Finding dose–volume constraints to reduce late rectal toxicity following 3D-conformal radiotherapy (3D-CRT) of prostate cancer

Radiation in Gastroenterology

The benefit of radiation is immense in the field of gastroenterology. Radiation is used daily in different gastrointestinal imaging and diagnostic and therapeutic interventional procedures. Radiotherapy is one of the primary modalities of treatment of gastrointestinal malignancies. There are various modalities of radiotherapy. Radiotherapy can injure malignant cells by directly damaging DNA, RNA, proteins, and lipids and indirectly by forming free radicals. External beam radiation, internal beam radiation and radio-isotope therapy are the major ways of delivering radiation to the malignant tissue. Radiation can also cause inflammation, fibrosis, organ dysfunction, and malignancy. Patients with repeated exposure to radiation for diagnostic imaging and therapeutic procedures are at slightly increased risk of malignancy. Gastrointestinal endoscopists performing fluoroscopy-guided procedures are also at increased risk of malignancy and cataract formation. The radiological protection society recommends certain preventive and protective measures to avoid side effects of radiation. Gastrointestinal complications related to radiation therapy for oncologic processes, and exposure risks for patients and health care providers involved in diagnostic or therapeutic imaging will be discussed in this review.

Organs at risk radiation dose constraints

Dose constraints are essential for performing dosimetry, especially for intensity modulation and for radiotherapy under stereotaxic conditions. We present the update of the recommendations of the French society of oncological radiotherapy for the use of these doses in classical current practice but also for reirradiation.

Risk Factors of Biochemical Failure in Locally Advanced Carcinoma Prostate Treated With Definitive External Beam Radiotherapy and Androgen Deprivation Therapy: Experience From Tertiary Care Center in North India

Background Locally advanced prostate cancer (LACAP), despite external beam radiotherapy (EBRT) along with antiandrogen therapy (ADT) has risk of prostate-specific antigen (PSA) progression. Furthermore, number of studies have emphasized on different prognostic factors. The purpose of our study is to analyze risk factors for biochemical failure (BF) in these patients treated at our institute. Methods Our study is a single-institution retrospective observational done at a tertiary care center in North India. Between January 2018 and December 2020, we retrospectively identified 34 patients managed at our institute as per multidisciplinary board (MBD). Demographic, clinical, radiological, pathological and treatment-related parameters were assessed as potential risk factors. End-point of the study was to find significant risk factors for BF. Statistical analysis was done on SPSS, version 20 (IBM Corp., Armonk, NY). Results All eligible patients received EBRT with ADT as per institution policy. Mean follow-up period was 20 months during which two (5.9%) patients had BF at a mean of 30 months after EBRT. Four-year PSA-progression-free survival rate was 73%. On univariate analysis, prognostic factors associated with high risk of BF were Gleason score and clinical T stage. Conclusion In summary, prognostic factors for high risk of BF leading to clinical progression are Gleason score 9 or 10 and clinical T3b stage.

Evaluating the predictive value of quantec rectum tolerance dose suggestions on acute rectal toxicity in prostate carcinoma patients treated with IMRT

Aim

To investigate the predictive value of convenience of rectum dosimetry with Quantitative Analysis of Normal Tissue Effects in the Clinic (QUANTEC) dose limits, maximum rectum dose (Dmax), total rectal volume (TVrectum), rectal volume included in PTV (VrectumPTV) on Grade 2-3 acute rectal toxicity for utilization in clinical practice.

Background

Numerous previous data have reported frequent acute proctitis after external-beam RT of prostate cancer. Predicting toxicity limited with dose information is inadequate in clinical practice due to comorbidities and medications used.

Materials and Method

Sixty-four non-metastatic prostate cancer patients treated with IMRT were enrolled. Patients were treated to a total dose of 70-76 Gy. Rectal dose volume histograms (DVH) of all patients were evaluated retrospectively, and a QUANTEC Score between 0 and 5 was calculated for each patient. The correlation between the rectal DVH data, QUANTEC score, TVrectum, VrectumPTV, rectum Dmax and Grade 2-3 rectal toxicity was investigated.

Results

In the whole group grade 1, 2 and 3 acute rectal toxicities were 25%, 18.8% and 3.1%, respectively. In the DVH data, rectum doses of all patients were under RTOG dose limits. Statistically significant correlation was found between grade 2-3 rectal toxicity and TVrectum (p = 0,043); however. It was not correlated with QUANTEC score, VrectumPTV and Dmax.

Conclusion

Our results were not able to show any significant correlation between increasing convenience with QUANTEC limits and lower rectal toxicity. Conclusively, new dosimetric definitions are warranted to predict acute rectal toxicity more accurately in prostate cancer patients during IMRT treatment.

Impact of image guidance on toxicity and tumour outcome in moderately hypofractionated external-beam radiotherapy for prostate cancer

