Dose/volume relationship of late rectal bleeding after external beam radiotherapy for localized prostate cancer: absolute or relative rectal volume?

Radiation Proctitis in Patients With Locally Advanced Cervical Cancer Treated by Chemoradiation: Analysis and Predictive Factors From a Retrospective Cohort

OBJECTIVES

Radiation proctitis is a misunderstanding complication of chemoradiation in locally advanced cervical cancer. The objective of our study is to provide a detailed description and analysis of predictive factors associated with radiation proctitis in a retrospective cohort of patients treated by chemoradiation for locally advanced cervical cancer.

METHODS

All patients treated by exclusive chemoradiation or chemoradiation followed by brachytherapy for locally advanced cervical cancer from 2011 to 2017 were included in the study. A bivariate analysis was conducted to establish correlations between the occurrence of radiation proctitis and various clinical and technical variables.

RESULTS

A total of 128 patients were included in the study. The mean dose (SD) to the planning target volume was 47.1 Gy (6.2). Fifty-nine (46.1%) patients underwent brachytherapy. Sixteen patients (12.5%) developed radiation proctitis, grade 2 or higher in 12 patients (9.3%). In univariate analysis, anticoagulant or antiplatelet treatments ( P =0.039), older age ( P =0.049), rectal volume irradiated at 40 Gy ( P =0.01) and 30 Gy ( P =0.037) were significantly associated with the occurrence of a grade ≥2 radiation proctitis. The delivered dose to 2 cm 3 of rectum (D2cm 3 ) showed a potential association with the occurrence of radiation proctitis of all grades ( P =0.064).

CONCLUSIONS

This study highlights clinical and technical factors that should be considered in assessing the risk of radiation proctitis. These results contribute to a better understanding of this complication.

Gastrointestinal Toxicity Prediction Not Influenced by Rectal Contour or Dose-Volume Histogram Definition

PURPOSE

Rectal dose delivered during prostate radiation therapy is associated with gastrointestinal toxicity. Treatment plans are commonly optimized using rectal dose-volume constraints, often whole-rectum relative-volumes (%). We investigated whether improved rectal contouring, use of absolute-volumes (cc), or rectal truncation might improve toxicity prediction.

METHODS AND MATERIALS

Patients from the CHHiP trial (receiving 74 Gy/37 fractions [Fr] vs 60 Gy/20 Fr vs 57 Gy/19 Fr) were included if radiation therapy plans were available (2350/3216 patients), plus toxicity data for relevant analyses (2170/3216 patients). Whole solid rectum relative-volumes (%) dose-volume-histogram (DVH), as submitted by treating center (original contour), was assumed standard-of-care. Three investigational rectal DVHs were generated: (1) reviewed contour per CHHiP protocol; (2) original contour absolute volumes (cc); and (3) truncated original contour (2 versions; ±0 and ±2 cm from planning target volume [PTV]). Dose levels of interest (V30, 40, 50, 60, 70, 74 Gy) in 74 Gy arm were converted by equivalent-dose-in-2 Gy-Fr (EQD2α/β= 3 Gy) for 60 Gy/57 Gy arms. Bootstrapped logistic models predicting late toxicities (frequency G1+/G2+, bleeding G1+/G2+, proctitis G1+/G2+, sphincter control G1+, stricture/ulcer G1+) were compared by area-undercurve (AUC) between standard of care and the 3 investigational rectal definitions.

RESULTS

The alternative dose/volume parameters were compared with the original relative-volume (%) DVH of the whole rectal contour, itself fitted as a weak predictor of toxicity (AUC range, 0.57-0.65 across the 8 toxicity measures). There were no significant differences in toxicity prediction for: (1) original versus reviewed rectal contours (AUCs, 0.57-0.66; P = .21-.98); (2) relative- versus absolute-volumes (AUCs, 0.56-0.63; P = .07-.91); and (3) whole-rectum versus truncation at PTV ± 2 cm (AUCs, 0.57-0.65; P = .05-.99) or PTV ± 0 cm (AUCs, 0.57-0.66; P = .27-.98).

CONCLUSIONS

We used whole-rectum relative-volume DVH, submitted by the treating center, as the standard-of-care dosimetric predictor for rectal toxicity. There were no statistically significant differences in prediction performance when using central rectal contour review, with the use of absolute-volume dosimetry, or with rectal truncation relative to PTV. Whole-rectum relative-volumes were not improved upon for toxicity prediction and should remain standard-of-care.

Is an Endorectal Balloon Beneficial for Rectal Sparing after Spacer Implantation in Prostate Cancer Patients Treated with Hypofractionated Intensity-Modulated Proton Beam Therapy? A Dosimetric and Radiobiological Comparison Study

BACKGROUND

The aim of this study is to examine the dosimetric influence of endorectal balloons (ERB) on rectal sparing in prostate cancer patients with implanted hydrogel rectum spacers treated with dose-escalated or hypofractionated intensity-modulated proton beam therapy (IMPT).

METHODS

Ten patients with localized prostate cancer included in the ProRegPros study and treated at our center were investigated. All patients underwent placement of hydrogel rectum spacers before planning. Two planning CTs (with and without 120 cm3 fluid-filled ERB) were applied for each patient. Dose prescription was set according to the h strategy, with 72 Gray (Gy)/2.4 Gy/5× weekly to prostate + 1 cm of the seminal vesicle, and 60 Gy/2 Gy/5× weekly to prostate + 2 cm of the seminal vesicle. Planning with two laterally opposed IMPT beams was performed in both CTs. Rectal dosimetry values including dose-volume statistics and normal tissue complication probability (NTCP) were compared for both plans (non-ERB plans vs. ERB plans).

RESULTS

For ERB plans compared with non-ERB, the reductions were 8.51 ± 5.25 Gy (RBE) (p = 0.000) and 15.76 ± 11.11 Gy (p = 0.001) for the mean and the median rectal doses, respectively. No significant reductions in rectal volumes were found after high dose levels. The use of ERB resulted in significant reduction in rectal volume after receiving 50 Gy (RBE), 40 Gy (RBE), 30 Gy (RBE), 20 Gy (RBE), and 10 Gy (RBE) with p values of 0.034, 0.008, 0.003, 0.001, and 0.001, respectively. No differences between ERB and non-ERB plans for the anterior rectum were observed. ERB reduced posterior rectal volumes in patients who received 30 Gy (RBE), 20 Gy (RBE), or 10 Gy (RBE), with p values of 0.019, 0.003, and 0.001, respectively. According to the NTCP models, no significant reductions were observed in mean or median rectal toxicity (late rectal bleeding ≥ 2, necrosis or stenosis, and late rectal toxicity ≥ 3) when using the ERB.

