Early clinical experience with anatomy-based inverse planning dose optimization for high-dose-rate boost of the prostate

Brachytherapy evolution as seen today

While brachytherapy is the oldest form of radiation therapy, it is also a very exciting field from both physics and clinical perspectives. From the physics standpoint, brachytherapy dosimetry is largely being governed by the inverse-square law, leading to an unparalleled dose deposition kernel (dose emitted by a seed or single dwell position), even compared to proton or heavy-ion beamlets. There is slightly more dose beyond the central deposition point, but comparatively very little prior to it, that is, little or no entrance dose! It is easy to sum multiple dwell positions that cover a tumor, and the intensity can be modulated quite effectively using dwell times. From a clinical perspective, what sets brachytherapy apart from other intraoperative modalities (e.g., laser, radiofrequency, cryogenic) is our ability to precisely calculate the energy deposited across the relevant patient geometry, anticipate the effect from known dose-outcome relationships, and deliver that energy with exquisite control and selectively to the target volume while sparing organs at risks. This targeting ability has improved substantially over the last two decades. It is built upon key foundational elements, many of which stem from the research and development within our medical physics community. This article provides an overview of these elements that combine to make brachytherapy a successful and developing radiotherapy modality.

Reduction of toxicity in brachytherapy using a new technique

PURPOSE

The purpose of the study was to elucidate the usefulness of a dose evaluation method for reducing late genitourinary (GU) toxicity in high-dose-rate brachytherapy (HDR-BT) of prostate cancer.

METHODS AND MATERIALS

GU toxicity was scored in accordance with the Common Terminology Criteria for Adverse Events version 4.0. The prostatic urethra was divided into three segments (base = B, midgland = M, apex = A), which were subclassified into seven subgroups (B, M, A, BM, BA, MA, BMA) using a D_10% color map of the urethra. Significance testing was conducted on urethral D_0.1% and D_10% among the seven subgroups. Grade < 2 GU toxicity was also implemented.

RESULTS

Data of 174 patients with localized prostate cancer treated with HDR-BT combined with external beam radiotherapy between November 2011 and July 2014 were analyzed retrospectively. Median age was 74 (53-84) years, and median followup period was 44 (6-69) months. The number of Grade < 2 and Grade ≥ 2 toxicity was significantly different in the M subgroup than in the other subgroups (p < 0.05), suggesting increased radioresistance in the midgland urethra.

CONCLUSIONS

A high-dose-area evaluation method using a urethral D_10% color map may be helpful in reducing late GU toxicity in HDR-BT for prostate cancer.

Simultaneous needle catheter selection and dwell time optimization for preplanning of high-dose-rate brachytherapy of prostate cancer

PURPOSE

Needle catheter positions critically affect the quality of treatment plans in prostate cancer high-dose-rate (HDR) brachytherapy. The current standard needle positioning approach is based on human intuition, which cannot guarantee a high-quality plan. This study proposed a method to simultaneously select needle catheter positions and determine dwell time for preplanning of HDR brachytherapy of prostate cancer.

METHODS

We formulated the needle catheter selection problem and inverse dwell time optimization problem in a unified framework. In addition to the dose objectives of the planning target volume (PTV) and organs at risk (OARs), the objective function incorporated a group-sparsity term with a needle-specific adaptive weighting scheme to generate high-quality plans with the minimal number of needle catheters. The optimization problem was solved by a fast-iterative shrinkage-thresholding algorithm. For validation purposes, we tested the proposed algorithm on 10 patient cases previously treated at our institution and compared the resulting plans with plans generated using needle catheters selected manually.

RESULTS

Compared to the plan with manually selected needle catheters, when normalizing both plans to the same PTV coverage V _100% = 95%, the plans generated by the proposed algorithm reduced median V _125% from 65% to 64%, but increased median V _150% from 35% to 38%, and V _200% from 14% to 16%. All planning objectives were met. All clinically important dosimetric parameters of OARs were reduced. D _1cc of bladder and rectum were reduced from 8.57 Gy to 8.50 Gy and from 7.24 Gy to 6.80 Gy, respectively. D _max of urethra was reduced from 15.85 Gy to 15.77 Gy. The median number of selected needle catheters was reduced by two. The computational time for solving the proposed optimization problem was ∼90 s using MATLAB.

CONCLUSION

The proposed algorithm was able to generate plans for prostate cancer HDR brachytherapy preplanning with increased median conformity index (0.73-0.77) and slightly lower median homogeneity index (0.64-0.62) with the number of selected needles reduced by two compared to the manual needle selection approach.

Phase I study of dose escalation to dominant intraprostatic lesions using high-dose-rate brachytherapy

Purpose

Radiation dose escalation for prostate cancer improves biochemical control but is limited by toxicity. Magnetic resonance spectroscopic imaging (MRSI) can define dominant intraprostatic lesions (DIL). This phase I study evaluated dose escalation to MRSI-defined DIL using high-dose-rate (HDR) brachytherapy.

Material and methods

Enrollment was closed early due to low accrual. Ten patients with prostate cancer (T2a-3b, Gleason 6-9, PSA < 20) underwent pre-treatment MRSI, and eight patients had one to three DIL identified. The eight enrolled patients received external beam radiation therapy to 45 Gy and HDR brachytherapy boost to the prostate of 19 Gy in 2 fractions. MRSI images were registered to planning CT images and DIL dose-escalated up to 150% of prescription dose while maintaining normal tissue constraints. The primary endpoint was genitourinary (GU) toxicity.

Results

The median total DIL volume was 1.31 ml (range, 0.67-6.33 ml). Median DIL boost was 130% of prescription dose (range, 110-150%). Median urethra V₁₂₀ was 0.15 ml (range, 0-0.4 ml) and median rectum V₇₅ was 0.74 ml (range, 0.1-1.0 ml). Three patients had acute grade 2 GU toxicity, and two patients had late grade 2 GU toxicity. No patients had grade 2 or higher gastrointestinal toxicity, and no grade 3 or higher toxicities were noted. There were no biochemical failures with median follow-up of 4.9 years (range, 2-8.5 years).

Conclusions

Dose escalation to MRSI-defined DIL is feasible. Toxicity was low but incompletely assessed due to limited patients’ enrollment.

Does prostate volume has an impact on biochemical failure in patients with localized prostate cancer treated with HDR boost?

PURPOSE

To compare biochemical failure free survival (BFFS) of patients with small and large prostate glands treated with external beam radiation therapy (EBRT) and HDR (high dose rate) brachytherapy boost.

MATERIALS AND METHODS

Between 2002 and 2012, 548 patients were treated with EBRT followed by HDR boost. The effect of covariates and prostate volume on biochemical failure was analyzed by survival analysis and Cox regression model.

RESULTS

The median follow-up and age were not different between the two groups. The mean prostate gland volume at the time of CT planning was 48.1 and 76.0cc in small (<60cc) and large (⩾ 60cc) prostate volume, respectively (p<0.001). When PSA bounces were excluded, there was no significant difference between the two groups with a 5-years BFFS of 95.8% vs 92.3%, p=0.094. There were no significant differences between the two groups for urinary symptoms (IPSS) as well as acute and late GI toxicities.

CONCLUSIONS

This study showed that a HDR brachytherapy boost in large prostate gland cases is feasible at the price of increased PSA bounces. When the benign bounces are excluded, there is no significant difference between the two groups for tumor control and toxicity. Therefore, in our experience, there is no rational precluding the use of HDR boost in patients with a prostate size of 60 cc or more so long as an adequate dosimetry is achievable.

Image-guided high-dose-rate brachytherapy boost to the dominant intraprostatic lesion using multiparametric magnetic resonance imaging including spectroscopy: Results of a prospective study

PURPOSE

To evaluate the long-term outcomes of image-guided high-dose-rate (HDR) brachytherapy boost to the dominant intraprostatic lesion (DIL) using multiparametric magnetic resonance imaging (MRI), including spectroscopy (MRI/magnetic resonance spectroscopy [MRS]).

METHODS AND MATERIALS

Between December 2009 and March 2011, 20 patients with intermediate-risk prostate cancer underwent multiparametric MRI/MRS protocol before treatment. All patients were treated with an external beam radiotherapy dose of 40 Gy, combined with an HDR brachytherapy boost of 15 Gy. Concurrently, the DIL received a boost of 18 Gy. Missing data during followup were handled with multiple imputations.

