|Year : 2015 | Volume
| Issue : 4 | Page : 639-644
The influence of the bowel and bladder preparation protocol for radiotherapy of prostate cancer using kilo-voltage cone beam CT: Our experience
SP Heng1, SH Low2, K Sivamany3
1 Radiotherapy Unit, Pantai Hospital Kuala Lumpur, 59100, Bukit Pantai, Kuala Lumpur, Malaysia
2 Cancer Institute, Pantai Hospital Kuala Lumpur, 59100, Bukit Pantai, Kuala Lumpur, Malaysia
3 University Sains, Malaysia
|Date of Web Publication||10-Mar-2016|
S P Heng
Radiotherapy Unit, Pantai Hospital Kuala Lumpur, 59100, Bukit Pantai, Kuala Lumpur
Source of Support: None, Conflict of Interest: None
The purpose of this study is to determine the influence of bladder and bowel preparation protocols on the dose-volume histograms (DVHs) of these organs using the cone beam computed tomography (CBCT)-based intensity modulated radiotherapy (IMRT) treatment planning for prostate cancer patients. The pelvic DVHs of 12 prostate cancer patients were studied using CBCT images obtained immediately before each treatment. Six patients had bladder and bowel preparation protocol whilst the other six patients were the control group. Contoured bladder and rectal volumes on CBCT images were compared with planning computed tomography. All patients were treated with IMRT with 7800 cGy in 39 fractions over 8 weeks. Compared with the patient with bladder preparation protocol, patients without bladder preparation instruction had higher bladder volume and dose variation. The maximum variation in bladder volume was as high as 98% in the control group. Without bowel preparation protocol, the rectal volumes were more variability. Owing to changes in rectal filling on the day of treatment, the maximum variation in rectal volume was as high as + 96%. With bowel preparation protocol, the maximum rectum volume variations were less than 25%. The changes in prostate target dose compared with planning dose were minimal as would be expected from positioning with daily image guidance and gold seed implanted.
Keywords: Bladder, cone beam computed tomography, prostate, rectum
|How to cite this article:|
Heng S P, Low S H, Sivamany K. The influence of the bowel and bladder preparation protocol for radiotherapy of prostate cancer using kilo-voltage cone beam CT: Our experience. Indian J Cancer 2015;52:639-44
|How to cite this URL:|
Heng S P, Low S H, Sivamany K. The influence of the bowel and bladder preparation protocol for radiotherapy of prostate cancer using kilo-voltage cone beam CT: Our experience. Indian J Cancer [serial online] 2015 [cited 2021 May 9];52:639-44. Available from: https://www.indianjcancer.com/text.asp?2015/52/4/639/178386
| » Introduction|| |
Intensity modulated radiotherapy (IMRT), an advanced radiotherapy technique, allows higher conformity of radiation dose to the tumor and minimizes the dose to the organs at risks (OARs). However, the effectiveness of the treatment plans is limited by inter-fraction and intra-fraction motion, tumor and normal tissues shape changes during the course of a fractionated treatment. With the advancement in diagnostic imaging and computerized treatment planning, the introduction of imaging devices in the treatment room has led to image guided radiation therapy (IGRT).,
The use of computed tomography (CT) imaging in IGRT technology to localize the prostate, bladder and rectum each day had made it possible to deliver the higher dose to the prostate more precisely. In a clinical trial from 1993 to 1998 for prostate cancer using conformal radiotherapy, Pollack et al., reported that an escalated dose of 78 Gy rather than 70 Gy to the isocenter was more beneficial. However escalated dose to the prostate target has given concern to late toxicity. Variability of the rectum and bladder volume from that in the planned CT may give rise dosimetric variations, which would affect normal tissue complication probability.
It is well-known that the confirmation of the relative position and shape of the target and OARs during daily-fractionated treatment is important for daily dose delivery accuracy. Although the primary aim of IGRT technologies in the treatment of prostate cancer is to accurately localize the tumor for precise targeting, these technologies are also capable of monitoring changes in the filling and shape of the bladder and rectum and also to track the actual dose delivered to them. Changes in the bladder and rectal volume affect the position of target (prostate and seminal vesicles). Furthermore, significant variations in bladder volume can confound the planned dose distributions while significant variations in rectal volume can affect late side-effect. Therefore, bladder and rectal volume must be kept consistent throughout the planning and treatment to reduce positional uncertainties (bladder) related to target and the risk of increased toxicity (rectum). For these reasons, we study the daily volumes and dose variations for bladder and rectum and investigate the usability of our bladder and bowel preparation protocol in both normal organs volume stability.
