Validation of prediction models for radiation-induced late rectal bleeding: evidence from a large pooled population of prostate cancer patients

PURPOSE

To validate published models for the risk estimate of grade≥1 (G1+), grade≥2 (G2+) and grade=3 (G3) late rectal bleeding (LRB) after radical radiotherapy for prostate cancer in a large pooled population from three prospective trials.

MATERIALS AND METHODS

The external validation population included patients from Europe, and Oceanian centres enrolled between 2003 and 2014. Patients received 3DCRT or IMRT at doses between 66-80 Gy. IMRT was administered with conventional or hypofractionated schemes (2.35-2.65 Gy/fr). LRB was prospectively scored using patient-reported questionnaires (LENT/SOMA scale) with a 3-year follow-up. All Normal Tissue Complication Probability (NTCP) models published until 2021 based on the Equivalent Uniform Dose (EUD) from the rectal Dose Volume Histogram (DVH) were considered for validation. Model performance in validation was evaluated through calibration and discrimination.

RESULTS

Sixteen NTCP models were tested on data from 1633 patients. G1+ LRB was scored in 465 patients (28.5%), G2+ in 255 patients (15.6%) and G3 in 112 patients (6.8%). The best performances for G2+ and G3 LRB highlighted the importance of the medium-high doses to the rectum (volume parameters n=0.24 and n=0.18, respectively). Good performance was seen for models of severe LRB. Moreover, a multivariate model with two clinical factors found the best calibration slope.

CONCLUSION

Five published NTCP models developed on non-contemporary cohorts were able to predict a relative increase in the toxicity response in a more recent validation population. Compared to QUANTEC findings, dosimetric results pointed toward mid-high doses of rectal DVH. The external validation cohort confirmed abdominal surgery and cardiovascular diseases as risk factors.

Spatial descriptions of radiotherapy dose: normal tissue complication models and statistical associations

For decades, dose-volume information for segmented anatomy has provided the essential data for correlating radiotherapy dosimetry with treatment-induced complications. Dose-volume information has formed the basis for modelling those associations via normal tissue complication probability (NTCP) models and for driving treatment planning. Limitations to this approach have been identified. Many studies have emerged demonstrating that the incorporation of information describing the spatial nature of the dose distribution, and potentially its correlation with anatomy, can provide more robust associations with toxicity and seed more general NTCP models. Such approaches are culminating in the application of computationally intensive processes such as machine learning and the application of neural networks. The opportunities these approaches have for individualising treatment, predicting toxicity and expanding the solution space for radiation therapy are substantial and have clearly widespread and disruptive potential. Impediments to reaching that potential include issues associated with data collection, model generalisation and validation. This review examines the role of spatial models of complication and summarises relevant published studies. Sources of data for these studies, appropriate statistical methodology frameworks for processing spatial dose information and extracting relevant features are described. Spatial complication modelling is consolidated as a pathway to guiding future developments towards effective, complication-free radiotherapy treatment.

Development of a novel and low-cost anthropomorphic pelvis phantom for 3D dosimetry in radiotherapy

Purpose

The aim of this study was to construct a low-cost, anthropomorphic, and 3D-printed pelvis phantom and evaluate the feasibility of its use to perform 3D dosimetry with commercially available bead thermoluminescent dosimeters (TLDs).

Material and methods

A novel anthropomorphic female phantom was developed with all relevant pelvic organs to position the bead TLDs. Organs were 3D-printed using acrylonitrile butadiene styrene. Phantom components were confirmed to have mass density and computed tomography (CT) numbers similar to relevant tissues. To find out clinically required spatial resolution of beads to cause no perturbation effect, TLDs were positioned with 2.5, 5, and 7.5 mm spacing on the surface of syringe. After taking a CT scan and creating a 4-field conformal radiotherapy plan, 3 dose planes were extracted from the treatment planning system (TPS) at different depths. By using a 2D-gamma analysis, the TPS reports were compared with and without the presence of beads. Moreover, the bead TLDs were placed on the organs’ surfaces of the pelvis phantom and exposed to high-dose-rate (HDR) ⁶⁰Co source. TLDs’ readouts were compared with the TPS calculated doses, and dose surface histograms (DSHs) of organs were plotted.