To report toxicity and efficacy outcome of moderately hypofractionated image-guided external-beam radiotherapy in a large series of patients treated for prostate cancer (PCa). Between 10/2006 and 12/2015, 572 T1-T3N0M0 PCa patients received 70.2 Gy in 26 fractions at 2.7 Gy/fraction: 344 patients (60%) with three-dimensional conformal radiotherapy (3D-CRT) and 228 (40%) with intensity-modulated radiotherapy (IMRT). Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria and Houston definition (nadir + 2) were used for toxicity and biochemical failure evaluation, respectively. Median age was 74 years (interquartile range 69-77). Compared with 3D-CRT, in IMRT group more high-risk patients (29% vs 18%; P = 0.002) and more high-volume target (75% vs 60%; P < 0.001) were included. Acute gastro-intestinal (GI) toxicity G > 1 were registered in 8% and in 11% IMRT and 3D-CRT patients, respectively, whereas late GI G > 1 were observed in 2% and 16% IMRT and 3D-CRT patients, respectively. Acute genito-urinary (GU) toxicity G > 1 were registered in 26% and 40% IMRT and 3D-CRT patients, respectively, whereas late GU G > 1 occurred in 5% IMRT and 15% 3D-CRT patients. Multivariate proportional hazard Cox models confirmed significantly greater risk of late toxicity with 3D-CRT compared to IMRT for GU > 1 (P = 0.004) and for GI > 1 (P < 0.001). With a median 4-year follow-up, overall survival (OS), clinical progression-free survival (cPFS) and biochemical PFS (bPFS) for the whole series were 91%, 92% and 91%, respectively. cPFS and bPFS were significantly different by risk groups. Multivariate Cox models for bPFS and cPFS showed no difference between irradiation techniques and a significant impact of risk group and initial PSA. Moderately hypofractionated radiotherapy is a viable treatment option for localized PCa with excellent tumour control and satisfactory toxicity profile. IMRT seems associated with a reduction in toxicity, whereas tumour control was equal between IMRT and 3D-CRT patients and depended mainly on the risk category.

Androgen Ablation Therapy Does not Increase the Risk of Late Morbidity following 3D-conformal Radiotherapy of Organ-confined Prostate Cancer: The Experience of the European Institute of Oncology

Aims and Background

Androgen ablation therapy in conjunction with radiotherapy-neoadjuvant and adjuvant – has consistently been shown to be associated with improved biochemical and local control, whereas controversy still remains as regards its benefit in terms of overall survival. The objective of this study is to determine the impact of androgen ablation in combination to 3D-conformal radiotherapy on late treatment-related toxicity.

Methods

236 patients were treated with 3D-conformal radiotherapy to a total dose ranging from 70 and 78.6 Gy. Fifty-six patients did not receive any form of androgen ablation whereas 176 were given at least 3 months of neoadjuvant androgen ablation. Of these, 64 stayed on androgen ablation for a median time of 6 months post-radiotherapy. Acute toxicity was evaluated weekly during the course of treatment. Late toxicity was assessed at 3-months intervals during the follow-up. Toxicity was scored according to the RTOG criteria.

Results

The median follow-up was 24.6 months (range, 12-62). The incidence of late genitourinary toxicity was: 3% G2, 3.5% G3, 0.5% G4. The incidence of late gastrointestinal toxicity was: 12% G2, 2% G3, 1% G4. No association was observed between the use of androgen ablation and late treatment-related toxicity. High-risk patients who continued on androgen ablation long-term were not found to have an increased risk of developing late toxicity with respect to those who never had any form of androgen ablation or those only treated neoadjuvantly.

Conclusions

In our experience, the use of androgen ablation does not impact on late toxicity following high dose 3D-conformal radiotherapy for prostate cancer.

Conformal Radiotherapy of Clinically Localized Prostate Cancer: Analysis of Rectal and Urinary Toxicity and Correlation with Dose-Volume Parameters

Aims and background

Rectal and urinary toxicities are the principal limiting factors in delivering a high target dose to patients affected by prostate cancer. The verification of such toxicity is an important step before starting a dose-escalation program. The present observational study reports on the acute and late rectal and urinary toxicity in relation with dose-volume parameters in 104 patients with localized prostate cancer treated with 3-dimensional conformal radiation therapy.

Methods and study design

One hundred and four patients with stage T1b-T3b prostate cancer were treated with three-dimensional conformal radiation therapy to a total dose of 74 Gy, 2 Gy per fraction. Rigid dose constraints were applied for rectum and bladder. Acute and late rectal and urinary toxicities were analyzed also in relation to dose-volume histograms. Biochemical relapse-free survival was defined according to the American Society of Therapeutic Radiation Oncology (ASTRO) criteria and to the RTOG-ASTRO Phoenix Consensus Conference Recommendations using the Kaplan-Meier method.

Results

No grade 3 toxicity was observed. Acute and late grade 2 toxicity rates were 5.8% and 9.0% for rectum and 12.5% and 2.0% for bladder, respectively. Rectal V70 influenced the occurrence of late grade 2 toxicity. A relationship between acute and late urinary toxicity was also found. After a median follow-up of 30 months (range, 20–50), the actuarial overall and biochemical relapse-free survival rates were 84% and 77%, respectively, with a significant difference between low-intermediate and high-risk patients.

Conclusions

Conformal radiotherapy to the dose of 74 Gy was administered with good compliance. The incidence of acute and late toxicity was relatively low in accord with our dose constraints. Rectal V70 proved to be a reliable prognosticator of late toxicity. Overall survival and biochemical relapse-free survival rates were more favorable for low and intermediate-risk and significantly less favorable for high-risk patients.

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.

No increase in toxicity of pelvic irradiation when intensity modulation is employed: clinical and dosimetric data of 208 patients treated with post-prostatectomy radiotherapy

OBJECTIVE

To compare the toxicity of image-guided intensity-modulated radiotherapy (IG-IMRT) to the pelvis or prostate bed (PB) only. To test the hypothesis that the potentially injurious effect of pelvic irradiation can be counterbalanced by reduced irradiated normal tissue volume using IG-IMRT.

METHODS

Between February 2010 and February 2012, 208 patients with prostate cancer were treated with adjuvant or salvage IG-IMRT to the PB (102 patients, Group PB) or the pelvis and prostate bed (P) (106 patients, Group P). The Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer criteria were used to evaluate toxicity.