RESULTS

The median followup was 62 months (range, 23-71 months). Six patients (31%) were classified as favorable intermediate risk and 13 patients (69%) as unfavorable intermediate risk. One patient experienced a prostate-specific antigen biochemical failure, and the 5-year biochemical failure-free survival rate was of 94.7%. The mean International Prostate Symptom Score rose from 7, with respect to baseline, to 10.42 1 month after treatment, and rapidly decreased to 6.97 after 3 months. Grade 1, 2, and 3 acute genitourinary toxicities were reported in 13 (68%), 3 (16%), and 1 (5%) patients, respectively. Grade 1 and 2 late genitourinary toxicities were reported in 9 (53%) and 3 (18%) patients, respectively. Only grade 1 acute and late gastrointestinal toxicities were reported in 4 (21%) and 3 (18%) patients, respectively.

CONCLUSIONS

Delivering an HDR brachytherapy boost to the DIL using image-guided multiparametric MRI/MRS is feasible with good outcomes for biochemical control, acute and late toxicities, and dosimetric constraints for critical organs.

Robustness of IPSA optimized high-dose-rate prostate brachytherapy treatment plans to catheter displacements

PURPOSE

Inverse planning simulated annealing (IPSA) optimized brachytherapy treatment plans are characterized with large isolated dwell times at the first or last dwell position of each catheter. The potential of catheter shifts relative to the target and organs at risk in these plans may lead to a more significant change in delivered dose to the volumes of interest relative to plans with more uniform dwell times.

MATERIAL AND METHODS

This study aims to determine if the Nucletron Oncentra dwell time deviation constraint (DTDC) parameter can be optimized to improve the robustness of high-dose-rate (HDR) prostate brachytherapy plans to catheter displacements. A set of 10 clinically acceptable prostate plans were re-optimized with a DTDC parameter of 0 and 0.4. For each plan, catheter displacements of 3, 7, and 14 mm were retrospectively applied and the change in dose volume histogram (DVH) indices and conformity indices analyzed.

RESULTS

The robustness of clinically acceptable prostate plans to catheter displacements in the caudal direction was found to be dependent on the DTDC parameter. A DTDC value of 0 improves the robustness of planning target volume (PTV) coverage to catheter displacements, whereas a DTDC value of 0.4 improves the robustness of the plans to changes in hotspots.

CONCLUSIONS

The results indicate that if used in conjunction with a pre-treatment catheter displacement correction protocol and a tolerance of 3 mm, a DTDC value of 0.4 may produce clinically superior plans. However, the effect of the DTDC parameter in plan robustness was not observed to be as strong as initially suspected.

Preventing Complications from High-Dose Rate Brachytherapy when Treating Mobile Tongue Cancer via the Application of a Modular Lead-Lined Spacer

PURPOSE

To point out the advantages and drawbacks of high-dose rate brachytherapy in the treatment of mobile tongue cancer and indicate the clinical importance of modular lead-lined spacers when applying this technique to patients.

METHODS

First, all basic steps to construct the modular spacer are shown. Second, we simulate and evaluate the dose rate reduction for a wide range of spacer configurations.

RESULTS

With increasing distance to the source absorbed doses dropped considerably. Significantly more shielding was obtained when lead was added to the spacer and this effect was most pronounced on shorter (i.e. more clinically relevant) distances to the source.

CONCLUSIONS

The modular spacer represents an important addition to the planning and treatment stages of mobile tongue cancer using HDR-ISBT.

Comparison of dose and catheter optimization algorithms in prostate high-dose-rate brachytherapy

PURPOSE

The purpose of this work was to compare the hybrid inverse treatment planning optimization (HIPO), inverse dose-volume histogram-based optimization (DVHO), and fast simulated annealing stochastic algorithm (IPSA). The catheter optimization algorithm HIPO was also compared with the Centroidal Voronoi Tessellation (CVT) algorithm.

METHODS AND MATERIALS

In this study, eight high-dose-rate prostate cases were randomly selected from an anonymized bank of patients. Oncentra Prostate v4.1 was used to run DVHO and the HIPO catheter optimization (HIPO_cat), whereas Oncentra Brachy v4.3 was used for the remaining. For fixed catheter configurations, DVHO plans were compared with IPSA and HIPO. For catheter positions optimization, CVT and HIPO_cat algorithms were compared with standard clinical template plans. CVT catheters were further restrained to the template grid (CVT_grid) and compared with HIPO_cat.

RESULTS

For dose optimization, IPSA and HIPO were not different from each other. The urethra D10 and the computation time were found significantly better with IPSA and HIPO compared with DVHO (p < 0.0001). All other dosimetric indices were not statistically different from each others (p > 0.05). For catheter placement, CVT plans were better, whereas HIPO_cat plans were significantly worse (p < 0.05) than standard clinical plans. CVT_grid plans were similar to clinical plans and fulfilling American Brachytherapy Society guidelines down to 12 catheters, whereas HIPO_cat plans do not for all catheter numbers. The CVT algorithm run time was significantly faster than HIPO_cat (p < 0.0001).

CONCLUSIONS

Dose optimization engines IPSA, DVHO, and HIPO give similar dosimetric results. The CVT approach was found to be better than HIPO_cat and was able to reduce the number of catheters significantly.

Comparison of manual and inverse optimisation techniques in high dose rate intracavitary brachytherapy of cervical cancer: A dosimetric study

AIMS AND OBJECTIVES

To compare dosimetrically the manual optimisation with IPSA using dose volume histograms (DVH) among patients treated for carcinoma of cervix with intracavitary brachytherapy.

BACKGROUND

With the advent of advanced imaging modalities, there has been a shift from conventional X-ray based planning to three-dimensional planning. Manual optimisation is widely used across various institutions but it is time consuming and operator dependant. Inverse planning simulated annealing (IPSA) is now available in various brachytherapy planning systems. But there is a paucity of studies comparing manual optimisation and IPSA in treatment of carcinoma cervix with intracavitary brachytherapy and hence this study.

MATERIALS AND METHODS

Fifteen consecutive patients treated between December 2013 and March 2014 with intracavitary brachytherapy for carcinoma of cervix were selected for this study. All patients were initially treated with external beam radiotherapy followed by intracavitary brachytherapy. The DVH was evaluated and compared between manually optimised plans and IPSA in the same set of patients.

RESULTS

There was a significant improvement in the HRCTV coverage, mean V100 of 87.75% and 82.37% (p = 0.001) and conformity index 0.67 and 0.6 (p = 0.007) for plans generated using IPSA and manual optimisation, respectively. Homogeneity index and dose to the OARs remained similar between the two groups.

CONCLUSION

The use of inverse planning in intracavitary brachytherapy of cervix has shown a significant improvement in the target volume coverage when compared with manual planning.

High-dose-rate brachytherapy delivered in two fractions as monotherapy for low-risk prostate cancer

PURPOSE

High-dose-rate (HDR) brachytherapy has been accepted as an effective and safe method to treat prostate cancer. The aim of this study was to describe acute toxicity following HDR brachytherapy to the prostate, and to examine the association between dosimetric parameters and urinary toxicity in low-risk prostate cancer patients.

MATERIAL AND METHODS

Patients with low-risk prostate cancer were given HDR brachytherapy as monotherapy in two 12.5 Gy fractions. Planning objectives for the planning target volume (PTV) were V100% ≥ 90% and V150% ≤ 35%. Planning objectives for organs at risk were V75% ≤ 1 cc for the bladder, rectum and perineum, and V125% ≤ 1 cc for the urethra. Toxicity was assessed three months after treatment using the Common Terminology Criteria for Adverse Events.

RESULTS

Seventy-three patients were included in the analysis. Thirty-three patients (45%) reported having any type of toxicity in the three months following HDR brachytherapy. Most toxicity cases (26%) were grade 1 urinary toxicity. Mean coverage index was 0.89 and mean V100 was 88.85. Doses administered to the urethra were associated with urinary toxicity. Patients who received more than 111.3% of the prescribed dose in 1 cc of the urethra were four times more likely to have urinary toxicity compared to patients receiving less than 111.3% (OR = 4.71, 95% CI: 1.43-15.6; p = 0.011).

CONCLUSIONS

High-dose-rate brachytherapy administered as monotherapy for prostate cancer proved to be a safe alternative treatment for patients with low-risk prostate cancer. Urinary toxicity was associated with the dose administered to 1 cc and 0.1 cc of the urethra and was remarkably inferior to the reported toxicity in similar studies.

Adaptation of the CVT algorithm for catheter optimization in high dose rate brachytherapy

PURPOSE

An innovative, simple, and fast method to optimize the number and position of catheters is presented for prostate and breast high dose rate (HDR) brachytherapy, both for arbitrary templates or template-free implants (such as robotic templates).