Results

3D-printed phantom organs agreed well with body tissues regarding both their design and radiation properties. Furthermore, the 2D-gamma analysis on the syringe showed more than 99% points passed 3%- and 3-mm criteria at different depths. By calculating the integral dose of DSHs, the percentage differences were –1.5%, 2%, 5%, and 10% for uterus, rectum, bladder, and sigmoid, respectively. Also, combined standard uncertainty was estimated as 3.5% (k = 1).

Conclusions

A customized pelvis phantom was successfully built and assessed to confirm properties similar to body tissues. Additionally, no significant perturbation effect with different bead resolutions was presented by the external TPS, with 0.1 mm dose grid resolution.

Proposal of a Lab Bench for the Unobtrusive Monitoring of the Bladder Fullness with Bioimpedance Measurements

(1) Background: millions of people, from children to the elderly, suffer from bladder dysfunctions all over the world. Monitoring bladder fullness with appropriate miniaturized textile devices can improve, significantly, their daily life quality, or even cure them. Amongst the existing bladder sensing technologies, bioimpedance spectroscopy seems to be the most appropriate one to be integrated into textiles. (2) Methods: to assess the feasibility of monitoring the bladder fullness with textile-based bioimpedance spectroscopy; an innovative lab-bench has been designed and fabricated. As a step towards obtaining a more realistic pelvic phantom, ex vivo pig's bladder and skin were used. The electrical properties of the fabricated pelvic phantom have been compared to those of two individuals with tetrapolar impedance measurements. The measurements' reproducibility on the lab bench has been evaluated and discussed. Moreover, its suitability for the continuous monitoring of the bladder filling has been investigated. (3) Results: although the pelvic phantom failed in reproducing the frequency-dependent electrical properties of human tissues, it was found to be suitable at 5 kHz to record bladder volume change. The resistance variations recorded are proportional to the conductivity of the liquid filling the bladder. A 350 mL filling with artificial urine corresponds to a decrease in resistance of 7.2%, which was found to be in the same range as in humans. (4) Conclusions: based on that resistance variation; the instantaneous bladder fullness can be extrapolated. The presented lab-bench will be used to evaluate the ability of textiles electrodes to unobtrusively monitor the bladder volume.

Short-term androgen suppression and radiotherapy versus intermediate-term androgen suppression and radiotherapy, with or without zoledronic acid, in men with locally advanced prostate cancer (TROG 03.04 RADAR): 10-year results from a randomised, phase 3, factorial trial

BACKGROUND

The optimal duration of androgen suppression for men with locally advanced prostate cancer receiving radiotherapy with curative intent is yet to be defined. Zoledronic acid is effective in preventing androgen suppression-induced bone loss, but its role in preventing castration-sensitive bone metastases in locally advanced prostate cancer is unclear. The RADAR trial assessed whether the addition of 12 months of adjuvant androgen suppression, 18 months of zoledronic acid, or both, can improve outcomes in men with locally advanced prostate cancer who receive 6 months of androgen suppression and prostatic radiotherapy. This report presents 10-year outcomes from this trial.

METHODS

For this randomised, phase 3, 2 × 2 factorial trial, eligible men were 18 years or older with locally advanced prostate cancer (either T2b-4, N0 M0 tumours or T2a, N0 M0 tumours provided Gleason score was ≥7 and baseline prostate-specific antigen [PSA] concentration was ≥10 μg/L). We randomly allocated participants in a 2 × 2 factorial design by computer-generated randomisation (using the minimisation technique, and stratified by centre, baseline PSA concentration, clinical tumour stage, Gleason score, and use of a brachytherapy boost) in a 1:1:1:1 ratio to four treatment groups. Patients in the control group received 6 months of neoadjuvant androgen suppression with leuprorelin (22·5 mg every 3 months, intramuscularly) and radiotherapy alone (short-term androgen suppression [STAS]); this treatment was either followed by another 12 months of adjuvant androgen suppression with leuprorelin (22·5 mg every 3 months, intramuscularly; intermediate-term androgen suppression [ITAS]), or accompanied by 18 months of zoledronic acid (4 mg every 3 months, intravenously) starting at randomisation (STAS plus zoledronic acid), or both (ITAS plus zoledronic acid). All patients received radiotherapy to the prostate and seminal vesicles, starting from the end of the fifth month of androgen suppression; dosing options were 66, 70, and 74 Gy in 2-Gy fractions per day, or 46 Gy in 2-Gy fractions followed by a high-dose-rate brachytherapy boost dose of 19·5 Gy in 6·5-Gy fractions. Treatment allocation was open label. The primary endpoint was prostate cancer-specific mortality and was analysed according to intention-to-treat using competing-risks methods. The trial is closed to follow-up and this is the final report of the main endpoints. This trial is registered with ClinicalTrials.gov, number NCT00193856.