RESULTS

Median follow-up was 27 months. Toxicity G ≥ 2 in Group PB: in the bowel acute and late toxicities were 11.8% and 10%, respectively; urinary acute and late toxicities were 10.8% and 15%, respectively. Toxicity G ≥ 2 in Group P: in the bowel acute and late toxicities were both 13.2%; urinary acute and late toxicities were 13.2% and 15.1%, respectively. No statistical difference in acute or late toxicity between the groups was found (bowel: p = 0.23 and p = 0.89 for acute and late toxicity, respectively; urinary: p = 0.39 and p = 0.66 for acute and late toxicity, respectively). Of the clinical variables, only previous abdominal surgery was correlated with acute bowel toxicity. Dosimetric parameters that correlated with bowel toxicity were identified.

CONCLUSION

The toxicity rates were low and similar in both groups, suggesting that IG-IMRT allows for a safe post-operative irradiation of larger volumes. Further investigation is warranted to exclude bias owing to non-randomized character of the study.

ADVANCES IN KNOWLEDGE

Our report shows that modern radiotherapy technology and careful planning allow maintaining the toxicity of pelvic lymph node treatment at the acceptable level, as it is in the case of PB radiotherapy.

Parametrized rectal dose and associations with late toxicity in prostate cancer radiotherapy

OBJECTIVE

We investigated possible associations between planned dose-volume parameters and rectal late toxicity in 170 patients having radical prostate cancer radiotherapy.

METHODS

For each patient, the rectum was outlined from anorectal junction to sigmoid colon, and rectal dose was parametrized using dose-volume (DVH), dose-surface (DSH) and dose-line (DLH) histograms. Generation of DLHs differed from previous studies in that the rectal dose was parametrized without first unwrapping onto 2-dimensional dose-surface maps. Patient-reported outcomes were collected using a validated Later Effects in Normal Tissues Subjective, Objective, Management and Analytic questionnaire. Associations between dose and toxicity were assessed using a one-sided Mann-Whitney U test.

RESULTS

Associations (p < 0.05) were found between equieffective dose (EQD23) and late toxicity as follows: overall toxicity with DVH and DSH at 13-24 Gy; proctitis with DVH and DSH at 25-36 Gy and with DVH, DSH and DLH at 61-67 Gy; bowel urgency with DVH and DSH at 10-20 Gy. None of these associations met statistical significance following the application of a Bonferroni correction.

CONCLUSION

Independently confirmed associations between rectal dose and late toxicity remain elusive. Future work to increase the accuracy of the knowledge of the rectal dose, either by accounting for interfraction and intrafraction rectal motion or via stabilization of the rectum during treatment, may be necessary to allow for improved dose-toxicity comparisons.

ADVANCES IN KNOWLEDGE

This study is the first to use parametrized DLHs to study associations with patient-reported toxicity for prostate radiotherapy showing that it is feasible to model rectal dose mapping in three dimensions.

Accumulated dose to the rectum, measured using dose-volume histograms and dose-surface maps, is different from planned dose in all patients treated with radiotherapy for prostate cancer

OBJECTIVE

We sought to calculate accumulated dose (DA) to the rectum in patients treated with radiotherapy for prostate cancer. We were particularly interested in whether dose-surface maps (DSMs) provide additional information to dose-volume histograms (DVHs).

METHODS

Manual rectal contours were obtained for kilovoltage and daily megavoltage CT scans for 10 participants from the VoxTox study (380 scans). Daily delivered dose recalculation was performed using a ray-tracing algorithm. Delivered DVHs were summated to create accumulated DVHs. The rectum was considered as a cylinder, cut and unfolded to produce daily delivered DSMs; these were summated to produce accumulated DSMs.

RESULTS

Accumulated dose-volumes were different from planned in all participants. For one participant, all DA levels were higher and all volumes were larger than planned. For four participants, all DA levels were lower and all volumes were smaller than planned. For each of these four participants, ≥1% of pixels on the accumulated DSM received ≥5 Gy more than had been planned.

CONCLUSION

Differences between accumulated and planned dose-volumes were seen in all participants. DSMs were able to identify differences between DA and planned dose that could not be appreciated from the DVHs. Further work is needed to extract the dose data embedded in the DSMs. These will be correlated with toxicity as part of the VoxTox Programme.

ADVANCES IN KNOWLEDGE

DSMs are able to identify differences between DA and planned dose that cannot be appreciated from DVHs alone and should be incorporated into future studies investigating links between DA and toxicity.

Rectal toxicity after intensity modulated radiotherapy for prostate cancer: which rectal dose volume constraints should we use?

BACKGROUND

To define rectal dose volume constraints (DVC) to prevent ⩾grade2 late rectal toxicity (LRT) after intensity modulated radiotherapy (IMRT) for prostate cancer (PC).

MATERIAL AND METHODS

Six hundred thirty-seven PC patients were treated with primary (prostate median dose: 78Gy) or postoperative (prostatic bed median dose: 74Gy (adjuvant)-76Gy (salvage)) IMRTwhile restricting the rectal dose to 76Gy, 72Gy and 74Gy respectively. The impact of patient characteristics and rectal volume parameters on ⩾grade2 LRT was determined. DVC were defined to estimate the 5% and 10% risk of developing ⩾grade2 LRT.

RESULTS

The 5-year probability of being free from ⩾grade2 LRT, non-rectal blood loss and persisting symptoms is 88.8% (95% CI: 85.8-91.1%), 93.4% (95% CI: 91.0-95.1%) and 94.3% (95% CI: 92.0-95.9%) respectively. There was no correlation with patient characteristics. All volume parameters, except rectal volume receiving ⩾70Gy (R70), were significantly correlated with ⩾grade2 LRT. To avoid 10% and 5% risk of ⩾grade2 LRT following DVC were derived: R40, R50, R60 and R65 <64-35%, 52-22%, 38-14% and 5% respectively.

CONCLUSION

Applying existing rectal volume constraints resulted in a 5-year estimated risk of developing late ⩾grade2 LRT of 11.2%. New rectal DVC for primary and postoperative IMRT planning of PC patients are proposed. A prospective evaluation is needed.

