Distinct effects of rectum delineation methods in 3D-conformal vs. IMRT treatment planning of prostate cancer

Interfraction variation and dosimetric changes during image-guided radiation therapy in prostate cancer patients

Purpose

The aim of this study was to identify volume changes and dose variations of rectum and bladder during radiation therapy in prostate cancer (PC) patients.

Materials and Methods

We analyzed 20 patients with PC treated with helical tomotherapy. Daily image guidance was performed. We re-contoured the entire bladder and rectum including its contents as well as the organ walls on megavoltage computed tomography once a week. Dose variations were analyzed by means of Dmedian, Dmean, Dmax, V₁₀ to V₇₅, as well as the organs at risk (OAR) volume. Further, we investigated the correlation between volume changes and changes in Dmean of OAR.

Results

During treatment, the rectal volume ranged from 62% to 223% of its initial volume, the bladder volume from 22% to 375%. The average Dmean ranged from 87% to 118% for the rectum and 58% to 160% for the bladder. The Pearson correlation coefficients between volume changes and corresponding changes in Dmean were -0.82 for the bladder and 0.52 for the rectum. The comparison of the dose wall histogram (DWH) and the dose volume histogram (DVH) showed that the DVH underestimates the percentage of the rectal and bladder volume exposed to the high dose region.

Conclusion

Relevant variations in the volume of OAR and corresponding dose variations can be observed. For the bladder, an increase in the volume generally leads to lower doses; for the rectum, the correlation is weaker. Having demonstrated remarkable differences in the dose distribution of the DWH and the DVH, the use of DWHs should be considered.

Dosimetric and volumetric effects in clinical target volume and organs at risk during postprostatectomy radiotherapy

PURPOSE

To assess the reproducibility of the dose-volume distribution of the initial simulation CT, generated using volumetric modulated arc therapy (VMAT) planning, during the radiotherapy of the prostatic bed based on weekly cone beam CTs (CBCT).

METHODS

Twenty-three patients, after radical prostatectomy were treated with adjuvant or salvage radiotherapy between July and December 2016 and considered for this evaluation. Weekly CBCT scans (n = 138) were imported into the treatment planning system, and the clinical tumor volume (CTV), the rectum and the bladder were contoured. The initially calculated dose distribution and the dose-volume histograms generated from weekly CBCTs were compared. The prostatic fossa dose coverage was assessed by the proportion of the CTV fully encompassed by the 95% and 98% isodose lines. Rectal and bladder volumes receiving 50, 60 and 65 Gy during the treatment were compared to the initial plan, with statistical significance determined using the one-sample t‑test.

RESULTS

Marked variations in the total organ volume of the rectum and the bladder were observed. The correlation between rectum volume and V₅₀ was not significant (p = 0.487), while the bladder volume and V₅₀ demonstrated a significant correlation. There was no correlation between urinary bladder volume and CTV. The change in rectal volume correlated significantly with CTV. The dose coverage (D_98% and D_95%) to the prostatic bed could be achieved for all patients due to the ventral shift in the volume differences of the rectum.

CONCLUSION

Weekly CBCTs can be considered as adequate verification tools to assess the interfractional variability of the CTV and organs at risk. The proven volume changes in the urinary bladder and the rectum do not compromise the final delivered dose in the CTV.

Radiation-induced acute toxicities after image-guided intensity-modulated radiotherapy versus three-dimensional conformal radiotherapy for patients with spinal metastases (IRON-1 trial) : First results of a randomized controlled trial

PURPOSE

Radiation therapy (RT) provides an important treatment approach in the palliative care of vertebral metastases, but radiation-induced toxicities in patients with advanced disease and low performance status can have substantial implications for quality of life. Herein, we prospectively compared toxicity profiles of intensity-modulated radiotherapy (IMRT) vs. conventional three-dimensional conformal radiotherapy (3DCRT).