FINDINGS

Between Oct 20, 2003, and Aug 15, 2007, 1071 men were enrolled and randomly assigned to STAS (n=268), ITAS (n=268), STAS plus zoledronic acid (n=268), and ITAS plus zoledronic acid (n=267). Median follow-up was 10·4 years (IQR 7·9-11·7). At this 10-year follow-up, no interactions were observed between androgen suppression and zoledronic acid so the treatment groups were collapsed to compare treatments according to duration of androgen suppression: 6 months of androgen suppression plus radiotherapy (6AS+RT) versus 18 months of androgen suppression plus radiotherapy (18AS+RT) and to compare treatments according to whether or not patients received zoledronic acid. The total number of deaths was 375 (200 men receiving 6AS+RT and 175 men receiving 18AS+RT), of which 143 (38%) were attributable to prostate cancer (81 men receiving 6AS+RT and 62 men receiving 18AS+RT). When analysed by duration of androgen suppression, the adjusted cumulative incidence of prostate cancer-specific mortality was 13·3% (95% CI 10·3-16·0) for 6AS+RT versus 9·7% (7·3-12·0) for 18AS+RT, representing an absolute difference of 3·7% (95% CI 0·3-7·1; sub-hazard ratio [sHR] 0·70 [95% CI 0·50-0·98], adjusted p=0·035). The addition of zoledronic acid did not affect prostate cancer-specific mortality; the adjusted cumulative incidence of prostate cancer-specific mortality was 11·2% (95% CI 8·7-13·7) with zoledronic acid vs 11·7% (9·2-14·1) without, representing an absolute difference of -0·5% (95% CI -3·8 to 2·9; sHR 0·95 [95% CI 0·69-1·32], adjusted p=0·78). Although safety analysis was not prespecified for this 10-year analysis, one new serious adverse event (osteonecrosis of the mandible, in a patient who received 18 months of androgen suppression plus zoledronic acid) occurred since our previous report, bringing the total number of cases of this serious adverse event to three (<1% out of 530 patients who received zoledronic acid evaluated for safety) and the total number of drug-related serious adverse events to 12 (1% out of all 1065 patients evaluable for safety). No treatment-related deaths occurred during the study.

INTERPRETATION

18 months of androgen suppression plus radiotherapy is a more effective treatment option for locally advanced prostate cancer than 6 months of androgen suppression plus radiotherapy, but the addition of zoledronic acid to this treatment regimen is not beneficial. Evidence from the RADAR and French Canadian Prostate Cancer Study IV trials suggests that 18 months of androgen suppression with moderate radiation dose escalation is an effective but more tolerable option than longer durations of androgen suppression for men with locally advanced prostate cancer including intermediate and high risk elements.

FUNDING

National Health and Medical Research Council of Australia, Novartis Pharmaceuticals Australia, AbbVie Pharmaceuticals Australia, New Zealand Health Research Council, New Zealand Cancer Society, Cancer Standards Institute New Zealand, University of Newcastle (Australia), Hunter Medical Research Institute, Calvary Mater Newcastle Radiation Oncology Fund, and Maitland Cancer Appeal.