Planning study to compare dynamic and rapid arc techniques for postprostatectomy radiotherapy of prostate cancer

PURPOSE

To compare our standard technique for postprostatectomy radiotherapy of prostate cancer, i.e. using two lateral conformal dynamic arcs with volumetric-modulated arc therapy (VMAT) performed with the RapidArc(®) (Varian Medical Systems, Palo Alto, CA, USA). The plans were referred to as DA and RA, respectively.

MATERIALS AND METHODS

The treatment plans of 44 patients receiving adjuvant/salvage radiotherapy in the first months of 2010 were compared. In all cases, the prescribed total dose was 66-68.2 Gy (2.2 Gy per fraction). Both DA and RA plans were optimized in terms of dose coverage and constraints.

RESULTS

Small differences between the techniques were observed for planning target volume (PTV) dose distribution, whereas significant differences in sparing of organs at risk (OARs) were recorded (p < 0.0001). The OAR values (median; 95 % confidence interval, CI) were: rectum: D30 % = 60.7 Gy (59.40-62.04 Gy) and 48.2 Gy (46.40-52.72 Gy), D60 % = 34.1 Gy (28.50-38.92 Gy) and 27.7 Gy (21.80-31.51 Gy); bladder: D30 % = 57.3 Gy (45.83-64.53 Gy) and 46.4 Gy (33.23-61.48 Gy), D50 % = 16.4 Gy (11.89-42.38 Gy) and 17.2 Gy (10.97-27.90 Gy), for DA and RA, respectively. Treatment times were very similar, whereas the monitor units (MU) were 550 ± 29 versus 277 ± 3 for RA and DA, respectively.

CONCLUSION

Dose-volume histograms (DVHs) show improvements in OAR sparing with RA. However, the RA technique is associated with almost double the number of MUs compared to DA. Regarding the PTV, DA is slightly superior in terms of D2 % and dose homogeneity. On the whole, the results suggest that RA be the favorable technique.

Transformation of physical DVHs to radiobiologically equivalent ones in hypofractionated radiotherapy analyzing dosimetric and clinical parameters: a practical approach for routine clinical practice in radiation oncology

Purpose. The purpose of this study was to transform DVHs from physical to radiobiological ones as well as to evaluate their reliability by correlations of dosimetric and clinical parameters for 50 patients with prostate cancer and 50 patients with breast cancer, who were submitted to Hypofractionated Radiotherapy. Methods and Materials. To achieve this transformation, we used both the linear-quadratic model (LQ model) and the Niemierko model. The outcome of radiobiological DVHs was correlated with acute toxicity score according to EORTC/RTOG criteria. Results. Concerning the prostate radiotherapy, there was a significant correlation between RTOG acute rectal toxicity and D₅₀ (P < 0.001) and V₆₀ (P = 0.001) dosimetric parameters, calculated for α/β = 10 Gy. Moreover, concerning the breast radiotherapy there was a significant correlation between RTOG skin toxicity and V_≥60 dosimetric parameter, calculated for both α/β = 2.3 Gy (P < 0.001) and α/β = 10 Gy (P < 0.001). The new tool seems reliable and user-friendly. Conclusions. Our proposed model seems user-friendly. Its reliability in terms of agreement with the presented acute radiation induced toxicity was satisfactory. However, more patients are needed to extract safe conclusions.

Gastrointestinal radiation injury: Prevention and treatment

With the recent advances in detection and treatment of cancer, there is an increasing emphasis on the efficacy and safety aspects of cancer therapy. Radiation therapy is a common treatment for a wide variety of cancers, either alone or in combination with other treatments. Ionising radiation injury to the gastrointestinal tract is a frequent side effect of radiation therapy and a considerable proportion of patients suffer acute or chronic gastrointestinal symptoms as a result. These side effects often cause morbidity and may in some cases lower the efficacy of radiotherapy treatment. Radiation injury to the gastrointestinal tract can be minimised by either of two strategies: technical strategies which aim to physically shift radiation dose away from the normal intestinal tissues, and biological strategies which aim to modulate the normal tissue response to ionising radiation or to increase its resistance to it. Although considerable improvement in the safety of radiotherapy treatment has been achieved through the use of modern optimised planning and delivery techniques, biological techniques may offer additional further promise. Different agents have been used to prevent or minimize the severity of gastrointestinal injury induced by ionising radiation exposure, including biological, chemical and pharmacological agents. In this review we aim to discuss various technical strategies to prevent gastrointestinal injury during cancer radiotherapy, examine the different therapeutic options for acute and chronic gastrointestinal radiation injury and outline some examples of research directions and considerations for prevention at a pre-clinical level.

Role of early proctoscopy in predicting late symptomatic proctitis after external radiation therapy for prostate carcinoma

PURPOSE

To determine whether acute radiation-proctitis, diagnosed by proctoscopy after radiation therapy for prostate cancer, can predict late clinical proctitis.

METHODS AND MATERIALS

A prospective study of 130 patients who underwent external radiation therapy (RT) for stage T1 to T4 prostate cancer between 1997 and 2008 was performed. Treatments were conventional (2-dimensional [2D]) in 61 patients and 3D conformal in 69, with a median target dose of 72 Gy (70-74 Gy). Within 1 week after RT, proctoscopy was performed to detect possible acute endoscopic proctitis (AEP). Acute clinical proctitis (ACP) and late clinical proctitis (LCP) were also evaluated. The median follow-up was 84 months (20-180 months). The influence of AEP and ACP on LCP occurrence was studied using the Cox model controlling for age, dose, prostatectomy, RT technique (2D vs 3D), and hormone therapy.