This study evaluates dosimetric changes resulting from volume validation associated with the treatment of prostate cancer and to access the stability of bladder and rectum volume with our rectum clearance and bladder preparation protocol. Dose coverage for the prostate was excluded in this study as it would be expected that the target would be adequately covered with gold seed implant and daily IGRT. Elekta synergy kilovoltage cone beam computed tomography (kV-CBCT) was used for localization and dose calculation. The planning computed tomography (pCT)-based electron density on CBCT images allows more accurate dose calculations on an individualized patient basis.
| » Materials and Methods|| |
Patient specific Hounsfield Units mapping
Electron density-image sampling on the CMS (Computerized Medical System, St. Louis) XiO was used for HU-ED mapping for CBCT dose calculation, known as patient specific HU-ED mapping method. This method involves various steps:First the CBCT images were imported as secondary study set to the pCT in the CMS XiO treatment planning system then the CBCT images were fused to the pCT and the region of interests (ROIs) from pCT were copied to CBCT images. A total of seven ROIs were used in generating the calibration curve, which included bone, soft-tissue, muscle, air, cord, bladder and skin. Then the image sampling was used to map the ROIs from pCT to CBCT images and recorded the average CBCT HU numbers of these seven ROIs, image sampling tool reports HU numbers and relative electron density at the ROIs. Finally, the HU numbers from the CBCT scan were then calibrated as those from a pCT scan so that electron densities are equivalent in both systems. The pCT-based electron density on CBCT images allows more accurate dose calculations on an individualized patient basis.
Dose-volume histograms and inter-fractional volume differences study
Between January 2012 and May 2012, a total of 12 patients underwent prostate curative radiotherapy at our department were selected in this study; age range 54-71 years, mean, 62.5 years old. All patients were treated with single-phase 1 (prostate and seminal vesicle) 7800 cGy in 39 daily fractions.
Gold seed was implanted before the day of planning for radiotherapy for these 12 patients and then divided them into two groups; each group consists of 6 patients. In group with bladder and bowel preparation protocol (patients 1-6), all patients were given mild laxative (macrogol 4000) to be taken 1 day (after dinner) before the day of planning, to obtain a reproducible rectal volume during CT acquisition and treatment sessions. They were asked to take light breakfast on the day of CT planning and throughout the treatment. The planning and treatment sessions were scheduled for after 10 morning because it was expected that most people would have empty their bowels in the morning.
During the planning visit, our radiation therapists explained the bladder preparation protocol. All patients received written instructions to empty their bladder and then drink five cups of water 1 h before acquisition of the pCT scan and before each treatment fraction to have comfortably full bladder at the time of planning and daily treatment. Patients above 65 years were given four cups of water (45 min) as they would not be able to hold their bladder during the treatment. For the control group patients (patients A-F), all patients were treated without any bowel and bladder preparation protocol. Patients 1-5 and patient A-E were enrolled for inter-fractional volume differences; whilst patient 6 and patient F was selected for DVHs analysis.
A total of six patients underwent prostate curative radiotherapy at our department were selected in this study; age range 54-71 years, mean, 62.5 years old. All patients were treated with single phase (prostate and seminal vesicle) to 7800 cGy in 39 daily fractions.
Gold seed was implanted before the day of planning for radiotherapy for these six patients and all patients were given mild laxative (macrogol 4000) to be taken 1 day (after dinner) before the day of planning, to obtain a reproducible rectal volume during CT acquisition and treatment sessions. During the planning visit, all patients received written instructions to empty their bladder and then drink four to five cups of water 1 h before acquisition of the pCT scan and before each treatment fraction to have comfortably full bladder at the time of planning and daily treatment. One full volumetric kV-CBCT study set was done for every patient from each day of treatment. A total of 10 CBCT study sets (day 1-10) were used for each patient to analyze the bladder and rectal volume changes and their impact on DVH.
