Dosimetry and Gastrointestinal Toxicity Relationships in a Phase II Trial of Pelvic Lymph Node Radiotherapy in Advanced Localised Prostate Cancer

Heuristic estimation of the α/β ratio for a cohort of Mexican patients with prostate cancer treated with external radiotherapy techniques

Background

The aim of the study was to Estimate and compare the radiobiological ratio α/β with the heuristic method for a cohort of Mexican patients with prostate cancer (PCa) who were treated with external radiotherapy (RT) techniques at three Hospital Institutions in Mexico City. With the Kaplan-Meier technique and the Cox proportional hazards model, the biochemical relapse-free survival (bRFS) is determined and characterized for cohorts of Mexican patients with PCa who received treatment with external RT. Using these clinical outcomes, the radiobiological parameter α/β is determined using the heuristic methodology of Pedicini et. al.

Materials and methods

The α/β is calculated from the survival curves for different treatment schemes implemented at three distinct hospitals. The Pedicini's techniques allow to determine the parameters α/β, k and N ₀ when treatments are not radiobiologically equivalent, therefore, are built up of a set of curved pairs for the biologically effective dose (BED) versus the ratio α/β, where the ratio is given by the intersection for each pair of curves.

Results

Six different values of α/β were found: the first α/β = 2.46 Gy, the second α/β = 3.30 Gy, the third for α/β = 3.25 Gy, the fourth α/β = 3.24 Gy, the fifth α/β = 3.38 Gy and the last α/β = 4.08 Gy. These values can be explained as follows: a) The bRFS of the schemes presents a statistical variation; b) The absorbed doses given to the patient present uncertainties on the physical dosimetry that are not on the modeling; c) Finally, in the model for the bRFS of Eq. (3), there are parameters that have to be considered, such as: the number of clonogenic tumor cells N ₀ , the overall treatment time (OTT), the kick-off time for tumor repopulation T _k and the repopulation doubling time. Therefore, the mean value to α/β for all schemes has an average value of 3.29 (± 0.52) Gy.

Conclusions

The value of α / β ¯ = 3.29   ( ± 0.52 )   Gy is determined from cohorts of Mexican patients with PC a treated with external radiotherapy using the time-dependent LQ model, which is a higher value with respect to the "dogma" value of α/β 1.5 Gy obtained with the LQ model without temporal dependence. Therefore, there is a possibility of optimizing treatments radiobiologically and improving the results of bRFS in Mexican patients with PCa treated with external radiotherapy.

Effect of patient thickness on acute gastrointestinal toxicities following radiotherapy for prostate cancer

Background

There is conflicting literature regarding the effect of patient size on radiotherapy toxicities. This study aimed to determine whether there is any association between patient thickness and severity and incidence of acute GI toxicities of prostate cancer patients receiving VMAT radiotherapy. The impact of confounding factors was also examined: rectal dose, age and lymph node irradiation.

Materials and methods

This study used a non-experimental, retrospective, descriptive and cross-sectional design. All patients who complied with the inclusion criteria (n = 96) were included. GI toxicity scores (baseline and last week of radiotherapy), rectal dose, lymph nodes irradiation and patient age at diagnosis were collected from the treatment file. Patient separations were measured from the CT-Simulator images. Statistical tests were performed to analyse the influence of these factors on acute GI toxicities.

Results

Patient thickness was shown to have no statistically significant effect on the incidence (p = 0.947 for antero-posterior and p = 0.839 for lateral thicknesses), and severity (p = 0.986 and 0.905, respectively) of acute GI toxicities. Severity of GI toxicities increased following radiotherapy: the Expanded Prostate Cancer Index Composite (EPIC) score increased by 2.64 from baseline (p < 0.001). The confounding factors had no statistically significant effect on toxicities (p > 0.05).

Conclusion

As expected, most patients experienced an increase in GI toxicity following radiotherapy. No relationship was established between patient thickness and the severity or incidence of acute GI toxicities, adding to the existing body of knowledge. Therefore, all patients should receive adequate follow up, irrespective of size. Side-effect recording tools should be implemented systematically for continuous assessment of this relationship.