RESULTS

AEP was detected in 15 patients (11.5%) and ACP in 67 (51.5%); in 13 cases (10%) AEP and ACP occurred simultaneously. Thirty-five cases of LCP were recorded. The 5-year probability of developing LCP was highest in patients with AEP and ACP (77%, 95% confidence interval [CI] 53%-94%) and lowest in asymptomatic patients (14%, 95% CI 7%-26%; P<.001). Compared to asymptomatic patients, the 5-year probability also was slightly increased in patients with ACP only (26%, 95% CI 16%-40%; P=.052). In multivariable analysis, the combination of AEP and ACP was the main predictor of LCP: compared to asymptomatic patients, the hazard ratio was 5.6 (2.1-15.2) in patients with AEP plus ACP (P=.001) and 2.1 (0.9-4.9) in those with ACP only (P=.103).

CONCLUSIONS

In patients with AEP and ACP, the risk of LCP was more than 5-fold increased compared to those who were asymptomatic, while a much smaller increase in risk occurred in patients with ACP only. Early proctoscopy can provide valuable information regarding the likelihood of late proctitis.

Do intermediate radiation doses contribute to late rectal toxicity? An analysis of data from radiation therapy oncology group protocol 94-06

PURPOSE

To investigate whether the volumes of rectum exposed to intermediate doses, from 30 to 50 Gy, contribute to the risk of Grade ≥ 2 late rectal toxicity among patients with prostate cancer receiving radiotherapy.

METHODS AND MATERIALS

Data from 1009 patients treated on Radiation Therapy Oncology Group protocol 94-06 were analyzed using three approaches. First, the contribution of intermediate doses to a previously published fit of the Lyman-Kutcher-Burman (LKB) normal tissue complication probability (NTCP) model was determined. Next, the extent to which intermediate doses provide additional risk information, after taking the LKB model into account, was investigated. Third, the proportion of rectum receiving doses higher than a threshold, VDose, was computed for doses ranging from 5 to 85 Gy, and a multivariate Cox proportional hazards model was used to determine which of these parameters were significantly associated with time to Grade ≥ 2 late rectal toxicity.

RESULTS

Doses <60 Gy had no detectable impact on the fit of the LKB model, as expected on the basis of the small estimate of the volume parameter (n = 0.077). Furthermore, there was no detectable difference in late rectal toxicity among cohorts with similar risk estimates from the LKB model but with different volumes of rectum exposed to intermediate doses. The multivariate Cox proportional hazards model selected V75 as the only value of VDose significantly associated with late rectal toxicity.

CONCLUSIONS

There is no evidence from these data that intermediate doses influence the risk of Grade ≥ 2 late rectal toxicity. Instead, the critical doses for this endpoint seem to be ≥ 75 Gy. It is hypothesized that cases of Grade ≥ 2 late rectal toxicity occurring among patients with V75 less than approximately 12% may be due to a "background" level of risk, likely due mainly to biological factors.

Physical and clinical implications of radiotherapy treatment of prostate cancer using a full bladder protocol

PURPOSE

To assess the dosimetric and clinical implication when applying the full bladder protocol for the treatment of the localized prostate cancer (PCA).

PATIENTS AND METHODS

A total of 26 consecutive patients were selected for the present study. Patients underwent two series of CT scans: the day of the simulation and after 40 Gy. Each series consisted of two consecutive scans: (1) full bladder (FB) and (2) empty bladder (EB). The contouring of clinical target volumes (CTVs) and organs at risk (OAR) were compared to evaluate organ motion. Treatment plans were compared by dose distribution and dose-volume histograms (DVH).

RESULTS

CTV shifts were negligible in the laterolateral and superior-inferior directions (the maximum shift was 1.85 mm). Larger shifts were recorded in the anterior-posterior direction (95% CI, 0.83-4.41 mm). From the dosimetric point of view, shifts are negligible: the minimum dose to the CTV was 98.5% (median; 95%CI, 95-99%). The potential advantage for GU toxicity in applying the FB treatment protocol was measured: the ratio between full and empty bladder dose-volume points (selected from our protocol) is below 0.61, excluding the higher dose region where DVHs converge.

CONCLUSION

Having a FB during radiotherapy does not affect treatment effectiveness, on the contrary it helps achieve a more favorable DVH and lower GU toxicities.

Usefulness of CT-MRI fusion in radiotherapy planning for localized prostate cancer

We compared the prostate volumes and rectal doses calculated by CT and CT-MRI fusion, and verified the usefulness of CT-MRI fusion in three-dimensional (3D) radiotherapy planning for localized prostate cancer. Three observers contoured the prostate and rectum of 13 patients with CT and CT-MRI fusion. Prostate delineations were classified into three sub-parts, and the volumes and distances to the rectum (PR distance) were calculated. 3D radiotherapy plans were generated. A dose-volume histogram (DVH) was constructed for the rectum. The intermodality and interobserver variations were assessed. CT-MRI fusion yielded a significantly lower prostate volume by 31%. In the sub-part analysis, the greatest difference was seen for the apical side. The PR distance was significantly extended by 3.5-mm, and the greatest difference was seen for the basal side. The irradiated rectal volume was reduced in the CT-MRI fusion-based plan. The reduction rates were greater in the relatively high-dose regions. The decrease of the prostate volume and length alteration of the distance between the prostate and rectum were correlated with the decrease of the irradiated rectal volume. The prostate volume delineated by CT-MRI fusion was negatively correlated with the decrease of the irradiated rectal volume. CT showed a tendency towards overestimation of the prostate volume and underestimation of the PR distance as compared to CT-MRI fusion. The rectal dose was significantly reduced in CT-MRI fusion-based plan. Using CT-MRI fusion, especially in cases with a small prostate, the irradiated rectal volume can be reduced, with consequent reduction in rectal complications.

