Prostate cancer radiation dose response: results of the M. D. Anderson phase III randomized trial

Acute and late toxicity after dose escalation to 82 GyE using conformal proton radiation for localized prostate cancer: initial report of American College of Radiology Phase II study 03-12

PURPOSE

Several randomized trials have shown a benefit of dose escalation to 78 to 79 Gy for men treated with external radiation for localized prostate cancer. Single-institution data suggest a benefit with even higher doses. American College of Radiology 03-12 is a Phase II trial testing the safety and efficacy of 82 GyE (Gray equivalent) delivered with conformal proton radiation.

METHODS AND MATERIALS

From 2003-2006, 85 men with localized prostate cancer were accrued to American College of Radiology 03-12. Eighty-four were eligible for analysis. They were treated with conformal proton radiation alone to a total dose of 82 GyE. The study was designed to test whether the rate of 18-month Grade 3+ late toxicity was greater than 10%.

RESULTS

The median follow-up was 31.6 months. Regarding treatment-related acute toxicity, there were 39 Grade 1 cases (46%), 19 Grade 2 cases (23%) and 2 Grade 3 cases (2%). Regarding genitourinary/gastrointestinal toxicity, there were 42 Grade 1 cases (50%), 12 Grade 2 cases (14%) and 1 Grade 3 case (1%). Regarding late toxicity, there were 28 Grade 1 cases (33%), 22 Grade 2 cases (26%), 6 Grade 3 cases (7%), and 1 Grade 4 case (1%). The late genitourinary/gastrointestinal rates were the same. The estimated rate of Grade 3+ late toxicity at 18 months was 6.08%.

CONCLUSIONS

Although not free of late toxicity, 82 GyE at 2 GyE per fraction delivered with conformal proton radiation did not exceed the late morbidity target tested in this trial. There was sufficient morbidity, however, that this may be the maximal dose that can be delivered safely with this technique and fractionation.

Long-term results after high-dose radiotherapy and adjuvant hormones in prostate cancer: how curable is high-risk disease?

PURPOSE

To analyze long-term outcome and prognostic factors for high-risk prostate cancer defined by National Comprehensive Cancer Network criteria treated with high-dose radiotherapy and androgen deprivation in a single institution.

METHODS AND MATERIALS

A total of 306 patients treated between 1995 and 2007 in a radiation dose-escalation program fulfilled the National Comprehensive Cancer Network high-risk criteria. Median International Commission on Radiation Units and Measurements radiation dose was 78 Gy (range, 66.0-84.1 Gy). Long-term androgen deprivation (LTAD) was administered in 231 patients, short-term androgen deprivation (STAD) in 59 patients, and no hormones in 16 patients. The Phoenix (nadir plus 2 ng/mL) consensus definition was used for biochemical control. Multivariate analysis was performed to determine the independent prognostic impact of clinical and treatment factors. Median follow-up time was 64 months (range, 24-171 months).

RESULTS

The actuarial overall survival at 5 and 10 years was 95.7% and 89.8%, respectively, and the corresponding biochemical disease-free survival (bDFS) was 89.5% and 67.2%, respectively. Fourteen patients (4.6%) developed distant metastasis. Multivariate analysis showed that Gleason score>7 (p=0.001), pretreatment prostate-specific antigen (PSA) level>20 ng/mL (p=0.037), higher radiation dose (p=0.005), and the use of adjuvant LTAD vs. STAD (p=0.011) were independent prognostic factors affecting bDFS in high-risk disease. The 5-year bDFS for patients treated with LTAD plus radiotherapy dose>78 Gy was 97%.

CONCLUSIONS

For high-risk patients the present series showed that the use of LTAD in conjunction with higher doses (>78 Gy) of radiotherapy was associated with improved biochemical tumor control. We observed that the presence of Gleason sum>7 and pretreatment PSA level>20 ng/mL in the same patient represents a 6.8 times higher risk of PSA failure. These men could be considered for clinical trials with addition of novel agents.

Propagation of target and organ at risk contours in radiotherapy of prostate cancer using deformable image registration

BACKGROUND

Successful deformable image registration is an essential component of both dose accumulation and plan adaptation in radiotherapy. The aim of this study was to evaluate the performance of a deformable image registration application for propagation of contours using repeat CT scans of the pelvis, a region where considerable deformations are expected.

MATERIAL AND METHODS

The study involved four prostate cancer patients, each with 9-11 repeat CT scans. An oncologist contoured bladder, rectum, clinical target volume of pelvic lymph nodes (CTV-ln) and prostate (CTV-p) in all CT scans. The reference CT was retrospectively registered to the repeat CT scans with both rigid and deformable registration using a recently released commercial clinical software application. Two different diffusion-based 'demons' deformable registration algorithms were applied, differing in the amount of deformations being allowed, with algorithm A being more generous than algorithm B. The evaluation of the propagated structures included both quantitative measures and qualitative scoring.

RESULTS

We found the differences between the algorithms to be most evident for bladder and rectum. An increase in mean Dice similarity coefficient relative the rigid registrations of 12% and 13% was obtained with algorithm A for bladder and rectum, compared to 2% with algorithm B. For bladder the mean sensitivity and positive predictive value was 0.92 and 0.87 with algorithm A and 0.82 and 0.83 with algorithm B. Corresponding values for rectum was 0.81 and 0.76 with algorithm A and 0.75 and 0.69 with algorithm B. This translated into 57% and 26% passing the clinical evaluation for bladder and rectum, with algorithm A, compared to 17% and 14% with algorithm B. For CTV-ln and CTV-p both algorithms performed well by all measures, e.g. with 86% of the target structures passing the clinical evaluation.

CONCLUSIONS

Deformable image registration improved contour propagation in the pelvis for all organs investigated. Differences in the performance of the algorithms were seen which became more pronounced for the highly deformable organs of bladder and rectum.

Emerging Technologies in Prostate Cancer Radiation Therapy: Improving the Therapeutic Window

Background

Radiation therapy is a standard of care in the treatment of prostate cancer. Relatively recent advances in technologies in the delivery of radiation therapy are altering our current approach to treatment of prostate cancer.

Methods

This review discusses the results of retrospective, prospective, and randomized clinical trials that have evaluated clinical outcomes in prostate cancer treated with newer radiation therapy technologies.