METHODS

Eight clinical cases were chosen randomly from a bank of patients, previously treated in our clinic to test our method. The 2D Centroidal Voronoi Tessellations (CVT) algorithm was adapted to distribute catheters uniformly in space, within the maximum external contour of the planning target volume. The catheters optimization procedure includes the inverse planning simulated annealing algorithm (IPSA). Complete treatment plans can then be generated from the algorithm for different number of catheters. The best plan is chosen from different dosimetry criteria and will automatically provide the number of catheters and their positions. After the CVT algorithm parameters were optimized for speed and dosimetric results, it was validated against prostate clinical cases, using clinically relevant dose parameters. The robustness to implantation error was also evaluated. Finally, the efficiency of the method was tested in breast interstitial HDR brachytherapy cases.

RESULTS

The effect of the number and locations of the catheters on prostate cancer patients was studied. Treatment plans with a better or equivalent dose distributions could be obtained with fewer catheters. A better or equal prostate V100 was obtained down to 12 catheters. Plans with nine or less catheters would not be clinically acceptable in terms of prostate V100 and D90. Implantation errors up to 3 mm were acceptable since no statistical difference was found when compared to 0 mm error (p > 0.05). No significant difference in dosimetric indices was observed for the different combination of parameters within the CVT algorithm. A linear relation was found between the number of random points and the optimization time of the CVT algorithm. Because the computation time decrease with the number of points and that no effects were observed on the dosimetric indices when varying the number of sampling points and the number of iterations, they were respectively fixed to 2500 and to 100. The computation time to obtain ten complete treatments plans ranging from 9 to 18 catheters, with the corresponding dosimetric indices, was 90 s. However, 93% of the computation time is used by a research version of IPSA. For the breast, on average, the Radiation Therapy Oncology Group recommendations would be satisfied down to 12 catheters. Plans with nine or less catheters would not be clinically acceptable in terms of V100, dose homogeneity index, and D90.

CONCLUSIONS

The authors have devised a simple, fast and efficient method to optimize the number and position of catheters in interstitial HDR brachytherapy. The method was shown to be robust for both prostate and breast HDR brachytherapy. More importantly, the computation time of the algorithm is acceptable for clinical use. Ultimately, this catheter optimization algorithm could be coupled with a 3D ultrasound system to allow real-time guidance and planning in HDR brachytherapy.

A method to estimate composite doses for organs at risk in prostate cancer patients treated with EBRT in combination with HDR BT

BACKGROUND

When evaluating late toxicity after combined external beam radiation therapy (EBRT) and high-dose rate brachytherapy (HDR BT) prostate cancer treatments, it is important that the composite dose distribution is taken into account. This can be challenging if organ-at-risk (OAR) dose data are incomplete, i.e. due to a limited ultrasound imaging field-of-view in the HDR BT procedure. This work proposes a method that provides estimates of composite OAR doses for such situations.

MATERIAL AND METHODS

Original EBRT, simulated HDR BT, and composite dose-volume histograms (DVHs) for 10 pelvic OARs in 30 prostate cancer cases were used for method implementation and evaluation (EBRT: 25×2.0 Gy+BT: 2×10.0 Gy). The proposed method used information from the EBRT DVH to estimate OAR BT doses (with or without fractionation correction). Coefficients of determination (R2) were calculated for linear relationships between several EBRT DVH parameters and a BT DVH parameter of interest. The largest R2 value decided the relationship that best predicted the BT DVH parameter. The composite dose value was then calculated by adding the EBRT DVH and the estimated BT DVH parameter values and was compared to the reference composite value (in 1200 OAR/patient/parameter cases).

RESULTS

The linear relationships had an average R2 of 0.68 (range 0.42-0.88). Only one ninth of the 1200 estimated composite DVH values differed more than 2 Gy from their reference values.

CONCLUSION

Given a successful implementation, the proposed method only requires original or simulated BT plan data for a subset of patients to estimate composite doses for large study populations in a time-efficient manner. This can assist in evaluating radiation-induced late toxicity in multimodality treatments with limited OAR dose data.

Inverse planning for combination of intracavitary and interstitial brachytherapy for locally advanced cervical cancer

The main purpose of this study was to compare three different treatment plans for locally advanced cervical cancer: (i) the inverse-planning simulated annealing (IPSA) plan for combination brachytherapy (BT) of interstitial and intracavitary brachytherapy, (ii) manual optimization based on the Manchester system for combination-BT, and (iii) the conventional Manchester system using only tandem and ovoids. This was a retrospective study of 25 consecutive implants. The high-risk clinical target volume (HR-CTV) and organs at risk were defined according to the GEC-ESTRO Working Group definitions. A dose of 6 Gy was prescribed. The uniform cost function for dose constraints was applied to all IPSA-generated plans. The coverage of the HR-CTV by IPSA for combination-BT was equivalent to that of manual optimization, and was better than that of the Manchester system using only tandem and ovoids. The mean V100 achieved by IPSA for combination-BT, manual optimization and Manchester was 96 ± 3.7%, 95 ± 5.5% and 80 ± 13.4%, respectively. The mean D100 was 483 ± 80, 487 ± 97 and 335 ± 119 cGy, respectively. The mean D90 was 677 ± 61, 681 ± 88 and 513 ± 150 cGy, respectively. IPSA resulted in significant reductions of the doses to the rectum (IPSA D2cm(3): 408 ± 71 cGy vs manual optimization D2cm(3): 485 ± 105 cGy; P = 0.03) and the bladder (IPSA D2cm(3): 452 ± 60 cGy vs manual optimization D2cm(3): 583 ± 113 cGy; P < 0.0001). In conclusion, combination-BT achieved better tumor coverage, and plans using IPSA provided significant sparing of normal tissues without compromising CTV coverage.

Evaluation of hybrid inverse planning and optimization (HIPO) algorithm for optimization in real-time, high-dose-rate (HDR) brachytherapy for prostate

The purpose of this study is to investigate the effectiveness of the HIPO planning and optimization algorithm for real‐time prostate HDR brachytherapy. This study consists of 20 patients who underwent ultrasound‐based real‐time HDR brachytherapy of the prostate using the treatment planning system called Oncentra Prostate (SWIFT version 3.0). The treatment plans for all patients were optimized using inverse dose‐volume histogram–based optimization followed by graphical optimization (GRO) in real time. The GRO is manual manipulation of isodose lines slice by slice. The quality of the plan heavily depends on planner expertise and experience. The data for all patients were retrieved later, and treatment plans were created and optimized using HIPO algorithm with the same set of dose constraints, number of catheters, and set of contours as in the real‐time optimization algorithm. The HIPO algorithm is a hybrid because it combines both stochastic and deterministic algorithms. The stochastic algorithm, called simulated annealing, searches the optimal catheter distributions for a given set of dose objectives. The deterministic algorithm, called dose‐volume histogram–based optimization (DVHO), optimizes three‐dimensional dose distribution quickly by moving straight downhill once it is in the advantageous region of the search space given by the stochastic algorithm. The PTV receiving 100% of the prescription dose (V100) was 97.56% and 95.38% with GRO and HIPO, respectively. The mean dose (Dmean) and minimum dose to 10% volume (D10) for the urethra, rectum, and bladder were all statistically lower with HIPO compared to GRO using the student pair t‐test at 5% significance level. HIPO can provide treatment plans with comparable target coverage to that of GRO with a reduction in dose to the critical structures.

PACS number: 87.55.‐X

Sector analysis of 125I permanent prostate brachytherapy provides a rapid and effective method of evaluating and comparing pre- and post-implant dosimetry

PURPOSE

To evaluate a sector analysis program in the assessment and comparison of pre- and post-implant dosimetric parameters during the development of an (125)I permanent prostate brachytherapy service.

METHODS AND MATERIALS

A total of 50 consecutive men being treated with permanent prostate brachytherapy had dose-volume analysis in 12 sectors of their pre-implant ultrasound (USpre) and post-implant CT (CTpost) studies. Individual sectors were created by dividing prostate into three equal lengths, namely base, midgland, and apex. Each of these volumes was then divided into four axial sectors. Dosimetric parameters were compared in adjoining sectors within each study and between studies.

RESULTS

There were statistically significant differences between individual sectors on USpre and CTpost volumes with CTpost higher than USpre (p=0.001). Statistically significant differences were found in corresponding sectors on USpre and CTpost for all dosimetric parameters. The dosimetric parameters were significantly lower on CTpost in the anterior base and midgland (p=0.001) and significantly higher at the posterior apex and midgland (p=0.05). Dose homogeneity was demonstrated in adjoining sectors in all USpre and most adjoining sectors on CTpost.

CONCLUSIONS

Sector analysis allows rapid assessment of USpre and CTpost dosimetry. It offers a scientific method of identifying areas of increased and reduced dosing on CTpost when compared with USpre, providing a learning tool to refine dosimetric analysis and highlight sectors where implant quality could be improved.

