An adaptive radiotherapy planning strategy for bladder cancer using deformation vector fields

Purpose

Adaptive radiotherapy (ART) has considerable potential in treatment of bladder cancer due to large inter-fractional changes in shape and size of the target. The aim of this study was to compare our clinically applied method for plan library creation that involves manual bladder delineations (Clin-ART) with a method using the deformation vector fields (DVFs) resulting from intensity-based deformable image registrations (DVF-based ART).

Materials and methods

The study included thirteen patients with urinary bladder cancer who had daily cone beam CTs (CBCTs) acquired for set-up. In both ART strategies investigated, three plan selection volumes were generated using the CBCTs from the first four fractions; in Clin-ART boolean combinations of delineated bladders were used, while the DVF-based strategy applied combinations of the mean and standard deviation of patient-specific DVFs. The volume ratios (VRs) of the course-averaged PTV for the two ART strategies relative the non-adaptive PTV were calculated.

Results

Both Clin-ART and DVF-based ART considerably reduced the course-averaged PTV, compared to non-adaptive RT. The VR for DVF-based ART was lower than for Clin-ART (0.65 vs. 0.73; p < 0.01).

Conclusions

DVF-based ART for bladder irradiation has a considerable normal tissue sparing potential surpassing our already highly conformal clinically applied ART strategy.     

Does the planning dose-volume histogram represent treatment doses in image-guided prostate radiation therapy? Assessment with cone-beam computerised tomography scans

Purpose

To assess the accuracy of the initial CT plan dose-volume histograms (DVH’s) for prostate, rectum and bladder by comparison to delivered doses determined from cone beam CT (CBCT) scans acquired during image-guided treatment.

Materials and methods

Twelve prostate patients were treated using daily implanted fiducial guidance and following local protocol for bladder and rectal preparation. CBCT scans were acquired twice weekly and contoured for prostate, rectum and bladder. The planned beams were applied to all CBCT scans to determine the delivered doses. Prostate dose coverage was assessed by the proportion of the CTV fully encompassed by the 95% and 98% isodose lines. Rectal and bladder volumes receiving 40 Gy, 60 Gy and 70 Gy at treatment were compared to the initial plan, with significance determined using the one-sample t-test.

Results

Four patients showed marginally compromised CTV coverage by the 95% isodose at all CBCT plans. For nine patients the initial plan rectal DVH was significantly outside the range of the treatment DVH’s.

Conclusions

Dose coverage of the prostate was not achieved for all patients. Observed rectal and bladder doses were higher than predicted. The initial treatment plan cannot be assumed to represent accurate normal tissue doses.     

Comparative dosimetry of three-phase adaptive and non-adaptive dose-painting IMRT for head-and-neck cancer

Purpose

The anatomical changes, which occur during the radiotherapy treatment for head-and-neck cancer, may compromise the effectiveness of the treatment. This study compares dosimetrical effects of adaptive (ART) and non-adaptive (RT) dose-painted radiotherapy.

Materials and methods

For 10 patients, three treatment phases were preceded by a planning PET/CT scan. In ART, phases II and III were planned using PET/CT₂ and PET/CT₃, respectively. In RT, phases II and III were planned on PET/CT₁ and recalculated on PET/CT₂ and PET/CT₃. Deformable image co-registration was used to sum the dose distributions and to propagate regions-of-interest (ROIs) drawn on PET/CT₁ to PET/CT₂, PET/CT₃ and a last-treatment-day CT-scan.

Results

Re-adjusted dose-painting ART provided higher minimum and lower maximum doses in target ROIs in comparison to RT. On average, ART reduced the parotids’ median dose and swallowing structures mean dose by 4.6–7.1% (p > 0.05) and 3% (p = 0.06), respectively. Dose differences for targets were from −1.6% to 6.6% and for organs-at-risk from −7.1% to 7.1%. Analysis of individual patient data showed large improvements of ROI dose/volume metrics by ART, reaching a 24.4% minimum-dose increase in the elective neck planning target volume and 21.1% median-dose decrease in swallowing structures.

