3D CT–based high-dose-rate breast brachytherapy implants: treatment planning and quality assurance

The use of hyaluronic acid hydrogel as a tumour bed marker in breast-conserving therapy

PURPOSE

To evaluate usefulness of hyaluronic acid (HA) hydrogel as a tumour bed marker in breast conserving therapy (BCT). To analyze inter- (Inter-OV) and intraobserver (Intra-OV) variability of contouring boost target volume (CTV_boost) in external beam radiotherapy (EBRT).

MATERIALS AND METHODS

Thirty-two patients in the HA group and 30 patients in the control group with an early stage breast cancer were included in the study. During the surgery 1-3 ml of HA hydrogel was injected into breast to mark the tumour bed for every patient in the HA group. Moreover, surgical clips were placed underneath the lumpectomy cavity. Patients in the control group were marked only by metal markers. Three radiation oncologists delineated CTV_boost twice for every patient. Three parameters were calculated to quantify contouring variability: coefficient of variation for volumes (COV_V), center of mass displacement (CoMd) and conformity index (CI).

RESULTS

There were no significant differences between mean values of COV_V for HA and control group, neither for Intra-OV (0.14 vs 0.13) nor Inter-OV (0.19 vs 0.18) calculations. The mean CoMd were 6.1 mm and 9.1 mm for Inter-OV calculations and 3.9 mm and 6.4 mm for Intra-OV in the HA and the control group respectively. The mean CI for Intra-OV improved from 0.61 to 0.65 and from 0.47 to 0.56 for Inter-OV in the control and HA group respectively.

CONCLUSION

HA hydrogel used as a tumour bed marker improves tumour bed visibility and reduces inter- and intraobserver variability of EBRT boost target volume delineations.

Long-Term Outcomes of Three-Dimensional High-Dose-Rate Brachytherapy for Locally Recurrent Early T-Stage Nasopharyngeal Carcinoma

Background: Brachytherapy (BT) is one of the techniques available for retreatment of patients with locally recurrent nasopharyng eal carcinoma (rNPC). In this study, we evaluated the treatment outcome and late toxicities of three-dimensional high-dose-rate brachytherapy (3D-HDR-BT) for patients with locally rNPC. Materials and Methods: This is a retrospective study involving 36 patients with histologically confirmed rNPC from 2004 to 2011. Of the 36 patients, 17 underwent combined-modality treatment (CMT) consisting of external beam radiotherapy (EBRT) followed by 3D-HDR-BT, while the other 19 underwent 3D-HDR-BT alone. The median dose of EBRT for the CMT group was 60 (range, 50-66) Gy, with an additional median dose of BT of 16 (range, 9-20) Gy. The median dose for the 3D-HDR-BT group was 32 (range, 20-36) Gy. The measured treatment outcomes were the 5- and 10-year locoregional recurrence-free survival (LRFS), disease-free survival (DFS), overall survival (OS), and late toxicities. Results: The median age at recurrence was 44.5 years. The median follow-up period was 70 (range, 6-142) months. The 5-year LRFS, DFS, and OS for the entire patient group were 75.4, 55.6, and 74.3%, respectively, while the 10-year LRFS, DFS, and OS for the entire patient group were 75.4, 44.2, and 53.7%, respectively. The 10-year LRFS in the CMT group was higher than that in the 3D-HDR-BT-alone group (93.8 vs. 58.8%, HR: 7.595, 95%CI: 1.233-61.826, p = 0.025). No grade 4 late radiotherapy-induced toxicities were observed. Conclusions: 3D-HDR-BT achieves favorable clinical outcomes with mild late toxicity in patients with locally rNPC.

Brachytherapy in the treatment of breast cancer

Brachytherapy is an important radio-therapeutic modality for a variety of malignancies, including prostate cancer, cervix cancer, breast cancer, vagina cancer, endometrium cancer, head and neck cancer, and many more. This technique has been shown to be an effective and safe non-pharmaceutical treatment with fewer serious complications and better outcome than other treatments for breast cancer. Every year, hundreds of thousands of patients around the world benefit from brachytherapy, which reliably delivers a relatively higher radiation dose to the intended target. However, the follow-up time, patient eligibility criteria, treatment strategy, and radiation doses used in published studies are somewhat inconsistent, making it difficult to strictly compare and evaluate the performance of the treatment. More rigorous studies are required to confirm the safety of this technique and to make outcome data more comparable. In this review, we focus on recent advances in breast brachytherapy techniques and provide an overview of outcomes, cosmetic outcome, toxicity, complications, and limitations of brachytherapy for the treatment of breast cancer. We also summarize the clinical outcomes and toxicity results in patients receiving or not receiving brachytherapy.

Treatment planning for multicatheter interstitial brachytherapy of breast cancer - from Paris system to anatomy-based inverse planning

In the last decades, treatment planning for multicatheter interstitial breast brachytherapy has evolved considerably from fluoroscopy-based 2D to anatomy-based 3D planning. To plan the right positions of the catheters, ultrasound or computed tomography (CT) imaging can be used, but the treatment plan is always based on postimplant CT images. With CT imaging, the 3D target volume can be defined more precisely and delineation of the organs at risk volumes is also possible. Consequently, parameters calculated from dose-volume histogram can be used for quantitative plan evaluation. The catheter reconstruction is also easier and faster on CT images compared to X-ray films. In high dose rate brachytherapy, using a stepping source, a number of forward dose optimization methods (manual, geometrical, on dose points, graphical) are available to shape the dose distribution to the target volume, and these influence dose homogeneities to different extent. Currently, inverse optimization algorithms offer new possibilities to improve dose distributions further considering the requirements for dose coverage, dose homogeneity, and dose to organs at risk simultaneously and automatically. In this article, the evolvement of treatment planning for interstitial breast implants is reviewed, different forward optimization methods are discussed, and dose-volume parameters used for quantitative plan evaluation are described. Finally, some questions of the inverse optimization method are investigated and initial experiences of the authors are presented.

Locoregional recurrence by molecular subtype after multicatheter interstitial accelerated partial breast irradiation: Results from the Pooled Registry Of Multicatheter Interstitial Sites research group

PURPOSE

To determine in breast tumor recurrence (IBTR) and regional nodal recurrence (RNR) rates for women treated with multicatheter interstitial accelerated partial breast irradiation.

METHODS AND MATERIALS

Data from five institutions were collected for patients treated from 1992 to 2013. We report outcomes of 582 breast cancers with ≥1 year of followup. Molecular subtype approximation was performed using estrogen receptor, progesterone receptor, Her2, and grade. The Kaplan-Meier method was used to calculate overall survival, IBTR, RNR, and distant recurrence rates. Univariate and multivariate Cox proportional hazard models were performed to estimate risks of IBTR and RNR.