CONCLUSION

ERB reduced rectal volumes exposed to intermediate or low dose levels. However, no significant reduction in rectal volume was observed in patients receiving high or intermediate doses. There was no benefit and also no disadvantage associated with the use of ERB for late rectal toxicity, according to available NTCP models.

Effect of Race and Ethnicity on Risk of Radiotherapy Toxicity and Implications for Radiogenomics

AIMS

Patient factors affect the risk of radiotherapy toxicity, but many are poorly defined. Studies have shown that race affects cancer incidence, survival, drug response, molecular pathways and epigenetics. Effects on radiosensitivity and radiotherapy toxicity are not well studied. The aim of the present study was to identify the effects of race and ethnicity on the risk of radiotherapy toxicity.

MATERIALS AND METHODS

A systematic review was carried out of PubMed, Ovid Medline and Ovid Embase with no year limit. PRISMA 2020 guidelines were followed. Two independent assessors reviewed papers.

RESULTS

Of 607 papers screened, 46 fulfilled the inclusion criteria. Papers were published between 1996 and 2021 and involved 30-28,354 individuals (median 433). Most involved patients with prostate (33%), breast (26%) and lung (9%) cancer. Both early and late toxicities were studied. Some studies reported a higher risk of toxicity in White men with prostate cancer compared with other races and ethnicities. For breast cancer patients, some reported an increased risk of toxicity in White women compared with other race and ethnic groups. In general, it was difficult to draw conclusions due to insufficient reporting and analysis of race and ethnicity in published literature.

CONCLUSIONS

Reporting of race and ethnicity in radiotherapy studies must be harmonised and improved and frameworks are needed to improve the quality of reporting. Further research is needed to understand how ancestral heritage might affect radiosensitivity and risk of radiotherapy toxicity.

Comparison of relative and absolute rectal dose-volume parameters and clinical correlation with acute and late radiation proctitis in prostate cancer patients

PURPOSE

To compare relative and absolute dose-volume parameters (DV) of the rectum and their clinical correlation with acute and late radiation proctitis (RP) after radiotherapy (RT) for prostate cancer (PCa).

PATIENTS AND METHODS

366 patients received RT for PCa. In total, 49.2% received definitive RT, 20.2% received postoperative RT and 30.6% received salvage RT for biochemical recurrence. In 77.9% of patients, RT was delivered to the prostate or prostate bed, and additional whole pelvic RT was performed in 22.1%. 33.9% received 3D-RT, and 66.1% received IMRT. The median follow-up was 59.5 months (18.0-84.0 months). The relative (in %) and absolute (in ccm) rectal doses from 20-75 Gy including the receiver operating characteristics curves (rAUC) from 30-65 Gy (in % and ccm) and several other clinical parameters were analyzed in univariate and multivariate analyses. We performed the statistical analyses separately for the entire cohort (n = 366), patients with (n = 81) and without (n = 285) pelvic RT, comparing RP vs. RP ≥ grade I.

RESULTS

With the exception of the V50_Gyccm (p = 0.02) in the univariate analyses for acute RP in the entire patient cohort, no absolute DV parameter (in ccm) was statistically significant associated with either acute or late RP. In the multivariate analyses, 3D-RT (p < 0.008) and rAUC_V30-50 Gy% (p = 0.006) were significant parameters for acute RP for the entire cohort, and the V50_Gy% (p = 0.01) was the significant parameter for patients with pelvic RT. The rAUC_V40-50 Gy% (p = 0.004) was significant for RT to the prostate/prostate bed. Regarding the statistical analysis for late RP, the rAUC_V30-65 Gy% (p = 0.001) was significant for the entire cohort, and rAUC_V30-50 Gy% (p = 0.001) was significant for RT of the prostate/prostate bed. No parameter was significant in patients with pelvic RT.

CONCLUSION

Absolute DV parameters in ccm are not required for RT in PCa patients.

Association between rectal bleeding and the absolute dose volume of the rectum following image-guided radiotherapy for patients with prostate cancer

The association between rectal bleeding and the received dose relative to the volume of the rectum is well established in prostate cancer patients who have undergone radiotherapy. The relative volume of the rectum is affected by the rectal anatomical volume, which depends on the definition of rectal length. Compared with the relative rectal volume, the absolute volume of the rectum may be more associated with rectal bleeding. The present study investigated the absolute volume of the rectum that may be used to predict late rectal bleeding following intensity-modulated radiotherapy (IMRT) and image-guided radiotherapy (IGRT). The cases of 82 patients of prostate cancer, who underwent IMRT and IGRT, were retrospectively evaluated by evaluating dose volume histograms. The median patient age was 73.4 years (range, 51.3-85.9 years). The median total prescribed dose was 76 Gy given in 38 fractions. The absolute and relative dose volumes of the rectum were evaluated by multivariate analysis, and the optimal dose to prevent rectal bleeding was determined. The actuarial ≥grade 1 rectal bleeding rate at 4 years was 4.5% (95% confidence interval, 1.5-13.4%) with a median observation period of 45.3 months. The absolute rectal volume (ml) treated with 60 Gy was the only significant risk factor for rectal bleeding (P<0.05), but the relative rectal volume (%) was not identified as a significant factor by the multivariate analysis. When the rectal volume of 5 or 10 ml received 60 Gy (D5cc and D10cc), rectal bleeding was expected to occur in 3.3 and 7.3% of the patients, respectively. Rectal D5cc ≤60 Gy is recommended to prevent late ≥grade 1 rectal bleeding in IGRT.

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.

A Phase II Study of Stereotactic Body Radiation Therapy for Low-Intermediate-High-Risk Prostate Cancer Using Helical Tomotherapy: Dose-Volumetric Parameters Predicting Early Toxicity

Endpoint: To assess early urinary (GU) and rectal (GI) toxicities after helical tomotherapy Stereotactic body radiation therapy (SBRT), and to determine their predictive factors.