Conclusion

Compared to RT, ART readjusts dose-painting, increases minimum and decreases maximum doses in target volumes and improves dose/volume metrics of organs-at-risk. The results favored the adaptive strategy, but also revealed considerable heterogeneity in patient-specific benefit. Reporting population-average effects underestimates the patient-specific benefits of ART.     

Modeling positioning uncertainties of prostate cancer external beam radiation therapy using pre-treatment data

Purpose

To investigate the influence of treatment plan data and image guidance (IG) on positioning uncertainty during prostate cancer (PCa) radiotherapy (RT).

Methods

Body mass index (BMI), planning target volume (PTV), bladder volume (BV), and rectal cross section area (RCS) were collected for 267 consecutive PCa patients undergoing daily IGRT. Radiographic isocenter corrections to intra-prostatic fiducials for 12,490 treatment fractions were used to derive random (RE) and systematic (SE) inter-fraction uncertainties for the cardinal axes. These data were used to simulate RE and SE for weekly IG and Action Level (AL)-IG treatment protocols.

Results

SE and RE were 2–5 and 3–4 mm in the cardinal axes, respectively, during simulation of no IG. Without IG, positive correlations (p < 0.01) were noted for (1) anterior-posterior RE vs. RCS and BV and (2) cranio–caudal RE vs. RCS, BV and BMI. The RE increase was 3 mm for the highest quartile of RCS, BV and BMI. Daily IGRT eliminated this relationship. 3D IG corrections of 1 cm or more occured in 27% of treatment fractions and in 97% of patients.

Conclusion

PCa patients with elevated pre-treatment BV, RCS and BMI have increased inter-fractionation positioning uncertainty and appear the primary candidates for daily IGRT.     

Developing a class solution for Prostate Stereotactic Ablative Body Radiotherapy (SABR) using Volumetric Modulated Arc Therapy (VMAT)

Background and purpose

To develop a class solution for prostate Stereotactic Ablative Radiotherapy (SABR) using Volumetric Modulated Arc Therapy (VMAT).

Materials and methods

Seven datasets were used to compare plans using one 360° arc (1FA), one 210° arc (1PA), two full arcs and two partial arcs. Subsequently using 1PA, fifteen datasets were compared using (i) 6 mm CTV–PTV margins, (ii) 8 mm CTV–PTV margins and (iii) including the proximal SV within the CTV. Monaco™ 3.2 (Elekta™) was used for planning with the Agility™ MLC system (Elekta™).

Results

Highly conformal plans were produced using all four arc arrangements. Compared to 1FA, 1PA resulted in significantly reduced rectal doses, and monitor units and estimated delivery times were reduced in six of seven cases. Using 6 mm CTV–PTV margins, planning constraints were met for all fifteen datasets. Using 8 mm margins required relaxation of the uppermost bladder constraint in three cases to achieve adequate coverage, and, compared to 6 mm margins, rectal and bladder doses significantly increased. Including the proximal SV required relaxation of the uppermost bladder and rectal constraints in two cases, and rectal and bladder doses significantly increased.

Conclusions

Prostate SABR VMAT is optimal using 1PA. 6 mm CTV–PTV margins, compatible with daily fiducial-based IGRT, are consistently feasible in terms of target objectives and OAR constraints.     

Patient-specific PTV margins in radiotherapy for bladder cancer - A feasibility study using cone beam CT

Purpose

To assess the feasibility of using cone beam computed tomography (CBCT) to generate patient-specific PTV margins for bladder cancer patients treated with radiation therapy (RT).

Methods

Eleven patients underwent CT simulation and daily RT (full bladder and empty rectum). CBCT was done prior to each fraction, and the whole bladder was contoured off-line. For the first 15 CBCTs of each patient, the bladder was aligned with CT-simulation bladder (pBladder) to create an occupancy volume (OV). A 5 mm isotropic margin was added to OV (OV + 5). A measurement-based PTV (mPTV) was generated by measuring maximal displacement between pBladder and OV in six directions. OV, OV + 5, mPTV, and a standard PTV (2 cm isotropic margin) were compared for absolute and relative volume differences. Using the final 10 CBCT of each patient, the ability of each study volume to encompass the entire CBCT bladder was determined.