Results

Randomized trials have demonstrated that higher doses of radiation therapy improve clinical outcomes but with increased toxicity to normal tissue. The introduction of more conformal radiation therapy techniques such as intensity-modulated radiation therapy, proton therapy, stereotactic body radiotherapy, and brachytherapy have allowed for further dose escalation with simultaneous reduction in toxicity. However, use of more conformal treatments requires a better understanding of prostate motion and the ability to track prostate movements in real time.

Conclusions

Technological advancements have improved radiation dose delivery to the prostate and have reduced normal tissue toxicity. Randomized trials are warranted to ultimately evaluate clinical benefit and outcomes.

Image-guided radiotherapy (IGRT) for prostate cancer comparing kV imaging of fiducial markers with cone beam computed tomography (CBCT)

PURPOSE

To present our single-institution experience with image-guided radiotherapy comparing fiducial markers and cone-beam computed tomography (CBCT) for daily localization of prostate cancer.

METHODS AND MATERIALS

From April 2007 to October 2008, 36 patients with prostate cancer received intensity-modulated radiotherapy with daily localization by use of implanted fiducials. Orthogonal kilovoltage (kV) portal imaging preceded all 1244 treatments. Cone-beam computed tomography images were also obtained before 286 treatments (23%). Shifts in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) dimensions were made from kV fiducial imaging. Cone-beam computed tomography shifts based on soft tissues were recorded. Shifts were compared by use of Bland-Altman limits of agreement. Mean and standard deviation of absolute differences were also compared. A difference of 5 mm or less was acceptable. Subsets including start date, body mass index, and prostate size were analyzed.

RESULTS

Of 286 treatments, 81 (28%) resulted in a greater than 5.0-mm difference in one or more dimensions. Mean differences in the AP, SI, and LR dimensions were 3.4 ± 2.6 mm, 3.1 ± 2.7 mm, and 1.3 ± 1.6 mm, respectively. Most deviations occurred in the posterior (fiducials, 78%; CBCT, 59%), superior (79%, 61%), and left (57%, 63%) directions. Bland-Altman 95% confidence intervals were -4.0 to 9.3 mm for AP, -9.0 to 5.3 mm for SI, and -4.1 to 3.9 mm for LR. The percentages of shift agreements within ±5 mm were 72.4% for AP, 72.7% for SI, and 97.2% for LR. Correlation between imaging techniques was not altered by time, body mass index, or prostate size.

CONCLUSIONS

Cone-beam computed tomography and kV fiducial imaging are similar; however, more than one-fourth of CBCT and kV shifts differed enough to affect target coverage. This was even more pronounced with smaller margins (3 mm). Fiducial imaging requires less daily physician input, is less time-consuming, and is our preferred method for prostate image-guided radiotherapy.

Current clinical evidence for proton therapy

Proton beam therapy provides the opportunity for more localized delivery of ionizing radiation with the potential for improved normal tissue avoidance to reduce treatment related morbidity and to allow for dose escalation to improve disease control and survival without increased toxicity. However, a systematic review of published peer-reviewed literature reported previously and updated here is devoid of any clinical data demonstrating benefit in terms of survival, tumor control, or toxicity in comparison with best conventional treatment for any of the tumors so far treated including skull base and ocular tumors, prostate cancer and childhood malignancies. The current lack of evidence for benefit of protons should provide a stimulus for continued research. Well designed in silico clinical trials using validated normal tissue complication probability-models are important to predict the magnitude of benefit for individual tumor sites but the future use of protons should be guided by clear evidence of benefit demonstrated in well-designed prospective studies, away from commercial influence, and this is likely to require international collaboration. Any complex and expensive technology, including proton therapy, should not be employed on the basis of belief alone and requires testing to avoid inappropriate use of potential detriment to future patients.

Impact of multileaf collimator width on intraprostatic dose painting plans for dominant intraprostatic lesion of prostate cancer

The aim of this study was to investigate the impact of multileaf collimator width (MLC‐W) on intraprostatic dose painting plans for prostate cancer.

Prostate cancer maps based on the histopathological findings were superimposed onto simulation CT images. Clinical target volume (CTV) 1 was defined as the prostate and the base of the seminal vesicles, and CTV2 was defined as the dominant intraprostatic lesions. Planning target volume (PTV) 1 and PTV2 were delineated by adding 5 mm margins to CTV1 and CTV2, respectively. For each case, two dose painting plans were created to deliver 74 Gy to PTV1 and 84 Gy to PTV2 with dynamic multileaf collimator technique using two different MLCs: m3 (MLC‐W: 3 mm) and Millennium (5 mm). Plans were evaluated by comparing the conformation number (CN), a quantity that defines the degree of conformality.

The CNs for plans using the m3 and Millennium were 0.68 and 0.67 for PTV1 and 0.59 and 0.58 for PTV2, respectively. The CNs tended to be higher for a thinner leaf width (p<0.05).

Dosimetric advantages associated with smaller leaves were observed. However, differences between 3 mm and 5 mm leaf width were relatively small, which suggested that 5 mm leaf width would be acceptable in dose painting plans for prostate cancer.

PACS numbers: 87.56.N‐, 87.56.nk, 87.55.D‐

Late toxicity after conformal and intensity-modulated radiation therapy for prostate cancer: impact of previous surgery for benign prostatic hyperplasia

OBJECTIVES

To retrospectively compare late toxicity of conventional-dose three-dimensional conformal radiation therapy (3D-CRT) and high-dose intensity-modulated radiation therapy (IMRT) for prostate cancer.

METHODS

A total of 340 patients with T1-3 prostate cancer were treated with 3D-CRT (n = 228) and IMRT (n = 112). The median follow-up time was 5.9 years and 3.0 years, respectively. The prescription dose was 70 Gy for 3D-CRT and 78 Gy for IMRT. Late gastrointestinal (GI) and genitourinary (GU) toxicities were graded according to the Fox Chase modification of the Radiation Therapy Oncology Group and Late Effects Normal Tissue Task Force criteria.

RESULTS

There was no difference between 3D-CRT and IMRT in the incidence of GI and GU toxicity at 3 years. On multivariate analysis, transurethral resection of prostate/open transvesical prostatectomy (TURP/TVPE) for benign prostatic hyperplasia, carried out before radiotherapy, significantly increased the risk of Grade >or=2 GU toxicity (risk ratio 1.88). Among patients who experienced TURP/TVPE, the 5-year actuarial likelihood of Grade 2-3 urinary incontinence was 23%, compared with 9% for those without prostate surgery (P = 0.01).

