Pulsed Dose Rate Brachytherapy Research Articles

Dosimetric Changes during Daily MR-Guided Pulse-Dose-Rate Brachytherapy for Cervix Cancer

Dosimetric Changes during Daily MR-Guided Pulse-Dose-Rate Brachytherapy for Cervix Cancer

Verification of High Dose Rate $^{192}$Ir Source Position During Brachytherapy Treatment Using Silicon Pixel Detectors

A system for in-vivo tracking of 192Ir source during high dose rate or pulsed dose rate brachytherapy treatment was built using 1 mm thick silicon pad detectors as image sensors and knife-edge lead pinholes as collimators. With source self-images obtained from a dual-pinhole system, location of the source could be reconstructed in three dimensions in real time. The system was tested with 192Ir clinical source (kerma rate in air at 1 m 2.38 Gy/h) in air and plexi-glass phantom. The locations of the source were tracked from a distance of 40 cm in a field of view of 20 × 20 × 20 cm3. Reconstruction precision, defined as the average distance between true and reconstructed source positions, with data collected in less than 1 s with 22 GBq 192Ir source was about 5 mm. The reconstruction precision was in our case mainly limited by imperfect alignment of detectors and pinholes. With perfect alignment the statistical error would allow precision of about 1 mm which could further be improved with larger detector placed at larger distance from the pinhole. However already the modest precision of few millimeters is sufficient for in-vivo detection of larger deviations from planned treatment caused by various misadministrations or malfunctioning of the brachytherapy treatment apparatus. Usage of silicon detectors offers a possibility for building a compact device which could be used as an independent online quality assurance system. In this paper details about sensors, readout system and reconstruction algorithm are described. Results from measurements with clinical source are presented.

Clinical Outcomes and Dosimetric Analysis of a Prospective Trial utilizing MRI-guided Single-line Source Intracavitary Pulsed-Dose Rate Brachytherapy in Locally Advanced Cervical Cancer

Clinical Outcomes and Dosimetric Analysis of a Prospective Trial utilizing MRI-guided Single-line Source Intracavitary Pulsed-Dose Rate Brachytherapy in Locally Advanced Cervical Cancer

Maximum HR-CTV Doses Achievable in MR-Guided Intracavitary Brachytherapy for Cervix Cancer

Image guided intracavitary brachytherapy (BT) for cervix cancer aims at delivering the prescribed dose to a high risk clinical target volume (HR-CTV) while minimizing doses to organs at risk (OAR): rectum, bladder, sigmoid. OAR doses approaching clinical thresholds are occasionally accepted when adequate target coverage is difficult to achieve. This study investigates the maximum dose that would be delivered to the HR-CTV when OAR (rectum, bladder, sigmoid, vagina) doses are allowed to equal GEC-ESTRO recommended thresholds. Ten patients who underwent MRI-guided tandem and ovoid PDR BT for cervix cancer (Dref = 35Gy in 58 pulses) following pelvic radiotherapy (PRT; 45 Gy in 25 f) were included in the study. Plans were created using both manual optimization (MO) of a standard Manchester loading and volume optimization (VO; Varian BrachyVision 8.6) to achieve: (i) an optimized plan (OPT) delivering HR-CTV D90 of 35 Gy while minimizing OAR doses (PRT+BT D2cc for rectum and sigmoid < 75 Gy; bladder < 90 Gy); and (ii) a maximized plan (MAX) giving the highest possible HR-CTV D90 by allowing OAR doses to equal tolerance values. Mean and standard deviation of D2cc for OARs, D90 and V100 for HR-CTV, and sparing factors (SF = D2cc(OAR)/D90(HR-CTV)) were calculated using data generated from DVHs. A two tailed t-test determined statistical significance of the results. Median HR-CTV volume was 37.7 cc (range: 14.2 to 71.5 cc); largest variation in dimension was the width (4.4 ± 1.0 cm). HR-CTV D90 of 37.2 ± 6.0 Gy was achieved with MOMAX and 40.0 ± 4.9 Gy with VOMAX. Difference in D90 coverage between MO and VO was not significant for OPT plans (p = 0.373) but was significant for MAX plans (p = 0.027). Also, a statistically significant difference was not observed in D90 when comparing MOOPT to MOMAX (p = 0.112) but was observed between VOOPT and VOMAX (p = 0.004). HR-CTV V100 showed no significant difference between MOMAX and VOMAX plans (p = 0.213). For rectum and bladder SFs: (i) VOMAX plans were significantly better than MOMAX plans (prec = 0.002; pbldr = 0.014) but (ii) OPT and MAX plans, for the same technique, showed no significant difference. Sigmoid SFs were similar for all planning techniques. For MAX plans, vaginal wall D2cc was < 200% Dref and dose rates were lower than for standard treatment (60 cGy/hr). Using either optimization technique, the maximum HR-CTV D90 could be increased, on average, to 115%Dref. HR-CTV and OAR volumes and their relative proximities control the SFs. Sigmoid and occasionally bladder were the major dose limiting structures. A more complete analysis should include doses to normal tissues surrounding the treated area. Acceptance of an increased HR-CTV D90 for treatment is, however, dependent on the clinical decision of the physician.