Results

161/165 CBCT images were of adequate quality for contouring. No daily trend in bladder volume variation was noted. The median absolute volumes (cm³) were: 221, 271, 426, 440, and 914 for pBladder, OV, OV + 5, mPTV, and standard PTV, respectively. The median ratios of the study volumes/pBladder were: 1.4 OV, 2.1 OV + 5, 2.4 mPTV, 4.1 standard PTV. OV + 5 was smaller than mPTV in 9 patients. There was considerable inter-patient variability in study volumes and no apparent association of the magnitude of margin expansion and pBladder. The bladder was encompassed in 69%, 99%, 99%, and 100% of the final 10 fractions by OV, OV + 5, mPTV, and standard PTV, respectively.

Conclusions

The use of daily CBCT to generate patient-specific PTV margins is feasible and results in a marked reduction in the irradiated volume compared to population-based margins. As daily bladder volume varied unpredictably with considerable differences between patients, these findings support the use of patient-specific PTV margin expansions for bladder radiotherapy.     

Necrosis predicts benefit from hypoxia-modifying therapy in patients with high risk bladder cancer enrolled in a phase III randomised trial

Background and purpose

Addition of carbogen and nicotinamide (hypoxia-modifying agents) to radiotherapy improves the survival of patients with high risk bladder cancer. The study investigated whether histopathological tumour features and putative hypoxia markers predicted benefit from hypoxia modification.

Materials and methods

Samples were available from 231 patients with high grade and invasive bladder carcinoma from the BCON phase III trial of radiotherapy (RT) alone or with carbogen and nicotinamide (RT + CON). Histopathological tumour features examined were: necrosis, growth pattern, growing margin, and tumour/stroma ratio. Hypoxia markers carbonic anhydrase-IX and glucose transporter-1 were examined using tissue microarrays.

Results

Necrosis was the only independent prognostic indicator (P = 0.04). Necrosis also predicted benefit from hypoxia modification. Five-year overall survival was 48% (RT) versus 39% (RT + CON) (P = 0.32) in patients without necrosis and 34% (RT) versus 56% (RT + CON) (P = 0.004) in patients with necrosis. There was a significant treatment by necrosis strata interaction (P = 0.001 adjusted). Necrosis was an independent predictor of benefit from RT + CON versus RT (hazard ratio [HR]: 0.43, 95% CI 0.25–0.73, P = 0.002). This trend was not observed when there was no necrosis (HR: 1.64, 95% CI 0.95–2.85, P = 0.08).

Conclusions

Necrosis predicts benefit from hypoxia modification in patients with high risk bladder cancer and should be used to select patients; it is simple to identify and easy to incorporate into routine histopathological examination.     

Beam orientation in stereotactic radiosurgery using an artificial neural network

Background and purpose

To investigate the feasibility of using an artificial neural network (ANN) to generate beam orientations in stereotactic radiosurgery (SRS).

Material and methods

A dataset of 669 intracranial lesions was used to build, train, and validate three ANNs. In ANN1, Cartesian coordinates described the localization of the PTV and OARs. In ANN2, a genetic algorithm was used to optimize the model. In ANN3, vectors were used to define the distance between the PTV and OARs. In all ANNs, inputs consisted of the treatment plan parameters plus the patient’s particular geometric parameters; outputs were beam and table angles. The ANN- and human-generated plans were then compared using dose–volume histograms, root-mean-square (RMS) and Gamma index methods.

Results

The mean volume of PTV covered by the 95% isodose was 99.2% in the MP’s plan vs. 99.3%, 98.5% and 99.2% for ANN1, ANN2, and ANN3, respectively. No significant differences were observed between the plans. ANN1 showed the best agreement (Gamma index) with the human planner. While RMS errors in the three ANN models were comparable, ANN1 showed the lowest (best) values.