METHODS

This was a prospective randomized monocentric explorative pilot trial to compare radiation-induced toxicity between IMRT and 3DCRT for patients with spinal metastases. A total of 60 patients were randomized between November 2016 and May 2017. In both cohorts, RT was delivered in 10 fractions of 3 Gy each. The primary endpoint was radiation-induced toxicity at 3 months.

RESULTS

Median follow-up was 4.3 months. Two patients suffered from grade 3 acute toxicities in the IMRT arm, along with 1 patient in the 3DCRT group. At 12 weeks after treatment (t2), 1 patient reported grade 3 toxicity in the IMRT arm vs. 4 patients in the 3DCRT group. No grade 4 or 5 adverse events occurred in either group. In the IMRT arm, the most common side effects by the end of irradiation (t1) were grade 1-2 xerostomia and nausea in 8 patients each (29.6%), and dyspnea in 7 patients (25.9%). In the 3DCRT group, the most frequent adverse events (t1) were similar: grade 1-2 xerostomia (n = 10, 35.7%), esophagitis (n = 10, 35.8%), nausea (n = 10, 35.8%), and dyspnea (n = 5, 17.9%).

CONCLUSION

This is the first randomized trial to evaluate radiation-induced toxicities after IMRT versus 3DCRT in patients with vertebral metastases. This trial demonstrated an additional improvement for IMRT in terms of acute side effects, although longer follow-up is required to further ascertain other endpoints.

Dosimetric impact in the dose-volume histograms of rectal and vesical wall contouring in prostate cancer IMRT treatments

AIM

The main purpose of this study was to evaluate the differences in dose-volume histograms of IMRT treatments for prostate cancer based on the delineation of the main organs at risk (rectum and bladder) as solid organs or by contouring their wall.

BACKGROUND

Rectum and bladder have typically been delineated as solid organs, including the waste material, which, in practice, can lead to an erroneous assessment of the risk of adverse effects.

MATERIALS AND METHODS

A retrospective study was made on 25 patients treated with IMRT radiotherapy for prostate adenocarcinoma. 76.32 Gy in 36 fractions was prescribed to the prostate and seminal vesicles. In addition to the delineation of the rectum and bladder as solid organs (including their content), the rectal and bladder wall were also delineated and the resulting dose-volume histograms were analyzed for the two groups of structures.

RESULTS

Data analysis shows statistically significant differences in the main parameters used to assess the risk of toxicity of a prostate radiotherapy treatment. Higher doses were received on the rectal and bladder walls compared to doses received on the corresponding solid organs.

CONCLUSIONS

The observed differences in terms of received doses to the rectum and bladder based on the method of contouring could gain greater importance in inverse planning treatments, where the treatment planning system optimizes the dose in these volumes. So, one should take into account the method of delineating of these structures to make a clinical decision regarding dose limitation and risk assessment of chronic toxicity.

Comparison of different contouring definitions of the rectum as organ at risk (OAR) and dose-volume parameters predicting rectal inflammation in radiotherapy of prostate cancer: which definition to use?

OBJECTIVE

The objective of this retrospective planning study was to find a contouring definition for the rectum as an organ at risk (OAR) in curative three-dimensional external beam radiotherapy (EBRT) for prostate cancer (PCa) with a predictive correlation between the dose-volume histogram (DVH) and rectal toxicity.

METHODS

In a pre-study, the planning CT scans of 23 patients with PCa receiving definitive EBRT were analyzed. The rectum was contoured according to 13 different definitions, and the dose distribution was correlated with the respective rectal volumes by generating DVH curves. Three definitions were identified to represent the most distinct differences in the shapes of the DVH curves: one anatomical definition recommended by the Radiation Therapy Oncology Group (RTOG) and two functional definitions based on the target volume. In the main study, the correlation between different relative DVH parameters derived from these three contouring definitions and the occurrence of rectal toxicity during and after EBRT was studied in two consecutive collectives. The first cohort consisted of 97 patients receiving primary curative EBRT and the second cohort consisted of 66 patients treated for biochemical recurrence after prostatectomy. Rectal toxicity was investigated by clinical investigation and scored according to the Common Terminology Criteria for Adverse Events. Candidate parameters were the volume of the rectum, mean dose, maximal dose, volume receiving at least 60 Gy (V₆₀), area under the DVH curve up to 25 Gy and area under the DVH curve up to 75 Gy in dependence of each chosen rectum definition. Multivariable logistic regression considered other clinical factors such as pelvine lymphatics vs local target volume, diabetes, prior rectal surgery, anticoagulation or haemorrhoids too.