RESULTS

With a median followup time of 5.4 years, the 5-year IBTR rate was 4.7% overall, 3.5% for Luminal A, 4.1% for Luminal B, 5.2% for Luminal Her2, 13.3% for Her2, and 11.3% for triple-negative breast cancer. Positive surgical margins and high grade were associated with increased risk for IBTR, as was Her2 subtype in comparison with Luminal A subtype. Other individual subtypes comparisons did not show a significant difference. Analysis of Luminal A vs. all other subtypes demonstrated lower IBTR risk for Luminal A (5-year IBTR 3.5% vs. 7.3%, p = 0.02). The 5-year RNR rate was 2.1% overall, 0.3% for Luminal A, 4.6% for Luminal B, 2.6% for Luminal Her2, 34.5% for Her2, and 2.3% for triple-negative breast cancer. RNR risk was higher for women with Her2 compared to the other four subtypes and for Luminal B compared to Luminal A subtype.

CONCLUSIONS

Molecular subtype influences IBTR and RNR rates in women treated with multicatheter interstitial accelerated partial breast irradiation.

Transition from Paris dosimetry system to 3D image-guided planning in interstitial breast brachytherapy

PURPOSE

The purpose of this study is to evaluate our first experience with 3D image-guided breast brachytherapy and to compare dose distribution parameters between Paris dosimetry system (PDS) and image-based plans.

MATERIAL AND METHODS

First 49 breast cancer patients treated with 3D high-dose-rate interstitial brachytherapy as a boost were selected for the study. Every patient underwent computed tomography, and the planning target volume (PTV) and organs at risk (OAR) were outlined. Two treatment plans were created for every patient. First, based on a Paris dosimetry system (PDS), and the second one, imaged-based plan with graphical optimization (OPT). The reference isodose in PDS implants was 85%, whereas in OPT plans the isodose was chosen to obtain proper target coverage. Dose and volume parameters (D90, D100, V90, V100), doses at OARs, total reference air kerma (TRAK), and quality assurance parameters: dose nonuniformity ratio (DNR), dose homogeneity index (DHI), and conformity index (COIN) were used for a comparison of both plans.

RESULTS

The mean number of catheters was 7 but the mean for 20 first patients was 5 and almost 9 for the next 29 patients. The mean value of prescribed isodose for OPT plans was 73%. The mean D90 was 88.2% and 105.8%, the D100 was 59.8% and 75.7%, the VPTV90 was 88.6% and 98.1%, the VPTV100 was 79.9% and 98.9%, and the TRAK was 0.00375 Gym(-1) and 0.00439 Gym(-1) for the PDS and OPT plans, respectively. The mean DNR was 0.29 and 0.42, the DHI was 0.71 and 0.58, and the COIN was 0.68 and 0.76, respectively.

CONCLUSIONS

The target coverage in image-guided plans (OPT) was significantly higher than in PDS plans but the dose homogeneity was worse. Also, the value of TRAK increased because of change of prescribing isodose. The learning curve slightly affected our results.

A Japanese prospective multi-institutional feasibility study on accelerated partial breast irradiation using interstitial brachytherapy: treatment planning and quality assurance

BACKGROUND

In Japan, breast-conserving surgery with closed cavity has generally been performed for breast cancer patients, and accelerated partial breast irradiation (APBI) is considered difficult because Asian females generally have smaller breast sizes than Western females. Therefore, common identification of target and treatment plan method in APBI is required. A prospective multicenter study was conducted in Japan to determine institutional compliance with APBI using high-dose-rate interstitial brachytherapy (ISBT) designed for Japanese female patients.

METHODS

For this study, 46 patients were recruited at eight institutions from January 2009 to December 2011. The reproducibility of the ISBT-APBI plan was evaluated using three criteria: (1) minimum clinical target volume dose with a clip dose ≥ 6 Gy/fraction, (2) irradiated volume constraint of 40-150 cm(3), and (3) uniformity of dose distribution, expressed as the dose non-uniformity ratio (DNR, V150/V100) < 0.35. The ISBT-APBI plan for each patient was considered reproducible when all three criteria were met. When the number of non-reproducible patients was ≤ 4 at study completion, APBI at this institution was considered statistically reproducible.

RESULTS

Half of the patients (52 %) had a small bra size (A/B cup). The mean values of the dose-constrained parameters were as follows: Vref, 117 cm(3) (range, 40-282), DNR, 0.30 (range, 0.22-0.51), and clip dose, 784 cGy (range, 469-3146). A total of 43/46 treatment plans were judged to be compliant and ISBT-APBI was concluded to be reproducible.

CONCLUSIONS

This study showed that multi-institutional ISBT-APBI treatment plan was reproducible for small breast patient with closed cavity.

Comparing a volume based template approach and ultrasound guided freehand approach in multicatheter interstitial accelerated partial breast irradiation

Purpose

Currently, there are two described methods of catheter insertion for women undergoing multicatheter interstitial accelerated partial breast irradiation (APBI). These are a volume based template approach (template) and a non-template ultrasound guidance freehand approach (non-template). We aim to compare dosimetric endpoints between the template and non-template approach.

Material and methods

Twenty patients, who received adjuvant multicatheter interstitial APBI between August 2008 to March 2010 formed the study cohort. Dosimetric planning was based on the RTOG 04-13 protocol. For standardization, the planning target volume evaluation (PTV-Eval) and organs at risk were contoured with the assistance of the attending surgeon. Dosimetric endpoints include D₉₀ of the PTV-Eval, Dose Homogeneity Index (DHI), V₂₀₀, maximum skin dose (MSD), and maximum chest wall dose (MCD). A median of 18 catheters was used per patient. The dose prescribed was 34 Gy in 10 fractions BID over 5 days.

Results

The average breast volume was 846 cm³ (526-1384) for the entire cohort and there was no difference between the two groups (p = 0.6). Insertion time was significantly longer for the non-template approach (mean 150 minutes) compared to the template approach (mean: 90 minutes) (p = 0.02). The planning time was also significantly longer for the non-template approach (mean: 240 minutes) compared to the template approach (mean: 150 minutes) (p < 0.01). The template approach yielded a higher D₉₀ (mean: 95%) compared to the non-template approach (mean: 92%) (p < 0.01). There were no differences in DHI (p = 0.14), V₂₀₀ (p = 0.21), MSD (p = 0.7), and MCD (p = 0.8).

Conclusions

Compared to the non-template approach, the template approach offered significant shorter insertion and planning times with significantly improved dosimetric PTV-Eval coverage without significantly compromising organs at risk dosimetrically.

Endoscope-guided interstitial intensity-modulated brachytherapy and intracavitary brachytherapy as boost radiation for primary early T stage nasopharyngeal carcinoma

BACKGROUND

Intracavitary brachytherapy (ICBT) is usually applied as boost radiotherapy for superficial residual of nasopharyngeal carcinoma (NPC) after primary extern-beam radiptherapy (ERT). Here, we evaluated the outcome of endoscope-guided interstitial intensity-modulated brachytherapy (IMBT) boost radiation for deep-seated residual NPC.