Credentialing of radiotherapy centres in Australasia for TROG 09.02 (Chisel), a Phase III clinical trial on stereotactic ablative body radiotherapy of early stage lung cancer

OBJECTIVE

A randomised clinical trial comparing stereotactic ablative body radiotherapy (SABR) with conventional radiotherapy for early stage lung cancer has been conducted in Australia and New Zealand under the auspices of the TransTasman Radiation Oncology Group (NCT01014130). We report on the technical credentialing program as prerequisite for centres joining the trial.

METHODS

Participating centres were asked to develop treatment plans for two test cases to assess their ability to create plans according to protocol. Dose delivery in the presence of inhomogeneity and motion was assessed during a site visit using a phantom with moving inserts.

RESULTS

Site visits for the trial were conducted in 16 Australian and 3 New Zealand radiotherapy facilities. The tests with low density inhomogeneities confirmed shortcomings of the AAA algorithm for dose calculation. Dose was assessed for a typical treatment delivery including at least one non-coplanar beam in a stationary and moving phantom. This end-to-end test confirmed that all participating centres were able to deliver stereotactic ablative body radiotherapy with the required accuracy while the planning study demonstrated that they were able to produce acceptable plans for both test cases.

CONCLUSION

The credentialing process documented that participating centres were able to deliver dose as required in the trial protocol. It also gave an opportunity to provide education about the trial and discuss technical issues such as four-dimensional CT, small field dosimetry and patient immobilisation with staff in participating centres. Advances in knowledge: Credentialing is an important quality assurance tool for radiotherapy trials using advanced technology. In addition to confirming technical competence, it provides an opportunity for education and discussion about the trial.

Association between measures of treatment quality and disease progression in prostate cancer radiotherapy: An exploratory analysis from the TROG 03.04 RADAR trial

INTRODUCTION

Quality assurance methods are incorporated into multicentre radiotherapy clinical trials for ensuring consistent application of trial protocol and quantifying treatment uncertainties. The study's purpose was to determine whether post-treatment disease progression is associated with measures of the quality of radiotherapy treatment.

METHODS

The TROG 03.04 RADAR trial tested the impact of androgen deprivation on prostate cancer patients receiving dose-escalated external beam radiation therapy. The trial incorporated a plan-review process and Level III dosimetric intercomparison at each centre, from which variables suggestive of treatment quality were collected. Kaplan-Meier statistics and Fine and Gray competing risk modelling were employed to test for associations between quality-related variables and the participant outcome local composite progression.

RESULTS

Increased 'dose-difference' at the prostatic apex and at the anterior rectal wall, between planned and measured dose, was associated with reduced progression. Participants whose treatment plans included clinical target volume (CTV) to planning target volume (PTV) margins exceeding protocol requirements also experienced reduced progression. Other quality-related variables, including total accrual from participating centres, measures of target coverage and other variations from protocol, were not significantly associated with progression.

CONCLUSIONS

This analysis has revealed the association of several treatment quality factors with disease progression. Increased dose and dose margin coverage in the prostate region can reduce disease progression. Extensive and rigorous monitoring has helped to maximise treatment quality, reducing the incidence of quality-indicator outliers, and thus reduce the chance of observing significant associations with progression rates.

Modelling late stool frequency and rectal pain after radical radiotherapy in prostate cancer patients: Results from a large pooled population

AIM

To investigate late gastrointestinal toxicity in a large pooled population of prostate cancer patients treated with radical radiotherapy. Normal tissue complication probability models were developed for late stool frequency and late rectal pain.

METHODS AND MATERIALS

Population included 1336 patients, 3-year minimum follow-up, treated with 66-80Gy. Toxicity was scored with LENT-SOMA-scale. Two toxicity endpoints were considered: grade ⩾2 rectal pain and mean grade (average score during follow-up) in stool frequency >1. DVHs of anorectum were reduced to equivalent uniform dose (EUD). The best-value of the volume parameter n was determined through numerical optimization. Association between EUD/clinical factors and the endpoints was investigated by logistic analyses. Likelihood, Brier-score and calibration were used to evaluate models. External calibration was also carried out.