Partial breast irradiation for locally recurrent breast cancer within a second breast conserving treatment: Alternative to mastectomy? Results from a prospective trial

PurposeTo assess the outcome of multi-catheter pulse dose rate (PDR) brachytherapy of re-irradiation for local ipsilateral breast tumour recurrence (IBTR) in regard to local control, survival, morbidity and quality of life (QoL). Patients and methodsBetween 1999 and 2006, 39 patients were included with histologically confirmed IBTR, Karnofsky index ⩾80% and refusal of mastectomy. Exclusion criteria were multicentric invasive growth pattern, unclear surgical margins, distant metastasis and a postoperative breast not suitable for interstitial brachytherapy. Primary endpoint was local tumour control. Morbidity, cosmetic outcome and QoL were assessed in 24/39 patients. ResultsThe five year actuarial local control rate was 93% after a mean follow up of 57 (±30) months with two second local relapses. Overall survival and disease free survival, both at 5years, were 87% and 77%, respectively. Late side effects Grade 1–2 were observed in 20/24 patients after a mean follow-up of 30 (±18) months. Late side effects ⩾Grade 3 occurred in 4/24 patients. Cosmetic outcome was excellent to fair in 76% of women. Overall QoL was comparable to a healthy control group. Mean scores of scales and items of QLQ-BR23 were comparable to primary breast conserving therapy. ConclusionsAccelerated PDR-brachytherapy following breast conserving surgery (BCS) for local IBTR results in local tumour control comparable to mastectomy. Morbidity is moderate; the cosmetic outcome is good and hardly any impairment on QoL is observed.

Image and laparoscopic guided interstitial brachytherapy for locally advanced primary or recurrent gynaecological cancer using the adaptive GEC ESTRO target concept

PurposeTo retrospectively assess treatment outcome of image and laparoscopic guided interstitial pulsed dose rate brachytherapy (PDR-BT) for locally advanced gynaecological cancer using the adaptive GEC ESTRO target concept. Materials and methodsBetween June 2005 and December 2010, 28 consecutive patients were treated for locally advanced primary vaginal (nine), recurrent endometrial (12) or recurrent cervical cancer (seven) with combined external beam radiotherapy (EBRT) and interstitial PDR-BT. Treatment was initiated with whole pelvic EBRT to a median dose of 45Gy followed by PDR-BT using the Martinez Universal Perineal Interstitial Template (MUPIT). All implants were virtually preplanned using MRI of the pelvis with a dummy MUPIT in situ. The GEC ESTRO high risk clinical target volume (HR CTV), intermediate risk clinical target volume (IR CTV) and the organs at risk (OAR) were contoured and a preplan for implantation was generated (BrachyVision, Varian). The subsequent implantation was performed under laparoscopic visualisation. Final contouring and treatment planning were done using a post-implant CT. Planning aim of PDR-BT was to deliver 30Gy in 50 hourly pulses to HR CTV. Manual dose optimisation was performed with the aim of reaching a D90>80Gy in the HR CTV calculated as the total biologically equivalent to 2Gy fractions of EBRT and BT (EQD2). Dose to the OAR were evaluated using dose volume constraints for D2cc of 90Gy for bladder and 70Gy for rectum and sigmoid. ResultsFor HR CTV the median volume was 26cm3 (7–91cm3). Coverage of the HR CTV was 97% (90–100%) and D90 was 82Gy (77–88Gy). The D2cc for bladder, rectum, and sigmoid were 65Gy (47–81Gy), 61Gy (50–77Gy), and 52Gy (44–68Gy), respectively. Median follow up was 18months (6–61 months). The actuarial 2years local control rate was 92% (SE 5), while disease-free survival and overall survival were 59% (SE 11) and 74%, respectively (SE 10). No complications to the laparoscopic guided implantation were encountered. Late grade 2 (CTC v 3.0) complications were recorded in nine (32%) patients. One patient had a grade 3 vaginal complication. No grade 4–5 complications have been recorded so far. ConclusionImage and laparoscopic guided interstitial PDR-BT using the GEC ESTRO target concept is applicable for locally advanced primary vaginal or recurrent endometrial and cervical cancer resulting in an excellent local control rate and limited morbidity.