Methods: Since May 2012, 45 prostate cancer patients were treated with eight fractions of 5.48 (low risk, 29%) or 5.65 Gy (intermediate-high risk, 71%) on alternative days over 2.5 weeks. The exclusion criteria were Gleason score 9–10, PSA >40 ng/mL, cT3b-4, IPSS ≥20, and history of acute urinary retention. During the follow-up, a set of potential prognostic factors was correlated with urinary or rectal toxicity.

Results: The median follow-up was 13.8 months (2–25 months). There were no grade ≥3 toxicities. Acute grade 2 GU complications were found in a 22.7% of men, but in 2.3% of patients at 1 month, 0% at 6 months, and 0% at 12 months. The correspondent figures for grade 2 GI toxicities were 20.4% (acute), 2.3% (1 month), 3.6% (6 months), and 5% (12 months). Acute GI toxicity was significantly correlated with the rectal volume (>15 cm³) receiving 28 Gy, only when expressed as absolute volume. The age (>72 years old) was a predictor of GI toxicity after 1 month of treatment. No correlation was found, however, between urinary toxicity and the other analyzed variables. IPSS increased significantly at the time of the last fraction and within the first month, returning to the baseline at sixth month. Urinary-related quality of life (IPSS question 8 score), it was not significantly worsen during radiotherapy returning to the baseline levels 1 month after the treatment. At 12 months follow-up patient’s perception of their urinary function improved significantly in comparison with the baseline.

Conclusion: Our scheme of eight fractions on alternative days delivered using helical tomotherapy is well tolerated. We recommend using actual volume instead of percentual volume in the treatment planning, and not to exceed 15 cm³ of rectal volume receiving ≥25 Gy in order to diminish acute GI toxicity.

[What is the level of evidence of new techniques in prostate cancer radiotherapy?]

Prostate cancer radiotherapy has evolved from the old 2D technique to conformal, and then to intensity-modulated radiation therapy (IMRT) and stereotactic radiotherapy. At the same time, image-guidance (IGRT) is routinely used. New techniques such as protontherapy or carbontherapy are being developed with the objective of increased efficacy, decreased treatment duration, toxicity or cost. This review summarizes the evidence-based medicine of new technologies in the treatment of prostate cancer.

Dosimetry estimation on variations of patient size in prostate volumetric-modulated arc therapy

This study investigated the dosimetric variations of the target and critical organs of patients who had weight loss associated with prostate volumetric-modulated arc therapy (VMAT). Five patients with prostate volumes ranging from 32-86.5 cm³ were selected from a group of 30 patients. Prostate VMAT plans were carried out on each patient using the 6-MV photon beam with a single 360° arc. Decrease of patient size as a result of weight loss was mimicked by contracting the patient's external contour in the anterior, left, and right directions with depths from 0.5-2 cm. Soft tissue excluded by the contracted external contour was replaced by air and the dose distribution was recalculated using the same beam geometry and dose prescription. Dose-volume histograms and dose-volume points such as D99% and D5% for the planning target volume (PTV), clinical target volume (CTV), rectum, bladder, and femoral heads were calculated with variations of reduced depth. In addition, the minimum, maximum, and mean doses for the target and critical organs were determined. PTV and CTV D99% were found to have increased 2.86 ± 0.30% per cm and 2.75 ± 0.38% per cm of reduced depth ranging from 0.5-2 cm. Moreover, the rectal and bladder D30% increased 2.20 ± 0.20% per cm and 2.31 ± 0.83% per cm, and the femoral head D5% increased 3.30 ± 0.11% per cm of reduced depth. Results from variations of the minimum, maximum, and mean doses of the PTV, CTV, rectum, bladder, and femoral heads showed that there was a >5% increase of dose when the reduced depth reached 2 cm. This study provided dosimetry estimation for radiation oncology staff to justify dose variations of the target and critical organs when patients' weight loss occurred in prostate VMAT. Dose variations >5% were seen when the patients' reduced depth was equal to 2 cm.

Cost-effectiveness of intensity-modulated radiotherapy in prostate cancer

AIMS

To compare the costs and effectiveness of intensity-modulated radiotherapy (IMRT) with three-dimensional conformal radiotherapy (3DCRT) for the radical treatment of localised prostate cancer at elevated doses (>70 Gy).

MATERIALS AND METHODS

A cost-effectiveness analysis model was developed using clinical effectiveness estimates from a systematic review. The base case analysis assumes equal biochemical survival for IMRT and 3DCRT, but lower frequency of gastrointestinal toxicity for IMRT. The costs of IMRT and 3DCRT were estimated through activity-based costing, incorporating input from radiation oncologists, physicists and treatment planners.

RESULTS

The delivery of IMRT produced 0.023 more quality-adjusted life-years (QALY) than 3DCRT at an additional cost of $621 (QALY and costs discounted at 5% per year), yielding an incremental cost-effectiveness ratio of $26 768 per QALY gained. The treatment cost of IMRT was $1019 more than 3DCRT, but IMRT resulted in less frequent gastrointestinal toxicity, thus avoiding $402 in the treatment of toxicity. In the scenario that compared a higher dose of IMRT (75.6 Gy) to 3DCRT (68.4 Gy), IMRT improved disease control with equal toxicity incidence, and the IMRT strategy dominated (less costly and more effective). In the base case scenario (no survival difference), the cost-effectiveness of IMRT was most sensitive to the treatment cost difference between IMRT and 3DCRT.

CONCLUSION

For radical radiation treatment (>70 Gy) of prostate cancer, IMRT seems to be cost-effective when compared with an equivalent dose of 3DCRT.

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.