IPIP: A new approach to inverse planning for HDR brachytherapy by directly optimizing dosimetric indices

PURPOSE

Many planning methods for high dose rate (HDR) brachytherapy require an iterative approach. A set of computational parameters are hypothesized that will give a dose plan that meets dosimetric criteria. A dose plan is computed using these parameters, and if any dosimetric criteria are not met, the process is iterated until a suitable dose plan is found. In this way, the dose distribution is controlled by abstract parameters. The purpose of this study is to develop a new approach for HDR brachytherapy by directly optimizing the dose distribution based on dosimetric criteria.

METHODS

The authors developed inverse planning by integer program (IPIP), an optimization model for computing HDR brachytherapy dose plans and a fast heuristic for it. They used their heuristic to compute dose plans for 20 anonymized prostate cancer image data sets from patients previously treated at their clinic database. Dosimetry was evaluated and compared to dosimetric criteria.

RESULTS

Dose plans computed from IPIP satisfied all given dosimetric criteria for the target and healthy tissue after a single iteration. The average target coverage was 95%. The average computation time for IPIP was 30.1 s on an Intel(R) Core 2 Duo CPU 1.67 GHz processor with 3 Gib RAM.

CONCLUSIONS

IPIP is an HDR brachytherapy planning system that directly incorporates dosimetric criteria. The authors have demonstrated that IPIP has clinically acceptable performance for the prostate cases and dosimetric criteria used in this study, in both dosimetry and runtime. Further study is required to determine if IPIP performs well for a more general group of patients and dosimetric criteria, including other cancer sites such as GYN.

Does help structures play a role in reducing the variation of dwell time in IPSA planning for gynaecological brachytherapy application?

PURPOSE

To report our experience of dosimetric comparison of IPSA and manual plans, with a focus on the use of help structures (HS) during optimization.

MATERIAL AND METHODS

33 patients who underwent MR image-based HDR intracavitary-brachytherapy for cervix cancer based on GYN-ESTRO recommendations were selected for evaluation. Tandem/ovoid (T/O) and Vienna applicators were used. HS of diameter of 5 mm were drawn around the tandem/needles/ovoid and ring. Three plans were generated: manual optimized plan (MOPT), IPSA without help structures (IPSA_woHS) and IPSA with help structures (IPSA_wHS). Dose-volume parameters and the loading pattern were evaluated.

RESULTS

For T/O, the use of HS did not make significant impact in the dose-volume parameters and in the loading of tandem and ovoids, however steep variation was found in the individual dwell time. In case of Vienna applicator, inclusion of HS in the optimization made a significant impact in loading of needles. The percentage ratio of total time of needles to the tandem (T(N/T%)) was found to be 14±2.5, 53±9, 22±6 for MOPT, IPSA_woHS and IPSA_wHS, respectively, which implies that in IPSA_woHS the dwell time in needles were half of the dwell time in the tandem, while in MOPT the needles were loaded only in 14%, and in IPSA_wHS it was 22% of the dwell time of tandem. Inclusion of HS in the optimization has reduced the contribution of dwell time of needle in IPSA_wHS. The individual variation of dwell time was also reduced in IPSA_wHS, however drawing of HS is a time consuming procedure and may not be practical for a routine practice.

CONCLUSION

The role of HS was evaluated for IPSA for T/O and Vienna-applicator, the use of HS may be beneficial in case of combined intracavitary - interstitial approach.

Dosimetric analysis and comparison of IMRT and HDR brachytherapy in treatment of localized prostate cancer

Radical radiotherapy is one of the options for the management of prostate cancer. In external beam therapy, 3D conformal radiotherapy (3DCRT) and intensity modulated radiotherapy (IMRT) are the options for delivery of increased radiation dose, as vital organs are very close to the prostate and a higher dose to these structures leads to an increased toxicity. In brachytherapy, low dose rate brachytherapy with permanent implant of radioactive seeds and high dose rate brachytherapy (HDR) with remote after loaders are available. A dosimetric analysis has been made on IMRT and HDR brachytherapy plans. Ten cases from each IMRT and HDR brachytherapy have been taken for the study. The analysis includes comparison of conformity and homogeneity indices, D100, D95, D90, D80, D50, D10 and D5 of the target. For the organs at risk (OAR), namely rectum and bladder, V100, V90 and V50 are compared. In HDR brachytherapy, the doses to 1 cc and 0.1 cc of urethra have also been studied. Since a very high dose surrounds the source, the 300% dose volumes in the target and within the catheters are also studied in two plans, to estimate the actual volume of target receiving dose over 300%. This study shows that the prescribed dose covers 93 and 92% of the target volume in IMRT and HDR brachytherapy respectively. HDR brachytherapy delivers a much lesser dose to OAR, compared to the IMRT. For rectum, the V50 in IMRT is 34.0cc whilst it is 7.5cc in HDR brachytherapy. With the graphic optimization tool in HDR brachytherapy planning, the dose to urethra could be kept within 120% of the target dose. Hence it is concluded that HDR brachytherapy may be the choice of treatment for cancer of prostate in the early stage.

A detailed dosimetric comparison between manual and inverse plans in HDR intracavitary/interstitial cervical cancer brachytherapy

PURPOSE

The purpose of this study was to compare two inverse planning algorithms for cervical cancer brachytherapy and a conventional manual treatment planning according to the MUW (Medical University of Vienna) protocol.

MATERIAL AND METHODS

For 20 patients, manually optimized, and, inversely optimized treatment plans with Hybrid Inverse treatment Planning and Optimization (HIPO) and with Inverse Planning Simulated Annealing (IPSA) were created. Dosimetric parameters, absolute volumes of normal tissue receiving reference doses, absolute loading times of tandem, ring and interstitial needles, Paddick and COIN conformity indices were evaluated.

RESULTS

HIPO was able to achieve a similar dose distribution to manual planning with the restriction of high dose regions. It reduced the loading time of needles and the overall treatment time. The values of both conformity indices were the lowest. IPSA was able to achieve acceptable dosimetric results. However, it overloaded the needles. This resulted in high dose regions located in the normal tissue. The Paddick index for the volume of two times prescribed dose was outstandingly low.

CONCLUSIONS

HIPO can produce clinically acceptable treatment plans with the elimination of high dose regions in normal tissue. Compared to IPSA, it is an inverse optimization method which takes into account current clinical experience gained from manual treatment planning.

Comparison of IPSA with dose-point optimization and manual optimization for interstitial template brachytherapy for gynecologic cancers

PURPOSE

To compare inverse planning simulated annealing (IPSA) algorithm with the dose-point optimized (DPO) plan and manual/graphically optimized (GrO) plan for interstitial template brachytherapy for gynecologic cancers.

METHODS AND MATERIALS

The data set of 10 consecutive patients was selected for this dosimetric study. For each patient, three plans were calculated: DPO, GrO, and IPSA. Dose-volume parameters from the three plans were compared to analyze the dosimetric outcome.

RESULTS

Coverage of the clinical target volume (CTV) with GrO plan and IPSA algorithm was significantly better (mean V(100) of 88.8% and 89.1%; p=0.006) as compared with DPO plan (83.7%; p=0.62). Similarly, mean D(90) was same in both GrO plan and IPSA, 3.96±0.23 and 3.96±0.15Gy, respectively. DPO plans were homogeneous with homogeneity index being 0.82 as compared with 0.68±0.05 of GrO plan and 0.71±0.04 of IPSA. However, IPSA resulted in high conformity with conformity index of 0.78 as compared with 0.72 (p=0.001) and 0.68 (p≤0.001) for GrO and DPO plans, respectively. The dose to rectum (3.3±1.06Gy) and bladder (3.17±0.5Gy) was generally high for DPO plan. GrO plan reduced the dose to the rectum (2.91±0.63; p=0.011) and bladder (2.89±0.63Gy; p=0.003) significantly. IPSA resulted in a further reduction of the dose to rectum (2.79±0.67Gy; p=0.046) and bladder (2.81±0.67Gy; p=0.035), however with no statistical significance as compared with GrO plan.

CONCLUSION

IPSA resulted in significant sparing of normal tissues without compromising CTV coverage as compared with DPO plan. However, IPSA did not show any significant improvement either in CTV coverage or in normal tissue sparing as compared with GrO plan. IPSA was found to be superior in terms of homogeneity and conformity as compared with GrO plan.

