Comparison of methods for calculating rectal dose after (125)I prostate brachytherapy implants

Rectal toxicity and rectal dosimetry in low-dose-rate (125)I permanent prostate implants: a long-term study in 1006 patients

OBJECTIVE

To describe the acute and late rectal toxicity in 1006 prostate brachytherapy patients implanted 1998-2003. To determine whether rectal dose-volume histogram as well as patient and treatment factors were associated with rectal toxicity.

METHODS AND MATERIALS

Median followup was 60.7 months. Rectal dosimetry was calculated as dose-volume histogram of the rectum using Day 28 CT-based dosimetry and expressed as volume of the rectum in cc receiving 50%, 100%, and 150% of the prescription dose (VR(50cc), VR(100cc), and VR(150cc), respectively). Univariate and multivariate analyses were performed to examine the influence of patient, implant, dosimetry, and learning curve factors on the development of acute and late toxicities using a modified Radiation Therapy Oncology Group (RTOG) scale. Acute toxicity was analyzed using logistic regression and late toxicity using Cox proportional hazards regression. Analysis of variance was used to examine the association between rectal toxicity and rectal dose.

RESULTS

Rectal dosimetry in 93.5% and rectal toxicity in 96.2% have been recorded. Median VR(100)=1.05cc. Late RTOG Grades 0, 1, 2, 3, and 4 were recorded in 68%, 23%, 7.3%, 0.9%, and 0.2% patients, respectively. On multivariate analysis, acute RTOG ≥2 rectal toxicity was associated with urinary retention (p=0.036) and learning curve (p=0.015); late RTOG ≥2 was associated with the presence of acute toxicity (p=0.0074), higher VR(100) (p=0.030) and learning curve (p=0.027).

CONCLUSIONS

Late rectal RTOG ≥2 rectal toxicity in this cohort was 8%. Increased VR(100), presence of acute rectal toxicity, and learning curve were associated with higher rate of late RTOG ≥2 toxicity. Severe late rectal toxicity after prostate brachytherapy was rare.

Evaluation of rectal bleeding factors associated with prostate brachytherapy

PURPOSE

To analyze rectal bleeding prognostic factors associated with prostate brachytherapy (PB) or in combination with external-beam radiation therapy (EBRT) and to examine dosimetric indications associated with rectal bleeding.

MATERIALS AND METHODS

The study included 296 patients followed up for >36 months (median, 48 months). PB was performed alone in 252 patients and in combination with EBRT in 44 patients. PB combined with EBRT is indicated for patients with a Gleason score >6. The prescribed dose was 144 Gy for monotherapy and 110 Gy for PB + EBRT (44-46 Gy).

RESULTS

Although 9.1% who received monotherapy had 2.3% grade 2 rectal bleeding, 36.3% who received combined therapy had 15.9% grade 2 rectal bleeding. Combined therapy was associated with higher incidence of rectal bleeding (P = 0.0049) and higher percentage of grade 2 bleeding (P = 0.0005). Multivariate analysis revealed that R-150 was the only significant factor for rectal bleeding, and modified Radiation Therapy Oncology Group (RTOG) grade in monotherapy and biologically equivalent dose (BED) were significant for combined therapy. Moreover, grade 2 rectal bleeding increased significantly at D90 > 130 Gy.

CONCLUSION

Although R-150 was the significant prognostic factor for rectal bleeding and modified RTOG rectal toxicity grade, BED was the significant prognostic factor for modified RTOG rectal toxicity grade.

Rectal Morbidity Following I-125 Prostate Brachytherapy in Relation to Dosimetry

BACKGROUND

To investigate rectal morbidity after I-125 prostate brachytherapy and to analyze predictive factors of rectal morbidity.

METHODS

A group of 227 consecutive patients with localized prostate cancer were treated with I-125 prostate brachytherapy with or without external beam radiotherapy (EBRT) between September 2003 and January 2005. Rectal morbidity (diarrhea, bleeding and pain) was evaluated using the Radiation Therapy Oncology Group (RTOG) criteria. Dosimetry was based on computerized tomography (CT) scan 1 month post-implant. The clinical, treatment-related and dosimetric factors were evaluated for the risk of grade 2 rectal morbidity. Rectal dosimetric factors included the rectal volume that received >100% and 150% of the prescribed dose, and the maximal rectal dose which was defined as the sum of the minimal dose received by 1% of the rectum volume and the prescribed dose of EBRT.