Conclusion

ANN models were able to determine beam orientation in SRS. ANN-generated treatment plans were comparable to human-designed plans.     

Preservation of the internal genital organs during radical cystectomy in selected women with bladder cancer: A report on 15 cases with long term follow-up

Purpose

To prospectively present the technique, functional and oncological outcome of internal genitalia sparing cystectomy for bladder cancer in 15 selected women.

Patients and methods

Between January 1995 and December 2010, 305 women underwent orthotopic neobladder after radical cystectomy. Of these, 15 cases with a mean age of 42 years underwent genitalia sparing. Inclusion criteria included stage (T2b N0 Mo or less, as assessed preoperatively, unifocal tumors away from the trigone, sexually active young women and internal genitalia free of tumor. Cystectomy with preservation of the uterus, vagina and ovaries and Hautmann neobladder were performed. Oncological, functional, urodynamic and sexual outcome using Female Sexual Function Index (FSFI) were evaluated.

Results

Definitive histopathology showed advanced stage not recognized preoperatively in 2 patients, who developed local recurrence and bony metastasis after 3–4 months. A third patient developed bony metastasis after 15 months. No recurrence developed in the retained genital organs. The remaining 12 patients remained free of disease with a mean follow-up of 70 months. Among women eligible for functional evaluation, daytime and nighttime continence were achieved in 13/13 (100%) and 12/13 (92)%, respectively. Chronic urinary retention was not noted. The urodynamic parameters were comparable to those in other patients without genital preservation. Sexual function (FSFI) was better in these patients than in others without genital preservation.

Conclusions

Genital sparing cystectomy for bladder cancer is feasible in selected women. It provides a good functional outcome, better sexual function and the potential for fertility preservation. So far, the oncological outcome is favorable.     

In vivo quality assurance of volumetric modulated arc therapy for ano-rectal cancer with thermoluminescent dosimetry and image-guidance

Objective

To assess in vivo dose distribution using cone-beam computed tomography scans (CBCTs) and thermoluminescent dosimeters (TLDs) in patients with anal or rectal cancer treated with volumetric modulated arc therapy (VMAT).

Methods

Intracavitary (IC) in vivo dosimetry (IVD) was performed in 11 patients using adapted endorectal probes containing TLDs, with extra measurements at the perianal skin (PS) for anal margin tumors. Measured doses were compared to calculated ones obtained from image fusion of CBCT with CT treatments plans.

Results

A total of 55 IC and 6 PS measurements were analyzed. IC TLD median planned and measured doses were 1.81 Gy (range, 0.25–2.02 Gy) and 1.82 Gy (range, 0.19–2.12 Gy), respectively. In comparison to the planned doses all IC TLD dose measurements differed by a median dose of 0.02 Gy (range, −0.11/+0.19 Gy, p = 0.102) (median difference of 1.1%, range −6.1%/+10.6%). Overall, 95% of IC measurements were within ±7.7% of the expected percentage doses and only 1 value was above +10%. For PS measurements, only one was not within ±7.7% of expected values (i.e., −8.9%).

Conclusions

Image guidance using CBCT for IVD with TLDs is helpful to validate the delivered doses in patients treated with VMAT for ano-rectal tumors.     

Direct use of multivariable normal tissue complication probability models in treatment plan optimisation for individualised head and neck cancer radiotherapy produces clinically acceptable treatment plans

Background and purpose

Recently, clinically validated multivariable normal tissue complication probability models (NTCP) for head and neck cancer (HNC) patients have become available. We test the feasibility of using multivariable NTCP-models directly in the optimiser for inverse treatment planning of radiotherapy to improve the dose distributions and corresponding NTCP-estimates in HNC patients.