New inverse planning technology for image-guided cervical cancer brachytherapy: description and evaluation within a clinical frame

PURPOSE

To test the feasibility of a new inverse planning technology based on the Hybrid Inverse treatment Planning and Optimisation (HIPO) algorithm for image-guided cervical cancer brachytherapy in comparison to conventional manual optimisation as applied in recent clinical practice based on long-term intracavitary cervical cancer brachytherapy experience.

MATERIALS AND METHODS

The clinically applied treatment plans of 10 tandem/ring (T/R) and 10 cases with additional needles (T/R+N) planned with PLATO v14.3 were included. Standard loading patterns were manually optimised to reach an optimal coverage with 7 Gy per fraction to the High Risk CTV and to fulfil dose constraints for organs at risk. For each of these patients an inverse plan was retrospectively created with Oncentra GYN v0.9.14. Anatomy based automatic source activation was based on the topography of target and organs. The HIPO algorithm included individual gradient and modification restrictions for the T/R and needle dwell times to preserve the spatial high-dose distribution as known from the long-term clinical experience in the standard cervical cancer brachytherapy and with manual planning.

RESULTS

HIPO could achieve a better target coverage (V100) for all T/R and 7 T/R+N patients. Changes in the shape of the overdose volume (V200/400) were limited. The D(2 cc) per fraction for bladder, rectum and sigmoid colon was on average lower by 0.2 Gy, 0.4 Gy, 0.2 Gy, respectively, for T/R patients and 0.6 Gy, 0.3 Gy, 0.3 Gy for T/R+N patients (a decrease from 4.5 to 4 Gy per fraction means a total dose reduction of 5 Gy EQD2 for a 4-fraction schedule). In general the dwell times in the additional needles were lower compared to manual planning. The sparing factors were always better for HIPO plans. Additionally, in 7 T/R and 7 T/R+N patients all three D(0.1 cc), D(1 cc) and D(2 cc) for vagina wall were lower and a smaller area of vagina was covered by the reference dose in HIPO plans. Overall loading times in the tandem, the ring and the needles, as well as dose distribution, were largely preserved with adaptations performed due to specific topographical variations, in particular in lateral and caudal directions.

CONCLUSIONS

Inverse planning based on the HIPO algorithm can produce treatment plans for cervical cancer brachytherapy which are comparable to plans based on manual optimisation as applied in clinical practice. It is essential to take into account the spatial dose distribution in addition to the DVH-based constraints. The proposed inverse planning concept is feasible for improving the therapeutic ratio and limiting substantial high-dose regions around needles.

Anatomy-based inverse planning simulated annealing optimization in high-dose-rate prostate brachytherapy: significant dosimetric advantage over other optimization techniques

PURPOSE

To perform an independent validation of an anatomy-based inverse planning simulated annealing (IPSA) algorithm in obtaining superior target coverage and reducing the dose to the organs at risk.

METHOD AND MATERIALS

In a recent prostate high-dose-rate brachytherapy protocol study by the Radiation Therapy Oncology Group (0321), our institution treated 20 patients between June 1, 2005 and November 30, 2006. These patients had received a high-dose-rate boost dose of 19 Gy to the prostate, in addition to an external beam radiotherapy dose of 45 Gy with intensity-modulated radiotherapy. Three-dimensional dosimetry was obtained for the following optimization schemes in the Plato Brachytherapy Planning System, version 14.3.2, using the same dose constraints for all the patients treated during this period: anatomy-based IPSA optimization, geometric optimization, and dose point optimization. Dose-volume histograms were generated for the planning target volume and organs at risk for each optimization method, from which the volume receiving at least 75% of the dose (V(75%)) for the rectum and bladder, volume receiving at least 125% of the dose (V(125%)) for the urethra, and total volume receiving the reference dose (V(100%)) and volume receiving 150% of the dose (V(150%)) for the planning target volume were determined. The dose homogeneity index and conformal index for the planning target volume for each optimization technique were compared.

RESULTS

Despite suboptimal needle position in some implants, the IPSA algorithm was able to comply with the tight Radiation Therapy Oncology Group dose constraints for 90% of the patients in this study. In contrast, the compliance was only 30% for dose point optimization and only 5% for geometric optimization.

CONCLUSIONS

Anatomy-based IPSA optimization proved to be the superior technique and also the fastest for reducing the dose to the organs at risk without compromising the target coverage.

Class solution in inverse planned HDR prostate brachytherapy for dose escalation of DIL defined by combined MRI/MRSI

PURPOSE

To establish an inverse planning set of parameters (class solution) to boost dominant intra-prostatic lesion (DIL) defined by MRI/MRSI.

METHODS

For 15 patients, DIL were contoured on CT or MR images and a class solution was developed to boost the DIL under the dosimetric requirements of the RTOG-0321 protocol. To determine the maximum attainable level of boost for each patient, 5 different levels were considered, at least 110%, 120%, 130%, 140% and 150% of the prescribed dose. The maximum attainable level was compared to the plan without boost using cumulative dose volume histogram (DVH).

RESULTS

DIL dose escalation was feasible for 11/15 patients under the requirements. The planning target volume (PTV) dose was slightly increased, while the DIL dose was significantly increased without any violation of requirements. With slight adjustments of the dose constraint parameters, the dose escalation was feasible for 13/15 patients under requirements.

CONCLUSION

Using a class solution, a dose escalation of the MRI/MRSI defined DIL up to 150% while complying with RTOG dosimetric requirements is feasible. This HDR brachytherapy approach to dose escalation allows a significant dose increase to the tumor while maintaining an acceptable risk of complications.

In vivo dosimetry of high-dose-rate interstitial brachytherapy in the pelvic region: use of a radiophotoluminescence glass dosimeter for measurement of 1004 points in 66 patients with pelvic malignancy

PURPOSE

To perform the largest in vivo dosimetry study for interstitial brachytherapy yet to be undertaken using a new radiophotoluminescence glass dosimeter (RPLGD) in patients with pelvic malignancy and to study the limits of contemporary planning software based on the results.

PATIENTS AND METHODS

Sixty-six patients with pelvic malignancy were treated with high-dose-rate interstitial brachytherapy, including prostate (n = 26), gynecological (n = 35), and miscellaneous (n = 5). Doses for a total of 1004 points were measured by RPLGDs and calculated with planning software in the following locations: rectum (n = 549), urethra (n = 415), vagina (n = 25), and perineum (n = 15). Compatibility (measured dose/calculated dose) was analyzed according to dosimeter location.

RESULTS

The compatibility for all dosimeters was 0.98 +/- 0.23, stratified by location: rectum, 0.99 +/- 0.20; urethra, 0.96 +/- 0.26; vagina, 0.91 +/- 0.08; and perineum, 1.25 +/- 0.32.

CONCLUSIONS

Deviations between measured and calculated doses for the rectum and urethra were greater than 20%, which is attributable to the independent movements of these organs and the applicators. Missing corrections for inhomogeneity are responsible for the 9% negative shift near the vaginal cylinder (specific gravity = 1.24), whereas neglect of transit dose contributes to the 25% positive shift in the perineal dose. Dose deviation of >20% for nontarget organs should be taken into account in the planning process. Further development of planning software and a real-time dosimetry system are necessary to use the current findings and to achieve adaptive dose delivery.

Inverse Planning Approach for 3-D MRI-Based Pulse-Dose Rate Intracavitary Brachytherapy in Cervix Cancer

PURPOSE

The purpose of this study was to evaluate the inverse planning simulated annealing (IPSA) software for the optimization of dose distribution in patients with cervix carcinoma treated with MRI-based pulsed-dose rate intracavitary brachytherapy.

METHODS AND MATERIALS

Thirty patients treated with a technique using a customized vaginal mold were selected. Dose-volume parameters obtained using the IPSA method were compared with the classic manual optimization method (MOM). Target volumes and organs at risk were delineated according to the Gynecological Brachytherapy Group/European Society for Therapeutic Radiology and Oncology recommendations. Because the pulsed dose rate program was based on clinical experience with low dose rate, dwell time values were required to be as homogeneous as possible. To achieve this goal, different modifications of the IPSA program were applied.

RESULTS

The first dose distribution calculated by the IPSA algorithm proposed a heterogeneous distribution of dwell time positions. The mean D90, D100, and V100 calculated with both methods did not differ significantly when the constraints were applied. For the bladder, doses calculated at the ICRU reference point derived from the MOM differed significantly from the doses calculated by the IPSA method (mean, 58.4 vs. 55 Gy respectively; p = 0.0001). For the rectum, the doses calculated at the ICRU reference point were also significantly lower with the IPSA method.

CONCLUSIONS

The inverse planning method provided fast and automatic solutions for the optimization of dose distribution. However, the straightforward use of IPSA generated significant heterogeneity in dwell time values. Caution is therefore recommended in the use of inverse optimization tools with clinical relevance study of new dosimetric rules.