CONCLUSIONS

Tolerance of 3D-CRT and IMRT was similar, despite the use of high radiation dose with IMRT. Previous TURP/TVPE increased the risk of GU toxicity.

Comparison of prostate IMRT and VMAT biologically optimised treatment plans

Recently, a new radiotherapy delivery technique has become clinically available--volumetric modulated arc therapy (VMAT). VMAT is the delivery of IMRT while the gantry is in motion using dynamic leaf motion. The perceived benefit of VMAT over IMRT is a reduction in delivery time. In this study, VMAT was compared directly with IMRT for a series of prostate cases. For 10 patients, a biologically optimized seven-field IMRT plan was compared with a biologically optimized VMAT plan using the same planning objectives. The Pinnacle RTPS was used. The resultant target and organ-at-risk dose-volume histograms (DVHs) were compared. The normal tissue complication probability (NTCP) for the IMRT and VMAT plans was calculated for 3 model parameter sets. The delivery efficiency and time for the IMRT and VMAT plans was compared. The VMAT plans resulted in a statistically significant reduction in the rectal V25Gy parameter of 8.2% on average over the IMRT plans. For one of the NTCP parameter sets, the VMAT plans had a statistically significant lower rectal NTCP. These reductions in rectal dose were achieved using 18.6% fewer monitor units and a delivery time reduction of up to 69%. VMAT plans resulted in reductions in rectal doses for all 10 patients in the study. This was achieved with significant reductions in delivery time and monitor units. Given the target coverage was equivalent, the VMAT plans were superior.

A randomized trial (Irish clinical oncology research group 97-01) comparing short versus protracted neoadjuvant hormonal therapy before radiotherapy for localized prostate cancer

PURPOSE

To examine the long-term outcomes of a randomized trial comparing short (4 months; Arm 1) and long (8 months; Arm 2) neoadjuvant hormonal therapy before radiotherapy for localized prostate cancer.

METHODS AND MATERIALS

Between 1997 and 2001, 276 patients were enrolled and the data from 261 were analyzed. The stratification risk factors were prostate-specific antigen level >20 ng/mL, Gleason score≥7, and Stage T3 or more. The intermediate-risk stratum had one factor and the high-risk stratum had two or more. Staging was done from the bone scan and computed tomography findings. The primary endpoint was biochemical failure-free survival.

RESULTS

The median follow-up was 102 months. The overall survival, biochemical failure-free survival. and prostate cancer-specific survival did not differ significantly between the two treatment arms, overall or at 5 years. The cumulative probability of overall survival at 5 years was 90% (range, 87-92%) in Arm 1 and 83% (range, 80-86%) in Arm 2. The biochemical failure-free survival rate at 5 years was 66% (range, 62-71%) in Arm 1 and 63% (range, 58-67%) in Arm 2.

CONCLUSION

No statistically significant difference was found in biochemical failure-free survival between 4 months and 8 months of neoadjuvant hormonal therapy before radiotherapy for localized prostate cancer.

[IMRT combined to IGRT: increase of the irradiated volume. Consequences?]

Image-guided radiotherapy (IGRT) combined or not with intensity-modulated radiation therapy (IMRT) are new and very useful techniques. However, these new techniques are responsible of irradiation at low dose in large volumes. The control of alignment, realignment of the patient and target positioning in external beam radiotherapy are increasingly performed by radiological imaging devices. The management of this medical imaging depends on the practice of each radiotherapy centre. The physical doses due to the IGRT are however quantifiable and traceable. In one hand, these doses appear justified for a better targeting and could be considered negligible in the context of radiotherapy. On the other hand, the potential impact of these low doses should deserve the consideration of professionals. It appears important therefore to report and consider not only doses in target volumes and in "standard" organs at risk, but also the volume of all tissue receiving low doses of radiation. The recent development of IMRT launches the same issue concerning the effects of low doses of radiation. Indeed, IMRT increases the volume of healthy tissue exposed to radiation. At low dose (<100mGy), many parameters have to be considered for health risk estimations: the induction of genes and activation of proteins, bystander effect, radio-adaptation, the specific low-dose radio-hypersensitivity and individual radiation sensitivity. With the exception of the latter, the contribution of these parameters is generally protective in terms of carcinogenesis. An analysis of secondary cancers arising out of field appears to confirm such notion. The risk of secondary tumours is not well known in these conditions of treatment associating IMRT and IGRT. It is therefore recommended that the dose due to imaging during therapeutic irradiation be reported.

Is there an optimal management for localized prostate cancer?

Widespread screening with prostate-specific antigen (PSA) has led to a significant increase in the detection of early stage, clinically localized prostate cancer (CaP). Various treatment options for localized CaP are discussed in this review article including active surveillance, radical prostatectomy, radiation therapy, and cryotherapy. The paucity of high-level evidence adds a considerable amount of controversy when choosing the "optimal" intervention, for both the treating physician and the patient. The long time course of CaP intervention outcomes, combined with continuing modifications in treatments, further complicate the matter. Lacking randomized trials that compare treatment options, this review article attempts to summarize the different treatment options and associated side-effects, including effects on health-related quality of life, from current published literature.

Treatment strategies for high-risk locally advanced prostate cancer

High-risk prostate cancer can be defined by the assessment of pretreatment prognostic factors such as clinical stage, Gleason score, and PSA level. High-risk features include PSA >20 ng/ml, Gleason score 8-10, and stage T3 tumors. Patients with adverse prognostic factors have historically fared poorly with monotherapeutic approaches. Multimodal treatment utilizing combined androgen suppression and radiotherapy has improved survival rates for patients with high-risk prostate cancer. In addition, multiple randomized trials in patients treated with primary radical prostatectomy have demonstrated improved outcomes with the addition of adjuvant radiotherapy. Improved radiotherapy techniques that allow for dose escalation, and new systemic therapy approaches such as adjuvant chemotherapy, present promising future therapeutic alternatives for patients with high-risk prostate cancer.

