The impact of postimplant edema on the urethral dose in prostate brachytherapy

DVH-Based Inverse Planning Using Monte Carlo Dosimetry for LDR Prostate Brachytherapy

PURPOSE

Inverse planning is an integral part of modern low-dose-rate brachytherapy. Current clinical planning systems do not exploit the total dose information and largely use the American Association of Physicists in Medicine TG-43 dosimetry formalism to ensure clinically acceptable planning times. Thus, suboptimal plans may be derived as a result of TG-43-related dose overestimation and nonconformity with dose distribution requirements. The purpose of this study was to propose an inverse planning approach that can improve planning quality by combining dose-volume information and precision without compromising the overall execution times.

METHODS AND MATERIALS

The dose map was generated by accumulating precomputed Monte Carlo (MC) dose kernels for each candidate source implantation site. The MC computational burden was reduced by using graphics processing unit acceleration, allowing accurate dosimetry calculations to be performed in the intraoperative environment. The proposed dose-volume histogram (DVH) fast simulated annealing optimization algorithm was evaluated using clinical plans that were delivered to 18 patients who underwent low-dose-rate prostate brachytherapy.

RESULTS

Our method generated plans in 37.5 ± 3.2 seconds with similar prostate dose coverage, improved prostate dose homogeneity of up to 6.1%, and lower dose to the urethra of up to 4.0%.

CONCLUSIONS

A DVH-based optimization algorithm using MC dosimetry was developed. The inclusion of the DVH requirements allowed for increased control over the optimization outcome. The optimal plan's quality was further improved by considering tissue heterogeneity.

Comparison of urethral diameters for calculating the urethral dose after permanent prostate brachytherapy

PURPOSE

No studies have yet evaluated the effects of a dosimetric analysis for different urethral volumes. We therefore evaluated the effects of a dosimetric analysis to determine the different urethral volumes.

METHODS

This study was based on computed tomography/magnetic resonance imaging (CT/MRI) combined findings in 30 patients who had undergone prostate brachytherapy. Postimplant CT/MRI scans were performed 30 days after the implant. The urethra was contoured based on its diameter (8, 6, 4, 2, and 0 mm). The total urethral volume-in cubic centimeters [UrV150/200(cc)] and percent (UrV150%/200%), of the urethra receiving 150% or 200% of the prescribed dose-and the doses (UrD90/30/5) in Grays to 90%, 30%, and 5% of the urethral volume were measured based on the urethral diameters.

RESULTS

The UrV150(cc) and UrD30 were statistically different between the of 8-, 6-, 4-, 2-, and 0-mm diameters, whereas the UrD5 was statistically different only between the 8-, 6-, and 4-mm diameters. Especially for UrD5, there was an approximately 40-Gy difference between the mean values for the 8- and 0-mm diameters.

CONCLUSION

We recommend that the urethra should be contoured as a 4- to 6-mm diameter circle or one side of a triangle of 5-7 mm. By standardizing the urethral diameter, the urethral dose will be less affected by the total urethral volume.

The influence of geometrical changes on the dose distribution after I-125 seed implantation of the prostate

PURPOSE

After prostate implantation, dose calculation is usually based on a single imaging session, assuming no geometrical changes occur during the months of dose accumulation. In this study, the effect of changes in anatomy and implant geometry on the dose distribution was investigated.

MATERIALS AND METHODS

One day, 1 month and 312 months after seed implantation, a combined TRUS-CT scan was made of 13 patients. Based on these scans changes in dose rate distribution were determined in prostate, urethra and bladder and a 'geometry corrected' dose distribution was estimated.

RESULTS

When based on the day-1 scan, parameters representing high dose volumes in prostate and urethra were largely underestimated: V150 of the prostate 18+/-10% and V120 of the urethra 47+/-32%. The dose to a 2cm(3) hotspot in the bladder wall (D2cc), however, was overestimated by 31+/-35%. Parameters based on scans 1 month post-implant or later were all within +/-5% of geometry corrected values.