METHODOLOGY/PRINCIPAL FINDINGS

Two hundred and thirteen patients with residual NPC who were salvaged with brachytherapy boost radiation during 2005-2009 were analyzed retrospectively. Among these patients, 171 patients had superficial residual NPC (≤1 cm below the nasopharyngeal epithelium) were treated with ICBT boost radiation, and interstitial IMBT boost radiation was delivered to 42 patients with deep-seated residual NPC (>1 cm below the nasopharyngeal epithelium). We found that IMBT boost subgroup had a higher ratio of T2b (81.0% VS 34.5%, P<0.001) and stage II (90.5% VS 61.4%, P = 0.001) than that of ICBT boost subgroup. The dosage of external-beam radiotherapy in the nasopharyngeal (63.0±3.8 VS 62.6±4.3 Gray (Gy), P = 0.67) and regional lymph nodes (55.8±5.0 VS 57.5±5.7 Gy, P = 0.11) was comparable in both groups. For brachytherapy, IMBT subgroup had a lower boost radiation dosage than ICBT subgroup (11.0±2.9 VS 14.8±3.2 Gy, P<0.01). Though the IMBT group had deeper residual tumors and received lower boost radiation dosages, both subgroups had the similar 5-year actuarial overall survival rate (IMBT VS ICBT group: 96.8% VS 93.6%, P = 0.87), progression-free survival rate (92.4% VS 86.5%, P = 0.41) and distant metastasis-free survival rate (94.9% VS 92.7%, P = 0.64). Moreover, IMBT boost radiation subgroup had a similar local (97.4% VS 94.4%, P = 0.57) and regional (95.0% VS 97.2%, P = 0.34) control to ICBT subgroup. The acute and late toxicities rates were comparable between the both subgroups.

CONCLUSIONS/SIGNIFICANCE

IMBT boost radiation may be a promising therapeutic selection for deep-seated residual NPC.

A Retrospective Six Years Analysis of Survival and Late Morbidity of Post-operative Gynaecological Malignancy Treated with External Radiotherapy Followed by Brachytherapy in Medical College & Hospitals, Kolkata

BACKGROUND

Cervical and endometrial carcinoma incidentally found in the surgical specimen with high risk pathological finding or with gross residual disease.

MATERIAL AND METHODS

Between 2004 and 2010, 320 cervical and endometrial cancer patients were treated with EBRT and brachytherapy after having undergone total/subtotal hysterectomy. Sixty patients were lost to follow-up.

RESULTS

Median follow-up was 21 months. Endometrial and cervical cancer with a high risk for local recurrence achieved CR 93.8 and 89 %, respectively. 56 % patients experienced CR with residual disease with cervical cancer. Median OS for endometrial and cervical cancer with residual disease was 8.5 and 24 months, respectively. Grade 3 adverse events were 5 and 3.5 % for rectum and bladder, respectively.

CONCLUSION

The incorporation of chemotherapy during pelvic radiotherapy followed by HDR interstitial brachytherapy for residual disease is inadequate and improves survival. We are still in learning phase of brachytherapy in post-operative gynaecological malignancy cases; expertise will be developed by practice.

Review of clinical brachytherapy uncertainties: analysis guidelines of GEC-ESTRO and the AAPM

Background and purpose

A substantial reduction of uncertainties in clinical brachytherapy should result in improved outcome in terms of increased local control and reduced side effects. Types of uncertainties have to be identified, grouped, and quantified.

Methods

A detailed literature review was performed to identify uncertainty components and their relative importance to the combined overall uncertainty.

Results

Very few components (e.g., source strength and afterloader timer) are independent of clinical disease site and location of administered dose. While the influence of medium on dose calculation can be substantial for low energy sources or non-deeply seated implants, the influence of medium is of minor importance for high-energy sources in the pelvic region. The level of uncertainties due to target, organ, applicator, and/or source movement in relation to the geometry assumed for treatment planning is highly dependent on fractionation and the level of image guided adaptive treatment. Most studies to date report the results in a manner that allows no direct reproduction and further comparison with other studies. Often, no distinction is made between variations, uncertainties, and errors or mistakes. The literature review facilitated the drafting of recommendations for uniform uncertainty reporting in clinical BT, which are also provided. The recommended comprehensive uncertainty investigations are key to obtain a general impression of uncertainties, and may help to identify elements of the brachytherapy treatment process that need improvement in terms of diminishing their dosimetric uncertainties. It is recommended to present data on the analyzed parameters (distance shifts, volume changes, source or applicator position, etc.), and also their influence on absorbed dose for clinically-relevant dose parameters (e.g., target parameters such as D₉₀ or OAR doses). Publications on brachytherapy should include a statement of total dose uncertainty for the entire treatment course, taking into account the fractionation schedule and level of image guidance for adaptation.

Conclusions

This report on brachytherapy clinical uncertainties represents a working project developed by the Brachytherapy Physics Quality Assurances System (BRAPHYQS) subcommittee to the Physics Committee within GEC-ESTRO. Further, this report has been reviewed and approved by the American Association of Physicists in Medicine.

Dosimetric and geometric evaluation of a novel stereotactic radiotherapy device for breast cancer: the GammaPod™

PURPOSE

A dedicated stereotactic gamma irradiation device, the GammaPod™ from Xcision Medical Systems, was developed specifically to treat small breast cancers. This study presents the first evaluation of dosimetric and geometric characteristics from the initial prototype installed at University of Maryland Radiation Oncology Department.

METHODS

The GammaPod™ stereotactic radiotherapy device is an assembly of a hemi-spherical source carrier containing 36 (60)Co sources, a tungsten collimator, a dynamically controlled patient support table, and the breast immobilization system which also functions as a stereotactic frame. The source carrier contains the sources in six columns spaced longitudinally at 60° intervals and it rotates together with the variable-size collimator to form 36 noncoplanar, concentric arcs focused at the isocenter. The patient support table enables motion in three dimensions to position the patient tumor at the focal point of the irradiation. The table moves continuously in three cardinal dimensions during treatment to provide dynamic shaping of the dose distribution. The breast is immobilized using a breast cup applying a small negative pressure, where the immobilization cup is embedded with fiducials also functioning as the stereotactic frame for the breast. Geometric and dosimetric evaluations of the system as well as a protocol for absorbed dose calibration are provided. Dosimetric verifications of dynamically delivered patient plans are performed for seven patients using radiochromic films in hypothetical preop, postop, and target-in-target treatment scenarios.

RESULTS

Loaded with 36 (60)Co sources with cumulative activity of 4320 Ci, the prototype GammaPod™ unit delivers 5.31 Gy/min at the isocenter using the largest 2.5 cm diameter collimator. Due to the noncoplanar beam arrangement and dynamic dose shaping features, the GammaPod™ device is found to deliver uniform doses to targets with good conformity. The spatial accuracy of the device to locate the radiation isocenter is determined to be less than 1 mm. Single shot profiles with 2.5 cm collimator are measured with radiochromic film and found to be in good agreement with respect to the Monte Carlo based calculations (congruence of FWHM less than 1 mm). Dosimetric verifications corresponding to all hypothetical treatment plans corresponding to three target scenarios for each of the seven patients demonstrated good agreement with gamma index pass rates of better than 97% (99.0% ± 0.7%).

