V. Carillo

Relationships between bladder dose–volume/surface histograms and acute urinary toxicity after radiotherapy for prostate cancer

BACKGROUND AND PURPOSE DUE01 is an observational study aimed at developing predictive models of genito-urinary toxicity of patients treated for prostate cancer with conventional (1.8-2Gy/fr, CONV) or moderate hypo-fractionation (2.35-2.7Gy/fr, HYPO). The current analysis focused on the relationship between bladder DVH/DSH and the risk of International Prostate Symptoms Score (IPSS)⩾15/20 at the end of radiotherapy. MATERIALS AND METHODS Planning and relevant clinical parameters were prospectively collected, including DVH/DSH, LQ-corrected (DVHc/DSHc) and weekly (DVHw/DSHw) histograms. Best parameters were selected by the differences between patients with/without IPSS⩾15/20 at the end of radiotherapy. Logistic uni- and backward multi-variable (MVA) analyses were performed. RESULTS Data of 247 patients were available (CONV: 116, HYPO: 131). Absolute DVHw/DSHw and DVHc/DSHc predicted the risk of IPSS⩾15 at the end of radiotherapy (n=77/247); an MVA model including baseline IPSS, anti-hypertensive, T stage, the absolute surface receiving ⩾8.5Gy/week and ⩾12.5Gy/week was developed (AUC=0.78, 95% CI: 0.72-0.83). Similar AUC values were found if replacing DSHw with DVHw/DVHc/DSHc parameters. The impact of dose-volume/surface parameters remained when excluding patients with baseline IPSS⩾15 and in HYPO. IPSS⩾20 at the end of radiotherapy (n=27/247) was mainly correlated to baseline IPSS and T stage. CONCLUSIONS Although the baseline IPSS was the main predictor, constraining v8.5w<56cc and v12.5w<5cc may significantly reduce acute GU toxicity.

First application of a pixel-wise analysis on bladder dose-surface maps in prostate cancer radiotherapy

PURPOSE To develop a method for investigating local dose effects on the bladder after prostate cancer radiotherapy based on dose-surface maps (DSMs). BACKGROUND AND PURPOSE DSMs of patients included in a prospective study (DUE01) were generated by virtually cutting bladder contours at the points intersecting the sagittal plane passing through its center-of-mass: maps were laterally normalized and aligned at the posterior inferior point. The average DSMs of patients with/without toxicity, the DSMs of differences and t statistic were used to select regions better discriminating patients with toxicity. A total of 72 patients with no/mild urinary symptoms before radiotherapy and who were treated with moderate hypo-fractionation (2.5-2.65Gy/fr, 70-74Gy) were considered, and the endpoint was an International Prostate Symptoms Score (IPSS)⩾15 at the end of therapy (IPSSend⩾15, n=25/72). RESULTS The DSMs of patients with/without toxicity were significantly different (p<0.05). The percentage of bladder circumference receiving >50-70Gy at 5-7mm from the base was associated with an IPSSend⩾15 (odds ratios: 1.03-1.07). Different patterns were recognized for specific symptoms. With frequency/urgency, a quasi-threshold effect on the absolute posterior dose at 5-12mm from the base (2Gy equivalent doses=80-82Gy, α/β=3-5Gy) was observed. CONCLUSIONS Local-dose effects for acute symptoms were detected in a group of patients treated within a moderately hypo-fractionated protocol. The results for frequency/urgency were consistent with a threshold effect on the trigone.

Multi-variable models predicting specific patient-reported acute urinary symptoms after radiotherapy for prostate cancer: Results of a cohort study.