A combined pretreatment of 1,25-dihydroxyvitamin D3 and sodium valproate enhances the damaging effect of ionizing radiation on prostate cancer cells

Radiotherapy is one of the curative treatment options for prostate cancer (PCa). However, effective doses of ionizing radiation (IR) have a high risk of side effects. To increase sensitivity of PCa to IR we pretreated human androgen-refractory DU145 PCa cells with a combination of sodium valproate (VPA), a well-tolerated drug with histone deacetylases inhibiting activity, and 1,25-dihydroxyvitamin D3, 1,25(OH)2D3, the active metabolite of vitamin D, a well known anticancer agent. The results show that irradiation (4Gy) of DU145 PCa cells pretreated with a combination of 1 mM VPA and 100 nM 1,25(OH)2D3 efficiently suppressed (87.9%) PCa cell proliferation. IR after combined pretreatment resulted in increased DNA double-strand breaks expressed as levels of phosphorylated histone H2A.X, compared with non-treated cells the increase was 58.1% in pretreated cells and 11.8% in non-pretreated cells (p<0.002). Combined pretreatment enhanced IR-induced activation of DNA damage checkpoint kinase Chk2, 39.0% in pretreated cells compared to 23.8% in non-pretreated cells (p<0.05). These molecular changes led to DNA replication blockade, S-phase cell-cycle arrest and enhanced apoptosis. Cumulatively, the results indicate that combined pretreatment with VPA and 1,25(OH)2D3 followed by IR is a highly effective treatment for human PCa cells. This observation may have important implications for reducing doses of radiation administered to cancer patients thus limiting the severity of side effects.

Locally recurrent prostate cancer after external beam radiation therapy: diagnostic performance of 1.5-T endorectal MR imaging and MR spectroscopic imaging for detection

PURPOSE

To determine if performing magnetic resonance (MR) spectroscopic imaging, compared with performing T2-weighted MR imaging alone, improves the detection of locally recurrent prostate cancer after definitive external beam radiation therapy.

MATERIALS AND METHODS

This retrospective single-institution study was approved by the committee on human research, with a waiver of informed consent, and was compliant with HIPAA requirements. Sixty-four men who underwent endorectal MR imaging, MR spectroscopic imaging, and transrectal ultrasonographically guided biopsy for suspected local recurrence of prostate cancer after definitive external beam radiation therapy were retrospectively identified. Thirty-three patients had also received androgen therapy. Recurrent cancer was determined to be present or absent in the left and right sides of the prostate at T2-weighted MR imaging and MR spectroscopic imaging by a radiologist and a spectroscopist, respectively. Area under the receiver operating characteristic curve (A(Z)) was calculated for T2-weighted MR imaging alone and combined T2-weighted MR imaging and MR spectroscopic imaging by using generalized estimating equations and by using biopsy results as the reference standard.

RESULTS

Recurrent prostate cancer was identified at biopsy in 37 (58%) of the 64 men. Recurrence was unilateral in 28 patients and bilateral in nine (total of 46 affected prostate sides). A(Z) analysis revealed that use of combined T2-weighted MR imaging and MR spectroscopic imaging (A(Z) = 0.79), as compared with T2-weighted MR imaging alone (A(Z) = 0.67), significantly improved the detection of local recurrence (P = .001).

CONCLUSION

The addition of MR spectroscopic imaging to T2-weighted MR imaging significantly improves the diagnostic accuracy of endorectal MR imaging in the detection of locally recurrent prostate cancer after definitive external beam radiation therapy.

Cross-linked hyaluronan gel reduces the acute rectal toxicity of radiotherapy for prostate cancer

PURPOSE

To prospectively analyze whether cross-linked hyaluronan gel reduces the mean rectal dose and acute rectal toxicity of radiotherapy for prostate cancer.

METHODS AND MATERIALS

Between September 2008 and March 2009, we transperitoneally injected 9 mL of cross-linked hyaluronan gel (Hylaform; Genzyme Corporation, Cambridge, MA) into the anterior perirectal fat of 10 early-stage prostate cancer patients to increase the separation between the prostate and rectum by 8 to 18 mm at the start of radiotherapy. Patients then underwent high-dose rate brachytherapy to 2,200 cGy followed by intensity-modulated radiation therapy to 5,040 cGy. We assessed acute rectal toxicity using the National Cancer Institute Common Terminology Criteria for Adverse Events v3.0 grading scheme.

RESULTS

Median follow-up was 3 months. The anteroposterior dimensions of Hylaform at the start and end of radiotherapy were 13 +/- 3mm (mean +/- SD) and 10 +/- 4mm, respectively. At the start of intensity-modulated radiation therapy, daily mean rectal doses were 73 +/- 13 cGy with Hylaform vs. 106 +/- 20 cGy without Hylaform (p = 0.005). There was a 0% incidence of National Cancer Institute Common Terminology Criteria for Adverse Events v3.0 Grade 1, 2, or 3 acute diarrhea in 10 patients who received Hylaform vs. a 29.7% incidence (n = 71) in 239 historical controls who did not receive Hylaform (p = 0.04).

CONCLUSIONS

By increasing the separation between the prostate and rectum, Hylaform decreased the mean rectal dose. This led to a significant reduction in the acute rectal toxicity of radiotherapy for prostate cancer.

Dosimetric impact of interfraction catheter movement in high-dose rate prostate brachytherapy

PURPOSE

To evaluate the impact of interfraction catheter movement on dosimetry in prostate high-dose-rate (HDR) brachytherapy.

METHODS AND MATERIALS

Fifteen patients were treated with fractionated HDR brachytherapy. Implants were performed on day 1 under transrectal ultrasound guidance. A computed tomography (CT) scan was performed. Inverse planning simulated annealing was used for treatment planning. The first fraction was delivered on day 1. A cone beam CT (CBCT) was performed on day 2 before the second fraction was given. A fusion of the CBCT and CT was performed using intraprostatic gold markers as landmarks. Initial prostate and urethra contours were transferred to the CBCT images. Bladder and rectum contours were drawn, and catheters were digitized on the CBCT. The planned treatment was applied to the CBCT dataset, and dosimetry was analyzed and compared to the initial dose distribution. This process was repeated after a reoptimization was performed, using the same constraints used on day 1.

RESULTS

Mean interfraction catheter displacement was 5.1 mm. When we used the initial plan on day 2, the mean prostate V100 (volume receiving 100 Gy or more) decreased from 93.8% to 76.2% (p < 0.01). Rectal V75 went from 0.75 cm(3) to 1.49 cm(3) (p < 0.01). A reoptimization resulted in a mean prostate V100 of 88.1%, closer to the initial plan (p = 0.05). Mean rectal V75 was also improved with a value of 0.59 cm(3). There was no significant change in bladder and urethra dose on day 2.

CONCLUSIONS

A mean interfraction catheter displacement of 5.1 mm results in a significant decrease in prostate V100 and an increase in rectum dose. A reoptimization before the second treatment improves dose distribution.