CONCLUSIONS

Dosimetric evaluation of the first GammaPod™ stereotactic breast radiotherapy unit was performed and the dosimetric and spatial accuracy of this novel technology is found to be feasible with respect to clinical radiotherapy standards. The observed level of agreement between the treatment planning system calculations and dosimetric measurements has confirmed that the system can deliver highly complex treatment plans with remarkable geometric and dosimetric accuracy.

3D-image-guided high-dose-rate intracavitary brachytherapy for salvage treatment of locally persistent nasopharyngeal carcinoma

Background

To evaluate the therapeutic benefit of 3D-image-guided high-dose-rate intracavitary brachytherapy (3D-image-guided HDR-BT) used as a salvage treatment of intensity modulated radiation therapy (IMRT) in patients with locally persistent nasopharyngeal carcinoma (NPC).

Methods

Thirty-two patients with locally persistent NPC after full dose of IMRT were evaluated retrospectively. 3D-image-guided HDR-BT treatment plan was performed on a 3D treatment planning system (PLATO BPS 14.2). The median dose of 16 Gy was delivered to the 100% isodose line of the Gross Tumor Volume.

Results

The whole procedure was well tolerated under local anesthesia. The actuarial 5-y local control rate for 3D-image-guided HDR-BT was 93.8%, patients with early-T stage at initial diagnosis had 100% local control rate. The 5-y actuarial progression-free survival and distant metastasis-free survival rate were 78.1%, 87.5%. One patient developed and died of lung metastases. The 5-y actuarial overall survival rate was 96.9%.

Conclusions

Our results showed that 3D-image-guided HDR-BT would provide excellent local control as a salvage therapeutic modality to IMRT for patients with locally persistent disease at initial diagnosis of early-T stage NPC.

iCycle: Integrated, multicriterial beam angle, and profile optimization for generation of coplanar and noncoplanar IMRT plans

PURPOSE

To introduce iCycle, a novel algorithm for integrated, multicriterial optimization of beam angles, and intensity modulated radiotherapy (IMRT) profiles.

METHODS

A multicriterial plan optimization with iCycle is based on a prescription called wish-list, containing hard constraints and objectives with ascribed priorities. Priorities are ordinal parameters used for relative importance ranking of the objectives. The higher an objective priority is, the higher the probability that the corresponding objective will be met. Beam directions are selected from an input set of candidate directions. Input sets can be restricted, e.g., to allow only generation of coplanar plans, or to avoid collisions between patient/couch and the gantry in a noncoplanar setup. Obtaining clinically feasible calculation times was an important design criterium for development of iCycle. This could be realized by sequentially adding beams to the treatment plan in an iterative procedure. Each iteration loop starts with selection of the optimal direction to be added. Then, a Pareto-optimal IMRT plan is generated for the (fixed) beam setup that includes all so far selected directions, using a previously published algorithm for multicriterial optimization of fluence profiles for a fixed beam arrangement Breedveld et al. [Phys. Med. Biol. 54, 7199-7209 (2009)]. To select the next direction, each not yet selected candidate direction is temporarily added to the plan and an optimization problem, derived from the Lagrangian obtained from the just performed optimization for establishing the Pareto-optimal plan, is solved. For each patient, a single one-beam, two-beam, three-beam, etc. Pareto-optimal plan is generated until addition of beams does no longer result in significant plan quality improvement. Plan generation with iCycle is fully automated.

RESULTS

Performance and characteristics of iCycle are demonstrated by generating plans for a maxillary sinus case, a cervical cancer patient, and a liver patient treated with SBRT. Plans generated with beam angle optimization did better meet the clinical goals than equiangular or manually selected configurations. For the maxillary sinus and liver cases, significant improvements for noncoplanar setups were seen. The cervix case showed that also in IMRT with coplanar setups, beam angle optimization with iCycle may improve plan quality. Computation times for coplanar plans were around 1-2 h and for noncoplanar plans 4-7 h, depending on the number of beams and the complexity of the site.

CONCLUSIONS

Integrated beam angle and profile optimization with iCycle may result in significant improvements in treatment plan quality. Due to automation, the plan generation workload is minimal. Clinical application has started.

Assessment of dose homogeneity in conformal interstitial breast brachytherapy with special respect to ICRU recommendations

Purpose

To present the results of dose homogeneity analysis for breast cancer patients treated with image-based conformal interstitial brachytherapy, and to investigate the usefulness of the ICRU recommendations.

Material and methods

Treatment plans of forty-nine patients who underwent partial breast irradiation with interstitial brachytherapy were analyzed. Quantitative parameters were used to characterize dose homogeneity. Dose non-uniformity ratio (DNR), dose homogeneity index (DHI), uniformity index (UI) and quality index (QI) were calculated. Furthermore, parameters recommended by the ICRU 58 such as minimum target dose (MTD), mean central dose (MCD), high dose volume, low dose volume and the spread between local minimum doses were determined. Correlations between the calculated homogeneity parameters and usefulness of the ICRU parameters in image-based brachytherapy were investigated.

Results

Catheters with mean number of 15 (range: 6-25) were implanted in median 4 (range: 3-6) planes. The volume of the PTV ranged from 15.5 cm³ to 176 cm³. The mean DNR was 0.32, the DHI 0.66, the UI 1.49 and the QI 1.94. Related to the prescribed dose, the MTD was 69% and the MCD 135%. The mean high dose volume was 8.1 cm³ (10%), while the low dose volume was 63.8 cm³ (96%). The spread between minimum doses in central plane ranged from −14% to +20%. Good correlation was found between the DNR and the DHI (R²=0.7874), and the DNR correlated well with the UI (R²=0.7615) also. No correlation was found between the ICRU parameters and any other volumetric parameters.

Conclusions

To characterize the dose uniformity in high-dose rate breast implants, DVH-related homogeneity parameters representing the full 3D dose distributions are mandatory to be used. In many respects the current recommendations of the ICRU Report 58 are already outdated, and it is well-timed to set up new recommendations, which are more feasible for image-guided conformal interstitial brachytherapy.