RESULTS

Grade 2 rectal bleeding occurred in 10 (4.4%): for nine patients within the first year and for one patient between the first and second year. Grade 2 diarrhea occurred in one patient (0.4%) within the first year. No patient reported grade 2 pain. In the univariate analysis with grade 2 rectal bleeding, there were significant correlations with number of seeds, supplemental EBRT, and all of the rectal dosimetric parameters. On subsequent multivariate analysis, the only significant factor was the maximal rectal dose (P < 0.001). Rectal dose > 160 Gy was correlated to grade 2 rectal morbidity. All the patients with rectal dose > 160 Gy received EBRT.

CONCLUSIONS

Manifestations of rectal morbidity are acceptable events after I-125 prostate brachytherapy. Rectal dose-volume histogram for the brachytherapy is a predictive method for assessing the risk of developing grade 2 rectal bleeding. Delivery of the rectal dose should not exceed 160 Gy in order to avoid rectal complications.

Prostate brachytherapy postimplant dosimetry: A comparison of suture-embedded and loose seed implants

PURPOSE

To compare postimplant dosimetry and seed embolization rates for prostate brachytherapy implants using suture-embedded and loose seeds.

METHODS AND MATERIALS

Dosimetric analysis of the whole prostate, prostate quadrants, rectum, and surrogate urethra was performed on 54 loose seed and 81 RAPIDStrand (RS) patients. Seed embolization rates were determined from chest radiographs.

RESULTS

Whole prostate V100 and D90 did not differ significantly for the loose seed (V100 = 90.5%, D90 =153.2 Gy) and RS groups (V100 = 91.5%, D90 = 151.6 Gy) (p = 0.43 and 0.65, respectively), but V150, V200, and contiguous V200 were higher (p < or = 0.003) for the RS group (59.9%, 28.3%, and 23.2%, respectively) than the loose seed group (52.5%, 22.8%, and 16.1%, respectively). Extraprostatic measures (conformity index and external index) were also different at the p < 0.05 level. The embolization rate was 40% in the loose seed group and 14% in the RS group.

CONCLUSIONS

The most significant difference between the two study groups was a decrease in the embolization rate. Although some statistically significant changes in postimplant dosimetry were observed, they were nevertheless small.

Rectal toxicity profile after transperineal interstitial permanent prostate brachytherapy: Use of a comprehensive toxicity scoring system and identification of rectal dosimetric toxicity predictors

PURPOSE

To better understand rectal toxicity after prostate brachytherapy, we employed the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE version 3.0), a comprehensive system with distinct and separately reported gastrointestinal adverse event items (unlike Radiation Therapy Oncology Group morbidity scoring), to evaluate item-specific postimplant rectal toxicities.

METHODS AND MATERIALS

We analyzed 135 patients treated with brachytherapy +/- hormonal therapy, using CTCAE v3.0 to score acute/late rectal toxicities (median follow-up, 41 months). Dosimetric parameters were evaluated for ability to predict toxicities.

RESULTS

Use of CTCAE yielded a novel rectal toxicity profile consisting of diarrhea, incontinence, urgency, proctitis, pain, spasms, and hemorrhage event rates. No item had a < 5% Grade 1-2 acute toxicity rate (except spasms). Rectal dosimetry predicted late toxicities: for diarrhea, 5% Grade 1 toxicity rate for %V25 (percent of rectal volume receiving 25% of prescribed prostate dose) < or = 25% vs. 60% for %V25 > 25% (p < 0.001); for maximum toxicity, 10% Grade 1 toxicity rate for %V10 < or = 40% vs. 44% for %V10 > 40% (p = 0.007).

CONCLUSIONS

A comprehensive understanding of item-specific postimplant rectal toxicities was obtained using CTCAE. Rectal %V25 > 25% and %V10 > 40% predicted worse late diarrhea and maximum toxicity, respectively.

Effect of post-implant edema on prostate brachytherapy treatment margins

PURPOSE

To determine if postimplant prostate brachytherapy treatment margins calculated on Day 0 differ substantially from those calculated on Day 30.