Material and methods

For 10 HNC cases, intensity-modulated radiotherapy plans were optimised either using objective functions based on the ‘generalised equivalent uniform dose’ (OF_gEUD) or based on multivariable NTCP-models (OF_NTCP). NTCP-models for patient-rated xerostomia, physician-rated RTOG grade II-IV dysphagia, and various patient-rated aspects of swallowing dysfunction were incorporated. The NTCP-models included dose–volume parameters as well as clinical factors contributing to a personalised optimisation process. Both optimisation techniques were compared by means of ‘pseudo Pareto fronts’ (target dose conformity vs. the sum of the NTCPs).

Results

Both optimisation techniques resulted in clinically realistic treatment plans with only small differences. For nine patients the sum-NTCP was lower for the OF_NTCP optimised plans (on average 5.7% (95%CI 1.7–9.9%, p < 0.006)). Furthermore, the OF_NTCP provided the advantages of fewer unknown optimisation parameters and an intrinsic mechanism of individualisation.

Conclusions

Treatment plan optimisation using multivariable NTCP-models directly in the OF is feasible as has been demonstrated for HNC radiotherapy.     

Swallowing-sparing intensity-modulated radiotherapy for head and neck cancer patients: Treatment planning optimization and clinical introduction

Purpose

To report on the potential benefits of swallowing-sparing intensity-modulated radiation therapy (SW-IMRT) in the first 100 SW-IMRT treated patients, as well as on the factors that influence the potential benefit of SW-IMRT relative to standard parotid sparing (ST)-IMRT.

Material and methods

One hundred consecutive head and neck cancer patients, scheduled for primary radiotherapy, were included in this prospective cohort study. For each patient, ST-IMRT and SW-IMRT treatment plans were created. All patients were eventually treated with SW-IMRT. Objectives for SW-IMRT were identical to those with ST-IMRT, with additional objectives to spare the swallowing organs at risk (SWOARs). After 20 patients, interim results were evaluated by a multidisciplinary committee.

Results

The mean gain of SW-IMRT relative to ST-IMRT in the first 20 patients was less than expected based on our previous planning comparative study. A critical review of all plans revealed that the results with SW-IMRT could be improved by: (1) gaining experience and attempting to reduce SWOAR dose as much as possible; (2) accepting a moderate shift of dose to unspecified tissues; (3) maximizing SWOAR sparing while keeping PTV coverage exactly according to protocol. In the additional 80 patients, the mean dose to the various SWOARs was further reduced significantly compared to ST-IMRT. Dose reductions with SW-IMRT were largest for patients who received neck irradiation, had a tumour located in the larynx, oropharynx, nasopharynx or oral cavity, and had <75% overlap between SWOARs and PTVs. The mean absolute reduction in predicted physician-rated RTOG grade 2–4 swallowing dysfunction for patients numbered 21–100 was 6.1%, ranging from 0.0% to 17.2%.

Conclusions

The benefit of SW-IMRT depends significantly on neck radiotherapy, tumour site and the amount of overlap between SWOARs and PTVs. Optimal clinical introduction requires a detailed evaluation and comparison between the standard (ST-IMRT) and new technique (SW-IMRT) in order to fully exploit the potential benefits.     

When is respiratory management necessary for partial breast intensity modulated radiotherapy: A respiratory amplitude escalation treatment planning study

Purpose

The impact of typical respiratory motion amplitudes (∼2 mm) on partial breast irradiation (PBI) is minimal; however, some patients have larger respiratory amplitudes that may negatively affect dose homogeneity. Here we determine at what amplitude respiratory management may be required to maintain plan quality.

Methods and Materials

Ten patients were planned with PBI IMRT. Respiratory motion (2–20 mm amplitude) probability density functions were convolved with static plan fluence to estimate the delivered dose. Evaluation metrics included target coverage, ipsilateral breast hotspot, homogeneity, and uniformity indices.