Quality assessment of interstitial implants in high- dose- rate brachytherapy after lumpectomy in patients of early stage breast cancer

To assess the quality of high dose rate (H,D,R.) interstitial implants in breast cancer by using different volumetric indices and correlating them with skin and subcutaneous tissue toxicity. Out of 15 patients who were selected for interstitial implants after undergoing breast conservation surgery, five were treated radically with 34 Gy in 10 fractions in 5 days @ 3.4 Gy # twice daily and 10 patients recieved boost dose of 12 Gy in 4 fractions @ 3 Gy /# twice daily. The median follow up was 15 months. During each follow up assessment of late skin and subcutaneous tissue toxicity as per RTOG criteria was done . Various dosimetric indices were analysed. Dose Volume Histogram for dose per unit volume of skin for 10cc,5cc,2cc,1cc,0.1cc and 0.01cc was calculated. Best estimates and correlation of toxicity was revealed by assessment of Dose Nonuniformity Ratio(DNR) which also correlated well with geometry defining indices like Uniformity Index (UI).Volumetric assessment of skin dose for less than 2 cc correlated most with toxicity. DNR and UI can help us to assess and correlate late skin and subcutaneous tissue toxicity and thus serve useful to determine the quality of implant.

3D-CT implanted interstitial brachytherapy for T2b nasopharyngeal carcinoma

Background

To compare the results of external beam radiotherapy in combination with 3D- computed tomography (CT)-implanted interstitial high dose rate brachytherapy (ERT/3D-HDR-BT) versus conventional external beam radiotherapy (ERT) for the treatment of stage T2b nasopharyngeal carcinoma (NPC).

Methods

Forty NPC patients diagnosed with stage T2b NPC were treated with ERT/3D-HDR-BT under local anesthesia. These patients received a mean dose of 60 Gy, followed by 12-20 Gy administered by 3D-HDR-BT. Another 101 patients diagnosed with non-metastatic T2b NPC received a mean dose of 68 Gy by ERT alone during the same period.

Results

Patients treated with ERT/3D-HDR-BT versus ERT alone exhibited an improvement in their 5-y local failure-free survival rate (97.5% vs. 80.2%, P = 0.012) and disease-free survival rate (92.5% vs. 73.3%, P = 0.014). Using multivariate analysis, administration of 3D-HDR-BT was found to be favorable for local control (P = 0.046) and was statistically significant for disease-free survival (P = 0.021). The incidence rate of acute and chronic complications between the two groups was also compared.

Conclusions

It is possible that the treatment modality enhances local control due to improved conformal dose distributions and the escalated radiation dose applied.

Improving the definition of tumor bed boost with the use of surgical clips and image registration in breast cancer patients

PURPOSE

To evaluate the accuracy of a boost technique.

METHODS AND MATERIALS

Twenty-two patients underwent tumorectomy with placement of two or more clips in the surgical cavity before breast remodeling. Preoperative and postoperative computed tomography scans, with match-point registration, were performed on all patients. The relationship between the location of the gross tumor volume (GTV), defined on the preoperative scan, and clip clinical target volume (CTV) (clips with a 5-mm margin on the postoperative scan) was then studied, by use of commercial volume analysis software.

RESULTS

Of the patients, 4 had two clips, 2 had three clips, 8 had four clips, and 8 had five clips. The median GTV was 1.06 mL (range, 0.2-5.3 mL); clip CTV ranged from 2.4 to 21.5 mL. Volumetric analysis showed that in 7 cases (32%), there was no intersection between the GTV and the clip CTV, with the following distribution: 4 patients with two clips, 1 patient with three clips, 1 patient with four clips, and 1 patient with five clips. The common contoured volume was defined as the percent ratio between the intersection of the GTV and clip CTV and the GTV. It was found to be significantly increased if three or more clips were used vs. only two clips (common contoured volume, 35.45% vs. 0.73%; p = 0.028). Finally, the GTV and clip CTV volume relationship can be presented as follows: 12.5% to 33% overlap in 8 patients (36.4%), 50% to 75% in 5 patients (22.7%), and greater than 90% in 2 patients (9%).

CONCLUSIONS

The use of three or more clips during tumorectomy increases the accuracy of tumor bed delineation.

How to boost the breast tumor bed? A multidisciplinary approach in eight steps

PURPOSE

To describe a new procedure for breast radiotherapy that will improve tumor bed localization and radiotherapy treatment using a multidisciplinary approach.

PATIENTS AND METHODS

This pilot study was conducted by departments of radiation oncology, surgery, and radiology. A new procedure has been implemented, summarized as eight steps: from pre-surgery contrast CT to surgery, tumor bed planning target volume (PTV) determination, and finally breast and tumor bed irradiation.

RESULTS

Twenty patients presenting with T1N0M0 tumors were enrolled in the study. All patients underwent lumpectomy with the placement of surgical clips in the tumor bed region. During surgery, 1 to 5 clips were placed in the lumpectomy cavity before the plastic procedure. All patients underwent pre- and postoperative CT scans in the treatment position. The two sets of images were registered with a match-point registration. All volumes were contoured and the results evaluated. The PTV included the clips region, the gross tumor volume, and the surgical scar, with an overall margin of 5-10 mm in all directions, corresponding to localization and setup uncertainties. For each patient the boost PTV was discussed and compared with our standard forward-planned PTV.

CONCLUSIONS

We demonstrate the feasibility of a tumor bed localization and treatment procedure that seems adaptable to routine practice. Our study shows the advantages of a multidisciplinary approach for tumor bed localization and treatment. The use of more than 1 clip associated with pre- to postoperative CT image registration allows better definition of the PTV boost volume.

The use of directional interstitial sources to improve dosimetry in breast brachytherapy

The purposes of this study were to investigate the feasibility of improving dosimetry with temporary low-dose-rate (LDR) multicatheter breast implants using directional 125I (iodine) interstitial sources and to provide a comparison of a patient treatment plan to that achieved by conventional high-dose-rate (HDR) interstitial breast brachytherapy. A novel 125I source emitting radiation in a specified direction has been developed. The directional sources contain an internal radiation shield that greatly reduces the intensity of radiation in the shielded direction. The sources have a similar dose distribution to conventional nondirectional sources on the unshielded side. The treatment plan for a patient treated with HDR interstitial brachytherapy with 192Ir (iridium) was compared with a directional 125I treatment plan using the same data set. Several dosimetric parameters are compared including target volume coverage, volume receiving 50%, 100%, and 150% of the prescription dose (V50, V100, and V150, respectively), dose homogeneity index (DHI), and the skin surface areas receiving 30%, 50%, and 80% of the prescription dose (S30, S50, and S80, respectively). The HDR and LDR prescription doses were 34 Gy in ten fractions delivered over five days and 45 Gy in 108 h, respectively. Similar and excellent target volume coverage was achieved by both directional LDR and HDR plans (99.2% and 97.5%, respectively). For a 170 cm3 target volume, the dosimetric parameters were similar for LDR and HDR: DHI was 0.82 in both cases, V100 was 214.4 cm3 and 225.7 cm3, and V150 was 39.1 cm3 and 40.4 cm3, respectively. However, with directional LDR, significant reductions in skin dose were achieved: S30 was reduced from 100.6 to 62.5 cm2, S50 from 50.6 to 16.1 cm2, and S80 from 2 cm2 to zero. The reduction in V50 for the whole breast was more than 100 cm3 (386.1 cm3 for LDR versus 489.2 cm3 for HDR). In this case study, compared with HDR, directional interstitial LDR 125I sources allow similar dose coverage to the subcutaneous target volume while lowering the skin dose due to a more conformal dose distribution and quicker falloff beyond the target. The improved dose distribution provided by directional interstitial brachytherapy might enable partial breast treatment to tumors closer to the skin or chest wall or in relatively small breasts.