Rectal dose constraints for intensity modulated radiation therapy of the prostate

Prostate dose escalation appears to have resulted in increased cancer control. Such escalation has been made possible by the ability to deliver more conformal treatment that spares normal tissue from the higher radiation doses. The supposition is that this has enabled higher doses, but without an increase in toxicity. The most disabling toxicity in prostate cancer radiotherapy is rectal. We evaluated the current status of conformal radiation and late rectal toxicity with the goal of determining whether reasonable rectal dose and volume constraints can be determined. Although the literature is inexact, we believe that some generalized constraints can be recommended and show that those recommendations are consistent with what is being used at experienced centers.

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.

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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

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Grants

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

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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

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Clinical toxicities and dosimetric parameters after whole-pelvis versus prostate-only intensity-modulated radiation therapy for prostate cancer

PURPOSE

To assess whether whole-pelvis (WP) intensity-modulated radiation therapy (IMRT) is associated with increased toxicity compared with prostate-only (PO) IMRT.

METHODS AND MATERIALS

We retrospectively analyzed all patients with prostate cancer undergoing definitive IMRT to 79.2 Gy with concurrent androgen deprivation at our institution from November 2005 to May 2007 with a minimum follow-up of 12 months. Thirty patients received initial WP IMRT to 45 Gy in 1.8-Gy fractions, and thirty patients received PO IMRT. Study patients underwent computed tomography simulation and treatment planning by use of predefined dose constraints. Bladder and rectal dose-volume histograms, maximum genitourinary (GU) and gastrointestinal (GI) Radiation Therapy Oncology Group toxicity grade, and late Grade 2 or greater toxicity-free survival curves were compared between the two groups by use of the Student t test, Fisher exact test, and Kaplan-Meier curve, respectively.

RESULTS

Bladder minimum dose, mean dose, median dose, volume receiving 5 Gy, volume receiving 20 Gy, volume receiving 40 Gy, and volume receiving 45 Gy and rectal minimum dose, median dose, and volume receiving 20 Gy were significantly increased in the WP group (all p values < 0.01). Maximum acute GI toxicity was limited to Grade 2 and was significantly increased in the WP group at 50% vs. 13% the PO group (p = 0.006). With a median follow-up of 24 months (range, 12-35 months), there was no difference in late GI toxicity (p = 0.884) or in acute or late GU toxicity.

CONCLUSIONS

Despite dosimetric differences in the volume of bowel, bladder, and rectum irradiated in the low-dose and median-dose regions, WP IMRT results only in a clinically significant increase in acute GI toxicity, in comparison to PO IMRT, with no difference in GU or late GI toxicity.

A comparison of dose-volume constraints derived using peak and longitudinal definitions of late rectal toxicity

BACKGROUND AND PURPOSE

Accurate reporting of complications following radiotherapy is an important part of the feedback loop to improve radiotherapy techniques. The definition of toxicity is normally regarded as the maximum or peak (P) grade of toxicity reported over the follow-up period. An alternative definition (integrated longitudinal toxicity (ILT)) is proposed which takes into account both the severity and the duration of the complication.

METHODS AND MATERIALS

In this work, both definitions of toxicity were used to derive dose-volume constraints for six specific endpoints of late rectal toxicity from a cohort of patients who received prostate radiotherapy in the MRC RT01 trial. The dose-volume constraints were derived using ROC analysis for 30, 40, 50, 60, 65 and 70 Gy.

RESULTS

Statistically significant dose-volume constraints were not derived for all dose levels tested for each endpoint and toxicity definition. However, where both definitions produced constraints, there was generally good agreement. Variation in the derived dose-volume constraints was observed to be larger between endpoints than between the two definitions of toxicity. For one endpoint (stool frequency (LENT/SOM)) statistically significant dose-volume constraints were only derived using ILT.

CONCLUSIONS

The longitudinal definition of toxicity (ILT) produced results consistent with those derived using peak toxicity and in some cases provided additional information which was not seen by analysing peak toxicity alone.

Acute toxicity of image-guided hypofractionated radiotherapy for prostate cancer: nonrandomized comparison with conventional fractionation

OBJECTIVES

To compare acute toxicity of prostate cancer image-guided hypofractionated radiotherapy (hypo-IGRT) with conventional fractionation without image-guidance (non-IGRT). To test the hypothesis that the potentially injurious effect of hypofractionation can be counterbalanced by the reduced irradiated normal tissue volume using IGRT approach.

MATERIALS AND METHODS

One hundred seventy-nine cT1-T2N0M0 prostate cancer patients were treated within the prospective study with 70.2 Gy/26 fractions (equivalent to 84 Gy/42 fractions, α/β 1.5 Gy) using IGRT (transabdominal ultrasound, ExacTrac X-Ray system, or cone-beam computer tomography). Their prospectively collected data were compared with data of 174 patients treated to 80 Gy/40 fractions with non-IGRT. The difference between hypo-IGRT and non-IGRT cohorts included fractionation (hypofractionation vs. conventional fractionation), margins (hypo-IGRT margins: 7 mm and 3 mm, for all but posterior margins; respectively; non-IGRT margins: 10 and 5 mm, for all but posterior margins, respectively), and use of image-guidance or not. Multivariate analysis was performed to define the tumor-, patient-, and treatment-related predictors for acute toxicity.

RESULTS

All patients completed the prescribed radiotherapy course. Acute toxicity in the hypo-IGRT cohort included rectal (G1: 29.1%; G2: 11.2%; G3: 1.1%) and urinary events (G1: 33.5%; G2: 39.1%; G3: 5%). Acute toxicity in the non-IGRT patients included rectal (G1: 16.1%; G2: 6.3%) and urinary events (G1: 36.2%; G2: 20.7%; G3: 0.6%). In 1 hypo-IGRT and 2 non-IGRT patients, radiotherapy was temporarily interrupted due to acute toxicity. The incidence of mild (G1-2) rectal and bladder complications was significantly higher for hypo-IGRT (P = 0.0014 and P < 0.0001, respectively). Multivariate analysis showed that hypo-IGRT (P = 0.001) and higher PSA (P = 0.046) are correlated with higher acute urinary toxicity. No independent factor was identified for acute rectal toxicity. No significant impact of IGRT system on acute toxicity was observed.