Measurement of craniocaudal catheter displacement between fractions in computed tomography-based high dose rate brachytherapy of prostate cancer

The objective of this work is to measure the cranio-caudal displacement of catheters occurring between consecutive fractions of transrectal ultrasound (TRUS) guided high dose rate (HDR) prostate brachytherapy. Ten consecutive patients were treated with 2 fractions of 9.5 Gy TRUS guided HDR brachytherapy using dental putty for the fixation of catheters. For each patient, a CT scan with 3 mm slice thickness was acquired before each of the two fractions. Two different references were employed to measure the catheter displacement between fractions: the ischial bone as a bony marker (BM) and the center of two gold markers (COGM) implanted in the prostate. The catheter displacement was calculated by multiplying the thickness of CT slice with the difference in number of CT slices between the reference slice and the slice containing the tip of a catheter. The average (range) magnitude of caudal catheter displacement was 2.7 mm (-6.0 to 13.5 mm) for BM method and 5.4 mm (-3.75 to 18.0 mm) for COGM method, respectively. The measurement data obtained from BM and COGM methods verified that both prostate movement and catheter displacement occurred independently between fractions. The most anterior and medial two catheters (catheter position 8 and 12) had the greatest tendency to be displaced in the caudal direction because they were located at the most distant position from the fulcrum, susceptible to the rotation of the dental putty in lateral plane due to the movement of patient legs between fractions. In conclusion, the use of both BM and COGM methods can demonstrate the prostate and catheter movement relative to the BM between fractions. We found a pattern of catheter displacement using our technique. Based on our finding further improvement of our results may be possible by modification of our current technique.

Optimization of HDR brachytherapy dose distributions using linear programming with penalty costs

Prostate cancer is increasingly treated with high-dose-rate (HDR) brachytherapy, a type of radiotherapy in which a radioactive source is guided through catheters temporarily implanted in the prostate. Clinicians must set dwell times for the source inside the catheters so the resulting dose distribution minimizes deviation from dose prescriptions that conform to patient-specific anatomy. The primary contribution of this paper is to take the well-established dwell times optimization problem defined by Inverse Planning by Simulated Annealing (IPSA) developed at UCSF and exactly formulate it as a linear programming (LP) problem. Because LP problems can be solved exactly and deterministically, this formulation provides strong performance guarantees: one can rapidly find the dwell times solution that globally minimizes IPSA's objective function for any patient case and clinical criteria parameters. For a sample of 20 prostates with volume ranging from 23 to 103 cc, the new LP method optimized dwell times in less than 15 s per case on a standard PC. The dwell times solutions currently being obtained clinically using simulated annealing (SA), a probabilistic method, were quantitatively compared to the mathematically optimal solutions obtained using the LP method. The LP method resulted in significantly improved objective function values compared to SA (P = 1.54 x 10(-7)), but none of the dosimetric indices indicated a statistically significant difference (P < 0.01). The results indicate that solutions generated by the current version of IPSA are clinically equivalent to the mathematically optimal solutions.

Comparative study of dosimetry between high-dose-rate and permanent prostate implant brachytherapies in patients with prostate adenocarcinoma

PURPOSE

To compare the dose coverage, conformity, and homogeneity between high-dose-rate (HDR) brachytherapy and permanent prostate implant (PPI) in the treatment of prostate adenocarcinoma.

METHODS AND MATERIALS

From January 2003 to August 2004, 54 patients (108 implants) underwent HDR brachytherapy of prostate cancer with iridium-192 stepping source. Of patients who underwent PPI brachytherapy with iodine-125, 72 patients were randomly selected for the purpose of dosimetric comparison. PPI preplan was done based on transrectal ultrasound study, and postplan was done using CT 1 month after implant. Dosimetric parameters of HDR were compared to that of PPI preplan and postplan.

RESULTS

HDR brachytherapy had lower D90 (111.5% vs. 120.2%), lower V100 (97.2% vs. 99.6%), lower natural dose ratio (1.03 vs. 1.13), higher conformal index (0.69 vs. 0.62), and higher homogeneity index (0.63 vs. 0.52) than PPI preplan (all p < 0.0001). All the dosimetric parameters of PPI postplan including D90 (86.7%), V100 (82.0%), natural dose ratio (0.92), conformal index (0.53), and homogeneity index (0.42) were inferior to HDR brachytherapy (all p < 0.0001).

CONCLUSIONS

HDR brachytherapy of the prostate can provide better dose coverage, conformity, and homogeneity compared to PPI.

Class solution for inversely planned permanent prostate implants to mimic an experienced dosimetrist

The purpose of this paper is to present a method for the selection of inverse planning parameters and to establish a set of inverse planning parameters (class solution) for the inverse planning included in a commercial permanent prostate implant treatment planning system. The manual planning of more than 750 patients since 1996 led to the establishment of general treatment planning rules. A class solution is tuned to fulfill the treatment planning rules and generate equivalent implants. For ten patients, the inverse planning is compared with manual planning performed by our experienced physicist. The prostate volumes ranged from 17 to 51 cc and are implanted with low activity 1-125 seeds. Dosimetric indices are calculated for comparison. The inverse planning needed about 15 s for each optimization (400 000 iterations on a 2.5 GHz PC). In comparison, the physicist needed about 20 min to perform each manual plan. A class solution is found that consistently produces dosimetric indices equivalent or better than the manual planning. Moreover, even with strict seed placement rules, the inverse planning can produce adequate prostate dose coverage and organ at risk protection. The inverse planning avoids implant with seeds outside of the prostate and too close to the urethra. It also avoids needles with only one seed and needles with three consecutive seeds. This reduces the risk of complication due to seed misplacement and edema. The inverse planning also uses a smaller number of needles, reducing the cause of trauma. The quality of the treatment plans is independent of the gland size and shape. A class solution is established that consistently and rapidly produces equivalent dosimetric indices as manual planning while respecting severe seed placement rules. The class solution can be used as a starting point for every patient, dramatically reducing the time needed to plan individual patient treatments. The class solution works with inverse preplanning, intraoperative inverse preplanning, and intraoperative real-time planning. This technology is not intended to replace the physicist but to accelerate the planning process, making intraoperative treatment planning more effective.

Potential dose-conformity advantages with multi-source intensity-modulated brachytherapy (IMBT)

The possibilities for optimizing brachytherapy by including additional degrees of freedom in source design were investigated. This included examining optimised dose delivery with a brachytherapy source that can provide intensity-modulated dose delivery in angle about the source travel direction (to achieve intensity-modulated brachytherapy-IMBT). A prostate HDR case was selected as an example. An inverse planning algorithm was used to define how an asymmetric radiation source can be controlled in multiple source catheters to maximize tumour dose coverage and minimize urethral and rectal doses. Substantial improvements in conformity in terms of tumour coverage and urethral dose reduction could be achieved when conventional HDR source positioning was used with IMBT. With the objective definition used in the example however, rectal doses could not be improved over those delivered via conventional HDR. When source position was included as a variable in IMBT, significant conformity improvements result for all structures. IMBT would be a technically challenging form of therapy that would be strongly influenced by the type of sources that could be created for it. This study has shown however that there is a potential for improving dose conformity with such a therapy. Introduction of IMBT techniques would require conventional brachytherapy concepts to be radically modified.

Anatomy-based inverse optimization in high-dose-rate brachytherapy combined with hypofractionated external beam radiotherapy for localized prostate cancer: Comparison of incidence of acute genitourinary toxicity between anatomy-based inverse optimization and geometric optimization

PURPOSE

To evaluate the advantages of anatomy-based inverse optimization (IO) in planning high-dose-rate (HDR) brachytherapy.

METHODS AND MATERIALS

A total of 114 patients who received HDR brachytherapy (9 Gy in two fractions) combined with hypofractionated external beam radiotherapy (EBRT) were analyzed. The dose distributions of HDR brachytherapy were optimized using geometric optimization (GO) in 70 patients and by anatomy-based IO in the remaining 44 patients. The correlation between the dose-volume histogram parameters, including the urethral dose and the incidence of acute genitourinary (GU) toxicity, was evaluated.

RESULTS

The averaged values of the percentage of volume receiving 80-150% of the prescribed minimal peripheral dose (V(80)-V(150)) of the urethra generated by anatomy-based IO were significantly lower than the corresponding values generated by GO. Similarly, the averaged values of the minimal dose received by 5-50% of the target volume (D(5)-D(50)) obtained using anatomy-based IO were significantly lower than those obtained using GO. Regarding acute toxicity, Grade 2 or worse acute GU toxicity developed in 23% of all patients, but was significantly lower in patients for whom anatomy-based IO (16%) was used than in those for whom GO was used (37%), consistent with the reduced urethral dose (p <0.01).