Identifying afterloading PDR and HDR brachytherapy errors using real-time fiber-coupled Al2O3:C dosimetry and a novel statistical error decision criterion

Background and purposeThe feasibility of a real-time in vivo dosimeter to detect errors has previously been demonstrated. The purpose of this study was to: (1) quantify the sensitivity of the dosimeter to detect imposed treatment errors under well controlled and clinically relevant experimental conditions, and (2) test a new statistical error decision concept based on full uncertainty analysis. Materials and methodsPhantom studies of two gynecological cancer PDR and one prostate cancer HDR patient treatment plans were performed using tandem ring applicators or interstitial needles. Imposed treatment errors, including interchanged pairs of afterloader guide tubes and 2–20mm source displacements, were monitored using a real-time fiber-coupled carbon doped aluminum oxide (Al2O3:C) crystal dosimeter that was positioned in the reconstructed tumor region. The error detection capacity was evaluated at three dose levels: dwell position, source channel, and fraction. The error criterion incorporated the correlated source position uncertainties and other sources of uncertainty, and it was applied both for the specific phantom patient plans and for a general case (source-detector distance 5–90mm and position uncertainty 1–4mm). ResultsOut of 20 interchanged guide tube errors, time-resolved analysis identified 17 while fraction level analysis identified two. Channel and fraction level comparisons could leave 10mm dosimeter displacement errors unidentified. Dwell position dose rate comparisons correctly identified displacements ⩾5mm. ConclusionThis phantom study demonstrates that Al2O3:C real-time dosimetry can identify applicator displacements ⩾5mm and interchanged guide tube errors during PDR and HDR brachytherapy. The study demonstrates the shortcoming of a constant error criterion and the advantage of a statistical error criterion.

WE‐A‐BRB‐06: Detecting Afterloaded Brachytherapy Errors in a Phantom Using Real‐Time Fiber‐Coupled Luminescence Dosimetry

Purpose: To explore the ability of a new dosimetry system to identify imposed PDR and HDR brachytherapy errors (needle swaps and displacements) in a phantom. Methods: The new dosimeter is based on the radioluminescence of a fiber‐coupled carbon doped aluminum oxide crystal. Treatment plans previously used for cervix PDR and prostate HDR brachytherapy in the hospital were replicated by mounting interstitial titanium needles on a perineal template. One needle carried the 1 mm diameter dosimeter probe, positioned in the reconstructed tumor region. The remaining needles were connected to PDR and HDR Varian GammaMed Plus afterloaders, carrying 192‐Ir sources. Irradiations were conducted with all needles submerged in water. Relative crystal and source dwell positions, used for reference TG43 dose calculations, were acquired from CT images of the HDR setup. Several errors were imposed by swapped needle pairs and 2, 5, 10, 20 or 30 mm displacements. Results: Dose measurements that deviated from the null case by more than three standard deviations were defined as potential treatment errors. The standard uncertainty, calculated as the quadrature sum of the repeatability and the position uncertainty, was smaller than 5.7% and 4.4% for all channels and the integrated dose for the PDR and HDR measurements, respectively. Comparisons on a channel‐to‐channel basis correctly revealed imposed treatment errors in 25 PDR cases out of 32. Only five errors were revealed based on the integrated dose comparisons for the complete pulse. The HDR measurements correctly identified 61 out of 72 possible guide tube connection errors. The 11 unidentified errors involved channels with similar dwell times and relative needle‐to‐dosimeter distances. Conclusions: The study demonstrated that time resolved dosimetry can detect errors in brachytherapy that are unseen by integrated dose measurements. The new system correctly identified over 8 out of 10 tested and clinically relevant PDR and HDR brachytherapy errors.