After pCT scan, the data were transferred to the radiotherapy planning system. The bladder and rectum were outlined in each of the CT studies. The bladder was defined as the outer contour of the organ and was outlined in all relevant slices.
The rectum was outlined from the first slice below the recto-sigmoid junction to the first slice above the anal verge. The defined rectal volume included the rectal wall as well as the contents of the rectum. The treatments were planned and optimized using the CMS XiO treatment planning system and the dose calculation was performed using a superposition algorithm. The actual dose delivered to the bladder and rectum for 10 patients was investigated by using the daily anatomy information provided by kV-CBCT images from the Elekta Synergy system.
One full volumetric kV-CBCT study set was done for every patient from each day of treatment. Three steel ball markers were placed on the patient's skin surface to mark the treatment field isocenter and the daily isocenter shifts were noted for isocenter placement on CBCT datasets. A total of 10 CBCT study sets (day 1-10) were used for each patient to analyze the bladder and rectal volume changes and their impact on DVH. DVHs served as useful tools in demonstrating the correlation between late toxicity and the irradiated volume.
Procedures for dose reconstruction
The kV-CBCT scans were exported to focal workstation and fused with the treatment pCT scans. Fusion based on gold-seed match was performed. The rectum and bladder were outlined in the same method on all CBCT scans to access the rectum and bladder DVH. The dose was recomputed on the CBCT datasets with the same treatment parameters and isocenter shift info from CBCT workstation.
Rectal toxicities were graded according to the Radiation Therapy Oncology Group (RTOG) toxicity scores. In the patient medical records, the type of toxicity and its grade were reported.
| » Results|| |
Rectum DVH during the first 10 fractions of IMRT in the protocol and the control groups
The inter-fractional rectal volume difference for all five patients (patient A-E) in the control group is shown in [Figure 1]. The rectal volume difference is computed from the rectum volume in CBCT and from the planned CT. [Figure 1] shows a large daily rectal volume variations occurred in all patients throughout the treatment period if no bowel preparation were done. Patient E showed the largest rectal volume difference, 96.4% (between 41.29 cc and 81.11 cc). Patient E has empty rectum during CT planning but hold a large quantity of contents on day 3, after having heavy lunch. Analysis of the DVH of the rectum showed that with reduced rectal volume, increased of rectal D17 was found in-patient F [Figure 2]. The increase in the dose to the rectum will cause late rectal toxicity in patients who have large rectal volume during CT planning but small rectal volume during treatment.
|Figure 1: Rectal volume difference during the treatment course for prostate cancer patient without bowel preparation|
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|Figure 2: Rectum volume and D17 difference during the first 10 fractions for prostate cancer patient 6 with bowel preparation protocol|
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[Figure 3] shows the rectal volume variation with respect to the rectal volume on CT planning for daily treatment of prostate cancer patients with bowel preparation protocol. The highest difference of 23% (between 38.11 cc and 46.87 cc) occurred in patient 3. The most of patients with bowel preparation protocol had smaller rectal volume on CT planning when compared with daily treatment course, which help to minimize late rectal toxicity since the plans were done based on empty rectum contour (it represents the worst scenario).
|Figure 3: Rectal volume difference during the treatment course for prostate cancer patient with bowel preparation|
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[Figure 4] shows the rectal D17 difference compared with the dose of D17 on pCT for patient 6. There is only small difference in D17 (<10%) during treatment with rectum preparation protocol, although this patient (the worst case) had smaller rectal volume during treatment course most of the time.
|Figure 4: Rectum volume and D17 difference during the first 10 fractions for prostate cancer patient 6 with bowel preparation protocol|
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Bladder DVH during the first 10 fractions of IMRT for patients in the protocol and the control groups
The individual difference in bladder volume between pCT and CBCT over time is shown in [Figure 5] and [Figure 6] for patients without and with bladder preparation protocol respectively. There was a large variation in bladder volumes, when compared against bladder volumes from the pCT. In this study, the bladder volumes seem to decrease during treatment when compared to bladder volume from pCT, except patient D. Several reports on bladder volume have found the same trend.,, For patient D, the maximum variation in bladder volume was as high as 98% at day 2.