CONCLUSION

Values meant to indicate the adequacy of dose coverage of the prostate, V100 and D90, were not influenced by geometrical changes and were independent of the post-implant scan date. Other parameters representing high dose volumes changed strongly within the first month after implantation.

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.

Factors predicting for urinary incontinence after prostate brachytherapy

PURPOSE

To define risk factors that predict for urinary incontinence after (125)I prostate brachytherapy.

METHODS AND MATERIALS

Urinary incontinence after (125)I prostate brachytherapy was evaluated using a patient self-assessment questionnaire based on the NCI Common Toxicity Criteria (version 2). Grade 0 is defined as no incontinence; Grade 1 incontinence occurs with coughing, sneezing, or laughing; Grade 2 is spontaneous incontinence with some control; and Grade 3 is no control. One hundred fifty-three patients received monotherapy (145 Gy) (125)I implants between October 1996 and December 2001, and 112 (75%) responded to our survey. Median follow-up was 47 months (range, 14-74 months). Patient characteristics included a preimplant prostate-specific antigen < or =10, Gleason score < or =6, and stage < or =T2b. CT-based postimplant dosimetry was analyzed approximately 30 days after the procedure, and dose-volume histograms of the prostate and the prostatic urethra were generated based on contoured volumes. Dosimetric parameters evaluated as predictive factors for incontinence included the prostate volume; total activity implanted; number of needles; number of seeds; seed activity; urethral D(5), D(10), D(25), D(50), D(75), and D(90) doses; prostate D(90) doses; and prostate V(100), V(200), and V(300). Clinical parameters evaluated included age, Gleason score, prostate-specific antigen, preimplant International Prostate Symptom Score (I-PSS), and length of follow-up.

RESULTS

Urethral D(10) dose and preimplant I-PSS predicted for urinary incontinence on multivariate analysis (p = 0.002 and p = 0.003, respectively). Twenty-eight patients reported Grade 1 incontinence (26%), and 5 patients reported Grade 2 (5%). Patients with Grade 1 and 2 incontinence were analyzed together, because of the small number of patients who experienced Grade 2. No patients reported Grade 3 incontinence. Mean urethral D(10) was 314 +/- 78 Gy in patients with Grade 0 compared with 394 +/- 147 Gy in patients with Grades 1, 2 incontinence (p = 0.002). The incidence of incontinence doubled as the urethral D(10) dose increased above 450 Gy. Patients with Grade 0 had a mean preimplant I-PSS score of 6.6 +/- 4.5 compared with 10.0 +/- 6.4 for Grades 1, 2 (p = 0.003). A significant increase in the incidence of incontinence was noted when the preimplant I-PSS was greater than 15. No relationship was noted between incontinence and prostate volume, total activity implanted, or the number of needles used (p = 0.83, p = 0.89, p = 0.36, respectively).

CONCLUSION

Urethral D(10) dose and preimplant I-PSS are predictive for patients at higher risk of urinary incontinence. To decrease the risk of this complication, an effort should be made to keep the urethral D(10) dose as close to the prescribed dose as possible, and the preimplant I-PSS should be thoroughly evaluated in an attempt to select patients with scores less than 15.

A Spanner in the works: the use of a new temporary urethral stent to relieve bladder outflow obstruction after prostate brachytherapy

PURPOSE

Assessment of the Spanner, a new temporary urethral stent to relieve bladder outflow obstruction and urinary symptoms after brachytherapy.

METHODS AND MATERIALS

Five patients with unusually severe urinary morbidity after (125)I brachytherapy were recruited. The mean time after implant was 40 days (range 25-90). Spanner intraprostatic stents were introduced using topical anesthetic without complication.

RESULTS

All patients were able to void spontaneously with no post-void residual volume of urine. The flow rates increased in all cases (p=0.03) and the International Prostate Symptom Scores were significantly improved after stent insertion in all patients (p=0.03). All patients experienced some degree of pain or dysuria during stent use.

CONCLUSIONS

Bladder outflow obstruction was effectively treated with the Spanner intraprostatic stent, however pain limited the use of the device in the early post-brachytherapy patient group. Pharmacotherapy, stent design modification, or smaller stent diameter may increase the utility of stents after brachytherapy.