METHODS

Thirty patients with 1997 American Joint Commission on Cancer clinical stage T1-T2 prostatic carcinoma underwent prostate brachytherapy with I-125 prescribed to 144 Gy. Treatment planning methods included using loose seeds in a modified peripheral loading pattern and treatment margins (TMs) of 5-8 mm. Postimplant plain radiographs, computed tomography scans, and magnetic resonance scans were obtained 1-4 hours after implantation (Day 0). A second set of imaging studies was obtained at 30 days after implantation (Day 30) and similarly analyzed. Treatment margins were measured as the radial distance in millimeters from the prostate edge to the 100% isodose line. The TMs were measured and tabulated at 90 degrees intervals around the prostate periphery at 0.6-cm intervals. Each direction was averaged to obtain the mean anterior, posterior, left, and right margins.

RESULTS

The mean overall TM increased from 2.6 mm (+/-2.3) on Day 0 to 3.5 mm (+/-2.4) on Day 30. The mean anterior margin increased from 1.2 mm on Day 0 to 1.8 mm on Day 30. The posterior margin increased from 1.2 mm on Day 0 to 2.8 mm on Day 30. The lateral treatment margins increased most over time, with mean right treatment margin increasing from 3.9 mm on Day 0 to 4.7 mm on Day 30.

CONCLUSION

Treatment margins appear to be durable in the postimplant period, with a clinically insignificant increase from Day 0 to Day 30.

Rectal fistulas after prostate brachytherapy

PURPOSE

To compare the rectal and prostatic radiation doses for a prospective series of 503 patients, 44 of whom developed persistent rectal bleeding, and 2 of whom developed rectal-prostatic fistulas.

METHODS AND MATERIALS

The 503 patients were randomized and treated by implantation with 125I vs. 103Pd alone (n = 290) or to 103Pd with 20 Gy vs. 44 Gy supplemental external beam radiotherapy (n = 213) and treated at the Puget Sound Veterans Affairs Medical Center (n = 227), Schiffler Cancer Center (n = 242) or University of Washington (n = 34). Patients were treated between September 1998 and October 2001 and had a minimum of 24 months of follow-up. The patient groups were treated concurrently. Treatment-related morbidity was monitored by mailed questionnaires, using standard American Urological Association and Radiation Therapy Oncology Group criteria, at 1, 3, 6, 12, 18, and 24 months. Patients who reported Grade 1 or greater Radiation Therapy Oncology Group rectal morbidity were interviewed by telephone to clarify details regarding their rectal bleeding. Those who reported persistent bleeding, lasting for >1 month were included as having Grade 2 toxicity. Three of the patients with rectal bleeding required a colostomy, two of whom developed a fistula. No patient was lost to follow-up. The rectal doses were defined as the rectal volume in cubic centimeters that received >50%, 100%, 200%, or 300% of the prescription dose. The rectum was considered as a solid structure defined by the outer wall, without attempting to differentiate the inner wall or contents.

RESULTS

Persistent rectal bleeding occurred in 44 of the 502 patients, 32 of whom (73%) underwent confirmatory endoscopy. In univariate analysis, multiple parameters were associated with late rectal bleeding, including all rectal brachytherapy indexes. In multivariate analysis, however, only the rectal volume that received >100% of the dose was significantly predictive of bleeding. Rectal fistulas occurred in 2 patients (0.4%), both of whom had received moderate rectal radiation doses and extensive intervention for rectal bleeding.

CONCLUSION

Partly on the basis of data from others and data presented here, we believe that the incidence of rectal fistulas can be much lower than in our series. High rectal radiation doses should be avoided a priori, to minimize the likelihood of rectal bleeding, and hence the likelihood that invasive procedures will be performed.

I-125 Versus Pd-103 for Low-Risk Prostate Cancer

BACKGROUND

We tested the hypothesis that the shorter half-life of Pd-103 versus I-125 results in different late radiation-related morbidities following prostate brachytherapy.

METHODS

As of June 14th, 2002, 352 of a planned total of 600 patients with 1997 American Joint Committee on Cancer (AJCC) clinical stage T1c-T2a prostatic carcinoma (Gleason grade 2-6, PSA 4-10 ng/mL) had been randomized to implantation with I-125 (144 Gy, TG-43) or Pd-103 (125 Gy, NIST-99). Treatment-related morbidity was monitored by questionnaires based on standard American Urologic Association (AUA) and Radiation Therapy Oncology Group (RTOG) criteria that were mailed at 1, 3, 6, 12, 18, and 24 months after implant. The use of alpha-blockers to relieve obstructive symptoms was not controlled for but was noted at each follow-up point. All patients reported here had a minimum follow-up of 2 years. Dosimetric parameters analyzed included the V100, which was defined as the percentage of the postimplant prostate volume covered by 100% of the prescription dose. Rectal doses were expressed as the R100, defined as the rectal volume (cc) that received at least 100% of the prescription dose. Statistical comparisons were by Student's unpaired t-test at specified follow-up times.