Dose Escalation Study with Two Different Hypofractionated Intensity Modulated Radiotherapy Techniques for Localized Prostate Cancer: Acute Toxicity

To assess acute gastrointestinal (GI) and genitourinary (GU) toxicities in patients with localized prostate cancer treated with a sequential dose escalation hypofractionated intensity-modulated radiotherapy (IMRT) study using two different delivery methods. Since 2003, 88 and 48 patients were sequentially treated to 56 Gy and to 60 Gy (4 Gy/fraction twice weekly), respectively. IMRT with 6 MV beams was delivered with five fields in Geneva and with nine in Barcelona. Acute GI and GU side effects were scored weekly during treatment and 6 weeks after treatment completion using the Radiation Therapy Oncology Group (RTOG) toxicity scale. Clinical, technical, and dosimetric parameters were analyzed in order to assess for a potential correlation with toxicity.

Grade 1–2, GU and GI toxicities during and 6 weeks after treatment completion were 64%, and 24%, and 35% and 12%, respectively. Only one Grade 4 GU toxicity, consisting of transitory urinary obstruction, was observed. Patients treated to 60 Gy in Geneva presented a higher rate of Grade 1–2 GU toxicity ( p = 0.01), while patients treated to both 56 and 60 Gy in Barcelona presented a higher Grade 1–2 GI toxicity ( p = 0.02). A lower rate of rectal toxicity was observed in the subgroup of 22 patients treated with a rectal balloon ( p = 0.02). The use of androgen deprivation therapy was associated with a higher rate of Grade 1–2 GU toxicity after the end of the treatment ( p = 0.02). Dose escalation with either 14 × 4 Gy or 15 × 4 Gy delivered with two different IMRT techniques is feasible and is associated with a tolerable acute toxicity.

Radiobiological impact of reduced margins and treatment technique for prostate cancer in terms of tumor control probability (TCP) and normal tissue complication probability (NTCP)

Dose escalation in prostate radiotherapy is limited by normal tissue toxicities. The aim of this study was to assess the impact of margin size on tumor control and side effects for intensity-modulated radiation therapy (IMRT) and 3D conformal radiotherapy (3DCRT) treatment plans with increased dose. Eighteen patients with localized prostate cancer were enrolled. 3DCRT and IMRT plans were compared for a variety of margin sizes. A marker detectable on daily portal images was presupposed for narrow margins. Prescribed dose was 82 Gy within 41 fractions to the prostate clinical target volume (CTV). Tumor control probability (TCP) calculations based on the Poisson model including the linear quadratic approach were performed. Normal tissue complication probability (NTCP) was calculated for bladder, rectum and femoral heads according to the Lyman-Kutcher-Burman method. All plan types presented essentially identical TCP values and very low NTCP for bladder and femoral heads. Mean doses for these critical structures reached a minimum for IMRT with reduced margins. Two endpoints for rectal complications were analyzed. A marked decrease in NTCP for IMRT plans with narrow margins was seen for mild RTOG grade 2/3 as well as for proctitis/necrosis/stenosis/fistula, for which NTCP <7% was obtained. For equivalent TCP values, sparing of normal tissue was demonstrated with the narrow margin approach. The effect was more pronounced for IMRT than 3DCRT, with respect to NTCP for mild, as well as severe, rectal complications.

Long-term failure patterns and survival in a randomized dose-escalation trial for prostate cancer. Who dies of disease?

PURPOSE

To report long-term failure patterns and survival in a randomized radiotherapy dose escalation trial for prostate cancer.

MATERIALS AND METHODS

A total of 301 patients with Stage T1b-T3 prostate cancer treated to 70 Gy versus 78 Gy now have a median follow-up of 9 years. Failure patterns and survival were compared between dose levels. The cumulative incidence of death from prostate cancer versus other causes was examined and regression analysis was used to establish predictive factors.

RESULTS

Patients with pretreatment prostate-specific antigen (PSA) >10 ng/mL or high-risk disease had higher biochemical and clinical failures rates when treated to 70 Gy. These patients also had a significantly higher risk of dying of prostate cancer. Patients <70 years old at treatment died of prostate cancer nearly three times more frequently than of other causes when they were radiated to 70 Gy, whereas those treated to 78 Gy died of other causes more frequently. Patients age 70 or older treated to 70 Gy died of prostate cancer as often as other causes, and those receiving 78 Gy never died of prostate cancer within 10 years of follow-up. In regression analysis, factors predicting for death from prostate cancer were pretreatment PSA >10.5 ng/mL, Gleason score 9 and 10, recurrence within 2.6 years of radiation, and doubling time of <3.6 months at the time of recurrence.

CONCLUSIONS

Moderate dose escalation (78 Gy) decreases biochemical and clinical failure as well as prostate cancer death in patients with pretreatment PSA >10 ng/mL or high-risk disease.

High-dose intensity-modulated radiotherapy as primary therapy for prostate cancer: report on dosimetry aspects and acute toxicity in the Indian scenario

BACKGROUND AND PURPOSE

Dose escalation improves local control in prostate cancer. In this study we assess the feasibility of dose escalation to prostate and / or seminal vesicles to 76 Gy with intensity-modulated radiotherapy (IMRT); report data on dosimetry and acute toxicity in 40 patients at P. D. Hinduja National Hospital and Medical Research Center, Mumbai.

MATERIALS AND METHODS

In the period from May 2006 to September 2008, 40 consecutive patients with localized prostate adenocarcinoma (T1- 3 N0) were definitively treated with IMRT to a dose of 76 Gy / 38 fractions. Patients were seen on a weekly basis during treatment, and one month (M1) and three months (M3) thereafter. The radiation therapy oncology group (RTOG) toxicity scale was used to evaluate acute gastrointestinal (GI) and genitourinary (GU) toxicities. Additional symptoms such as rectal blood loss, urgency, dysuria, urinary frequency, nocturia, incontinence were scored as well.

RESULTS

All 40 patients completed treatment successfully. Acute RTOG Grade 1 and Grade 2 GI toxicities were noted in 47.5% (19 patients) and 12.5% (five patients) respectively, leaving 40% (16 patients) free of any acute toxicity. Thirty-six (90%) and four patients (10%) had Grade 0-1 and Grade 2 acute RTOG-scaled GU toxicity respectively. There was no Grade 3 or higher GI / GU toxicity.