VMAT vs. 7-field-IMRT: assessing the dosimetric parameters of prostate cancer treatment with a 292-patient sample

We compared normal tissue radiation dose for the treatment of prostate cancer using 2 different radiation therapy delivery methods: volumetric modulated arc therapy (VMAT) vs. fixed-field intensity-modulated radiation therapy (IMRT). Radiotherapy plans for 292 prostate cancer patients treated with VMAT to a total dose of 7740 cGy were analyzed retrospectively. Fixed-angle, 7-field IMRT plans were created using the same computed tomography datasets and contours. Radiation doses to the planning target volume (PTV) and organs at risk (bladder, rectum, penile bulb, and femoral heads) were measured, means were calculated for both treatment methods, and dose-volume comparisons were made with 2-tailed, paired t-tests. The mean dose to the bladder was lower with VMAT at all measured volumes: 5, 10, 15, 25, 35, and 50% (p < 0.05). The mean doses to 5 and 10% of the rectum, the high-dose regions, were lower with VMAT (p < 0.05). The mean dose to 15% of the rectal volume was not significantly different (p = 0.95). VMAT exposed larger rectal volumes (25, 35, and 50%) to more radiation than fixed-field IMRT (p < 0.05). Average mean dose to the penile bulb (p < 0.05) and mean dose to 10% of the femoral heads (p < 0.05) were lower with VMAT. VMAT therapy for prostate cancer has dosimetric advantages for critical structures, notably for high-dose regions compared with fixed-field IMRT, without compromising PTV coverage. This may translate into reduced acute and chronic toxicity.

Assessment of normal tissue complications following prostate cancer irradiation: comparison of radiation treatment modalities using NTCP models

PURPOSE

Normal tissue complication probability (NTCP) of the rectum, bladder, urethra, and femoral heads following several techniques for radiation treatment of prostate cancer were evaluated applying the relative seriality and Lyman models.

METHODS

Model parameters from literature were used in this evaluation. The treatment techniques included external (standard fractionated, hypofractionated, and dose-escalated) three-dimensional conformal radiotherapy (3D-CRT), low-dose-rate (LDR) brachytherapy (I-125 seeds), and high-dose-rate (HDR) brachytherapy (Ir-192 source). Dose-volume histograms (DVHs) of the rectum, bladder, and urethra retrieved from corresponding treatment planning systems were converted to biological effective dose-based and equivalent dose-based DVHs, respectively, in order to account for differences in radiation treatment modality and fractionation schedule.

RESULTS

Results indicated that with hypofractionated 3D-CRT (20 fractions of 2.75 Gy/fraction delivered five times/week to total dose of 55 Gy), NTCP of the rectum, bladder, and urethra were less than those for standard fractionated 3D-CRT using a four-field technique (32 fractions of 2 Gy/fraction delivered five times/week to total dose of 64 Gy) and dose-escalated 3D-CRT. Rectal and bladder NTCPs (5.2% and 6.6%, respectively) following the dose-escalated four-field 3D-CRT (2 Gy/fraction to total dose of 74 Gy) were the highest among analyzed treatment techniques. The average NTCP for the rectum and urethra were 0.6% and 24.7% for LDR-BT and 0.5% and 11.2% for HDR-BT.

CONCLUSIONS

Although brachytherapy techniques resulted in delivering larger equivalent doses to normal tissues, the corresponding NTCPs were lower than those of external beam techniques other than the urethra because of much smaller volumes irradiated to higher doses. Among analyzed normal tissues, the femoral heads were found to have the lowest probability of complications as most of their volume was irradiated to lower equivalent doses compared to other tissues.

Comparison of prostate IMRT and VMAT biologically optimised treatment plans

Recently, a new radiotherapy delivery technique has become clinically available--volumetric modulated arc therapy (VMAT). VMAT is the delivery of IMRT while the gantry is in motion using dynamic leaf motion. The perceived benefit of VMAT over IMRT is a reduction in delivery time. In this study, VMAT was compared directly with IMRT for a series of prostate cases. For 10 patients, a biologically optimized seven-field IMRT plan was compared with a biologically optimized VMAT plan using the same planning objectives. The Pinnacle RTPS was used. The resultant target and organ-at-risk dose-volume histograms (DVHs) were compared. The normal tissue complication probability (NTCP) for the IMRT and VMAT plans was calculated for 3 model parameter sets. The delivery efficiency and time for the IMRT and VMAT plans was compared. The VMAT plans resulted in a statistically significant reduction in the rectal V25Gy parameter of 8.2% on average over the IMRT plans. For one of the NTCP parameter sets, the VMAT plans had a statistically significant lower rectal NTCP. These reductions in rectal dose were achieved using 18.6% fewer monitor units and a delivery time reduction of up to 69%. VMAT plans resulted in reductions in rectal doses for all 10 patients in the study. This was achieved with significant reductions in delivery time and monitor units. Given the target coverage was equivalent, the VMAT plans were superior.

A method to separate the rectum from the prostate during proton beam radiotherapy of prostate cancer patients

The use of protons for curative treatment of prostate cancer is increasing, either as a single treatment modality or in combination with conventional radiotherapy. The proximity between prostate (target) and rectum (organ at risk) often leads to a compromise between dose to target and organ at risk.

MATERIAL AND METHODS

The present study describes a method where the distance between prostate and rectum is increased by retraction of the rectum in dorsal direction. Comparative treatment plans with and without retraction of the rectum in the same patients have been studied. Nine patients with biopsy proven, localised adenocarcinoma of the prostate were studied. A cylindrical rod of Perspex was inserted into the rectum. This device allows the rectum to be retracted posteriorly. The patients were given a proton boost of 20 Gy in four fractions of 5 Gy in addition to a conventional photon beam treatment to a dose of 50 Gy in 25 fractions of 2 Gy.

RESULTS

Comparative treatment planning shows that the treatment plan with rectal retraction significantly reduces (p<0.01) the volume of the rectal wall receiving high doses (equal to 70 Gy in 2 Gy fractions) in all patients.

CONCLUSIONS

The proton boost treatment with retraction of rectum during treatment decreases the rectal dose substantially. This is expected to reduce rectal side effects.

The lessons of QUANTEC: recommendations for reporting and gathering data on dose-volume dependencies of treatment outcome

The 16 clinical articles in this issue review the dose-volume dependence of toxicities of external beam radiotherapy. They are limited by the difficulty of synthesizing results from different publications. The major problems stem from incomplete reporting of results and use of incompatible or ambiguous endpoints. Here we specify these problems; give recommendations to authors, editors, and reviewers on standards of reporting; and provide methods of defining endpoints suitable for the dose-volume analysis of toxicity. Adopting these recommendations will facilitate meta-analysis and increase the utility of individual studies of the dependence of complications on dose distributions.