RESULTS

4% of patients (45/1122) reported mean stool frequency grade >1; grade ⩾2 rectal pain was present in the TROG 03.04 RADAR population only (21/677, 3.1%): for this endpoint, the analysis was limited to this population. Analysis of DVHs highlighted the importance of mid-range doses (30-50Gy) for both endpoints. EUDs calculated with n=1 (OR=1.04) and n=0.35 (OR=1.06) were the most suitable dosimetric descriptors for stool frequency and rectal pain respectively. The final models included EUD and cardiovascular diseases (OR=1.78) for stool frequency and EUD and presence of acute gastrointestinal toxicity (OR=4.2) for rectal pain.

CONCLUSION

Best predictors of stool frequency and rectal pain are consistent with findings previously reported for late faecal incontinence, indicating an important role in optimization of mid-range dose region to minimize these symptoms highly impacting the quality-of-life of long surviving patients.

Gastrointestinal dose-histogram effects in the context of dose-volume-constrained prostate radiation therapy: analysis of data from the RADAR prostate radiation therapy trial

PURPOSE

To use a high-quality multicenter trial dataset to determine dose-volume effects for gastrointestinal (GI) toxicity following radiation therapy for prostate carcinoma. Influential dose-volume histogram regions were to be determined as functions of dose, anatomical location, toxicity, and clinical endpoint.

METHODS AND MATERIALS

Planning datasets for 754 participants in the TROG 03.04 RADAR trial were available, with Late Effects of Normal Tissues (LENT) Subjective, Objective, Management, and Analytic (SOMA) toxicity assessment to a median of 72 months. A rank sum method was used to define dose-volume cut-points as near-continuous functions of dose to 3 GI anatomical regions, together with a comprehensive assessment of significance. Univariate and multivariate ordinal regression was used to assess the importance of cut-points at each dose.

RESULTS

Dose ranges providing significant cut-points tended to be consistent with those showing significant univariate regression odds-ratios (representing the probability of a unitary increase in toxicity grade per percent relative volume). Ranges of significant cut-points for rectal bleeding validated previously published results. Separation of the lower GI anatomy into complete anorectum, rectum, and anal canal showed the impact of mid-low doses to the anal canal on urgency and tenesmus, completeness of evacuation and stool frequency, and mid-high doses to the anorectum on bleeding and stool frequency. Derived multivariate models emphasized the importance of the high-dose region of the anorectum and rectum for rectal bleeding and mid- to low-dose regions for diarrhea and urgency and tenesmus, and low-to-mid doses to the anal canal for stool frequency, diarrhea, evacuation, and bleeding.

CONCLUSIONS

Results confirm anatomical dependence of specific GI toxicities. They provide an atlas summarizing dose-histogram effects and derived constraints as functions of anatomical region, dose, toxicity, and endpoint for informing future radiation therapy planning.

Impact of treatment planning and delivery factors on gastrointestinal toxicity: an analysis of data from the RADAR prostate radiotherapy trial

BACKGROUND

To assess the impact of incremental modifications of treatment planning and delivery technique, as well as patient anatomical factors, on late gastrointestinal toxicity using data from the TROG 03.04 RADAR prostate radiotherapy trial.

METHODS

The RADAR trial accrued 813 external beam radiotherapy participants during 2003-2008 from 23 centres. Following review and archive to a query-able database, digital treatment plans and data describing treatment technique for 754 patients were available for analysis. Treatment demographics, together with anatomical features, were assessed using uni- and multivariate regression models against late gastrointestinal toxicity at 18-, 36- and 54-month follow-up. Regression analyses were reviewed in the context of dose-volume data for the rectum and anal canal.

RESULTS

A multivariate analysis at 36-month follow-up shows that patients planned using a more rigorous dose calculation algorithm (DCA) was associated with a lower risk of stool frequency (OR: 0.435, CI: 0.242-0.783, corrected p = 0.04). Patients using laxative as a method of bowel preparation had higher risk of having increased stool frequency compared to patients with no dietary intervention (OR: 3.639, CI: 1.502-8.818, corrected p = 0.04). Despite higher risks of toxicities, the anorectum, anal canal and rectum dose-volume histograms (DVH) indicate patients using laxative had unremarkably different planned dose distributions. Patients planned with a more rigorous DCA had lower median DVH values between EQD23 = 15 Gy and EQD23 = 35 Gy. Planning target volume (PTV), conformity index, rectal width and prescription dose were not significant when adjusted for false discovery rate. Number of beams, beam energy, treatment beam definition, positioning orientation, rectum-PTV separation, rectal length and mean cross sectional area did not affect the risk of toxicities.