Dosimetric consequences of using a surrogate urethra to estimate urethral dose after brachytherapy for prostate cancer

PURPOSE

To assess the accuracy and dosimetric consequences of defining a surrogate urethra at the geometric center of the prostate in postimplant CT scans.

METHODS AND MATERIALS

Eighty postimplant CT scans were obtained with a Foley catheter in place at Day 0 and at 1 month for 40 patients who had undergone (125)I prostate brachytherapy. The percentage of urethral volume receiving at least 275% of the prescribed dose (uV(275)), uV(250), uV(200), uV(150), maximal dose received by 90% of urethral volume (uD(90)), uD(70), uD(30), and uD(1) were measured for the Foley catheter and surrogate urethra. The distance between the Foley catheter and surrogate urethra was measured at the base, middle, and apex of the prostate.

RESULTS

A statistically significant difference was found in all the above-listed dosimetric parameters between the Foley catheter and surrogate urethra at Day 0 (p <or= 0.001). At 1 month, the uD(90), uD(70), and uD(1) remained significantly different between the Foley catheter and surrogate urethra (p <or= 0.05). The difference in the uV(275) (p = 0.055) and uV(150) (p = 0.059) between the Foley catheter and surrogate urethra showed a trend toward statistical significance at 1 month. The uV(250), uV(200), and uD(30) were greater for the surrogate urethra than for the Foley catheter at 1 month, but were not significantly different statistically. The mean distance between the Foley catheter and the surrogate urethra was greatest at the base (1.2 cm) in the vertical axis at Day 0 and decreased substantially to 0.87 cm at 1 month (p = 0.0004).

CONCLUSION

Using a surrogate urethra at the geometric center of the prostate may significantly overestimate the urethral dose at Day 0 and certain dosimetric parameters at 1 month. An alternative position for a surrogate urethra accounting for the difference in the location of the Foley catheter near the base of the prostate at Day 0 and 1 month could be considered in future studies.

Image guidance for precise conformal radiotherapy

PURPOSE

To review the state of the art in image-guided precision conformal radiotherapy and to describe how helical tomotherapy compares with the image-guided practices being developed for conventional radiotherapy.

MATERIALS AND METHODS

Image guidance is beginning to be the fundamental basis for radiotherapy planning, delivery, and verification. Radiotherapy planning requires more precision in the extension and localization of disease. When greater precision is not possible, conformal avoidance methodology may be indicated whereby the margin of disease extension is generous, except where sensitive normal tissues exist. Radiotherapy delivery requires better precision in the definition of treatment volume, on a daily basis if necessary. Helical tomotherapy has been designed to use CT imaging technology to plan, deliver, and verify that the delivery has been carried out as planned. The image-guided processes of helical tomotherapy that enable this goal are described.

RESULTS

Examples of the results of helical tomotherapy processes for image-guided intensity-modulated radiotherapy are presented. These processes include megavoltage CT acquisition, automated segmentation of CT images, dose reconstruction using the CT image set, deformable registration of CT images, and reoptimization.

CONCLUSIONS

Image-guided precision conformal radiotherapy can be used as a tool to treat the tumor yet spare critical structures. Helical tomotherapy has been designed from the ground up as an integrated image-guided intensity-modulated radiotherapy system and allows new verification processes based on megavoltage CT images to be implemented.

Feasibility of insertion/implantation of 2.0-mm-diameter gold internal fiducial markers for precise setup and real-time tumor tracking in radiotherapy

PURPOSE

To examine the feasibility and reliability of insertion of internal fiducial markers into various organs for precise setup and real-time tumor tracking in radiotherapy (RT).

MATERIALS AND METHODS

Equipment and techniques for the insertion of 2.0-mm-diameter gold markers into or near the tumor were developed for spinal/paraspinal lesions, prostate tumors, and liver and lung tumors. Three markers were used to adjust the center of the mass of the target volume to the planned position in spinal/paraspinal lesions and prostate tumors (the three-marker method). The feasibility of the marker insertion and the stability of the position of markers were tested using stopping rules in the clinical protocol (i.e., the procedure was abandoned if 2 of 3 or 3 of 6 patients experienced marker dropping or migration). After the evaluation of the feasibility, the stability of the marker positions was monitored in those patients who entered the dose-escalation study.