Schedule for CT image guidance in treating prostate cancer with helical tomotherapy

The aim of this study was to determine the effect of reducing the number of image guidance sessions and patient-specific target margins on the dose distribution in the treatment of prostate cancer with helical tomotherapy. 20 patients with prostate cancer who were treated with helical tomotherapy using daily megavoltage CT (MVCT) imaging before treatment served as the study population. The average geometric shifts applied for set-up corrections, as a result of co-registration of MVCT and planning kilovoltage CT studies over an increasing number of image guidance sessions, were determined. Simulation of the consequences of various imaging scenarios on the dose distribution was performed for two patients with different patterns of interfraction changes in anatomy. Our analysis of the daily set-up correction shifts for 20 prostate cancer patients suggests that the use of four fractions would result in a population average shift that was within 1 mm of the average obtained from the data accumulated over all daily MVCT sessions. Simulation of a scenario in which imaging sessions are performed at a reduced frequency and the planning target volume margin is adapted provided significantly better sparing of organs at risk, with acceptable reproducibility of dose delivery to the clinical target volume. Our results indicate that four MVCT sessions on helical tomotherapy are sufficient to provide information for the creation of personalised target margins and the establishment of the new reference position that accounts for the systematic error. This simplified approach reduces overall treatment session time and decreases the imaging dose to the patient.

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.

Evidence behind use of intensity-modulated radiotherapy: a systematic review of comparative clinical studies

Since its introduction more than a decade ago, intensity-modulated radiotherapy (IMRT) has spread to most radiotherapy departments worldwide for a wide range of indications. The technique has been rapidly implemented, despite an incomplete understanding of its advantages and weaknesses, the challenges of IMRT planning, delivery, and quality assurance, and the substantially increased cost compared with non-IMRT. Many publications discuss the theoretical advantages of IMRT dose distributions. However, the key question is whether the use of IMRT can be exploited to obtain a clinically relevant advantage over non-modulated external-beam radiation techniques. To investigate which level of evidence supports the routine use of IMRT for various disease sites, we did a review of clinical studies that reported on overall survival, disease-specific survival, quality of life, treatment-induced toxicity, or surrogate endpoints. This review shows evidence of reduced toxicity for various tumour sites by use of IMRT. The findings regarding local control and overall survival are generally inconclusive.

Is there a limit to dose escalation for rectal cancer?

The radiation tolerance of the rectum is not fully understood. Published studies on the radiation treatment of cancers of the prostate, cervix and rectum have been reviewed to determine currently recommended dose-volume guidelines. The need for further studies directed specifically at the treatment of primary rectal cancer and perirectal node metastases is discussed. There seems to be room for escalation of the external beam doses currently given.

Hypofractionated Intensity-Modulated Radiotherapy (70 Gy at 2.5 Gy Per Fraction) for Localized Prostate Cancer: Cleveland Clinic Experience

PURPOSE

To study the outcomes in patients treated for localized prostate cancer with 70 Gy delivered at 2.5-Gy/fraction within 5 weeks.

METHODS AND MATERIALS

The study sample included all 770 consecutive patients with localized prostate cancer treated with hypofractionated intensity-modulated radiotherapy at the Cleveland Clinic between 1998 and 2005. The median follow-up was 45 months (maximum, 86). Both the American Society for Therapeutic Radiology and Oncology (ASTRO) biochemical failure definition and the alternate nadir + 2 ng/mL definition were used.

RESULTS

The overall 5-year ASTRO biochemical relapse-free survival rate was 82% (95% confidence interval, 79-85%), and the 5-year nadir + 2 ng/mL rate was 83% (95% confidence interval, 79-86%). For patients with low-risk, intermediate-risk, and high-risk disease, the 5-year ASTRO rate was 95%, 85%, and 68%, respectively. The 5-year nadir + 2 ng/mL rate for patients with low-, intermediate-, and high-risk disease was 94%, 83%, and 72%, respectively. The Radiation Therapy Oncology Group acute rectal toxicity scores were 0 in 51%, 1 in 40%, and 2 in 9% of patients. The acute urinary toxicity scores were 0 in 33%, 1 in 48%, 2 in 18%, and 3 in 1% of patients. The late rectal toxicity scores were 0 in 89.6%, 1 in 5.9%, 2 in 3.1%, 3 in 1.3%, and 4 in 0.1% (1 patient). The late urinary toxicity scores were 0 in 90.5%, 1 in 4.3%, 2 in 5.1%, and 3 in 0.1% (1 patient).

CONCLUSION

The outcomes after high-dose hypofractionation were acceptable in the entire cohort of patients treated with the schedule of 70 at 2.5 Gy/fraction.

Normal Tissue Tolerance Dose Metrics for Radiation Therapy of Major Organs

Late organ toxicity from therapeutic radiation is a function of many confounding variables. The total dose delivered to the organ and the volumes of organ exposed to a given dose of radiation are 2 important variables that can be used to predict the risk of late toxicity. Three-dimensional radiation planning enables accurate calculation of the volume of tissue exposed to a given dose of radiation, graphically depicted as a dose-volume histogram. Dose metrics obtained from this 3-dimensional dataset can be used as a quantitative measure to predict late toxicity. This review summarizes the published clinical data on the risk of late toxicity as a function of quantitative dose metrics and attempts to offer suggested dose constraints for radiation treatment planning.

Relationships between rectal wall dose-volume constraints and radiobiologic indices of toxicity for patients with prostate cancer

PURPOSE

The purpose of this article was to investigate how exceeding specified rectal wall dose-volume constraints impacts on the risk of late rectal bleeding by using radiobiologic calculations.

METHODS AND MATERIALS

Dose-volume histograms (DVH) of the rectal wall of 250 patients with prostate cancer were analyzed. All patients were treated by three-dimensional conformal radiation therapy, receiving mean target doses of 80 Gy. To study the main features of the patient population, the average and the standard deviation of the distribution of DVHs were generated. The mean dose <D>, generalized equivalent uniform dose formulation (gEUD), modified equivalent uniform dose formulation (mEUD)(0), and normal tissue complication probability (NTCP) distributions were also produced. The DVHs set was then binned into eight classes on the basis of the exceeding or the fulfilling of three dose-volume constraints: V(40) = 60%, V(50) = 50%, and V(70) = 25%. Comparisons were made between them by <D>, gEUD, mEUD(0), and NTCP.