Long-Term Results of a Prospective Dose Escalation Phase-II Trial: Interstitial Pulsed-Dose-Rate Brachytherapy as Boost for Prostate Cancer

Purpose: We reviewed our ten-year single institution experience with pulsed dose rate brachytherapy by dose escalation Phase-II study in patients with intermediateand high-risk prostate cancer (according the definition by d’Amico). Materials andMethods:We treated a total of 130 patients for intermediate and high risk prostate cancer between 2000 and 2007 using PDRbrachytherapy as a boost after conformal external beam radiation therapy to 45-50 Gy. Boost brachytherapy doses ranged from 25 to 35 Gy e 33 pts. received 25 Gy (total dose 70 Gy), 63 pts. 30 Gy (total dose 75-80 Gy) and 34 pts. 35 Gy,(total dose 85 Gy) given in one session (dose per pulse was 0.60 -0.70 Gy delivered for 24 h per day, night and day, with a time interval of 1 h between two pulses, total time 48-50 hours). PSArecurrence-free survival according to Kaplan-Meier was calculated and changes in American Urological Association symptom scores and also acute and chronic toxicities according Common Toxicity Criteria scale were assessed. Results: At the time of analysis with a median followup of 66 months local control according to the Phoenix definition was achieved by 88% of patients e only 16/130 patients (12,3%) developed a biochemical relapse. A strong correlation between frequency of a local control according to the Phoenix definition and the brachytherapy dose has been documented: At time of analysis 82%, 86% and 97% of our patients were disease-free for boost doses in values of 25 Gy, 30 Gy and 35 Gy, respectively. The side effects of therapy were negligible: There were 18 cases (14%) of grade 1/2 rectal proctitis, one case (0.8%) grade 3 proctitis, 18 cases (14%) of grade 1/2 cystitis, no cases (0%) with dysuria grade 3. No patient had new onset incontinence or a bulbourethral stricture requiring dilation. Conclusions: Image-guided conformal PDR-brachytherapy as boost after external beam radiation therapy is a very effective treatment option with very lowmorbidity by patientswith intermediate or high risk prostate cancer.

Image-guided brachytherapy for cervical cancer: A Canadian Brachytherapy Group survey

Purpose To survey the current use and future plans for image-guided brachytherapy (BT) for cervical cancer by radiation oncologists in Canada. Methods and Materials Canadian radiation oncologists treating gynecologic malignancies were identified in January 2009. A 29-item questionnaire (English and French) querying the current practice in the use of imaging in BT planning, and plans for transition to three-dimensional (3D) image guidance for BT for cervical cancer (curative intent, intact cervix), was electronically circulated. Questionnaire responses were tabulated and analyzed by respondent and by center. Results Response rate was 62% (36 of 58 radiation oncologists), representing 71% (22 of 31) of Canadian radiation oncology centers with a gynecologic BT facility. Most of the centers were using high-dose-rate BT (68%), followed by low-dose-rate BT (23%) and pulsed dose-rate BT (10%). Main imaging used for treatment planning by center was plain X-ray (50%), computerized tomography (CT) (45%), and magnetic resonance imaging (MRI) (5%). For respondents using CT or MRI for planning, point A was the most common dose prescription point (50%), followed by gross tumor volume/clinical target volume as per Groupe Européen de Curiethérapie and the European Society for Therapeutic Radiology and Oncology guidelines (44%). For centers using plain X-rays for planning, 73% planned to transition to a 3D image-based approach, with the majority to adopt CT imaging. Eighty percent of respondents agreed that 3D image-guided BT should become standard of care for treatment of cervical cancer in Canada, and additionally support the development of national guidelines. Conclusions Most of the Canadian radiation oncologists surveyed and Canadian cancer centers are either using 3D imaging and planning or transitioning to a 3D image-based approach within the next year. Point A remained a commonly documented prescription point. Access to MRI was very low. These results may lead to national treatment guidelines.

Long term results of PDR brachytherapy for lip cancer.