RESULTS

In Cohort 1 (primary EBRT), the mean rectal volumes for definitions "RTOG", planning target volume "(PTV)-based" and "PTV-linked" were 100 cm³ [standard deviation (SD) 43 cm³], 60 cm³ (SD 26 cm³) and 74 cm³ (SD 31 cm³), respectively (p < 0.01; analysis of variance). The mean rectal doses according to these definitions were 35 Gy (SD 8 Gy), 48 Gy (SD 4 Gy) and 44 Gy (SD 5 Gy) (p < 0.01). In Cohort 2 (salvage EBRT), the mean rectal volumes were 114 cm³ (SD 47 cm³), 64 cm³ (SD 26 cm³) and 81 cm³ (SD 30 cm³) (p < 0.01) and the mean doses received by the rectum were 36 Gy (SD 8 Gy), 49 Gy (SD 5 Gy) and 44 Gy (SD 5 Gy) (p < 0.01). Acute or subacute rectal inflammation occurred in 69 (71.9%) patients in Cohort 1 and in 43 (70.5%) in Cohort 2. We did not find a correlation between all investigated DVH parameters and rectal toxicity, irrespective of the investigated definition. By adding additional variables in multivariate analysis, the predictive ability was substantially improved. Still, there was essentially no difference in the probability of predicting rectal inflammation occurrence between the tested contouring definitions.

CONCLUSION

The RTOG anatomy-based recommendations are questionable in comparison with functional definitions, as they result in higher variances in several relative DVH parameters. Moreover, the anatomy-based definition is no better and no worse in the predictive value concerning clinical end points. Advances in knowledge: Functional definitions for the rectum as OAR are easier to apply, faster to contour, have smaller variances and do not offer less information than the anatomy-based RTOG definition.

Dosimetric analysis of rectal filling on rectal doses during vaginal cuff brachytherapy

PURPOSE

Several studies have analyzed the effect of bladder filling during vaginal cuff brachytherapy (VCB), but the effect of rectum filling has not been studied. We sought to evaluate the effects of rectal volume on rectal doses during postoperative VCB.

METHODS AND MATERIALS

Brachytherapy planning CT scans (334 sets) obtained from 92 consecutive patients treated with VCB were resegmented (bladder and rectum) and replanned retrospectively using the same parameters to homogenize data and improve analysis. Rectal volume and a set of values derived from dose-volume histograms (DVHs) were extracted (maximal dose [Dmax], D0.1cc, D1cc, and D2cc). Univariate and multivariate analyses were carried out to evaluate the association between rectal volume and DVH metrics after adjusting for other clinical factors.

RESULTS

A positive significant correlation was observed between rectal volume correlated and Dmax, D0.1cc, D1cc, and D2cc. Multiple linear regression models found that rectal volume, cylinder angle position, and cylinder diameter variables correlated significantly with the different DVH parameters analyzed. These variables explained the 14.5% and 18% of variance on regression models.

CONCLUSIONS

Larger rectal volumes are associated with higher rectal dose parameters during VCB fractions. Prospective studies are needed to investigate whether these data are linked to differences in rectal toxicity.

The effect of delineation method and observer variability on bladder dose-volume histograms for prostate intensity modulated radiotherapy

PURPOSE

To quantify the effect of delineation method on bladder DVH, observer variability (OV) and contouring time for prostate IMRT plans.