Dose-volume characteristics of a 50-kV electronic brachytherapy source for intracavitary accelerated partial breast irradiation

PURPOSE

To describe dose-volume data from a 50-kV electronic brachytherapy source in intracavitary accelerated partial breast irradiation.

METHODS AND MATERIALS

Three spherical balloon applicators were imaged on a CT scanner in a water phantom and inflated throughout their suggested fill volume range. The planning target volume (PTV) was defined as a 1-cm margin around the balloon surface. Plans were created achieving 80%, 85%, and 90% coverage of the PTV, with a prescription dose of 34Gy in 10 fractions. The PTV, V(90), V(100), V(150), V(200), and V(300) were recorded for each plan.

RESULTS

For 80% target coverage, the V(200) varies from 11 to 14 cm(3) and the V(150) from 26 to 49 cm(3) over all the balloon applicators and fill volumes. For 85% coverage, the V(200) varies from 14 to 18 cm(3) and the V(150) from 27 to 53 cm(3). For 90% coverage, the V(200) varies from 16 to 22 cm(3) and the V(150)cm(3) from 30 to 61 cm(3).

CONCLUSIONS

Fifty-kilovolt electronic brachytherapy can provide PTV coverage similar to (192)Ir in the setting of intracavitary accelerated partial breast irradiation.

Prevention of tumor recurrence and distant metastasis formation in a breast cancer mouse model by biodegradable implant of 131I-norcholesterol

Brachytherapy has many potential roles in cancer therapy. However, major constraints are associated with placement and removal procedures of the brachytherapy machinery. An attractive approach would be the use of a biodegradable implant loaded with a radioisotope, thus enabling targeted radiotherapy, while reducing the need for surgical procedures for the removal of brachytherapy hardware. In this study, crosslinked chitosan (Ct) hydrogels were prepared and loaded with (131)I-norcholesterol ((131)I-NC). The radioactive hydrogels ((131)I-NC-Ct) were implanted adjacent to 4T1 cell-induced tumors in two different xenograft mice models either as primary therapy or surgical adjuvant therapy of breast cancer. Non-treated mice and mice implanted with naive (non-radioactive) hydrogels served as control groups. In the primary therapy model, the progression rate of the tumor was delayed by two weeks compared with the non-treated and the naive-implant control animals, resulting in a one-week extension in the survival of the treated animals. In the adjuvant therapy model, for the treatment of minimal residual disease, (131)I-NC-Ct implants were able to prevent 69% of tumor recurrence, and to prevent metastatic spread resulting in long-term survival, compared with 0% long-term survival of the non-treated and the naive control groups. Imaging of the hydrogel's in vivo elimination revealed a first order process with a half-life of 14 days. The degradation was caused by oxidation of the Ct as was assessed by in vitro H&E stain. Biodegradable radioactive implants are suggested as a novel platform for the delivery of brachytherapy. This radiotherapy regimen may prevent locoregional recurrence and metastatic spread after tumor resection.

Increased Skin Dose With the Use of a Custom Mattress for Prone Breast Radiotherapy

The purpose of this study was to measure and compare the loss of buildup to the skin of the breast in the prone position due to 2 different positioning systems during tangential external beam irradiation. Two experiments were performed; one with a standard nylon-covered foam support and another with a novel helium-filled Mylar bag support. The choice of helium-filled Mylar was to reduce the contamination to as low as possible. The experiments were designed to allow a surface dose measurement and a depth dose profile with the pads placed in the path of the beam in front of the detector. All measurements were taken using a Capintec PS-033 thin-window parallel plate ionization chamber. The standard nylon-covered foam pad caused the surface dose to rise as it got closer to the skin. When the pad was directly touching the surface, the surface dose increased by 300% compared to the result when no pad was present. This loss of buildup to the surface was similar to that of a custom bolus material. The opposite effect occurred with the use of the helium-filled Mylar bag, namely the surface dose gradually decreased as the pad got closer to the phantom. When the Mylar pad was directly touching the phantom, the surface dose was decreased by 7% compared to when no pad was present. The use of a foam pad could potentially result in a significant higher dose to the skin, resulting in an enhanced acute skin reaction. Therefore, special care should be taken in this clinical scenario and further investigation of an air- or helium-based mylar support pad should be investigated in the context of definitive breast radiation treatment.

A Dosimetric Comparison of Accelerated Partial Breast Irradiation Techniques: Multicatheter Interstitial Brachytherapy, Three-Dimensional Conformal Radiotherapy, and Supine Versus Prone Helical Tomotherapy

PURPOSE

To compare dosimetrically four different techniques of accelerated partial breast irradiation (APBI) in the same patient.

METHODS AND MATERIALS

Thirteen post-lumpectomy interstitial brachytherapy (IB) patients underwent imaging with preimplant computed tomography (CT) in the prone and supine position. These CT scans were then used to generate three-dimensional conformal radiotherapy (3D-CRT) and prone and supine helical tomotherapy (PT and ST, respectively) APBI plans and compared with the treated IB plans. Dose-volume histogram analysis and the mean dose (NTD(mean)) values were compared.

RESULTS

Planning target volume coverage was excellent for all methods. Statistical significance was considered to be a p value <0.05. The mean V100 was significantly lower for IB (12% vs. 15% for PT, 18% for ST, and 26% for 3D-CRT). A greater significant differential was seen when comparing V50 with mean values of 24%, 43%, 47%, and 52% for IB, PT, ST, and 3D-CRT, respectively. The IB and PT were similar and delivered an average lung NTD(mean) dose of 1.3 Gy(3) and 1.2 Gy(3), respectively. Both of these methods were statistically significantly lower than the supine external beam techniques. Overall, all four methods yielded similar low doses to the heart.

CONCLUSIONS

The use of IB and PT resulted in greater normal tissue sparing (especially ipsilateral breast and lung) than the use of supine external beam techniques of 3D-CRT or ST. However, the choice of APBI technique must be tailored to the patient's anatomy, lumpectomy cavity location, and overall treatment goals.

Evaluation of radiograph-based interstitial implant dosimetry on computed tomography images using dose volume indices for head and neck cancer

Conventional radiograph-based implant dosimetry fails to correlate the spatial dose distribution on patient anatomy with lack in dosimetry quality. Though these limitations are overcome in computed tomography (CT)-based dosimetry, it requires an algorithm which can reconstruct catheters on the multi-planner CT images. In the absence of such algorithm, we proposed a technique in which the implanted geometry and dose distribution generated from orthogonal radiograph were mapped onto the CT data using coordinate transformation method.