RESULTS

The radiobiologic calculations suggest that late rectal toxicity is mostly influenced by V(70). The gEUD and mEUD(0) are risk factors of toxicity always concordant with NTCP, inside each DVH class. The mean dose, although a reliable index, may be misleading in critical situations.

CONCLUSIONS

Both in three-dimensional conformal radiation therapy and particularly in intensity-modulated radiation therapy, it should be known what the relative importance of each specified dose-volume constraint is for each organ at risk. This requires a greater awareness of radiobiologic properties of tissues and radiobiologic indices may help to gradually become aware of this issue.

Intensity-modulated radiotherapy improves lymph node coverage and dose to critical structures compared with three-dimensional conformal radiation therapy in clinically localized prostate cancer

PURPOSE

The aim of this study was to quantify gains in lymph node coverage and critical structure dose reduction for whole-pelvis (WP) and extended-field (EF) radiotherapy in prostate cancer using intensity-modulated radiotherapy (IMRT) compared with three-dimensional conformal radiotherapy (3DCRT) for the first treatment phase of 45 Gy in the concurrent treatment of lymph nodes and prostate.

METHODS AND MATERIALS

From January to August 2005, 35 patients with localized prostate cancer were treated with pelvic IMRT; 7 had nodes defined up to L5-S1 (Group 1), and 28 had nodes defined above L5-S1 (Group 2). Each patient had 2 plans retrospectively generated: 1 WP 3DCRT plan using bony landmarks, and 1 EF 3DCRT plan to cover the vascular defined volumes. Dose-volume histograms for the lymph nodes, rectum, bladder, small bowel, and penile bulb were compared by group.

RESULTS

For Group 1, WP 3DCRT missed 25% of pelvic nodes with the prescribed dose 45 Gy and missed 18% with the 95% prescribed dose 42.75 Gy, whereas WP IMRT achieved V(45 Gy) = 98% and V(42.75 Gy) = 100%. Compared with WP 3DCRT, IMRT reduced bladder V(45 Gy) by 78%, rectum V(45 Gy) by 48%, and small bowel V(45 Gy) by 232 cm3. EF 3DCRT achieved 95% coverage of nodes for all patients at high cost to critical structures. For Group 2, IMRT decreased bladder V(45 Gy) by 90%, rectum V(45 Gy) by 54% and small bowel V(45 Gy) by 455 cm3 compared with EF 3DCRT.

CONCLUSION

In this study WP 3DCRT missed a significant percentage of pelvic nodes. Although EF 3DCRT achieved 95% pelvic nodal coverage, it increased critical structure doses. IMRT improved pelvic nodal coverage while decreasing dose to bladder, rectum, small bowel, and penile bulb. For patients with extended node involvement, IMRT especially decreases small bowel dose.

Treatment of a radiation-induced rectal ulcer with hyperbaric oxygen therapy in a man with prostate cancer

Late radiation proctopathy is a painful and vexing complication of prostate radiation. We report a case of a 55-year-old man with prostate cancer, and complaints of tenesmus and severe rectal pain after radiation therapy. The patient was diagnosed with a locally advanced Gleason score 8 prostate cancer and an increased prostate-specific antigen of 42.3 ng/ml. His past medical history was notable for a history of bilateral lymph node dissection complicated by Clostridium difficile colitis. He subsequently received 3-dimensional conformal radiation therapy. Seven months after completing therapy, minor rectal bleeding and significant pain developed, requiring increasing doses of opioid analgesics. Fourteen months after 3-dimensional conformal radiation therapy, sigmoidoscopy revealed a single chronic deep ulcer at the anorectal junction. As an alternative to diverting colostomy, the patient underwent a course of hyperbaric oxygen. Within 1 month of completing hyperbaric oxygen treatment, his symptoms completely resolved. Nine months from completion of hyperbaric oxygen therapy, he has had no recurrence of symptoms. Hyperbaric oxygen therapy can be considered a treatment option after failure of standard treatments in patients with severe radiation proctopathy.

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

Background

The dose distribution to the rectum, delineated as solid organ, rectal wall and rectal surface, in 3D conformal (3D-CRT) and intensity-modulated radiotherapy treatment (IMRT) planning for localized prostate cancer was evaluated.

Materials and methods

In a retrospective planning study 3-field, 4-field and IMRT treatment plans were analyzed for ten patients with localized prostate cancer. The dose to the rectum was evaluated based on dose-volume histograms of 1) the entire rectal volume (DVH) 2) manually delineated rectal wall (DWH) 3) rectal wall with 3 mm wall thickness (DWH₃) 4) and the rectal surface (DSH). The influence of the rectal filling and of the seminal vesicles' anatomy on these dose parameters was investigated. A literature review of the dose-volume relationship for late rectal toxicity was conducted.

Results

In 3D-CRT (3-field and 4-field) the dose parameters differed most in the mid-dose region: the DWH showed significantly lower doses to the rectum (8.7% ± 4.2%) compared to the DWH₃ and the DSH. In IMRT the differences between dose parameters were larger in comparison with 3D-CRT. Differences were statistically significant between DVH and all other dose parameters and between DWH and DSH. Mean doses were increased by 23.6% ± 8.7% in the DSH compared to the DVH in the mid-dose region. Furthermore, both the rectal filling and the anatomy of the seminal vesicles influenced the relationship between the dose parameters: a significant correlation of the difference between DVH and DWH and the rectal volume was seen in IMRT treatment.

Discussion

The method of delineating the rectum significantly influenced the dose representation in the dose-volume histogram. This effect was pronounced in IMRT treatment planning compared to 3D-CRT. For integration of dose-volume parameters from the literature into clinical practice these results have to be considered.