RESULTS

The AUA scores peaked at the 1-month postimplant time point for both isotopes and gradually declined. The difference in AUA scores between patients who received I-125 versus those who received Pd-103 was greatest at 1 and 6 months following implantation. At 1 month, I-125 patients had a mean AUA score of 14.8 (+/-9.5) compared with 18.6 (+/-9.8) for the Pd-103 patients (P = 0.0009). By 6 months, mean AUA scores for the I-125 patients had decreased to 12.0 (+/-9.1) compared with 9.9 (+/-8.7) for the Pd-103 patients (P = 0.04). The use of alpha-blockers was similar between groups at all time points. Radiation proctitis (persistent bleeding) occurred in 29 of 314 patients (9%). There was an overall trend toward more proctitis in I-125 patients (P = 0.21). However, only four of the 163 patients (2%) with an R100 below the recommended 1.0 cc developed bleeding, which did not differ between isotopes (P = 0.49).

DISCUSSION

Patients treated with Pd-103 had more intense radiation prostatitis in the first month after implantation, but they recovered from their radiation-related symptoms sooner than I-125 patients, consistent with palladium's shorter half-life. The trend toward more proctitis in the I-125 patient group likely reflects their higher R100 values due to less rapid dose fall-off that can be overcome with judicious treatment planning and implant execution.

Factors predictive of rectal bleeding after 103Pd and supplemental beam radiation for prostate cancer

PURPOSE

To evaluate the contribution of various clinical and radiation treatment parameters to the likelihood of late rectal bleeding after brachytherapy plus supplemental beam radiation (EB).

METHODS

A total of 161 intermediate risk patients, with Gleason score 7 or higher and/or PSA 10-20 ng/ml randomized to implantation with (103)Pd (90 versus 115 Gy) with 44 versus 20 Gy EB (2 Gy/day) were studied. Beam radiation was delivered with a four-field arrangement designed to cover the prostate and seminal vesicles with a 2 cm margin (reduced to 1.0 cm posteriorly). Isotope implantation was performed by standard techniques, using a modified peripheral loading pattern. A postimplant CT scan (3 mm slice thickness) was obtained 1-4 h after implantation. Dose volume histograms of the prostate and rectum were calculated using the outer prostatic and rectal margins identified on CT scan by one investigator (KW). Rectal doses were expressed as the R100, R200, and R300, defined as the rectal volume (cc) that received at least 100%, 200%, or 300% of the prescription dose, respectively. External beam doses were expressed as EB75% (cc)-the volume of rectum that received 75% of the beam prescription dose. Treatment-related rectal morbidity was monitored by mailed questionnaires, using Radiation Therapy Oncology Group (RTOG) criteria, at 1, 3, 6, 12, 24, and 36 months. Patients who reported Grade 1 or higher RTOG morbidity were contacted by telephone to obtain more details regarding their rectal bleeding.

RESULTS

In univariate analysis, rectal bleeding was statistically related to the R100, R200, and R300 values, with p-values of 0.0055, 0.0007, and 0.012, respectively. Bleeding was not related to gap times, prostate size, patient age, V100 or D90 values. The EB75% values were similar in 44 Gy patients with or without late bleeding.

CONCLUSION

Considering the potential severity of rectal morbidities and their relationship to implant dose, we urge our colleagues to routinely monitor the rectal implant doses of their own patients to make sure that such doses are kept within an accepted range.

Perirectal seeds as a risk factor for prostate brachytherapy-related rectal bleeding

PURPOSE

To correlate rectal wall doses and perirectal seed numbers with late rectal bleeding after prostate brachytherapy.

METHODS AND MATERIALS

We studied 148 patients randomized to implantation with I-125 vs. Pd-103 at the VA Puget Sound HCS from 1998 through 2001 and for whom postimplant dosimetry was available. Implants were performed by standard techniques, using a modified peripheral loading pattern. A postimplant computed tomography (CT) scan (3 mm slice thickness) was obtained 1-4 h after implantation. Rectal doses were expressed as the R100, R200, and R300, defined as the rectal volume (cc) that received more than 100%, 200%, or 300% of the prescription dose, respectively. The rectum was considered to be a solid structure defined by the outer wall, without attempting to differentiate the inner wall or contents. In addition to conventional dose parameters, each patient's postimplant CT scan was reviewed for the number of seeds within 0, 0.1-2, and 2.1-4 mm of the outer rectal wall. The proximal edge of the seed was used for distance determinations from the outer rectal wall. Patients who reported Grade 1 or higher Radiation Therapy Oncology Group morbidity were contacted by telephone to obtain more details regarding their rectal bleeding. Those who reported persistent bleeding lasting for more than 1 month were categorized as Grade 2.