RESULTS

Each of the following was shown to be feasible: bronchoscopic insertion for the peripheral lung; image-guided transcutaneous insertion for the liver; cystoscopic and image-guided percutaneous insertion for the prostate; and surgical implantation for spinal/paraspinal lesions. Transcutaneous insertion of markers for spinal/paraspinal lesions and bronchoscopic insertion for central lung lesions were abandoned. Overall, marker implantation was successful and was used for real-time tumor tracking in RT in 90 (90%) of 100 lesions. No serious complications related to the marker insertion were noted for any of the 100 lesions. Using three markers surgically implanted into the vertebral bone, the mean +/- standard deviation in distance among the three markers was within 0.2 +/- 0.6 mm (range -1.4 to 0.8) through the treatment period of 30 days. The distance between the three markers gradually decreased during RT in five of six prostate cancers, consistent with a mean rate of volume regression of 9.3% (range 0.015-13%) in 10 days.

CONCLUSIONS

Internal 2.0-mm-diameter gold markers can be safely inserted into various organs for real-time tumor tracking in RT using the prescribed equipment and techniques. The three-marker method has been shown to be a useful technique for precise setup for spinal/paraspinal lesions and prostate tumors.

The effects of edema on urethral dose following palladium-103 prostate brachytherapy

The effects of edema on urethral dose after interstitial prostate brachytherapy with palladium-103 (103Pd) were studied. Fifty patients underwent a 90-Gy 103Pd implant followed by dosimetric computed tomography (CT). Twenty-one days later, a Foley catheter was reinserted and a dosimetric CT was repeated. The mean reduction in prostate volume between day 0 and day 21 was 16%. Median prostate D90 on day 0 was 89.7 Gy (range 59.5 to 127) and 99.5 Gy (range 62.5 to 130) on day 21. Median prostate V100 was 90% (range 63 to 98%) on day 0 and 96% (range 66 to 99%) on day 21. Median V150 was 61% (range 31 to 85%) on day 0 and 75% (range 39 to 93%) on day 21. Median urethral D50 was 107 Gy (range 57 to 201) on day 0 and 126 Gy (range 64 to 193) on day 21. Regression analysis demonstrated a significant correlation between the decrease in the prostate volume and the increased urethral D50 (r 0.58, p < 0.05). Acute urinary toxicity was 32% grade 0, 38% grade 1, and 30% grade 2. The median urethral D50 increased by a mean of 18% with a correlation coefficient of 0.58 (p < 0.05). Catheterization of the urethra was well tolerated and was of value in better characterizing urethral dose after 103Pd brachytherapy.

Urethral and periurethral dosimetry in prostate brachytherapy: is there a convenient surrogate?

PURPOSE

To assess and compare two models for a surrogate urethra to be used for postimplant dosimetry in prostate brachytherapy.

METHODS AND MATERIALS

Twenty men with a urinary catheter present at the time of postimplant computed tomographic imaging were studied. Urethral and periurethral volumes were defined as 5-mm and 10-mm diameter volumes, respectively. Three contours of each were used: one contour of the true urethra (and periurethra), and two surrogate models. The true volumes were centered on the catheter center. One surrogate model used volumes centered on the geometrical center of each prostate contour (centered surrogate). The other surrogate model was based on the average deviation of the true urethra from a reference line through the geometrical center of the axial midplane of the prostate (deviated surrogate). Maximum point doses and the D(10), D(25), D(50), D(90), V(100), V(120), and V(150) of the true and surrogate volumes were measured and compared (D(n) is the minimum dose [Gy] received by n% of the structure, and V(m) is the volume [%] of the structure that received m% of the prescribed dose) as well as the distances between the surrogate urethras and the true urethra.