CONCLUSIONS

The escalated dose of 76 Gy to the prostate with IMRT was very well tolerated by all our patients with acceptable acute GU and GI toxicity, thereby, establishing the feasibility of dose escalation in the Indian scenario.

A method to separate the rectum from the prostate during proton beam radiotherapy of prostate cancer patients

The use of protons for curative treatment of prostate cancer is increasing, either as a single treatment modality or in combination with conventional radiotherapy. The proximity between prostate (target) and rectum (organ at risk) often leads to a compromise between dose to target and organ at risk.

MATERIAL AND METHODS

The present study describes a method where the distance between prostate and rectum is increased by retraction of the rectum in dorsal direction. Comparative treatment plans with and without retraction of the rectum in the same patients have been studied. Nine patients with biopsy proven, localised adenocarcinoma of the prostate were studied. A cylindrical rod of Perspex was inserted into the rectum. This device allows the rectum to be retracted posteriorly. The patients were given a proton boost of 20 Gy in four fractions of 5 Gy in addition to a conventional photon beam treatment to a dose of 50 Gy in 25 fractions of 2 Gy.

RESULTS

Comparative treatment planning shows that the treatment plan with rectal retraction significantly reduces (p<0.01) the volume of the rectal wall receiving high doses (equal to 70 Gy in 2 Gy fractions) in all patients.

CONCLUSIONS

The proton boost treatment with retraction of rectum during treatment decreases the rectal dose substantially. This is expected to reduce rectal side effects.

A volumetric trend analysis of the prostate and seminal vesicles during a course of intensity-modulated radiation therapy

PURPOSE

The purpose of this study was to evaluate the volumetric changes of the prostate and seminal vesicles (SV) during a definitive course of intensity-modulated radiation therapy using a combined computed tomography (CT)-linear accelerator system.

METHODS AND MATERIALS

Fifteen patients were enrolled in this IRB-approved prospective study. The treatment plan was designed to deliver a total dose of 75.6 Gy over 42 fractions to 98% of the planning target volume. In-room CT scans were acquired using a CT-on-rails system 3 times weekly just before daily treatment throughout the course of radiation therapy. Rates of volume change over time for the prostate and SV were calculated using linear regression analysis.

RESULTS

Fifteen patients had a total of 369 CT scans during the study. For 53% of patients (N = 8), there was a statistically significant decrease in prostate volume over time (range, 0.05-0.47 mL/d or 0.7%-3.5% per week). The median volume reduction was -11.5% (4.9 mL) at the end of the treatment. There was no significant change in the volume of the SV during the course of treatment. The decrease in prostate volume was significantly correlated with the initial volume of the prostate, with larger glands shrinking more during treatment (P = 0.001).

CONCLUSION

Patients with enlarged prostates may experience volumetric reduction in their gland size during a protracted course of radiation therapy. However, the magnitude of the volume reduction is relatively small. In the current era of dose escalation, future studies with adaptive radiation therapy strategy may be appropriate to minimize radiation exposure to normal tissues.

[Is proton beam therapy the future of radiotherapy? Part I: clinical aspects]

Proton beam therapy uses positively charged particles, protons, whose physical properties improve dose-distribution (Bragg peak characterized by a sharp distal and lateral penumbra) compared with conventional photon-based radiation therapy (X-ray). These ballistic advantages apply to the treatment of deep-sited tumours located close to critical structures and requiring high-dose levels. [60-250 MeV] proton-beam therapy is now widely accepted as the "gold standard" in specific indications in adults--ocular melanoma, chordoma and chondrosarcoma of the base of skull --and is regarded as a highly promising treatment modality in the treatment of paediatric malignancies (brain tumours, sarcomas…). This includes the relative sparing of surrounding normal organs from low and mid-doses that can cause deleterious side-effects such as radiation-induced secondary malignancies. Other clinical studies are currently testing proton beam in dose-escalation evaluations, in prostate, lung, hepatocellular cancers, etc. Clinical validation of these new indications appears necessary. To date, over 60,000 patients worldwide have received part or all of their radiation therapy program by proton beams, in approximately 30 treatment facilities.

Rectal dose variation during the course of image-guided radiation therapy of prostate cancer

BACKGROUND AND PURPOSE

To investigate the change in rectal dose during the treatment course for intensity-modulated radiotherapy (IMRT) of prostate cancer with image-guidance.

MATERIALS AND METHODS

Twenty prostate cancer patients were recruited for this retrospective study. All patients have been treated with IMRT. For each patient, MR and CT images were fused for target and critical structure delineation. IMRT treatment planning was performed on the simulation CT images. Inter-fractional motion during the course of treatment was corrected using a CT-on-rails system. The rectum was outlined on both the original treatment plan and the subsequent daily CT images from the CT-on-rails by the same investigator. Dose distributions on these daily CT images were recalculated with the isocenter shifts relative to the simulation CT images using the leaf sequences/MUs based on the original treatment plan. The rectal doses from the subsequent daily CTs were compared with the original doses planned on the simulation CT using our clinical acceptance criteria.

RESULTS

Based on 20 patients with 139 daily CT sets, 28% of the subsequent treatment dose distributions did not meet our criterion of V(40) < 35%, and 27% did not meet our criterion of V(65) < 17%. The inter-fractional rectal volume variation is significant for some patients.

CONCLUSIONS

Due to the large inter-fractional variation of the rectal volume, it is more favorable to plan prostate IMRT based on an empty rectum and deliver treatment to patients with an empty rectum. Over 70% of actual treatments showed better rectal doses than our clinical acceptance criteria. A significant fraction (27%) of the actual treatments would benefit from adaptive image-guided radiotherapy based on daily CT images.

Choline PET based dose-painting in prostate cancer--modelling of dose effects

BACKGROUND

Several randomized trials have documented the value of radiation dose escalation in patients with prostate cancer, especially in patients with intermediate risk profile. Up to now dose escalation is usually applied to the whole prostate. IMRT and related techniques currently allow for dose escalation in sub-volumes of the organ. However, the sensitivity of the imaging modality and the fact that small islands of cancer are often dispersed within the whole organ may limit these approaches with regard to a clear clinical benefit. In order to assess potential effects of a dose escalation in certain sub-volumes based on choline PET imaging a mathematical dose-response model was developed.

METHODS

Based on different assumptions for alpha/beta, gamma 50, sensitivity and specificity of choline PET, the influence of the whole prostate and simultaneous integrated boost (SIB) dose on tumor control probability (TCP) was calculated. Based on the given heterogeneity of all potential variables certain representative permutations of the parameters were chosen and, subsequently, the influence on TCP was assessed.