Radiothérapie conformationnelle du cancer de la prostate : technique et résultats

A number of retrospective and prospective studies have demonstrated that radiotherapy of prostate cancer must be actually conformal. Three-dimensional (3D) treatment planning consists in an as accurate as possible definition of target-volume, usually by CT-scan, and design of radiation fields shaped to this target-volume. Several steps are required, each step being important for the overall quality of the treatment. Conformal radiotherapy is better tolerated than conventional irradiation, with significantly less rectal toxicity. It allows dose-escalation up to 80 Gy. It is now possible to go beyond this dose with intensity-modulated radiotherapy. The benefit of these high doses was demonstrated by some large retrospective studies and some prospective dose-escalation trials. Several randomized trials are in progress, preliminary results of two of them have been published, both showing an improvement in disease control with the higher doses. The advantage of higher doses is clearly evident for patients in the intermediate prognostic group, but is still discussed for patients with a low risk tumour or treated in combination with hormone therapy. Late proctitis is the main toxicity of these high doses. Some volume constraints have been defined during the last years and will allow a decrease of the rate of rectal toxicity. Because of these technological improvements, results of radiation therapy are now similar to those of surgery: no direct comparison with a randomized trial is available, but large comparative studies show that long-term disease control are identical with both techniques. Radiation therapy must be proposed to all patients with a prostate carcinoma as an alternative to surgery.

Impact of neoadjuvant hormonal therapy on dose-volume histograms in patients with localized prostate cancer under radical radiation therapy

INTRODUCTION

Prostate volume involves a defined toxicity predictor in the radiation therapy of localized prostate cancer. Neoadjuvant hormone therapy (nHT) can reduce prostate volume and, therefore, the planned volume. The objective of this study was to establish if the value of nHT reduces the planned volume and if this reduction correlates with a reduction of the dose received in the target organs.

MATERIAL AND METHODS

28 patients diagnosed of localized prostate cancer and referred to our departments for radiation therapy with radical intention, in the period ranging between April 2002 and October 2003, were included prospectively. The patients received nHT (triptorelin + flutamide) for 2 months and adjuvant HT until completing 2 years in the high-risk cases. A transrectal ultrasound study was performed in all patients, simulation CT and planning before the start of HT and after 2 months of treatment. The radiation therapy was carried out with 6 or 18 MV LINAC photons, with a dose fractioning scheme of 5 x 180-200 cGy, a total dosage of 66-72 Gy to prostate, 56 Gy to seminal vesicles and, in the high-risk cases, 46 Gy to pelvic lymph nodes.

RESULTS

The distribution according to risk group was: low risk 3.6%, intermediate risk 28.6% and high risk 67.9%. By transrectal ultrasound, prostate volume on diagnosis was 50.65 cc pre HT and 38.97 cc post HT (p < 0.001), which means a volume reduction of 24%. The comparative analysis of the dose-volume histograms of the first versus the second CT shows a reduction in the planned volume GTV1 (prostate) (81.33 cc vs 63.96 cc, p < 0.05), PTV1 (prostate and margin) (197.51 cc vs 168.38 cc, p < 0.001) and PTV2 (prostate, vesicles and margin) (340.5 cc vs 307.26 cc, p < 0.05), a reduction of the maximum dose in the seminal vesicles (70.2 versus 68.75 Gy, p < 0.05), a reduction of the mean dose in the seminal vesicles (65.07 Gy versus 63.07 Gy, p < 0.05), PTV2 (67.72 Gy versus 66.9 Gy, p < 0.01) and PTV3 (prostate, vesicles, pelvic lymph nodes and margin) (58.86 Gy versus 57.21 Gy, p < 0.01), a reduction of the D90 in the seminal vesicles (61.83 Gy versus 60.06 Gy, p < 0.05) and PTV2 (61.04 Gy versus 59.45 Gy, p < 0.05) and a reduction of V60 of the rectum (32.45% versus 28.22%, p < 0.05) and V60 of the bladder (41.78% versus 31.67%, p < 0.005).

CONCLUSIONS

Neoadjuvant hormone therapy reduces significantly prostate volume and as a result the planned volume and consequently the rectal and bladder V60 can be significantly reduced.

The potential of proton beam radiation therapy in prostate cancer, other urological cancers and gynaecological cancers

A group of Swedish oncologists and hospital physicists have estimated the number of patients in Sweden suitable for proton beam therapy. The estimations have been based on current statistics of tumour incidence, number of patients potentially eligible for radiation treatment, scientific support from clinical trials and model dose planning studies and knowledge of the dose-response relations of different tumours and normal tissues. In prostate cancer it is estimated that annually about 300 patients and in gynaecological cancer about 50 patients, are candidates for proton beam therapy. Owing to major uncertainties, it has not been possible to give an estimate of the number of potential patients with urinary bladder cancer.

Localized volume effects for late rectal and anal toxicity after radiotherapy for prostate cancer

PURPOSE

To identify dosimetric parameters derived from anorectal, rectal, and anal wall dose distributions that correlate with different late gastrointestinal (GI) complications after three-dimensional conformal radiotherapy for prostate cancer.

METHODS AND MATERIALS

In this analysis, 641 patients from a randomized trial (68 Gy vs. 78 Gy) were included. Toxicity was scored with adapted Radiation Therapy Oncology Group/European Organization for the Research and Treatment of Cancer (RTOG/EORTC) criteria and five specific complications. The variables derived from dose-volume histogram of anorectal, rectal, and anal wall were as follows: % receiving > or =5-70 Gy (V5-V70), maximum dose (Dmax), and mean dose (D(mean)). The anus was defined as the most caudal 3 cm of the anorectum. Statistics were done with multivariate Cox regression models. Median follow-up was 44 months.

RESULTS

Anal dosimetric variables were associated with RTOG/EORTC Grade > or =2 (V5-V40, D(mean)) and incontinence (V5-V70, D(mean)). Bleeding correlated most strongly with anorectal V55-V65, and stool frequency with anorectal V40 and D(mean). Use of steroids was weakly related to anal variables. No volume effect was seen for RTOG/EORTC Grade > or =3 and pain/cramps/tenesmus.

CONCLUSION

Different volume effects were found for various late GI complications. Therefore, to evaluate the risk of late GI toxicity, not only intermediate and high doses to the anorectal wall volume should be taken into account, but also the dose to the anal wall.

Dose-volume analysis of predictors for chronic rectal toxicity after treatment of prostate cancer with adaptive image-guided radiotherapy

PURPOSE

We analyzed our experience treating localized prostate cancer with image-guided off-line correction with adaptive high-dose radiotherapy (ART) in our Phase II dose escalation study to identify factors predictive of chronic rectal toxicity.