RESULTS

Doses determined from both surrogate urethral and periurethral volumes were in good agreement with the true urethral and periurethral doses except in the superior third of the gland. The deviated surrogate provided a physically superior likeness to the true urethra. Certain dose-volume histogram (DVH)-based parameters could also be predicted reasonably well on the basis of the surrogates. Correlation coefficients > or =0.85 were seen for D(25), D(50), V(100), V(120), and V(150) for both models. All the other parameters had correlation coefficients in the range of 0.73 - 0.85.

CONCLUSIONS

Both surrogate models predicted true urethral dosimetry reasonably well. It is recommended that the simpler deviated surrogate would be a more suitable surrogate for routine clinical practice.

Impact of postimplant edema on V(100) and D(90) in prostate brachytherapy: can implant quality be predicted on day 0?

PURPOSE

To determine the effect of edema on the dosimetric parameters V(100) (percentage of prostate volume that received a dose equal to or greater than the prescribed dose) and D(90) (minimal dose delivered to 90% of prostate volume) in 125I prostate brachytherapy and to determine whether the edema can be used to predict implant quality on the day of the implant (Day 0).

METHODS AND MATERIALS

Fifty consecutive patients treated with (125)I implants who had two postimplant CT scans were selected for this study. The mean interval between the studies was 46 +/- 23 days. The implants were preplanned to deliver 150 Gy to the prostate plus a 3-5-mm symmetric dose margin using peripherally loaded 0.4-0.6-mCi (NIST-99) (125)I seeds. A dose-volume histogram was compiled for each postimplant CT scan. The V(100) and D(90) from the first and second CT scans were compared to determine the effect of edema on these parameters. A multivariate regression analysis was performed to define the linear relationships for predicting the V(100) or D(90) at 30-60 days after implant from the magnitude of the edema and the values of V(100) and D(90) on Day 0.

RESULTS

V(100) and D(90) increased by 5% +/- 6% and 15% +/- 17%, respectively, during the interval between the first and second postimplant CT scans. The mean edema was 1.53 +/- 0.20. The increases in V(100) and D(90) were found to be proportional to the edema and the values of V(100) and D(90) on Day 0. The increase in V(100) was also found to depend on the width of the preplan dose margin. Linear relationships were derived that predict the V(100) and D(90) at 30-60 days after implant with a standard error of +/-4% and +/-24 Gy, respectively.

CONCLUSION

V(100) and D(90) increased by 5% +/- 6% and 15% +/- 17%, respectively, during the first 30-60 days after implant. The results of a multivariate linear regression analysis showed that the increases in V(100) and D(90) were proportional to both the magnitude of the edema and the values of these parameters on Day 0. The relationships derived by linear regression analysis predict V(100) and D(90) at 30-60 days after implant to within +/-4% and +/-24 Gy, respectively. However, predicting the 30-60-day V(100) and D(90) on Day 0 is a poor substitute for obtaining a 30-60-day CT scan, because the uncertainty in the predicted values is greater by a factor of > or =2. Nevertheless, on average, the predicted values should provide a more reliable estimate of the actual V(100) and D(90) than the Day 0 values that ignore the effect of edema altogether. The increase in V(100) was also found to depend on the width of the preplan dose margin; therefore, our results for V(100) are only valid for implants planned with a 3-5-mm margin.

A comparison of permanent prostate brachytherapy techniques: preplan vs. hybrid interactive planning with postimplant analysis

PURPOSE

To compare preparation time, procedure time in the operating room, equipment needs, and Day 0 postimplant dosimetry between two different Mick implant techniques performed at a single institution.

METHODS AND MATERIALS

One hundred consecutive monotherapy patients treated from 1999 to 2000 with 125I transperineal permanent implantation of the prostate using an afterloading Mick applicator were evaluated. The first 40 patients were treated with a preplanned modified peripheral loading Mick technique. The next 60 were treated with a hybrid interactive image-guided Mick technique. The analysis included planning the following: ultrasound volume, time required of preplanning, Day 0 CT volume, number of seeds, number of needles, activity per seed, total activity of the implant, and procedure time. Dosimetric parameters included D(90), V(100), and V(150).