MATERIALS AND METHODS

Planning CT scans and IMRT plans of 30 prostate cancer patients were anonymized. For 20 patients, 1 observer delineated the bladder using 9 methods. The effect of delineation method on the DVH curve, discrete dose levels and delineation time was quantified. For the 10 remaining CTs, 6 observers delineated bladder wall using 4 methods. Observer-based volume variation and intraclass correlation coefficient (ICC) were used to describe the dosimetric effects of OV.

RESULTS

Manual delineation of the bladder wall (BW_m) was significantly slower than any other method (mean: 20 min vs. ≤ 13 min) and the dosimetric effect of OV was significantly larger (V70 Gy ICC: 0.78 vs. 0.98). Only volumes created using a 2.5mm contraction from the outer surface, and a method providing a consistent wall volume, showed no notable dosimetric differences from BW_m in both absolute and relative volume.

CONCLUSIONS

Automatic contractions from the outer surface provide quicker, more reproducible and reasonably accurate substitutes for BW_m. The widespread use of automatic contractions to create a bladder wall volume would assist in the consistent application of IMRT dose constraints and the interpretation of reported dose.

Temporary sacral nerve stimulation for faecal incontinence following pelvic radiotherapy

Temporary sacral nerve stimulation for faecal incontinence caused by pelvic radiation injuries was successful in 7 of 13 patients (54%). The improvement of total incontinence episodes during the temporary stimulation period was a median of 83% (range 25-93%). This may be a viable treatment option for radiation-induced faecal incontinence.

Dose–Volume Comparison of Proton Therapy and Intensity-Modulated Radiotherapy for Prostate Cancer

PURPOSE

The contrast in dose distribution between proton radiotherapy (RT) and intensity-modulated RT (IMRT) is unclear, particularly in regard to critical structures such as the rectum and bladder.

METHODS AND MATERIALS

Between August and November 2006, the first 10 consecutive patients treated in our Phase II low-risk prostate proton protocol (University of Florida Proton Therapy Institute protocol 0001) were reviewed. The double-scatter proton beam plans used in treatment were analyzed for various dosimetric endpoints. For all plans, each beam dose distribution, angle, smearing, and aperture margin were optimized. IMRT plans were created for all patients and simultaneously analyzed. The IMRT plans were optimized through multiple volume objectives, beam weighting, and individual leaf movement. The patients were treated to 78 Gray-equivalents (GE) in 2-GE fractions with a biologically equivalent dose of 1.1.

RESULTS

All rectal and rectal wall volumes treated to 10-80 GE (percentage of volume receiving 10-80 GE [V(10)-V(80)]) were significantly lower with proton therapy (p < 0.05). The rectal V(50) was reduced from 31.3% +/- 4.1% with IMRT to 14.6% +/- 3.0% with proton therapy for a relative improvement of 53.4% and an absolute benefit of 16.7% (p < 0.001). The mean rectal dose decreased 59% with proton therapy (p < 0.001). For the bladder and bladder wall, proton therapy produced significantly smaller volumes treated to doses of 10-35 GE (p < 0.05) with a nonsignificant advantage demonstrated for the volume receiving < or =60 GE. The bladder V(30) was reduced with proton therapy for a relative improvement of 35.3% and an absolute benefit of 15.1% (p = 0.02). The mean bladder dose decreased 35% with proton therapy (p = 0.002).

CONCLUSION

Compared with IMRT, proton therapy reduced the dose to the dose-limiting normal structures while maintaining excellent planning target volume coverage.

Does intensity modulated radiation therapy (IMRT) prevent additional toxicity of treating the pelvic lymph nodes compared to treatment of the prostate only?

BACKGROUND

To evaluate the risk of rectal, bladder and small bowel toxicity in intensity modulated radiation therapy (IMRT) of the prostate only compared to additional irradiation of the pelvic lymphatic region.