CONCLUSIONS

The RADAR study dataset has allowed an assessment of technical modifications on gastrointestinal toxicity. A number of interesting associations were subsequently found and some factors, previously hypothesised to influence toxicity, did not demonstrate any significant impact. We recommend trial registries be encouraged to record technical modifications introduced during the trial in order for more powerful evidence to be gathered regarding the impact of the interventions.

Short-term androgen suppression and radiotherapy versus intermediate-term androgen suppression and radiotherapy, with or without zoledronic acid, in men with locally advanced prostate cancer (TROG 03.04 RADAR): an open-label, randomised, phase 3 factorial trial

BACKGROUND

We investigated whether 18 months of androgen suppression plus radiotherapy, with or without 18 months of zoledronic acid, is more effective than 6 months of neoadjuvant androgen suppression plus radiotherapy with or without zoledronic acid.

METHODS

We did an open-label, randomised, 2 × 2 factorial trial in men with locally advanced prostate cancer (either T2a N0 M0 prostatic adenocarcinomas with prostate-specific antigen [PSA] ≥10 μg/L and a Gleason score of ≥7, or T2b-4 N0 M0 tumours regardless of PSA and Gleason score). We randomly allocated patients by computer-generated minimisation--stratified by centre, baseline PSA, tumour stage, Gleason score, and use of a brachytherapy boost--to one of four groups in a 1:1:1:1 ratio. Patients in the control group were treated with neoadjuvant androgen suppression with leuprorelin (22·5 mg every 3 months, intramuscularly) for 6 months (short-term) and radiotherapy alone (designated STAS); this procedure was either followed by another 12 months of androgen suppression with leuprorelin (intermediate-term; ITAS) or accompanied by 18 months of zoledronic acid (4 mg every 3 months for 18 months, intravenously; STAS plus zoledronic acid) or by both (ITAS plus zoledronic acid). The primary endpoint was prostate cancer-specific mortality. This analysis represents the first, preplanned assessment of oncological endpoints, 5 years after treatment. Analysis was by intention-to-treat. This trial is registered with ClinicalTrials.gov, number NCT00193856.

