysis, only the 60-Gy group predicted for a better bPFS (P=.016, hazard ratio = 4.58).

CONCLUSIONS

A single 4-Gy additional fraction in patients treated with a hypofractionated protracted IMRT schedule of 14 × 4 Gy resulted in a similar and minimal acute toxicity, in worse moderate to severe urinary and GI late effects, but a significantly better biochemical control.

Repopulation of tumor cells during fractionated radiotherapy and detection methods (Review)

Repopulation of tumor cells during radiotherapy is believed to be a significant cause for treatment failure. The phenomenon of tumor repopulation during fractionated radiotherapy was found from clinical observations that identified that the local control rate decreased with a prolonged treatment time. A series of animal experiments with varied overall treatment time and fractionated doses were performed to demonstrate tumor cell repopulation during radiotherapy in various mouse xenograft models. However, conventional detection methods are challenging, as it is difficult to separate viable cells from those destined for apoptosis during fractionated radiotherapy. In essence, the mechanism of tumor repopulation involves the continuing proliferation of clonogenic tumor cells. In vivo imaging, tracking and targeting of the repopulation of these cells has been of clinical interest so as to administer a higher dose to the tumor repopulation regions. Currently, functional imaging methods, including 3'-deoxy-3'-¹⁸F-fluorothymidine positron emission tomography (¹⁸F-FLT PET), are showing promise in assessing the proliferation activity of tumors in vivo. This review mainly focuses on the phenomenon of tumor repopulation during radiotherapy and its conventional and novel detection methods, particularly on the feasibility of ¹⁸F-FLT PET for the detection of tumor-cell repopulation.

Radiobiological comparison of two radiotherapy treatment techniques for high-risk prostate cancer

BACKGROUND

To make a radiobiological comparison, for high risk prostate cancer (T3a, PSA > 20 ng/ml or Gleason > 7) of two radiotherapy treatment techniques. One technique consists of a treatment in three phases of the pelvic nodes, vesicles and prostate using a conventional fractionation scheme of 2 Gy/fraction (SIMRT). The other technique consists of a treatment in two phases that gives simultaneously different dose levels in each phase, 2 Gy/fraction, 2.25 Gy/fraction and 2.5 Gy/fraction to the pelvic nodes, vesicles and prostate, respectively (SIBIMRT).

MATERIALS AND METHODS

The equivalent dose at fractionation of 2 Gy (EQD2), calculated using the linear quadratic model with α/β prostate = 1.5 Gy, was the same for both treatment strategies. For comparison the parameters employed were D95, mean dose and Tumour Control Probabilities for prostate PTV and D15, D25, D35, D50, mean dose and Normal Tissue Complication Probabilities for the rectum and bladder, with physical doses converted to EQD2. Parameters were obtained for α/β prostate = 1.5, 3 and 10 Gy and for α/β oar = 1, 2, 3, 4, 6 and 8.

RESULTS

For prostate PTV, both treatment strategies are equivalent for α/β prostate = 1.5 Gy but for higher α/β prostate, EQD2 and TCP, decrease for the SIBIMRT technique. For the rectum and bladder when α/β oar ≤ 2 Gy, EQD2 and NTCP are lower for the SIMRT technique or equal in both techniques. For α/β oar ≥ 2-3 Gy, EQD2 and NTCP increase for the SIMRT treatment.

CONCLUSIONS

A comparison between two radiotherapy techniques is presented. The SIBIMRT technique reduces EQD2 and NTCP for α/β oar from 2 to 8 Gy.

Compensability index for compensation radiotherapy after treatment interruptions

BACKGROUND

The goal of our work was to develop a simple method to evaluate a compensation treatment after unplanned treatment interruptions with respect to their tumour- and normal tissue effect.

METHODS

We developed a software tool in java programming language based on existing recommendations to compensate for treatment interruptions. In order to express and visualize the deviations from the originally planned tumour and normal tissue effects we defined the compensability index.

RESULTS

The compensability index represents an evaluation of the suitability of compensatory radiotherapy in a single number based on the number of days used for compensation and the preference of preserving the originally planned tumour effect or not exceeding the originally planned normal tissue effect. An automated tool provides a method for quick evaluation of compensation treatments.

CONCLUSIONS

The compensability index calculation may serve as a decision support system based on existing and established recommendations.

Hypofractionation for radiotherapy of prostate cancer using a low alfa/beta ratio--possible reasons for concerns? An example of five dimensional radiotherapy

It is very attractive, due to the assumed low alfa/beta ratio of prostate cancer (PC), to construct new treatment schedules for prostate cancer using only a few large fractions of radiation (hypofractionation). This will widen the therapeutic window since the ratio for PC might be lower than that of the organs at risk (OAR). PC is an extremely variable disease and often contains both highly and poorly differentiated cells. It is reasonable to assume that different cells have different patterns of radiosensitivity, i.e. alfa/beta ratios and proliferation. In this study we will simulate the effect on the outcome of the treatment with different fractionations and different ratios.

MATERIAL AND METHODS

In this simulation we use an extension of the Linear Quadratic (LQ)/Biological Effective Dose (BED) formula called the dose volume inhomogeneity corrected BED (DVIC-BED). In the formula the tumour volume is divided in 50 subvolumes (step of 2%) and it is possible to calculate the relative effect of the treatment with different ratios (1.5, 4 and 6.5) in different subvolumes.

RESULTS

The simulations demonstrate that only a small portion (5-10%) of cells with a higher ratio will dramatically change the effect of the treatment. Increasing the total dose can compensate this, but this will on the other hand increase the dose to the OAR and also the risk for severe side effects.

CONCLUSION

These simulations highlight possible reasons for concerns about the use of hypofractionation for pathologically heterogeneous tumours, such as prostate cancer, and also demonstrate the need for testing new treatment schedules using both high and low ratios.