Results

Degradation of dose homogeneity was the limiting factor in reduction of plan quality due to respiratory motion, not loss of coverage. Hotspot increases were observed even at typical motion amplitudes. At 2 and 5 mm, 2/10 plans had a hotspot greater than 107% and at 10 mm this increased to 5/10 plans. Target coverage was only compromised at larger amplitudes: 5/10 plans did not meet coverage criteria at 15 mm amplitude and no plans met minimum coverage at 20 mm.

Conclusions

We recommend that if respiratory amplitude is greater than 10 mm, respiratory management or alternative radiotherapy should be considered due to an increase in the hotspot in the ipsilateral breast and a decrease in dose homogeneity.     

Reduction of the treated volume to involved node radiation therapy as part of combined modality treatment for early stage aggressive non-Hodgkin’s lymphoma

Background and purpose

This retrospective study investigated whether focused involved node radiation therapy (INRT) can safely replace involved field RT (IFRT) in patients with early stage aggressive NHL.

Patients and methods

We included 258 patients with stage I/II aggressive NHL who received combined modality treatment (87%) or primary RT alone (13%). RT consisted of a total dose of 30–40 Gy in 15–20 fractions IFRT or INRT. We compared survival, relapse pattern, radiation-related toxicity and quality of life for both RT techniques.

Results

Type of RT was not related to the outcome in either the uni- or multivariate survival analysis. Relapses developed in 59 of 252 patients (23%) of which 47 (80%) were documented as distant recurrence only. Failure of the INRT technique was noted in one patient. There was no significant difference in acute radiation-related toxicity between RT-groups but IFRT showed a significantly higher incidence of higher grade toxicities. Patients treated with INRT had a significantly better physical functioning and global quality of life compared to the IFRT group.

Conclusions

Given the retrospective nature of this study, no solid conclusions can be drawn. However, in view of the equivalent efficacy and more favorable toxicity profile, the replacement of IFRT by INRT in combination with chemo-(immuno)-therapy looks very attractive for patients with early stage aggressive NHL.     

Effectiveness of radiation therapy alone for elderly patients with unresected stage III non-small cell lung cancer

Purpose

Chemoradiotherapy is the standard of care for unresectable stage III non-small cell lung cancer (NSCLC). Elderly patients, who are often considered unfit for combined chemoradiotherapy, frequently receive radiation therapy (RT) alone. Using population-based data, we evaluated the effectiveness and tolerability of lone RT in unresected elderly stage III NSCLC patients.

Methods and materials

Using the Surveillance, Epidemiology and End Results (SEER) registry linked to Medicare records we identified 10,376 cases of unresected stage III NSCLC that were not treated with chemotherapy, diagnosed between 1992 and 2007. We used logistic regression to determine propensity scores for RT treatment using patients’ pre-treatment characteristics. We then compared survival of patients who underwent lone RT vs. no treatment using a Cox regression model adjusting for propensity scores. The adjusted odds for toxicity among patients treated with and without RT were also estimated.

Results

Overall, 6468 (62%) patients received lone RT. Adjusted analyses showed that RT was associated with improved overall survival in unresected stage III NCSLC (hazard ratio [HR]: 0.76; 95% confidence interval [CI]: 0.74–0.79) after controlling for propensity scores. RT treated patients had an increased adjusted risk of hospitalization for pneumonitis (odds ratio [OR]: 89, 95% CI: 12–636), and esophagitis (OR: 8, 95% CI: 3–21).

Conclusions

These data suggest that use of RT alone may improve the outcomes of elderly patients with unresected stage III NSCLC. Severe toxicity, however, was considerably higher in the RT treated group. The potential risks and benefits of RT should be carefully discussed with eligible elderly NSCLC patients.     

Evaluation of DVH-based treatment plan verification in addition to gamma passing rates for head and neck IMRT

Background and purpose

Treatment plan verification of intensity modulated radiotherapy (IMRT) is generally performed with the gamma index (GI) evaluation method, which is difficult to extrapolate to clinical implications. Incorporating Dose Volume Histogram (DVH) information can compensate for this. The aim of this study was to evaluate DVH-based treatment plan verification in addition to the GI evaluation method for head and neck IMRT.