FINDINGS

Between Oct 20, 2003, and Aug 15, 2007, 1071 men were randomly assigned to STAS (n=268), STAS plus zoledronic acid (n=268), ITAS (n=268), and ITAS plus zoledronic acid (n=267). Median follow-up was 7·4 years (IQR 6·5-8·4). Cumulative incidences of prostate cancer-specific mortality were 4·1% (95% CI 2·2-7·0) in the STAS group, 7·8% (4·9-11·5) in the STAS plus zoledronic acid group, 7·4% (4·6-11·0) in the ITAS group, and 4·3% (2·3-7·3) in the ITAS plus zoledronic acid group. Cumulative incidence of all-cause mortality was 17·0% (13·0-22·1), 18·9% (14·6-24·2), 19·4% (15·0-24·7), and 13·9% (10·3-18·8), respectively. Neither prostate cancer-specific mortality nor all-cause mortality differed between control and experimental groups. Cumulative incidence of PSA progression was 34·2% (28·6-39·9) in the STAS group, 39·6% (33·6-45·5) in the STAS plus zoledronic acid group, 29·2% (23·8-34·8) in the ITAS group, and 26·0% (20·8-31·4) in the ITAS plus zoledronic acid group. Compared with STAS, no difference was noted in PSA progression with ITAS or STAS plus zoledronic acid; however, ITAS plus zoledronic acid reduced PSA progression (sub-hazard ratio [SHR] 0·71, 95% CI 0·53-0·95; p=0·021). Cumulative incidence of local progression was 4·1% (2·2-7·0) in the STAS group, 6·1% (3·7-9·5) in the STAS plus zoledronic acid group, 1·5% (0·5-3·7) in the ITAS group, and 3·4% (1·7-6·1) in the ITAS plus zoledronic acid group; no differences were noted between groups. Cumulative incidences of bone progression were 7·5% (4·8-11·1), 14·6% (10·6-19·2), 8·4% (5·5-12·2), and 7·6% (4·8-11·2), respectively. Compared with STAS, STAS plus zoledronic acid increased the risk of bone progression (SHR 1·90, 95% CI 1·14-3·17; p=0·012), but no differences were noted with the other two groups. Cumulative incidence of distant progression was 14·7% (10·7-19·2) in the STAS group, 17·3% (13·0-22·1) in the STAS plus zoledronic acid group, 14·2% (10·3-18·7) in the ITAS group, and 11·1% (7·6-15·2) in the ITAS plus zoledronic acid group; no differences were recorded between groups. Cumulative incidence of secondary therapeutic intervention was 25·6% (20·5-30·9), 28·9% (23·5-34·5), 20·7% (16·1-25·9), and 15·3% (11·3-20·0), respectively. Compared with STAS, ITAS plus zoledronic acid reduced the need for secondary therapeutic intervention (SHR 0·67, 95% CI 0·48-0·95; p=0·024); no differences were noted with the other two groups. An interaction between trial factors was recorded for Gleason score; therefore, we did pairwise comparisons between all groups. Post-hoc analyses suggested that the reductions in PSA progression and decreased need for secondary therapeutic intervention with ITAS plus zoledronic acid were restricted to tumours with a Gleason score of 8-10, and that ITAS was better than STAS in tumours with a Gleason score of 7 or lower. Long-term morbidity and quality-of-life scores were not affected adversely by 18 months of androgen suppression or zoledronic acid.

INTERPRETATION

Compared with STAS, ITAS plus zoledronic acid was more effective for treatment of prostate cancers with a Gleason score of 8-10, and ITAS alone was effective for tumours with a Gleason score of 7 or lower. Nevertheless, these findings are based on secondary endpoint data and post-hoc analyses and must be regarded cautiously. Long- term follow-up is necessary, as is external validation of the interaction between zoledronic acid and Gleason score. STAS plus zoledronic acid can be ruled out as a potential therapeutic option.

FUNDING

National Health and Medical Research Council of Australia, Novartis Pharmaceuticals Australia, Abbott Pharmaceuticals Australia, New Zealand Health Research Council, New Zealand Cancer Society, University of Newcastle (Australia), Calvary Health Care (Calvary Mater Newcastle Radiation Oncology Fund), Hunter Medical Research Institute, Maitland Cancer Appeal, Cancer Standards Institute New Zealand.

Results from a multicenter prostate IMRT dosimetry intercomparison for an OCOG-TROG clinical trial

PURPOSE

A multi-institution dosimetry intercomparison has been undertaken of prostate intensity modulated radiation therapy (IMRT) delivery. The dosimetry intercomparison was incorporated into the quality assurance for site credentialing for the Trans-Tasman Radiation Oncology Group Prostate Fractionated Irradiation Trial 08.01 clinical trial.

METHODS

An anthropomorphic pelvic phantom with realistic anatomy was used along with multiplanar dosimetry tools for the assessment. Nineteen centers across Australia and New Zealand participated in the study.

RESULTS

In comparing planned versus measured dose to the target at the isocenter within the phantom, all centers were able to achieve a total delivered dose within 3% of planned dose. In multiplanar analysis with radiochromic film using the gamma analysis method to compare delivered and planned dose, pass rates for a 5%/3 mm criterion were better than 90% for a coronal slice through the isocenter. Pass rates for an off-axis coronal slice were also better than 90% except for one instance with 84% pass rate.

CONCLUSIONS

Strengths of the dosimetry assessment procedure included the true anthropomorphic nature of the phantom used, the involvement of an expert from the reference center in carrying out the assessment at every site, and the ability of the assessment to detect and resolve dosimetry discrepancies.