CONCLUSION

The results of this study suggest that anatomy-based IO is superior to GO for dose optimization in HDR brachytherapy for prostate cancer.

3D inverse treatment planning for the tandem and ovoid applicator in cervical cancer

PURPOSE

Three-dimensional treatment planning systems and inverse planning optimization for brachytherapy are becoming commercially available. Guidelines for target delineation and dose constrictions have not been established using this new software. In this study we describe a method of target delineation for the tandem and ovoids applicator. We then compare inverse planning dose distributions with the traditional methods of prescribing dose.

METHODS AND MATERIALS

Target and organ-at-risk volumes were defined using systematic guidelines on 15 patients treated in our department with high-dose-rate brachytherapy for cervical cancer using tandem and ovoids. High-dose-rate distributions were created according to three different dose optimization protocols: inverse planning simulated annealing (IPSA), point A, and point A with a normalization of 2 cc of the bladder receiving 80% of the dose (bladder-sparing method). An uniform cost function for dose constraints was applied to all IPSA generated plans, and no manual optimization was allowed for any planning method.

RESULTS

Guidelines for target and structure-at-risk volumes, as well as dose constraint cost functions, were established. Dose-volume histogram analysis showed that the IPSA algorithm indicated no difference in tumor coverage compared with point A optimization while decreasing dose to the bladder and rectum. The IPSA algorithm provided better target volume coverage compared with bladder-sparing method with equivalent doses to the bladder and rectum.

CONCLUSION

This study uses a systematic approach for delineating target and organ-at-risk volumes and a uniform cost function for generating IPSA plans for cervical cancer using tandem and ovoids. Compared with conventional dose prescription methods, IPSA provides a consistent method of optimization that maintains or improves target coverage while decreasing dose to normal structures. Image-guided brachytherapy and inverse planning improve brachytherapy dosimetry.

Optimization of dose distribution for HDR brachytherapy of the prostate using Attraction-Repulsion Model

PURPOSE

To optimize dose distribution for high-dose-rate brachytherapy for prostate cancer, we have developed a new algorithm named Attraction-Repulsion Model (ARM). In this study, we compared the ARM with geometric optimization (GO).

METHODS AND MATERIALS

The ARM was used to optimize the dose distribution by finding the best dwell time combination. ARM requires grids inside the clinical target volume (CTV) and critical organs. These grids generate attraction or repulsion based on specific dose constraints. After calculations were performed repeatedly until the attraction and repulsion forces reached equilibrium, the optimal dwell time distribution was established. We compared the ARM with GO for 10 patients using dose-volume histograms.

RESULTS

The CTV ranged from 23 to 48 cc, and the CTV V150 ranged from 52% to 79%, and 23% to 44% for GO and ARM, respectively. This indicates that the dose homogeneity indices, as well as the conformal indices, were higher for ARM than for GO. The urethra V150 was 0-99% and 0-1% for GO and ARM, respectively.

CONCLUSION

The ARM proved to be superior to GO in minimizing the dose to normal structures and in improving dose homogeneity for the target while reducing the dose to normal tissues.

Acute genitourinary toxicity after high dose rate (HDR) brachytherapy combined with hypofractionated external-beam radiation therapy for localized prostate cancer: Second analysis to determine the correlation between the urethral dose in HDR brachytherapy and the severity of acute genitourinary toxicity

PURPOSE

We have been treating localized prostate cancer with high-dose-rate (HDR) brachytherapy combined with hypofractionated external beam radiation therapy (EBRT) at our institution. We recently reported the existence of a correlation between the severity of acute genitourinary (GU) toxicity and the urethral radiation dose in HDR brachytherapy by using different fractionation schema. The purpose of this study was to evaluate the role of the urethral dose in the development of acute GU toxicity more closely than in previous studies. For this purpose, we conducted an analysis of patients who had undergone HDR brachytherapy with a fixed fractionation schema combined with hypofractionated EBRT.

METHODS AND MATERIALS

Among the patients with localized prostate cancer who were treated by 192-iridium HDR brachytherapy combined with hypofractionated EBRT at Gunma University Hospital between August 2000 and November 2004, we analyzed 67 patients who were treated by HDR brachytherapy with the fractionation schema of 9 Gy x two times combined with hypofractionated EBRT. Hypofractionated EBRT was administered at a fraction dose of 3 Gy three times weekly, and a total dose of 51 Gy was delivered to the prostate gland and seminal vesicles using the four-field technique. No elective pelvic irradiation was performed. After the completion of EBRT, all the patients additionally received transrectal ultrasonography-guided HDR brachytherapy. The planning target volume was defined as the prostate gland with a 5-mm margin all around, and the planning was conducted based on computed tomography images. The tumor stage was T1c in 13 patients, T2 in 31 patients, and T3 in 23 patients. The Gleason score was 2-6 in 12 patients, 7 in 34 patients, and 8-10 in 21 patients. Androgen ablation was performed in all the patients. The median follow-up duration was 11 months (range 3-24 months). The toxicities were graded based on the Radiation Therapy Oncology Group and the European Organization for Research and Treatment of Cancer toxicity criteria.

RESULTS

The main symptoms of acute GU toxicity were dysuria and increase in the urinary frequency or nocturia. The grade distribution of acute GU toxicity in the patients was as follows: Grade 0-1, 42 patients (63%); Grade 2-3, 25 patients (37%). The urethral dose in HDR brachytherapy was determined using the following dose-volume histogram (DVH) parameters: V30 (percentage of the urethral volume receiving 30% of the prescribed radiation dose), V80, V90, V100, V110, V120, V130, and V150. In addition, the D5 (dose covering 5% of the urethral volume), D10, D20, and D50 of the urethra were also estimated. The V30-V150 values in the patients with Grade 2-3 acute GU toxicity were significantly higher than those in patients with Grade 0-1 toxicity. The D10 and D20, but not D5 and D50, values were also significantly higher in the patients with Grade 2-3 acute GU toxicity than in those with Grade 0-1 toxicity. Regarding the influence of the number of needles implanted, there was no correlation between the number of needles implanted and the severity of acute GU toxicity or the V30-V150 values and D5-D50 values.

CONCLUSIONS

It was concluded that HDR brachytherapy combined with hypofractionated EBRT is feasible for localized prostate cancer, when considered from the viewpoint of acute toxicity. However, because the urethral dose was closely associated with the grade of severity of the acute GU toxicity, the urethral dose in HDR brachytherapy must be kept low to reduce the severity of acute GU toxicity.

Acute genitourinary toxicity after high-dose-rate (HDR) brachytherapy combined with hypofractionated external-beam radiation therapy for localized prostate cancer: Correlation between the urethral dose in HDR brachytherapy and the severity of acute genitourinary toxicity

PURPOSE

Several investigations have revealed that the alpha/beta ratio for prostate cancer is atypically low, and that hypofractionation or high-dose-rate (HDR) brachytherapy regimens using appropriate radiation doses may be expected to yield tumor control and late sequelae rates that are better or at least as favorable as those achieved with conventional radiation therapy. In this setting, we attempted treating localized prostate cancer patients with HDR brachytherapy combined with hypofractionated external beam radiation therapy (EBRT). The purpose of this study was to evaluate the feasibility of using this approach, with special emphasis on the relationship between the severity of acute genitourinary (GU) toxicity and the urethral dose calculated from the dose-volume histogram (DVH) of HDR brachytherapy.

METHODS AND MATERIALS

Between September 2000 and December 2003, 70 patients with localized prostate cancer were treated by iridium-192 HDR brachytherapy combined with hypofractionated EBRT at the Gunma University Hospital. Hypofractionated EBRT was administered in fraction doses of 3 Gy, three times per week; a total dose of 51 Gy was delivered to the prostate gland and the seminal vesicles using the four-field technique. No elective pelvic irradiation was performed. After the completion of EBRT, all the patients additionally received transrectal ultrasonography (TRUS)-guided HDR brachytherapy. The fraction size and the number of fractions in HDR brachytherapy were prospectively changed, whereas the total radiation dose for EBRT was fixed at 51 Gy. The fractionation in HDR brachytherapy was as follows: 5 Gy x 5, 7 Gy x 3, 9 Gy x 2, administered twice per day, although the biologic effective dose (BED) for HDR brachytherapy combined with EBRT, assuming that the alpha/beta ratio is 3, was almost equal to 138 in each fractionation group. The planning target volume was defined as the prostate gland with 5-mm margin all around, and the planning was conducted based on computed tomography images. The number of patients in each fractionation group was as follows: 13 in the 5-Gy group; 19 in the 7-Gy group, and 38 in the 9-Gy group. The tumor stage was T1 in 10 patients, T2 in 36 patients, and T3 in 24 patients. The Gleason score was 2-6 in 11 patients, 7 in 34 patients, and 8-10 in 25 patients. Androgen ablation was performed in all the patients. The median follow-up duration was 14 months (range 3-42 months). The toxicities were graded based on the Radiation Therapy Oncology Group/European Organization for Research and Treatment of Cancer toxicity criteria.