METHODS

For ten patients with localized prostate cancer, IMRT plans with a simultaneous integrated boost (SIB) were generated for treatment of the prostate only (plan-PO) and for additional treatment of the pelvic lymph nodes (plan-WP). In plan-PO, doses of 60 Gy and 74 Gy (33 fractions) were prescribed to the seminal vesicles and to the prostate, respectively. Three plans-WP were generated with prescription doses of 46 Gy, 50.4 Gy and 54 Gy to the pelvic target volume; doses to the prostate and seminal vesicles were identical to plan-PO. The risk of rectal, bladder and small bowel toxicity was estimated based on NTCP calculations.

RESULTS

Doses to the prostate were not significantly different between plan-PO and plan-WP and doses to the pelvic lymph nodes were as planned. Plan-WP resulted in increased doses to the rectum in the low-dose region </= 30 Gy, only, no difference was observed in the mid and high-dose region. Normal tissue complication probability (NTCP) for late rectal toxicity ranged between 5% and 8% with no significant difference between plan-PO and plan-WP. NTCP for late bladder toxicity was less than 1% for both plan-PO and plan-WP. The risk of small bowel toxicity was moderately increased for plan-WP.

DISCUSSION

This retrospective planning study predicted similar risks of rectal, bladder and small bowel toxicity for IMRT treatment of the prostate only and for additional treatment of the pelvic lymph nodes.

A comparison between 2-Step IMRT and conventional IMRT planning

BACKGROUND AND PURPOSE

2-Step intensity modulated radiation therapy (2-Step IMRT) is an IMRT segmentation procedure based on analytical approximations [Bratengeier K. 2-Step IMAT and 2-Step IMRT: a geometrical approach. Med Phys 2005;32:777-785; Bratengeier K. 2-Step IMAT and 2-Step IMRT in three dimensions. Med Phys 2005;32:3849-3861]. The aim was to benchmark it with other IMRT algorithms and to establish it as planning tool for fast IMRT application with a reduced number of segments.

MATERIALS AND METHODS

2-Step IMRT plans were compared with IMRT-solutions obtained with methods from a commercial planning system (Pinnacletrade mark TPS). The four clinical cases chosen were: paraspinal tumour, carcinoma of the prostate, head and neck carcinoma and breast carcinoma. In addition the "Quasimodo" phantom study was used to compare the quality of the 2-Step IMRT method with respect to other planning procedures in the ESTRO study.

RESULTS

The number of segments (and - to a minor degree - the monitor units per dose) of the majority of 2-Step IMRT plans was lower than for the commercial algorithms. The quality of the 2-Step IMRT-plan was comparable. In the Quasimodo comparison 2-Step IMRT plans with nine beams would place in the mid-range of all participants, whereas the 15-beam arrangements could compete with the best results.

CONCLUSIONS

2-Step IMRT is a valuable IMRT segmentation method, especially if the number of segments is to be limited (e.g. for reasons of precision, speed and leakage radiation).

Intensity-modulated radiotherapy for the treatment of pelvic lymph nodes in prostate cancer

Evaluation of: Wang-Chesebro A, Xia P, Coleman J, Akazawa C, Roach M 3rd: Intensity-modulated radiotherapy improves lymph node coverage and dose to critical structures compared with 3D conformal radiation therapy in clinically localized prostate cancer. Int. J. Radiat. Oncol. Biol. Phys. 66, 654–662 (2006). A large randomized Phase III trial (RTOG 94–13) demonstrated improved progression-free survival for the irradiation of the pelvic lymphatics compared with treatment of the prostate only in patients with a high risk of lymph node involvement. Recent studies have indicated that the conventional target volume might miss substantial parts of the lymphatic drainage of the prostate. This retrospective planning study compared conventional, 3D-conformal and intensity-modulated radiotherapy (IMRT) for the treatment of pelvic lymph nodes. Field-shaping based on bony landmarks was shown to result in inadequate target coverage compared with 3D-conformal and IMRT planning. Regarding sparing of rectum, bladder, small bowl and penile bulb, the IMRT plans were highly superior. In summary, IMRT may result in increased rates of regional control with simultaneously decreased rates of toxicity. Integration of functional imaging into treatment planning and image guidance during treatment is expected to further improve the therapeutic ratio.