PURPOSE A prospective trial started in 2010, aiming at developing models for urinary toxicity and erectile dysfunction after radiotherapy for prostate cancer. This analysis is finalised at highlighting correlations between clinical/dosimetric factors and acute urinary specific symptoms, as measured by single questions of the International Prostate Symptom Score (IPSS). MATERIALS/METHODS IPSS was prospectively collected before and at the end of radiotherapy; absolute weekly bladder dose-surface histograms (DSHw) were chosen as dosimetric descriptors. Relevant clinical factors were prospectively gathered. Backward feature selection was used to identify variables to be included in logistic models for moderate-severe (scores⩾4) urinary symptoms. RESULTS Complete data of 262 patients (120 conventional fractionation, 142 hypofractionation) were available. Smoking was a strong predictor for feeling of incomplete emptying, frequency, intermittency, urgency and straining; neoadjuvant hormonal therapy and use of antihypertensive drugs were risk factors for intermittency and weak stream, respectively. The baseline score was a major predictor for all symptoms with the exception of intermittency. DSHw were correlated to increased risk of frequency, intermittency, urgency and nocturia. Most models showed moderate-high discrimination (AUC≈0.60-0.79). CONCLUSIONS Smoking and other clinical and dosimetric factors predict for specific moderate-severe acute urinary symptoms; baseline condition heavily modulated the risk in most endpoints.

Multi-variable models of large International Prostate Symptom Score worsening at the end of therapy in prostate cancer radiotherapy

PURPOSE/OBJECTIVE Prospectively assessing clinical/dosimetry factors affecting the acute worsening of urinary functionality after radiotherapy for prostate cancer. MATERIAL/METHODS DUE01 population was considered, including patients treated with conventional or moderate hypo-fractionation (2.2-2.7 Gy/fr). Relevant clinical factors were collected, urinary symptoms were self-reported through the International Prostate Symptom Score (IPSS) before and at the end of radiotherapy; while absolute weekly dose-surface histograms (DSHw) were chosen as dosimetry descriptors. An IPSS increase of at least 10 and 15 points (ΔIPSS ⩾ 10 and ΔIPSS ⩾ 15) were chosen as endpoints. Patients with baseline IPSS>20 were excluded. Relevant factors were chosen through a bootstrap-based in silico methodology. RESULTS Complete information was available for 380 patients: 77/380 (20%) and 28/380 (7%) with ΔIPSS ⩾ 10 and ΔIPSS ⩾ 15, respectively. Neoadjuvant hormone was protective (OR=0.49 and 0.69). DSHw at 8.5 Gy/week and 12 Gy/week were risk factors, with additional risk for patients who use cardiovascular drugs and anti-hypercholesterolemia drugs. In the hypo-fractionated subgroup (n=209) the role of cardiovascular drugs (OR=2.16) for ΔIPSS ⩾ 10 and anti-hypercholesterolemia drugs (OR=2.80) for ΔIPSS⩾15, together with DSHw (10 Gy/week and 12.5 Gy/week, respectively), was confirmed. CONCLUSION Current study shows a dose-surface/volume effect for acute large worsening of urinary functionality; several clinical variables largely impact the risk and especially all the factors related with vascular diseases.

Correlation between surrogates of bladder dosimetry and dose-volume histograms of the bladder wall defined on MRI in prostate cancer radiotherapy.

The correlation between bladder dose-wall-histogram (DWH) and dose-volume-histogram (DVH), dose-surface-histogram (DSH), and DVH-5/10 was investigated in a group of 28 patients; bladder walls were drawn on T2-MRI. DVH showed the poorest correlation with DWH; DSH or DVH-5/10 should be preferred in planning; absolute DVH may be used for radical patients, although less robust.

Bladder dose–surface maps and urinary toxicity: Robustness with respect to motion in assessing local dose effects

The purpose of this study was to quantify the impact of inter-fraction modifications of bladder during RT of prostate cancer on bladder dose surface maps (DSM). Eighteen patients treated with daily image-guided Tomotherapy and moderate hypofractionation (70-72.8Gy at 2.5-2.6Gy/fr in 28 fractions and full bladder) were considered. Bladder contours were delineated on co-registered daily Megavoltage CT (MVCT) by a single observer and copied on the planning CT to generate dose-volume/surface histograms (DVH/DSH) and bladder DSMs. Discrepancies between planned and daily absorbed doses were analyzed through the average of individual systematic errors, the population systematic errors and the population random errors for the DVH/DSHs and DSMs. In total, 477 DVH/DSH and 472 DSM were available. DSH and DVH showed small population systematic errors of absolute surfaces (<3.4cm(2)) and volumes (<8.4cm(3)) at the highest doses. The dose to the posterior bladder base assessed on DSMs showed a mean systematic error below 1Gy, with population systematic and random errors within 4 and 3Gy, respectively. The region surrounding this area shows higher mean systematic errors (1-3Gy), population systematic (8-11Gy) and random (5-7Gy) errors. In conclusion, DVH/DSH and DSMs are quite stable with respect to inter-fraction variations in the high-dose region, within about 2cm from bladder base. Larger systematic variations occur in the anterior portion and cranially 2.5-3.5cm from the base. Results suggest that dose predictors related to the high dose area (including the trigone dose) are likely to be sufficiently reliable with respect to the expected variations due to variable bladder filling.