MATERIALS AND METHODS

From 1999-2002, 331 patients with clinical stage T1-T3N0M0 prostate cancer were prospectively treated in our Phase II 3D conformal dose escalation ART study to a median dose of 75.6 Gy (range, 63.0-79.2 Gy), minimum dose to confidence limited-planning target volume (cl-PTV) in 1.8 Gy fractions (median isocenter dose = 79.7 Gy). Seventy-four patients (22%) also received neoadjuvant/adjuvant androgen deprivation therapy. A patient-specific cl-PTV was constructed using 5 computed tomography scans and 4 sets of electronic portal images by applying an adaptive process to assure target accuracy and minimize PTV margin. For each case, the rectum (rectal solid) was contoured from the sacroiliac joints or rectosigmoid junction (whichever was higher) to the anal verge or ischial tuberosities (whichever was lower), with a median volume of 81.2 cc. The rectal wall was defined using the rectal solid with an individualized 3-mm wall thickness (median volume = 29.8 cc). Rectal wall dose-volume histogram was used to determine the prescribed dose. Toxicity was quantified using the National Cancer Institute Common Toxicity Criteria 2.0. Multiple dose-volume endpoints were evaluated for their association with chronic rectal toxicity.

RESULTS

Median follow-up was 1.6 years. Thirty-four patients (crude rate = 10.3%) experienced Grade 2 chronic rectal toxicity at a median interval of 1.1 years. Nine patients (crude rate = 2.7%) experienced Grade > or =3 chronic rectal toxicity (1 was Grade 4) at a median interval of 1.2 years. The 3-year rates of Grade > or =2 and Grade > or =3 chronic rectal toxicity were 20% and 4%, respectively. Acute toxicity predicted for chronic: Acute Grade 2-3 rectal toxicity (p < 0.001) including any acute rectal Grade 2-3 tenesmus (p = 0.02) and pain (p = 0.008) were significant predictors of chronic Grade > or =2 rectal toxicity. Any acute rectal toxicity (p = 0.001), any acute tenesmus (p = 0.03), and any acute diarrhea (p < 0.001) were also found to be predictive for chronic toxicity, as continuous variables. Dose-volume histogram predicted for chronic toxicity: Rectal wall absolute and relative V50, V60, V66.6, V70, and V72 and rectal solid relative V60-V72 were significantly associated with chronic Grade > or =2 rectal toxicity both as categorical and continuous variables (t test, linear regression) and when divided into subgroups (chi-square table). The chronic rectal toxicity Grade > or =2 risk was 9%, 18%, and 25% for the rectal wall relative V70 <15%, 25%-40%, and >40% respectively. The volume of rectum or rectal wall radiated to > or =50 Gy was a strong predictor for chronic rectal toxicity. Nonpredictive factors: Rectal solid/wall absolute or relative volumes irradiated to < or =40 Gy, dose level, and use of androgen deprivation were not found predictive.

CONCLUSIONS

In our ART dose escalation study, rectal wall or rectum relative > or =V50 are closely predictive for chronic rectal toxicity. If rectal dose-volume histogram constraints are used to select the dose level, the risk of chronic rectal toxicity will reflect the risk of toxicity of the selected constraint rather than the dose selected as found in our study using an adaptive process. To select the prescribed dose, different dose-volume histogram constraints may be used including the rectal wall V70. Patients experiencing acute rectal toxicity are more likely to experience chronic toxicity.

Phase II dose escalation study of image-guided adaptive radiotherapy for prostate cancer: Use of dose–volume constraints to achieve rectal isotoxicity

PURPOSE

In our Phase II prostate cancer Adaptive Radiation Therapy (ART) study, the highest possible dose was selected on the basis of normal tissue tolerance constraints. We analyzed rectal toxicity rates in different dose levels and treatment groups to determine whether equivalent toxicity rates were achieved as hypothesized when the protocol was started.

METHODS AND MATERIALS

From 1999 to 2002, 331 patients with clinical stage T1 to T3, node-negative prostate cancer were prospectively treated with three-dimensional conformal adaptive RT. A patient-specific confidence-limited planning target volume was constructed on the basis of 5 CT scans and 4 sets of electronic portal images after the first 4 days of treatment. For each case, the rectum (rectal solid) was contoured in its entirety. The rectal wall was defined by use of a 3-mm wall thickness (median volume: 29.8 cc). The prescribed dose level was chosen using the following rectal wall dose constraints: (1) Less than 30% of the rectal wall volume can receive more than 75.6 Gy. (2) Less than 5% of the rectal wall can receive more than 82 Gy. Low-risk patients (PSA < 10, Stage < or = T2a, Gleason score < 7) were treated to the prostate alone (Group 1). All other patients, intermediate and high risk, where treated to the prostate and seminal vesicles (Group 2). The risk of chronic toxicity (NCI Common Toxicity Criteria 2.0) was assessed for the different dose levels prescribed. HIC approval was acquired for all patients. Median follow-up was 1.6 years.

RESULTS

Grade 2 chronic rectal toxicity was experienced by 34 patients (10%) (9% experienced rectal bleeding, 6% experienced proctitis, 3% experienced diarrhea, and 1% experienced rectal pain) at a median interval of 1.1 year. Nine patients (3%) experienced grade 3 or higher chronic rectal toxicity (1 Grade 4) at a median interval of 1.2 years. The 2-year rates of Grade 2 or higher and Grade 3 or higher chronic rectal toxicity were 17% and 3%, respectively. No significant difference by dose level was seen in the 2-year rate of Grade 2 or higher chronic rectal toxicity. These rates were 27%, 15%, 14%, 17%, and 24% for dose levels equal to or less than 72, 73.8, 75.6, 77.4, and 79.2 Gy, respectively (p = 0.3). Grade 2 or higher chronic rectal bleeding was significantly greater for Group 2 than for Group 1, 17% vs. 8% (p = 0.035).

CONCLUSIONS

High doses (79.2 Gy) were safely delivered in selected patients by our adaptive radiotherapy process. Under the rectal dose-volume histogram constraints for the dose level selection, the risk of chronic rectal toxicity is similar among patients treated to different dose levels. Therefore, rectal chronic toxicity rates reflect the dose-volume cutoff used and are independent of the actual dose levels. On the other hand, a larger PTV will increase the rectal wall dose and chronic rectal toxicity rates. PTV volume and dose constraints should be defined, considering their potential benefit.