|Figure 5: Bladder volume difference during the treatment course for prostate cancer patient without bladder preparation|
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|Figure 6: Bladder volume difference during the treatment course for prostate cancer patient with bladder preparation|
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Nakamura et al., report that although various protocols intended to achieve reproducible bladder volumes were used in previous reports, a decreasing trend in bladder volume was a common finding. However our study showed a non-constant change in bladder volumes during the treatment course with bladder preparation protocol because in Naoki's report, patients were encouraged to drink an unspecified volume of liquid rather a fix volume of water.
[Figure 7] shows the bladder dose, D25 difference compared with pCT in patient F (without bladder preparation protocol). There was a large difference in D25 on day 3, up to 162%. The bladder was larger during treatment as this patient only emptied his bladder before CT planning and not during the subsequent treatment. The bladder DVH was improved, but there was increased in target motion variation from the daily IGRT.
|Figure 7: The bladder dose (D25) difference during the first 10 fractions for the prostate cancer patient F without bladder preparation protocol|
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[Figure 8] shows the bladder dose, D25 difference compared with pCT in patient 6 with bladder preparation protocol. Even though, there were some variation in bladder volume, but all D25 still within RTOG 0126 criteria, which is no more than 25% of the bladder should receive more than 65 Gy.
|Figure 8: The bladder dose (D25) difference during the first 10 fractions for the prostate cancer patient 6 with bladder preparation protocol|
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The median follow-up was 24 months. Rectal toxicity profile was very favorable in the group with bowel preparation guidelines: None of the patients experienced grade 3 and above rectal toxicity. One of the patients in the control group (1/6) developed grade 4 toxicity (rectal bleeding).
| » Discussion|| |
Recent improvement in radiotherapy treatment techniques such as IMRT and IGRT make it possible to dose escalate due to the increase in accuracy of radiation delivery and imaging system. However, the accuracy of delivery depends much more on the consistency of the treatment volume and the target itself. If the target volume and its surrounding structures are constantly changing in contour, position, size and shape, it is impossible to achieve good target coverage despite the best imaging and targeting radiation technology. This consistency in internal organ structures is especially important in the curative treatment setting of prostate cancer. Failing which the cancer may recur if the target is missed and the late complications to the rectum and bladder if the surrounding structures are overdose. The consistency in the position and size of the rectum and bladder is especially difficult to achieve in view of the constant changes in the rectal air/feces content and the bladder urine volume. Many different techniques have been employed and reported to keep the consistency of these volumes. Some have employed the used of rectal balloons, which has been shown to be very effective, but the technique is costly and uncomfortable to the patients. Some reports with laxatives and simple bladder filling are more practical and easily applied in most centers.,
In our center, a simple laxative (macrogol 4000) every evening was selected as it is well tolerated and very effective in most patients. With the use of simple bladder filling protocol of four to five cups of 250 ml of water 1 h before the treatment, it is possible to achieve a fairly constant bladder as well. Our study showed that it is possible to keep a good dose consistency in terms of DVHs to the rectal and bladder using this protocol.
Data also show that there were large bladder and rectum volumes variation in the control group, the variations were very random. The dose increases with decreased volume; hence, the constraints defined in RTOG0126 protocol varied from day to day, same findings as reported by Varadhan et al. Patient with large rectal volume during simulation make the treatment planning easier, but if the rectum became smaller during subsequent treatments, the dose to the rectum might exceed the tolerance defined in RTOG0126 and increased the late toxicity. In control group, patient F developed acute rectal toxicities after radiotherapy. No patient with rectum preparation developed rectal toxicity.
Based on daily cone beam CT, implementation of bladder preparation instructions was shown to improve bladder volume consistency. This is important especially in the first phase of the treatment when the lymph nodes are included in the radiation portal. A constant comfortable full bladder will push the small bowel out of the radiation portals hence decrease the radiation doses to the small intestines.
| » Conclusion|| |
Our data confirm that rectum and bladder preparation protocol can improve the treatment accuracy, both volumes and DVHs consistency with the help of CBCT.
| » References|| |
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8]
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