Radiograph-based implant dosimetry was generated for five head and neck cancer patients on Plato Sunrise treatment planning system. Dosimetry was geometrically optimized on volume, and dose was prescribed according to the natural prescription dose. The final dose distribution was retrospectively mapped onto the CT data set of the same patients using coordinate transformation method, which was verified in a phantom prior to patient study. Dosimetric outcomes were evaluated qualitatively by visualizing isodose distribution on CT images and quantitatively using the dose volume indices, which includes coverage index (CI), external volume index (EI), relative dose homogeneity index (HI), overdose volume index (OI) and conformal index (COIN).

The accuracy of coordinate transformation was within ±1 mm in phantom and ±2 mm in patients. Qualitative evaluation of dosimetry on the CT images shows reasonably good coverage of target at the expense of excessive normal tissue irradiation. The mean (SD) values of CI, EI and HI were estimated to be 0.81 (0.039), 0.55 (0.174) and 0.65 (0.074) respectively. The maximum OI estimated was 0.06 (mean 0.04, SD = 0.015). Finally, the COIN computed for each patient ranged from 0.4 to 0.61 (mean 0.52, SD = 0.078).

The proposed technique is feasible and accurate to implement even for the most complicated implant geometry. It allows the physicist and physician to evaluate the plan both qualitatively and quantitatively. Dose volume indices derived from CT data set are useful for evaluating the implant and comparing different brachytherapy plans. COIN index is an important tool to assess the target coverage and sparing of normal tissues in brachytherapy.

The emergence of advanced brachytherapy techniques for common malignancies

The recent advent and integration of sophisticated radiation planning and imaging modalities has improved the quality of brachytherapy treatments, allowing for more conformal radiation delivery. Further investigation and follow-up are necessary to demonstrate improvements in outcome and morbidity with these refined approaches.

A pilot study of wider use of accelerated partial breast irradiation: intraoperative margin-directed re-excision combined with sole high-dose-rate interstitial brachytherapy

BACKGROUND

Accelerated partial breast irradiation (APBI) is generally limited to patients at extremely low risk of local recurrence. The significance of the risk factors, however, depends on the extent of surgery, radiation, and systemic therapy. In Japan, wide excision is generally supplemented by intraoperative margin-directed re-excision if the frozen section examination yields positive results. This approach combined with conventional radiotherapy achieved an excellent 10-year local control rate of 93%, and young age and ductal carcinoma in situ were not risk factors for local recurrence. To reduce the treatment duration, high-dose-rate interstitial brachytherapy (HDRIB) was employed. The first APBI phase I / II trial in Japan was conducted to determine if wider indications for early breast cancer patients were appropriate.

METHODS

The subjects comprised 20 patients including those with extensive intraductal component (n=7), ductal carcinoma in situ (n=2), positive final margins (n=3), and of younger age (< or = 45 years; n=5). Breast-conserving surgery using an intraoperative re-excision approach was followed by intraoperative implantation of applicators. Sole HDRIB of a 36-42 Gy in 6-7 fractions was delivered postoperatively over 3-4 days. Tumors were staged as follows: cT1 (n=12), cT2 (n=8), cN0 (n=20). Systemic therapy was used in 16 patients (80%). The median follow-up period was 52 months (range, 26-86 months).

RESULTS

Te five-year crude local, distant control, and Kaplan-Meier cause-specific survival rates were 95%, 95%, and 89%, respectively. Fat necrosis developed in 1 patient.

CONCLUSIONS

Sole HDRIB with intraoperative margin-directed re-excision was feasible under wider indications compared to other contemporary APBI series, and achieved acceptable and similar results to these series in terms of the local control rate and complications.

Three-Dimensional Conformal External Beam Radiotherapy (3D-CRT) for Accelerated Partial Breast Irradiation (APBI)

OBJECTIVE

This study is an evaluation of the biologic equivalence of the dose prescriptions for brachytherapy and 3-dimensional conformal external beam radiotherapy (3D-CRT) accelerated partial breast irradiation (APBI), using actual patient dose matrix data, and is based on the concept of equivalent uniform biologically effective dose (EUBED). This formalism allows a nonuniform dose distribution to be reduced to an equivalent uniform dose, while also accounting for fraction size.

MATERIALS AND METHODS

Five computed tomography scans were selected from a group of patients treated with multicatheter interstitial APBI. Dose matrices for the brachytherapy plans were computed and analyzed with in-house software. For each patient, the EUBED for the brachytherapy dose matrix was generated based on calculations performed at the voxel-level. These EUBED values were then used to calculate the biologically equivalent fraction size for 3D-CRT (eud).

RESULTS

The mean equivalent fraction size (eudmean) and maximum equivalent fraction size (eudmax) were calculated for each patient using 100 different values of the alpha/beta ratio. The eudmean ranged from 3.67 to 3.69 Gy, while the eudmax ranged from 3.79 to 3.82 Gy. For all values of the alpha/beta ratio, the maximum fraction size calculated to deliver a biologically equivalent dose with 3D-CRT was 3.82 Gy, with an equivalent total prescription dose of 38.2 Gy.

CONCLUSION

Utilizing a wide range of established radiobiological parameters, this study suggests that the maximum fraction size needed to deliver a biologically equivalent dose using 3D-CRT is 3.82 Gy, supporting the continued use of 3.85Gy BID in the current national cooperative trial.

Dosimetric comparisons between high dose rate interstitial and MammoSite™ balloon brachytherapy for breast cancer

BACKGROUND AND PURPOSE

To make a quantitative dosimetric comparison between treatment plans of multicatheter-based interstitial brachytherapy (IB) and MammoSite brachytherapy (MSB) for breast cancer.

PATIENTS AND METHODS

Seventeen patients treated with IB and twenty-four with MSB were selected for the study. The irradiations for IB patients were planned using conventional two-film reconstruction technique. Following the implantation each patient was CT scanned, then the planning target volume (PTV) was retrospectively defined on the CT data set, and the original plan was reconstructed (CONV plans). Furthermore, conformal plans were also created by dose optimization on target (CONF plans). The planning for MammoSite applicator was based on CT imaging. The dose distributions were evaluated with dose-volume histograms. The following parameters were calculated and compared: volume of the PTV and its percentage receiving 90, 100, 150 and 200% of the prescribed dose (V90, V100, V150 and V200, respectively), percentage dose covering 90% of the PTV (D90), minimum dose in the PTV (D(min)), maximum dose in the PTV (D(max)) for MSB only, dose homogeneity index (DHI), and conformal index (COIN). To assess the dose to organs at risk maximum point dose to skin, lung and heart was used.