RESULTS

Using schedules with 74 Gy within the whole prostate and a SIB dose of 90 Gy the TCP increase ranged from 23.1% (high detection rate of choline PET, low whole prostate dose, high gamma 50/ASTRO definition for tumor control) to 1.4% TCP gain (low sensitivity of PET, high whole prostate dose, CN + 2 definition for tumor control) or even 0% in selected cases. The corresponding initial TCP values without integrated boost ranged from 67.3% to 100%. According to a large data set of intermediate-risk prostate cancer patients the resulting TCP gains ranged from 22.2% to 10.1% (ASTRO definition) or from 13.2% to 6.0% (CN + 2 definition).

DISCUSSION

Although a simplified mathematical model was employed, the presented model allows for an estimation in how far given schedules are relevant for clinical practice. However, the benefit of a SIB based on choline PET seems less than intuitively expected. Only under the assumption of high detection rates and low initial TCP values the TCP gain has been shown to be relevant.

CONCLUSIONS

Based on the employed assumptions, specific dose escalation to choline PET positive areas within the prostate may increase the local control rates. Due to the lack of exact PET sensitivity and prostate alpha/beta parameter, no firm conclusions can be made. Small variations may completely abrogate the clinical benefit of a SIB based on choline PET imaging.

Simultaneous MRI diffusion and perfusion imaging for tumor delineation in prostate cancer patients

BACKGROUND AND PURPOSE

A study was performed to investigate if we can quantify if the two imaging modalities diffusion weighted imaging (DWI) and dynamic contrast-enhanced (DCE)-MRI are consistent in what voxels they determine as being suspicious of tumor tissue.

MATERIAL AND METHODS

Twenty-one patients with biopsy proven prostate cancer underwent a DWI and a DCE-MRI scan. These scans were compared using a receiver operating curve (ROC) analysis, where either one of the two imaging modalities was thresholded and taken as a reference. The resulting area under the curve (AUC) reflects the consistency between target delineations based on the two imaging techniques. This analysis was performed for the complete prostate and the peripheral zone (PZ).

RESULTS

Consistency between DWI and DCE-MRI parameter maps varied greatly between patients. Values of the AUC up to 0.90 were found. However, on average AUC values were 0.60. The AUC values were related to the patient's PSA and clinical stage.

CONCLUSIONS

Large variation in consistency between the two imaging modalities was found. This did not depend on the precise thresholds used. For making decisions on dose painting in the prostate, the knowledge about the inconsistency must be taken into account.

An automated method for adaptive radiation therapy for prostate cancer patients using continuous fiducial-based tracking

Electromagnetic tracking technology is primarily used for continuous prostate localization during radiotherapy, but offers potential value for evaluation of dosimetric coverage and adequacy of treatment for dynamic targets. We developed a highly automated method for daily computation of cumulative dosimetric effects of intra- and inter-fraction target motion for prostate cancer patients using fiducial-based electromagnetic tracking. A computer program utilizing real-time tracking data was written to (1) prospectively determine appropriate rotational/translational motion limits for patients treated with continuous isocenter localization; (2) retrospectively analyze dosimetric target coverage after daily treatment, and (3) visualize three-dimensional rotations and translations of the prostate with respect to the planned target volume and dose matrix. We present phantom testing and a patient case to validate and demonstrate the utility of this application. Gamma analysis of planar dose computed by our application demonstrated accuracy within 1%/1 mm. Dose computation of a patient treatment revealed high variation in minimum dose to the prostate (D(min)) over 40 fractions and a drop in the D(min) of approximately 8% between a 5 mm and a 3 mm PTV margin plan. The infrastructure has been created for patient-specific treatment evaluation using continuous tracking data. This application can be used to increase confidence in treatment delivery to targets influenced by motion.

Dose-volume constraints to reduce rectal side effects from prostate radiotherapy: evidence from MRC RT01 Trial ISRCTN 47772397

PURPOSE

Radical radiotherapy for prostate cancer is effective but dose limited because of the proximity of normal tissues. Comprehensive dose-volume analysis of the incidence of clinically relevant late rectal toxicities could indicate how the dose to the rectum should be constrained. Previous emphasis has been on constraining the mid-to-high dose range (>/=50 Gy). Evidence is emerging that lower doses could also be important.

METHODS AND MATERIALS

Data from a large multicenter randomized trial were used to investigate the correlation between seven clinically relevant rectal toxicity endpoints (including patient- and clinician-reported outcomes) and an absolute 5% increase in the volume of rectum receiving the specified doses. The results were quantified using odds ratios. Rectal dose-volume constraints were applied retrospectively to investigate the association of constraints with the incidence of late rectal toxicity.

RESULTS

A statistically significant dose-volume response was observed for six of the seven endpoints for at least one of the dose levels tested in the range of 30-70 Gy. Statistically significant reductions in the incidence of these late rectal toxicities were observed for the group of patients whose treatment plans met specific proposed dose-volume constraints. The incidence of moderate/severe toxicity (any endpoint) decreased incrementally for patients whose treatment plans met increasing numbers of dose-volume constraints from the set of V30

CONCLUSION

Considering the entire dose distribution to the rectum by applying dose-volume constraints such as those tested here in the present will reduce the incidence of late rectal toxicity.

Collapse

Key Words Collapse

MESH Headings

• Dose-Response Relationship, Radiation
• Gastrointestinal Hemorrhage/etiology
• Humans
• Male
• Odds Ratio
• Prostatic Neoplasms/radiotherapy
• Radiation Injuries/complications
• Radiation Injuries/prevention & control
• Radiotherapy Dosage
• Rectal Diseases/etiology
• Rectum/pathology
• Rectum/radiation effects

Collapse

Grants

• G0501019 Medical Research Council
• MC_U122861330 Medical Research Council
• C46/A2131 Cancer Research UK

Collapse

Affiliation(s)

Sarah L Gulliford Joint Department of Physics, Institute of Cancer Research and Royal Marsden National Health Service Foundation Trust, Sutton, United Kingdom
Kerwyn Foo
Rachel C Morgan
Edwin G Aird
A Margaret Bidmead
Helen Critchley
Philip M Evans
Stefano Gianolini
W Philip Mayles
A Rollo Moore
Beatriz Sánchez-Nieto
Mike Partridge
Matthew R Sydes
Steve Webb
David P Dearnaley

Collapse

Metastasis after radical prostatectomy or external beam radiotherapy for patients with clinically localized prostate cancer: a comparison of clinical cohorts adjusted for case mix

PURPOSE

We assessed the effect of radical prostatectomy (RP) and external beam radiotherapy (EBRT) on distant metastases (DM) rates in patients with localized prostate cancer treated with RP or EBRT at a single specialized cancer center.