RESULTS

Mean planning ultrasound volume (33 vs. 37 cc), Day 0 CT volume (49 vs. 47 cc), mCi/seed (0.30 vs. 0.34 mCi/seed), number of seeds (121 vs. 96), total activity of the implant (36 vs. 32 mCi), D(90) (132 vs. 149 Gy), V(100) (86% vs. 91%), and V(150) (51% vs. 38%) were comparable. Significant differences (p < 0.01) were noted in mean preplan time (30 vs. 7 min), number of needles (32 vs. 19), and procedure time (90 vs. 40 min).

CONCLUSIONS

Hybrid interactive Mick prostate brachytherapy consistently reduces preplanning time, procedure time, and number of needles used, reducing patient treatment time and costs while maintaining excellent dosimetric coverage. Use of hybrid interactive Mick prostate brachytherapy results in improved therapeutic ratios, i.e., maintains Day 0 D(90) >140 Gy, V(100) >90%, and V(150) <40%, without the need for sophisticated three-dimensional intraoperative planning technology.

Predictive factors of urinary retention following prostate brachytherapy

PURPOSE

To evaluate the incidence and duration of urinary retention requiring catheterization and the factors predictive for these end points.

METHODS AND MATERIALS

Two hundred eighty-two patients treated with prostate brachytherapy alone were evaluated. Clinical and treatment-related factors examined included: age, baseline International Prostate Symptom Score (IPSS), presence of comorbidity, planning ultrasound target volume (PUTV), postimplant prostate CT scan volume, the CT:PUTV ratio, number of seeds inserted, number of needles used, use of neoadjuvant hormones, procedural physician, clinical stage, Gleason score, and pretreatment PSA. Dosimetric quality indicators were also examined.

RESULTS

Urinary obstruction after prostate brachytherapy developed in 43 (15%) patients. The median duration of catheter insertion was 21 days (mean 49, range 1-365). Univariate analysis demonstrated that presence of diabetes, preimplant volume, postimplant volume, CT:PUTV ratio, number of needles, and dosimetric parameters were predictive for catheterization. However, in multivariate analysis, only the baseline IPSS, CT:PUTV ratio, and presence of diabetes were significant independent predictive factors for catheterization.

CONCLUSION

Baseline IPSS was the most important predictive factor for postimplantation catheterization. The extent of postimplant edema, as reflected by the CT:PUTV ratio, predicted for need and duration of catheterization. The presence of diabetes was predictive for catheterization, but may relate to the absence of prophylactic steroids, and therefore requires further evaluation.

Prostate brachytherapy: comparison of dose distribution with different 125I source designs

PURPOSE

To evaluate the interchangeability of various commercially available iodine 125 ((125)I) sources and to assess the dosimetric effect of a change in source.

MATERIALS AND METHODS

A modified peripherally loading prostate brachytherapy plan to deliver 145 Gy was devised by using a model (125)I source, which until recently was the only available (125)I source. A dose-volume histogram was generated. By using the available radial dose functions and anisotropy distributions for eight other currently commercially available sources, the same implant placement was planned and dose-volume histogram distributions tabulated. This exercise was performed for 15-, 45-, and 60-cm(3) glands. No implants were placed, and no physical radiation measurements were made. Dose calculations were theoretic: They were generated by using a widely available treatment planning system.

RESULTS

There was little difference in dose distribution to the volume receiving 100% of the prescribed dose (<6%); only one source showed a difference greater than 2%. Large differences, up to -40% to +60%, were seen in the volume of tissue encompassed within internal high-dose regions receiving 150% or 200% of the prescribed dose. These findings held true, irrespective of gland size, within a clinically relevant range (15-60 cm(3)) and for a uniformly loaded radionuclide distribution.

CONCLUSION

Reviewing only peripheral dose at or near the prescription dose of 145 Gy revealed little difference in doses for various source designs. Marked differences in high-dose regions were seen and may affect the dose received by internal sites. Effects of these changes on cure and/or complications remain speculative.