RESULTS

The main symptoms of acute GU toxicity were dysuria and increase in urinary frequency or nocturia. The grade distribution of acute GU toxicity in the patients was as follows: Grade 0-1, 39 patients (56%), and Grade 2-4, 31 patients (44%). One patient who developed acute urinary obstruction was classified as having Grade 4 toxicity. Comparison of the distribution of the grade of acute GU toxicity among the different fractionation groups revealed no statistically significant differences among the groups. The urethral dose in HDR brachytherapy was evaluated using the following DVH parameters: V30 (percentage of the urethral volume receiving 30% of the prescribed radiation dose), V80, V90, V100, V110, V120, V130, and V150. The V30-110 values in the patients with Grade 2-4 acute GU toxicity were significantly higher than those in patients with Grade 0-1 toxicity. On the other hand, there were no significant differences in the V120-150 values between patients with Grade 0-1 and Grade 2-4 toxicity. Regarding the influence of the number of needles implanted for the radiation therapy, patients with 11 needles or less showed a significantly higher incidence of Grade 2-4 acute GU toxicity compared with those with 12 needles or more (p < 0.05).

CONCLUSIONS

It was concluded that HDR brachytherapy combined with hypofractionated EBRT is feasible for localized prostate cancer when considered from the viewpoint of acute toxicity. Increase in the fraction dose or reduction in the number of fractions in HDR brachytherapy did not affect the severity of acute GU toxicity, and the volume of urethra receiving an equal or lower radiation dose than the prescribed dose was more closely associated with the grade severity of acute GU toxicity than that receiving a higher than the prescribed dose.

Anatomy-based inverse planning dose optimization in HDR prostate implant: A toxicity study

BACKGROUND AND PURPOSE

The aim of this study is to evaluate the acute and late complications in patients who have received HDR implant boost using inverse planning, and to determine dose volume correlations.

PATIENTS AND METHODS

Between September 1999 and October 2002, 44 patients with locally advanced prostate cancer (PSA>/=10 ng/ml, and/or Gleason score>/=7, and/or Stage T2c or higher) were treated with 40-45 Gy external pelvic field followed by 2--3 fraction of inverse-planned HDR implant boost (6--9.5 Gy /fraction). Median follow-up time was 1.7 years with 81.8% of patients who had at least 12 months of follow up (range 8.6--42.5. Acute and late morbidity data were collected and graded according to RTOG criteria. Questionnaires were used to collect prostate related measures of quality of life, and international prostate symptom score (IPSS) before and after treatment. Dose-volume histograms for prostate, urethra, bladder, penis bulb and rectum were analyzed.

RESULTS

The median patient age was 64 years. Of these, 32% were in the high risk group, and 61% in the intermediate risk group. 3 patients (7%) had no adverse prognostic factors. A single grade 3 GU acute toxicity was reported but no grade 3--4 acute GI toxicity. No grade 3--4 late GU or GI toxicity was reported. Acute (late) grade 2 urinary and rectal symptoms were reported in 31.8 (11.4%) and 4.6% (4.6%) of patients, respectively. A trend for predicting acute GU toxicity is seen for total HDR dose of more than 18 Gy (OR=3.6, 95%CI=[0.96--13.5], P=0.058). The evolution of toxicity is presented for acute and late GU/GI toxicity. Erectile dysfunction occurs in approximately 27% of patients who were not on hormonal deprivation, but may be taking sildenafil. The IPSS peaked on averaged 6 weeks post-implant and returned to the baseline at a median of 6 months.

CONCLUSIONS

Inverse-planned HDR brachytherapy is a viable option to deliver higher dose to the prostate as a boost without increasing GU or rectal complication. Further HDR dose escalation to the prostate is feasible.

Comparison of inverse planning simulated annealing and geometrical optimization for prostate high-dose-rate brachytherapy

PURPOSE

An inverse planning simulated annealing (IPSA) algorithm for optimization of high-dose-rate (HDR) brachytherapy has been previously described. In this study, IPSA is compared with geometrical optimization (GO) for prostate brachytherapy.

METHODS AND MATERIALS

Using CT data collected from 10 patients, treatment plans were prepared using GO and IPSA. The clinical target volume (CTV) and critical organs (CO) including bladder, rectum, and urethra were contoured using Plato Version 14.2.1 (Nucletron Corp., Veenendaal, The Netherlands). Implant catheters were digitized using the CT planning system. All dwell positions outside of the CTV were turned off. Two optimized plans were generated for each implant using GO and IPSA. The same set of dose constraints were used for all inverse planning calculations and no manual adjustment of the dwell weight was used. Two prescription methods were used. Using the first method, coverage was prioritized: the prescription dose was normalized to the isodose volume that covers 98% of the CTV (V100 = 98% of CTV). The dose volume histograms (DVH) of CO were generated for comparison. Using the second method, sparing was prioritized: the prescription dose was normalized such that no urethra volume received 150% of the prescription dose (V150-urethra = 0 cc). The DVH of CTV and CO were generated, and the homogeneity index (HI) and conformal index (COIN) were calculated for comparison and compared using the Wilcoxon matched-pairs test.

RESULTS

Using the coverage-prioritized method, the difference in V80-bladder dose was not statistically significant (p = 0.09; median: IPSA = 0.62 cc, GO = 1.05 cc). The V80-rectum ranged from 0.20-4.8 cc, and 0.05-1.4 cc using GO and IPSA, respectively. IPSA's V80-rectum was significantly lower (p = 0.005; median: IPSA=0.38 cc, GO = 1.31 cc). V150-urethra ranged from 0.02-0.75 cc and 0.0-0.01 cc using GO and IPSA, respectively. The V150-urethra was significantly lower using IPSA (p = 0.005; median: IPSA = 0.00 cc, GO = 0.33 cc). Using the sparing prioritized method, the V100-prostate ranged from 30-97% and 95-100% using GO and IPSA, respectively. This difference was statistically significant (p = 0.008). The HI and COIN were statistically higher using IPSA (p = 0.005).

CONCLUSION

Anatomy-based inverse optimization using IPSA is superior to dwell-position-based optimization using GO as it: (1) Improves target coverage and conformality while sparing normal structures, (2) Improves dose homogeneity within the target, and (3) Minimizes volume of non-contoured normal tissue irradiated. Routine application of three-dimensional brachytherapy planning and anatomy-based inverse dwell time optimization is recommended.

In vivo dosimetry of high-dose-rate brachytherapy: study on 61 head-and-neck cancer patients using radiophotoluminescence glass dosimeter

PURPOSE

The largest in vivo dosimetry study for interstitial brachytherapy yet examined was performed using new radiophotoluminescence glass dosimeters (RPLGDs). Based on the results, a dose prescription technique achieving high reproducibility and eliminating large hyperdose sleeves was studied.

METHODS AND MATERIALS

For 61 head-and-neck cancer patients who underwent high-dose-rate interstitial brachytherapy, new RPLGDs were used for an in vivo study. The Paris System was used for implant. An arbitrary isodose surface was selected for dose prescription. Locations of 83 dosimeters were categorized as on target (n = 52) or on nontarget organ (n = 31) and were also scaled according to % basal dose isodose surface (% BDIS). Compatibility (measured dose/calculated dose) was analyzed according to location. The hyperdose sleeve was assessed in terms of prescription surface expressed in % BDIS.

RESULTS

The spread of compatibilities was larger for on nontarget organ (1.06 +/- 0.32) than for on target (0.87 +/- 0.17, p = 0.01). Within on target RPLGDs, compatibility on <95% BDIS (0.95 +/- 0.10) was better than on > or =95% BDIS (0.84 +/- 0.18, p = 0.02). The number of patients with diameter of hyperdose sleeve > or =10 mm was increased with a dose prescription to <77% BDIS (p = 0.046). For nontarget organs, the maximal positive deviation was 84% of the calculated dose.

CONCLUSIONS

Dose prescription is recommended to >77% and <95% BDIS for reproducibility and elimination of excessive hyperdose sleeve. For organs at risk, radioprotection should be considered even when calculated dose seems sufficiently low. Further development of planning software is necessary to prevent overestimation.