RESULTS

The median number of implanted catheters for IB was 11 (range: 6-13), the average balloon volume for MSB was 59.1cm(3) (range: 43.4-75.3 cm(3)). The average volume of PTV was 63.4 and 109.6 cm(3) for IB and MSB patients, respectively. The average V90, V100, V150, V200 were 76, 70, 26 and 9% for IB(CONV); 92, 87, 55 and 32% for IB(CONF) and 96, 88, 27 and 3% for MSB, respectively. The average D90 was 72, 94 and 99%, the D(min) was 47, 58 and 67%, respectively. The mean D(max) was 258% for MSB. The average DHI was 0.63, 0.37 and 0.70 for IB(CONV), IB(CONF) and MSB, respectively. D(max) to skin, lung and heart were 45, 54 and 31% for IB(CONV), 50, 55 and 29% for IB(CONF,) 97, 66 and 27% for MSB, respectively.

CONCLUSIONS

Target volume coverage was better for MSB than conventional IB, and it was comparable to conformal IB. The suboptimal coverage for IB patients is due to radiography based planning, which is unable to provide 3D information of the target. Dose homogeneity was somewhat better for MSB than IB(CONV), but the dose to skin and lung was higher for MSB. The MSB provides dosimetrically acceptable dose plans. The quality of interstitial implants can be improved with image-guided catheter insertions regarding both homogeneity and conformality.

Image-guided breast brachytherapy: an alternative to whole-breast radiotherapy

Lumpectomy and whole-breast radiotherapy (ie, breast-conservation treatment) are accepted as viable alternatives to mastectomy in locoregional management of breast cancer. These techniques are used to keep morbidity to a minimum, optimise cosmesis, and maintain treatment outcomes. Pathological and clinical data suggest that most recurrences of cancer in the ipsilateral breast are in the vicinity of the index lesion, and that remote recurrences are uncommon, whether or not whole-breast radiotherapy is delivered. These data lend support to the idea of partial-breast radiotherapy. Such a restricted treatment volume allows safe delivery of an accelerated hypofractionated regimen over a shortened course of 1 week. This technique differs from that of standard whole-breast tangential external-beam radiotherapy and necessitates investigation of accelerated partial-breast irradiation (APBI). Several techniques of APBI are being investigated; however, most experience, and the most favourable early outcomes, has been obtained with image-guided breast brachytherapy. This review highlights the rationale and outcomes of brachytherapy techniques.

Accelerated partial breast irradiation: An analysis of variables associated with late toxicity and long-term cosmetic outcome after high-dose-rate interstitial brachytherapy

PURPOSE

To perform a detailed analysis of variables associated with late tissue effects of high-dose-rate (HDR) interstitial brachytherapy accelerated partial breast irradiation (APBI) in a large cohort of patients with prolonged follow-up.

METHODS AND MATERIALS

Beginning in 1995, 75 women with Stage I/II breast cancer were enrolled in identical institutional trials evaluating APBI as monotherapy after lumpectomy. Patients eligible included those with T1-2, N0-1 (<or=3 nodes positive), M0 tumors of nonlobular histology with negative surgical margins, no extracapsular nodal extension, and negative results on postexcision mammogram. All patients underwent surgical excision and postoperative irradiation with HDR interstitial brachytherapy. The planning target volume was defined as the excision cavity plus a 2-cm margin. Treatment was delivered with a high-activity Ir-192 source at 3.4 Gy per fraction twice daily for 5 days to a total dose of 34 Gy. Dosimetric analyses were performed with three-dimensional postimplant dose and volume reconstructions. All patients were evaluated at 3-6-month intervals and assessed with a standardized cosmetic rating scale and according to Radiation Therapy Oncology Group late normal tissue toxicity scoring criteria. Clinical and therapy-related features were analyzed for their relationship to cosmetic outcome and toxicity rating. Clinical features analyzed included age, volume of resection, history of diabetes or hypertension, extent of axillary surgery, and systemic therapies. Therapy-related features analyzed included volume of tissue encompassed by the 100%, 150%, and 200% isodose lines (V100, V150, and V200, respectively), the dose homogeneity index (DHI), number of source dwell positions, and planar separation.

RESULTS

The median follow-up of all patients was 73 months (range, 43-118 months). The cosmetic outcome at last follow-up was rated as excellent, good, and fair/poor in 67%, 24%, and 9% of patients, respectively. Suboptimal cosmetic outcome was significantly associated with the number of source dwell positions, V150, and V200 and inversely associated with DHI (0.77 vs. 0.73; p=0.05). Late skin toxicity was rated as Grade 0, 1, or 2 in 77%, 19%, and 4% of patients, respectively. The risk of Grade 1/2 skin toxicity was significantly associated with V150 and V200 and inversely associated with DHI (0.77 vs. 0.71; p=0.009). Late subcutaneous toxicity was rated as Grade 0, 1, 2, 3, or 4 in 55%, 15%, 12%, 5%, and 13% of patients, respectively. The risk of Grade 0/1 vs. Grade 2-4 subcutaneous toxicity was significantly associated only with a lower value of DHI (0.77 vs. 0.73; p=0.02). To further explore factors that might contribute to the risk of fat necrosis (symptomatic or asymptomatic), a separate analysis showed that only dose hotspots as reflected in V150 and V200 were significantly associated with elevated risk. The use of adriamycin-based chemotherapy after APBI was found to be associated with a significant increase in the incidence of higher-grade skin toxicity and a higher risk of fat necrosis and suboptimal cosmetic outcome. Patient age, volume of resection, extent of axillary surgery, a history of diabetes or hypertension, and the use of tamoxifen were not found to be significantly associated with cosmetic outcome or late normal tissue complications.

CONCLUSIONS

Long-term cosmetic results and the risk of late skin and subcutaneous toxicity after APBI with interstitial HDR brachytherapy can be correlated with specific treatment-related variables. These data provide dosimetric parameters that might be used to minimize the risk of normal tissue injury after APBI interstitial brachytherapy.

Quality assurance of treatment plans for interstitial and intracavitary high-dose-rate brachytherapy

PURPOSE

Quality assurance for complex high-dose-rate (HDR) treatment planning has always been a challenge to the physics community because of the time constraint between HDR planning and the delivery of the treatment. This study proposes an efficient, precise, and easy method for checking the complex computer calculation.

METHODS AND MATERIALS

Posttreatment, three-dimensional dose-volume study was performed for 98 patients with 128 new treatment plans along with 30 library plans. Volumes covered by the 100% isodose line, source activity (Ci), total dwell time (s), and the prescription dose (100%) were recorded. Variation of R(V) defined as (irradiated time x activity/elongation factor x prescribed dose) with volume was studied for different catheter systems.

RESULTS

Parametric fit of R(V) with volume for three different systems that cover most of the interstitial and intracavitary brachytherapy implants agrees within +/-6%.

CONCLUSIONS

The excellent agreement of R(V) derived from this simplistic point source model with three-dimensional dose calculations for individual HDR treatment plans clearly establishes that for an implant with known number of catheters, the time needed to deliver a prescribed dose to a given prescription volume can be easily predicted.