RESULTS

Patients had a wide range of rectal wall doses, with R100 values ranging from 0.0 to 10.4 cc (median, 0.95 cc). Similarly, the number of perirectal seeds within 0.0 to 2.0 mm of the rectum varied widely, ranging from 0 to 12 seeds (median: 1 seed). Seven patients (7 of 144 = 5%) developed persistent rectal bleeding, one of whom required a colostomy. Both rectal radiation doses and the number of perirectal seeds were higher in patients with persistent rectal bleeding. The number of perirectal seeds < or =2.0 mm of the rectal wall was higher in patients with rectal bleeding (p = 0.037), but the number of seeds 2-4 mm from the wall were not related (p = 0.72). In multivariate regression analysis including prostatic D90 (the dose that covers 90% of the postimplant prostate), preimplant transrectal ultrasound volume, R300, and the number of seeds < or =2 mm from the rectal wall as independent variables, only the R300 was statistically significantly associated with the likelihood of persistent rectal bleeding (p = 0.025).

CONCLUSION

A limited number of errant perirectal sources in itself does not appear to place patients at increased risk of rectal bleeding, providing that the overall rectal wall doses are within acceptable values.

Probability of late rectal morbidity in 125I prostate brachytherapy

PURPOSE

Rectal toxicity is a concern in prostate brachytherapy because it is difficult to avoid delivering a dose equal to, or greater than, the prescription dose to the anterior surface of the rectum. The purpose of this study was to define the probability that a patient will experience Grade 2 (bleeding/ulceration) late rectal morbidity after 125I prostate brachytherapy according to the rectal dosimetry.

METHODS AND MATERIALS

Ninety-eight consecutive patients who received monotherapy 125I prostate implants for treatment of Stage T1-T2, favorable-risk adenocarcinoma of the prostate were evaluated for Radiation Therapy Oncology Group Grade 2 late rectal morbidity. All reported incidences of late morbidity were retrospectively confirmed by colonoscopy. All patients had at least 15 months follow-up after implantation. The median follow-up was 32 months (range 15-54). The rectal dosimetry was based on a CT scan obtained at 3-9 weeks after implantation. The rectum was contoured on each CT image between the base and apex of the prostate. A dose-surface histogram was compiled for each implant, and the relative surface area that received a dose > or =100, > or =150, > or =200, > or =300, > or =400, and > or =500 Gy was recorded. The probability of developing late rectal toxicity was calculated by logistic regression analysis as a function of dose and the percentage of the rectal surface that received that dose.

RESULTS

Of the 98 patients, 10 developed Grade 2 late rectal morbidity. The percentage of the rectal surface that received 100, 150, 200, and 300 Gy was significantly greater (p < or =0.02) for patients who experienced late rectal morbidity. The probability of late rectal morbidity increased with both the dose and the percentage of the rectal surface that received that dose. The probability was < or =1% when 20%, 7%, and 0% of the rectal surface received 100, 150, and 200 Gy, respectively. The probability increased to < or =5% when 31%, 19%, and 9% of the rectal surface received these doses. The probability of late rectal morbidity can also be expressed in terms of the maximal rectal dose. The probability of late morbidity was 0.4%, 1.2%, and 4.7% when the maximal rectal dose was 150, 200, and 300 Gy, respectively.

CONCLUSION

The percentage of the rectal surface that receives a dose > or =100 Gy is predictive of Grade 2 (bleeding/ulceration) late rectal morbidity after 125I prostate brachytherapy. The probability of late morbidity depends on both the dose and the percentage of the rectal surface that received that dose. Our results indicate that the rectum can tolerate doses of 100, 150, and 200 Gy to approximately 30%, 20%, and 10% of the rectal surface with a < or =5% risk of late morbidity. Our results also indicate that the practical guideline for limiting the incidence of late morbidity to 1%, 3%, or 5% is to keep the maximal rectal dose to <200, 250, and 300 Gy, respectively.