Patient-reported intestinal toxicity from whole pelvis intensity-modulated radiotherapy: First quantification of bowel dose–volume effects

BACKGROUND AND PURPOSE Intestinal toxicity is commonly experienced during whole-pelvis intensity-modulated radiotherapy (WPRT) for prostate cancer. The aim of the current study was to assess bowel dose-volume relationships for acute patient-reported intestinal symptoms of patients treated with WPRT for prostate cancer. MATERIALS AND METHODS Complete data of 206 patients were available; the median dose to pelvic nodes was 51.8Gy (range 50.4-54.4, 1.7-2Gy/fr). Intestinal symptoms were assessed as changes in the Inflammatory Bowel Disease Questionnaire scores relative to the Bowel Domain (IBDQ-B) between baseline and radiotherapy mid-point/end. The 25th percentiles of the most severe worsening from baseline (ΔIBDQ-B) were set as end-points. The impact of bowel loops and sigmoid colon dose-volume/surface parameters as well as selected clinical parameters were investigated using multivariate logistic regression. RESULTS Analyses were focused on the four questions showing a median ΔIBDQ-B>0. No dose volume/surface parameters were predictive, other than ΔIBDQ5≥3 (loose stools): when grouping patients according to bowel DVHs (high risk: V20>470cc, V30>245cc, V42>110cc; low risk: all the remaining patients), a two-variable model including high-risk DVH-shape (OR: 9.3) and age (protective, OR: 0.94) was assessed. The model showed good calibration (slope: 1.003, R2=0.92) and was found to be robust after bootstrap-based internal validation. CONCLUSIONS Constraining the bowel loops may reduce the risk of loose stools. The risk is higher for younger patients.

PV-0377: Inter-fraction bladder variations in RT of prostate cancer: impact on dose surface maps

ESTRO 35 2016 _____________________________________________________________________________________________________ Purpose or Objective: Contrast enhancement and respiration management are widely used during image acquisition for radiotherapy treatment planning of liver tumors along with respiration management at the treatment unit. However, neither respiration management nor intravenous contrast is commonly used during cone-beam CT (CBCT) image acquisition for alignment prior to radiotherapy. In this study, the authors investigate the potential gains of injecting an iodinated contrast agent in combination with respiration management during CBCT acquisition for liver tumor radiotherapy.

Modeling acute urinary toxicity after radiotherapy for prostate cancer.

156 Background: DUE-01 is a multi-centric observational study aimed at developing predictive models of genito-urinary toxicity and erectile dysfunction for prostate cancer patients treated with conventional (1.8-2Gy/fr, CONV) or moderate hypofractionation (2.5-2.7Gy/fr, HYPO). Current analysis focused on modelling the relationship between the risk of IPSS≥15 (IPSS15end) at the end of radiotherapy and clinincal/dosimetric risk factors. Methods: Planning data and relevant clinical factors were prospectively collected, including DVH/DSH referred to the whole treatment and to the weekly delivered dose (DVHw/DSHw). Best discriminating DVH/DSH parameters were selected by the differences between patients with/without IPSS15end=1 (t-test). Bootstrap variable selection techniques (300 resamples) in the framework of logistic backward feature selection was used to improve model building (El Naqa, IJROBP 2006). Graphical and quantitative analyses of the variable selection process applied to bootstrap data replicates ...