CONCLUSIONS

The acute toxicity rates were low and similar in both study groups with some increase in mild acute urinary injury in the hypo-IGRT patients (most probably due to the under-reporting in the retrospectively analyzed non-IGRT cohort). The higher incidence of acute bowel reactions observed in hypo-IGRT group was not significant in the multivariate analysis. Further investigation is warranted in order to exclude the bias due to the nonrandomized character of the study.

Assessing correlations between the spatial distribution of the dose to the rectal wall and late rectal toxicity after prostate radiotherapy: an analysis of data from the MRC RT01 trial (ISRCTN 47772397)

Many studies have been performed to assess correlations between measures derived from dose-volume histograms and late rectal toxicities for radiotherapy of prostate cancer. The purpose of this study was to quantify correlations between measures describing the shape and location of the dose distribution and different outcomes. The dose to the rectal wall was projected on a two-dimensional map. In order to characterize the dose distribution, its centre of mass, longitudinal and lateral extent, and eccentricity were calculated at different dose levels. Furthermore, the dose-surface histogram (DSH) was determined. Correlations between these measures and seven clinically relevant rectal-toxicity endpoints were quantified by maximally selected standardized Wilcoxon rank statistics. The analysis was performed using data from the RT01 prostate radiotherapy trial. For some endpoints, the shape of the dose distribution is more strongly correlated with the outcome than simple DSHs. Rectal bleeding was most strongly correlated with the lateral extent of the dose distribution. For loose stools, the strongest correlations were found for longitudinal extent; proctitis was most strongly correlated with DSH. For the other endpoints no statistically significant correlations could be found. The strengths of the correlations between the shape of the dose distribution and outcome differed considerably between the different endpoints. Due to these significant correlations, it is desirable to use shape-based tools in order to assess the quality of a dose distribution.

Volumetric modulated arc therapy (VMAT) vs. serial tomotherapy, step-and-shoot IMRT and 3D-conformal RT for treatment of prostate cancer

INTRODUCTION

Volumetric modulated arc therapy (VMAT), a complex treatment strategy for intensity-modulated radiation therapy, may increase treatment efficiency and has recently been established clinically. This analysis compares VMAT against established IMRT and 3D-conformal radiation therapy (3D-CRT) delivery techniques.

METHODS

Based on CT datasets of 9 patients treated for prostate cancer step-and-shoot IMRT, serial tomotherapy (MIMiC), 3D-CRT and VMAT were compared with regard to plan quality and treatment efficiency. Two VMAT approaches (one rotation (VMAT1x) and one rotation plus a second 200 degrees rotation (VMAT2x)) were calculated for the plan comparison. Plan quality was assessed by calculating homogeneity and conformity index (HI and CI), dose to normal tissue (non-target) and D(95%) (dose encompassing 95% of the target volume). For plan efficiency evaluation, treatment time and number of monitor units (MU) were considered.

RESULTS

For MIMiC/IMRT(MLC)/VMAT2x/VMAT1x/3D-CRT, mean CI was 1.5/1.23/1.45/1.51/1.46 and HI was 1.19/1.1/1.09/1.11/1.04. For a prescribed dose of 76 Gy, mean doses to organs-at-risk (OAR) were 50.69 Gy/53.99 Gy/60.29 Gy/61.59 Gy/66.33 Gy for the anterior half of the rectum and 31.85 Gy/34.89 Gy/38.75 Gy/38.57 Gy/55.43 Gy for the posterior rectum. Volumes of non-target normal tissue receiving > or =70% of prescribed dose (53 Gy) were 337 ml/284 ml/482 ml/505 ml/414 ml, for > or =50% (38 Gy) 869 ml/933 ml/1155 ml/1231 ml/1993 ml and for > or =30% (23 Gy) 2819 ml/3414 ml/3340 ml/3438 ml /3061 ml. D(95%) was 69.79 Gy/70.51 Gy/71,7 Gy/71.59 Gy/73.42 Gy. Mean treatment time was 12 min/6 min/3.7 min/1.8 min/2.5 min.

CONCLUSION

All approaches yield treatment plans of improved quality when compared to 3D-conformal treatments, with serial tomotherapy providing best OAR sparing and VMAT being the most efficient treatment option in our comparison. Plans which were calculated with 3D-CRT provided good target coverage but resulted in higher dose to the rectum.

Reduced rectal toxicity with ultrasound-based image guided radiotherapy using BAT (B-mode acquisition and targeting system) for prostate cancer

PURPOSE

To evaluate the effect of image guided radiotherapy with stereotactic ultrasound BAT (B-mode acquisition and targeting system) on rectal toxicity in conformal radiotherapy of prostate cancer.

PATIENTS AND METHODS

42 sequential patients with prostate cancer undergoing radiotherapy before and after the introduction of BAT were included. Planning computed tomography (CT) was performed with empty rectum and moderately filled bladder. The planning target volume (PTV) included the prostate and seminal vesicles with a safety margin of 1.5 cm in anterior and lateral direction. In posterior direction the anterior 1/3 of the rectum circumference were included. Total dose was 66 Gy and a boost of 4 Gy excluding the seminal vesicles. 22 patients (BAT group) were treated with daily stereotactic ultrasound positioning, for the other 20 patients (NoBAT group) an EPID (electronic portal imaging device) was performed once a week. Acute and late genito-urinary (GU) and rectal toxicity and PSA values were evaluated after 1.5, 3, 6, 9 and 12 months. The total median follow up of toxicity was 3 years in the BAT group and 4 years in the NoBAT group.