Materials and methods

Dose verifications of 700 subsequent head and neck cancer IMRT treatment plans were categorised according to gamma and DVH-based action levels. Fractionation dependent absolute dose limits were chosen. The results of the gamma- and DVH-based evaluations were compared to the decision of the medical physicist and/or radiation oncologist for plan acceptance.

Results

Nearly all treatment plans (99.7%) were accepted for treatment according to the GI evaluation combined with DVH-based verification. Two treatment plans were re-planned according to DVH-based verification, which would have been accepted using the evaluation alone. DVH-based verification increased insight into dose delivery to patient specific structures increasing confidence that the treatment plans were clinically acceptable. Moreover, DVH-based action levels clearly distinguished the role of the medical physicist and radiation oncologist within the Quality Assurance (QA) procedure.

Conclusions

DVH-based treatment plan verification complements the GI evaluation method improving head and neck IMRT-QA.     

Suggestion for the prostatic fossa clinical target volume in adjuvant or salvage radiotherapy after a radical prostatectomy

Background and purpose

To assess the location of recurrent tumors and suggest the optimal target volume in adjuvant or salvage radiotherapy (RT) after a radical prostatectomy (RP).

Material and methods

From January 2000 to December 2012, 113 patients had been diagnosed with suspected recurrent prostate cancer by MRI scan and received salvage RT in the Samsung Medical Center. This study assessed the location of the suspected tumor recurrences and used the inferior border of the pubic symphysis as a point of reference.

Results

There were 118 suspect tumor recurrences. The most common site of recurrence was the anastomotic site (78.8%), followed by the bladder neck (15.3%) and retrovesical area (5.9%). In the cranial direction, 106 (87.3%) lesions were located within 30 mm of the reference point. In the caudal direction, 12 lesions (10.2%) were located below the reference point. In the transverse plane, 112 lesions (94.9%) were located within 10 mm of the midline.

Conclusions

A MRI scan acquired before salvage RT is useful for the localization of recurrent tumors and the delineation of the target volume. We suggest the optimal target volume in adjuvant or salvage RT after RP, which includes 97% of suspected tumor recurrences.     

Image-Guided Radiation Therapy for Muscle-Invasive Carcinoma of the Urinary Bladder with Cone Beam CT Scan: Use of Individualized Internal Target Volumes for a Single Patient

Introduction

While planning radiation therapy (RT) for a carcinoma of the urinary bladder (CaUB), the intra-fractional variation of the urinary bladder (UB) volume due to filling-up needs to be accounted for. This internal target volume (ITV) is obtained by adding internal margins (IM) to the contoured bladder. This study was planned to propose a method of acquiring individualized ITVs for each patient and to verify their reproducibility.

Methods

One patient with CaUB underwent simulation with the proposed ‘bladder protocol’. After immobilization, a planning CT scan on empty bladder was done. He was then given 300 ml of water to drink and the time (T) was noted. Planning CT scans were performed after 20 min (T+20), 30 min (T+30) and 40 min (T+40). The CT scan at T+20 was co-registered with the T+30 and T+40 scans. The bladder volumes at 20, 30 and 40 min were then contoured as CTV20, CTV30 and CTV40 to obtain an individualized ITV for our patient. For daily treatment, he was instructed to drink water as above, and the time was noted; treatment was started after 20 min. Daily pre- and post-treatment cone beam CT (CBCT) scans were done. The bladder visualized on the pre-treatment CBCT scan was compared with CTV20 and on the post-treatment CBCT scan with CTV30.

Results

In total, there were 65 CBCT scans (36 pre- and 29 post-treatment). Individualized ITVs were found to be reproducible in 93.85% of all instances and fell outside in 4 instances.

Conclusions

The proposed bladder protocol can yield a reproducible estimation of the ITV during treatment; this can obviate the need for taking standard IMs.Key words: Radiation therapy, Carcinoma of the urinary bladder, Urinary bladder volume, Individualized internal target volume