NRG Oncology Updated International Consensus Atlas on Pelvic Lymph Node Volumes for Intact and Postoperative Prostate Cancer

PURPOSE

In 2009, the Radiation Therapy Oncology Group (RTOG) genitourinary members published a consensus atlas for contouring prostate pelvic nodal clinical target volumes (CTVs). Data have emerged further informing nodal recurrence patterns. The objective of this study is to provide an updated prostate pelvic nodal consensus atlas.

METHODS AND MATERIALS

A literature review was performed abstracting data on nodal recurrence patterns. Data were presented to a panel of international experts, including radiation oncologists, radiologists, and urologists. After data review, participants contoured nodal CTVs on 3 cases: postoperative, intact node positive, and intact node negative. Radiation oncologist contours were analyzed qualitatively using count maps, which provided a visual assessment of controversial regions, and quantitatively analyzed using Sorensen-Dice similarity coefficients and Hausdorff distances compared with the 2009 RTOG atlas. Diagnostic radiologists generated a reference table outlining considerations for determining clinical node positivity.

RESULTS

Eighteen radiation oncologists' contours (54 CTVs) were included. Two urologists' volumes were examined in a separate analysis. The mean CTV for the postoperative case was 302 cm3, intact node positive case was 409 cm3, and intact node negative case was 342 cm3. Compared with the original RTOG consensus, the mean Sorensen-Dice similarity coefficient for the postoperative case was 0.63 (standard deviation [SD] 0.13), the intact node positive case was 0.68 (SD 0.13), and the intact node negative case was 0.66 (SD 0.18). The mean Hausdorff distance (in cm) for the postoperative case was 0.24 (SD 0.13), the intact node positive case was 0.23 (SD 0.09), and intact node negative case was 0.33 (SD 0.24). Four regions of CTV controversy were identified, and consensus for each of these areas was reached.

CONCLUSIONS

Discordance with the 2009 RTOG consensus atlas was seen in a group of experienced NRG Oncology and international genitourinary radiation oncologists. To address areas of variability and account for new data, an updated NRG Oncology consensus contour atlas was developed.

Seven or less Fractions is Not the Standard of Care for Intermediate-Risk Prostate Cancer

Evidence is accumulating for seven and less fractions in localised prostate cancer, including one large randomised trial. However, there is much more evidence yet to come and changing practice in advance of this may be premature. We review the reasons to persist with moderate hypofractionation for prostate cancer radiotherapy, until the results of further phase III studies are known.

Late toxicity and quality of life with prostate only or whole pelvic radiation therapy in high risk prostate cancer (POP-RT): A randomised trial

AIM

To report toxicity and quality of life (QOL) outcomes from a randomised trial of prostate only versus whole pelvic radiotherapy in high risk, node negative prostate cancer.

MATERIALS/METHODS

Patients with localised prostate adenocarcinoma and nodal involvement risk > 20%, were randomised to prostate only (PORT, 68 Gy/25# to prostate) and whole pelvis (WPRT, 68 Gy/25# to prostate and 50 Gy/25# to pelvis) arms with stratification for TURP, Gleason score, baseline PSA, and type of androgen deprivation therapy (ADT). Image guided intensity modulated radiotherapy (IG-IMRT) and two years of ADT were mandatory. Acute and late genitourinary (GU) and gastrointestinal (GI) toxicities were graded using RTOG grading. QOL was assessed using EORTC QLQ-C30 and PR-25 questionnaire pre-treatment and every 3-6 months post RT.

RESULTS

Total 224 patients were randomised (PORT 114, WPRT 110) from November 2011 to August 2017. Median follow up was 44.5 months. No RTOG grade IV toxicity was observed. Acute GI and GU toxicities were similar between both the arms. Cumulative ≥ grade II late GI toxicity was similar for WPRT and PORT (6.5% vs. 3.8%, p = 0.39) but GU toxicity was higher (17.7% vs. 7.5%, p = 0.03). Dosimetric analysis showed higher bladder volume receiving 30-40 Gy in the WPRT arm (V30, 60% vs. 36%, p < 0.001; V40, 41% vs. 25%, p < 0.001). There was no difference in QOL scores of any domain between both arms.

CONCLUSION

Pelvic irradiation using hypofractionated IG-IMRT resulted in increased grade II or higher late genitourinary toxicity as compared to prostate only RT, but the difference was not reflected in patient reported QOL. CLINICALTRIALS.GOV NCT02302105: Prostate Only or Whole Pelvic Radiation Therapy in High Risk Prostate Cancer (POP-RT).