RESULTS

In the NoBAT group significant more rectal toxicity occurred, while in GU toxicity no difference was seen. Two patients in the NoBAT group showed late rectal toxicity grade 3, no toxicity>grade 2 occurred in the BAT group. There was no significant difference in PSA reduction between the groups.

CONCLUSION

Without BAT significant more acute and a trend to more late rectal toxicity was found. With regard to dose escalation this aspect is currently evaluated with a larger number of patients using intensity-modulated radiotherapy (IMRT).

Sooner or later? Outcome analysis of 431 prostate cancer patients treated with postoperative or salvage radiotherapy

PURPOSE

To evaluate the outcome of postoperative radiotherapy (PORT) and salvage RT (SART) using a three-dimensional conformal two-dynamic arc (3D-ART) or 3D six-field technique in 431 prostate cancer patients.

METHODS AND MATERIALS

Of the 431 patients, 258 underwent PORT (started <6 months after radical prostatectomy) and 173 underwent SART because of biochemical failure after radical prostatectomy. The median patient age, preoperative prostate-specific antigen level, and Gleason score was 66 years, 9.4 ng/mL, and 7, respectively. The median radiation dose was 70 Gy in 35 fractions for both PORT and SART. The 3D six-field and 3D-ART techniques were used in 25.1% and 74.9% of patients, respectively. Biochemical failure was defined as a post-RT prostate-specific antigen nadir plus 0.1 ng/mL.

RESULTS

Acute toxicity included rectal events (PORT, 44.2% and 0.8% Grade 1-2 and Grade 3, respectively; SART, 42.2% and 1.2% Grade 1-2 and Grade 3, respectively) and urinary events (PORT, 51.2% and 2.3% Grade 1-2 and Grade 3-4, respectively; SART, 37.6% and 0% Grade 1-2 and Grade 3, respectively). Late toxicity also included rectal events (PORT, 14.7% and 0.8% Grade 1-2 and Grade 3-4, respectively; SART, 15.0% and 0.6% Grade 1-2 and Grade 3, respectively) and urinary events (PORT, 28.3% and 3.7% Grade 1-2 and Grade 3-4, respectively; SART, 19.3% and 0.6% Grade 1-2 and Grade 3, respectively). After a median follow-up of 48 months, failure-free survival, including biochemical and clinical failure, was significantly longer in the PORT patients (79.8% vs. 60.5%, p < 0.0001). Multivariate analysis showed that a prostate-specific antigen level postoperatively but before RT of >/=0.2 ng/mL (p < 0.001), Gleason score >6 (p = 0.025) and use of preoperative androgen deprivation (p = 0.002) correlated significantly with shorter failure-free survival. Multivariate analysis showed that PORT and the 3D-ART technique correlated with greater late urinary toxicity.

CONCLUSION

PORT and early referral for SART offer better disease control after radical prostatectomy. The greater urinary toxicity occurring after PORT and 3D-ART requires further investigation to improve the therapeutic index.

Pilot study: rectal contouring variability in patients treated with radical radiotherapy for prostate cancer: impact on rectum dose–volume histograms

Purpose: The organ at risk in prostate radiotherapy is the anterior rectal wall . This pilot study was conducted to quantify the inter-observer variability of rectal contouring in conformal prostate radiotherapy planning using four contouring methods and to determine a standard rectal contouring definition.

Methods and materials: Ten patients with T1/T2 disease and six clinical oncologists were recruited. Two cross-sectional and two length limits generated four rectal volumes. Each clinician contoured the four volumes for each patient and the dose–volume histograms (DVHs) were analysed. The percentage rectal volume receiving 20%, 50%, 80%, 90% and 95% of the total delivered dose and the mean and median rectal doses were calculated. Data were presented as mean ± 2 standard deviations.

Results: The Sh Rec method (contouring the rectum including its contents extending from 2 cm above the upper limit of the prostate to 2 cm below the prostatic apex) was the least variable in the 80%, 90% and 95% percentage ranges. The mean difference in Sh Rec-contoured volume was 18.7 cm3 (± 22.3 cm3).

Conclusions: The Sh Rec-contouring method showed the least inter-observer variability. The results are informative and will help define a standard rectal contouring method.

Dosimetric and anatomic indicators of late rectal toxicity after high-dose intensity modulated radiation therapy for prostate cancer

We seek to identify dosimetric and anatomic indicators of late rectal toxicity in prostate cancer patients treated with intensity modulated radiation therapy (IMRT). Data from 49 patients sampled from 698 patients treated for clinically localized prostate cancer at the Memorial Sloan-Kettering Cancer Center with IMRT to a dose of 81 Gy were analyzed. The end point of the study was late Grade 2 or worse rectal toxicity within 30 months of treatment. Dosimetric analysis was performed on the rectum surface in three dimensions and on two-dimensional dose maps obtained by flattening the rectum surface using a conformal mapping procedure. Several parameters including the percentage and absolute surface area of the rectum irradiated, mean dose as a function of location on the rectum, planning target volume (PTV) size and rectum size were analyzed for correlation to toxicity. Significance was set at p < 0.05 for a two-sided t-test. Correlation between absolute areas irradiated and toxicity was observed on both the rectum surface and flattened rectum. Patients with toxicity also received a significantly higher mean dose to the superior 25% of the rectum surface and 15% of the flattened rectum. PTV volume, PTV height, rectum surface area and average cross-sectional area were significantly larger in patients with toxicity. The conformal mapping procedure has potential utility for evaluating dose to the rectum and risk of toxicity. Late rectal toxicity was related to the irradiation of the upper part of the rectum and also to the absolute area irradiated, PTV size, and rectum size on the planning computed tomography (CT) scan.