PurposeTo evaluate the long time outcome with regard to local tumour control and side effects of a pulsed dose rate (PDR) monobrachytherapy of primary or recurrent cancer of the lip.Material and methodsBetween 1995 and 2007 we treated 43 patients with primary or recurrent clinical T1-T3N0 lip cancers. There were 22 T1 patients (51%), 16 T2 (37%) and 5 T3 cases (12%). A median dose of 60 (55-66) Gy was given, depending on the tumour volume. The PDR treatment was delivered with 0.83 Gy/pulse every second hour for 5.5-6.5 days. The patients were followed for a median of 55 (1-158) months.ResultsThe 2-, 5- and 10-year rates of actuarial local control were 97.6%, 94.5% and 94.5%, overall survival 88.0%, 58.9% and 39.1%, disease free survival 92.7%, 86.4% and 86.4% respectively. The regional control rate was 93%. One patient (2%) developed distant metastases. A dosimetrical analysis showed a mean treated volume of 14.9 (3.0-56.2) cm3. Long-term side effects were mild and the cosmetic outcome excellent, except for 1 case (2%) of soft tissue necrosis and 1 case (2%) of osteoradionecrosis.ConclusionsLocal outcome is excellent and similar to other published studies of continuous low dose rate (cLDR) brachytherapy.

Changes in Tumor Anatomy and Dosimetry during MR-Guided Pulsed Dose Rate Brachytherapy for Cervix Cancer

Changes in Tumor Anatomy and Dosimetry during MR-Guided Pulsed Dose Rate Brachytherapy for Cervix Cancer

Development of Late Toxicity and International Prostate Symptom Score Resolution After External-Beam Radiotherapy Combined With Pulsed Dose Rate Brachytherapy for Prostate Cancer

To investigate the development of gastrointestinal (GI) toxicity, genitourinary (GU) toxicity, erectile dysfunction, and International Prostate Symptom Score (IPSS) resolution in a cohort of patients treated with external-beam radiotherapy (EBRT) followed by a brachytherapy pulsed dose rate (PDR) boost. Between 2002 and 2008, 110 patients were treated with 46-Gy EBRT followed by PDR brachytherapy (24.96-28.80 Gy). The investigated outcome variables, GI toxicity, GU toxicity, erectile dysfunction, and IPSS were prospectively scored at several time points during follow-up. Association between time (as continuous and categorical variable) and the outcome variables was assessed using generalized linear models. No statistically significant association was found between time (continuous) and GI toxicity (odds ratio [OR], 0.97; 95% confidence interval [CI], 0.89-1.06), GU toxicity (OR, 0.97; 95% CI, 0.91-1.03), erectile dysfunction (OR, 1.06; 95% CI, 0.99-1.11), and IPSS (-0.11; 95% CI, -0.41-0.20). Also, no statistically significant association was found between these variables and time as a categorical variable. GU toxicity was associated with IPSS resolution (OR, 1.16; 95% CI, 1.09-1.24). Posttreatment IPSS was associated with pretreatment IPSS (0.52; 95% CI, 0.25-0.79). No accumulation of high-grade toxicity over time could be established for a group of patients treated with EBRT and PDR brachytherapy for prostate cancer, probably because high-grade late toxicity resolves with time. Also, differences in IPSS values among patients are smaller after treatment than before treatment.

Accelerated Partial Breast Irradiation With Interstitial Implants: Risk Factors Associated With Increased Local Recurrence

To analyze patient, disease, and treatment-related factors regarding their impact on local control after interstitial multicatheter accelerated partial breast irradiation (APBI). Between November 2000 and April 2005, 274 patients with early breast cancer were recruited for the German-Austrian APBI Phase II trial (ClinicalTrials.gov identifier: NCT00392184). In all, 64% (175/274) of the patients received pulsed-dose-rate (PDR) brachytherapy and 36% (99/274) received high-dose-rate (HDR) brachytherapy. Prescribed reference dose for HDR brachytherapy was 32 Gy in eight fractions of 4 Gy, twice daily. Prescribed reference dose in PDR brachytherapy was 49.8 Gy in 83 consecutive fractions of 0.6 Gy each hour. Total treatment time was 3 to 4 days. The median follow-up time was 64 months (range, 9-110). The actuarial 5-year local recurrence free survival rate (5-year LRFS) was 97.7%. Comparing patients with an age <50 years (49/274) vs. ≥50 years (225/274), the 5-year LRFS resulted in 92.5% and 98.9% (exact p = 0.030; 99% confidence interval, 0.029-0.032), respectively. Antihormonal treatment (AHT) was not applied in 9% (24/274) of the study population. The 5-year LRFS was 99% and 84.9% (exact p = 0.0087; 99% confidence interval, 0.0079-0.0094) in favor of the patients who received AHT. Lobular histology (45/274) was not associated with worse local control compared with all other histologies (229/274). The 5-year LRFS rates were 97.6% and 97.8%, respectively. Local control at 5 years is excellent and comparable to therapeutic successes reported from corresponding whole-breast irradiation trials. Our data indicate that patients <50 years of age ought to be excluded from APBI protocols, and that patients with hormone-sensitive breast cancer should definitely receive adjuvant AHT when interstitial multicatheter APBI is performed. Lobular histology need not be an exclusion criterion for future APBI trials.