PATIENTS AND METHODS

Patients with clinical stages T1c-T3b prostate cancer were treated with intensity-modulated EBRT (> or = 81 Gy) or RP. Both cohorts included patients treated with salvage radiotherapy or androgen-deprivation therapy for biochemical failure. Salvage therapy for patients with RP was delivered a median of 13 months after biochemical failure compared with 69 months for EBRT patients. DM was compared controlling for patient age, clinical stage, serum prostate-specific antigen level, biopsy Gleason score, and year of treatment.

RESULTS

The 8-year probability of freedom from metastatic progression was 97% for RP patients and 93% for EBRT patients. After adjustment for case mix, surgery was associated with a reduced risk of metastasis (hazard ratio, 0.35; 95% CI, 0.19 to 0.65; P < .001). Results were similar for prostate cancer-specific mortality (hazard ratio, 0.32; 95% CI, 0.13 to 0.80; P = .015). Rates of metastatic progression were similar for favorable-risk disease (1.9% difference in 8-year metastasis-free survival), somewhat reduced for intermediate-risk disease (3.3%), and more substantially reduced in unfavorable-risk disease (7.8% in 8-year metastatic progression).

CONCLUSION

Metastatic progression is infrequent in men with low-risk prostate cancer treated with either RP or EBRT. RP patients with higher-risk disease treated had a lower risk of metastatic progression and prostate cancer-specific death than EBRT patients. These results may be confounded by differences in the use and timing of salvage therapy.

Disturbed colonic motility contributes to anorectal symptoms and dysfunction after radiotherapy for carcinoma of the prostate

PURPOSE

To evaluate the role of colonic motility in the pathogenesis of anorectal symptoms and dysfunction after radiotherapy (RT) for carcinoma of the prostate.

PATIENTS AND METHODS

Thirty-eight patients, median age 71 (range, 50-81) years with localized prostate carcinoma randomized to one of two radiation dose schedules underwent colonic transit scintigraphy and assessment of anorectal symptoms (questionnaire), anorectal function (manometry), and anal sphincteric morphology (endoanal ultrasound) before and at 1 month and 1 year after RT.

RESULTS

Whole and distal colonic transit increased 1 month after RT, with faster distal colonic transit only persisting at 1 year. Frequency and urgency of defecation, fecal incontinence, and rectal bleeding increased 1 month after RT and persisted at 1 year. Basal anal pressures remained unchanged, but progressive reductions occurred in anal squeeze pressures and responses to increased intra-abdominal pressure. Rectal compliance decreased progressively in the patients, although no changes in anorectal sensory function ensued. Radiotherapy had no effect on the morphology of the internal and external anal sphincters. Distal colonic retention was weakly related to rectal compliance at 1 month, but both faster colonic transit and reduced rectal compliance were more frequent with increased fecal urgency. At 1 year, a weak inverse relationship existed between colonic half-clearance time and frequency of defecation, although both faster whole-colonic transit and reduced rectal compliance occurred more often with increased stool frequency.

CONCLUSION

Colonic dysmotility contributes to anorectal dysfunction after RT for carcinoma of the prostate. This has implications for improving the management of anorectal radiation sequelae.

Outcome in intermediate or high risk prostate cancer patients receiving radiation dose and hormone therapy

BACKGROUND

To analyse the impact of radiation dose escalation and hormone treatment in prostate cancer patients according to risk groups.

MATERIAL AND METHODS

Totally 494 prostate cancer patients received external beam radiation therapy, with or without androgen deprivation, between January 1990 and December 1999. The patients were divided into three risk groups, where the low risk group (stage T(1c), pretreatment prostate-specific antigen (PSA) level < or =10 ng/ml and WHO Grade 1) included 26 patients, the intermediate risk group (either stage T(2), PSA 10.1-20 ng/ml or WHO Grade 2) comprised 149 patients whereas the high-risk group (either stage T(3), PSA >20 ng/ml or WHO Grade 3) included 319 patients.

RESULTS

In the intermediate risk group, the 5-years bNED rate was 92%, 69% and 61% after a radiation dose of 70 Gy, 66 Gy or 64 Gy, respectively (p < 0.001). In the high-risk group, the 5-year bNED rate was 79%, 69% and 34% for the same dose levels (p < 0.001). The 5-years CSS rates were not significantly different between the dose levels in the intermediate risk group while for the high-risk group it was 93%, 92% and 80% for the three dose levels (p < 0.001). Risk group and radiation doses were independent predictors of bNED, CSS and overall survival, for bNED also hormone treatment was independent predictors.

CONCLUSION

Radiation dose is important for the outcome in intermediate and high risk prostate cancer patients. A dose of 70 Gy should be considered the minimal dose for these patients.

The radiation response of androgen-refractory prostate cancer cell line C4-2 derived from androgen-sensitive cell line LNCaP

Radiation therapy is a relatively effective therapeutic method for localized prostate cancer (PCa) patients. However, radioresistance occurs in nearly 30% of patients treated with potentially curative doses. Therapeutic synergy between radiotherapy and androgen ablation treatment provides a promising strategy for improving the clinical outcome. Accordingly, the androgen deprivation-induced signaling pathway may also mediate radiosensitivity in PCa cells. The C4-2 cell line was derived from the androgen-sensitive LNCaP parent line under androgen-depleted condition and had acquired androgen-refractory characteristics. In our study, the response to radiation was evaluated in both LNCaP and C4-2. Results showed that C4-2 cells were more likely to survive from irradiation and appeared more aggressive in their resistance to radiation treatment compared with LNCaP, as measured by clonogenic assays and cell viability and cell cycle analyses. Gene expression analyses revealed that a set of genes involved in cell cycle arrest and DNA repair were differentially regulated in LNCaP and C4-2 in response to radiation, which was also consistent with the radiation-resistant property observed in C4-2 cells. These results strongly suggested that the radiation-resistant property may develop with progression of PCa to androgen-independent status. Not only can the LNCaP and C4-2 PCa progression model be applied for investigating androgen-refractory progression, but it can also be used to explore the development of radiation resistance in PCa.