Treatment Results of PDR Brachytherapy Combined With External Beam Radiotherapy in 106 Patients With Intermediate- to High-Risk Prostate Cancer

To evaluate treatment outcome of pulsed dose-rate brachytherapy (PDR) combined with external-beam radiotherapy (EBRT) for the treatment of prostate cancer. Between 2002 and 2007, 106 patients were treated by EBRT combined with PDR and followed prospectively. Two, 38, and 66 patients were classified as low-, intermediate-, and high-risk disease respectively according to the National Comprehensive Cancer Network criteria. EBRT dose was 46 Gy in 2.0-Gy fractions. PDR dose was increased stepwise from 24.96 to 28.80 Gy. Biochemical disease free survival and overall survival were determined by the Kaplan-Meier method. Cumulative incidence of late gastrointestinal (GI) and genitourinary (GU) toxicity were scored, according to the Common Terminology Criteria for Adverse Events. The 3- and 5-year biochemical nonevidence of disease (bNED) were 92.8% (95% confidence interval [CI], 87.1-98.5) and 89.5% (95% CI, 85.2-93.8), respectively. Overall survival at 3 and 5 years was 99% (95% CI, 96-100) and 96% (95% CI, 90-100), respectively. The 3- and 5-year Grade 2 GI toxicity was 5.3% (95% CI, 0-10.6) and 12.0% (95% CI, 1.4-22.6), respectively. No Grade 3 or higher GI toxicity was observed. The 3- and 5-year Grade 2 or higher GU toxicity was 18.7% (95% CI, 10.3-27.1) and 26.9% (95% CI, 15.1-38.7), respectively. Results on tumor control and late toxicity of EBRT combined with PDR are good and comparable toresults obtained with EBRT combined with high-dose-rate brachytherapy for the treatment of prostate cancer.

Évaluation économique de la curiethérapie de débit pulsé gynécologique (PDR) avec optimisation de la dose pour les cancers du col utérin

Purpose Our study aims at evaluating the cost of pulsed dose-rate (PDR) brachytherapy with optimized dose distribution versus traditional treatments (iridium wires, cesium, non-optimized PDR). Issues surrounding reimbursement were also explored. Materials and methods This prospective, multicentre, non-randomised study conducted in the framework of a project entitled “Support Program for Costly Diagnostic and Therapeutic Innovations” involved 21 hospitals. Patients with cervix carcinoma received either classical brachytherapy or the innovation. The direct medical costs of staff and equipment, as well as the costs of radioactive sources, consumables and building renovation were evaluated from a hospital point of view using a microcosting approach. Subsequent costs per brachytherapy were compared between the four strategies. Results The economic study included 463 patients over two years. The main resources categories associated with PDR brachytherapy (whether optimized or not) were radioactive sources (1053 €) and source projectors (735 €). Optimized PDR induced higher cost of imagery and dosimetry (respectively 130 € and 367 €) than non-optimized PDR (47 € and 75 €). Extra costs of innovation over the less costly strategy (iridium wires) reached more than 2100 € per treatment, but could be reduced by half in the hypothesis of 40 patients treated per year (instead of 24 in the study). Conclusion Aside from staff, imaging and dosimetry, the current hospital reimbursements largely underestimated the cost of innovation related to equipment and sources.

Influence of length of interval between pulses in PDR brachytherapy (PDRBT) on value of Biologically Equivalent Dose (BED) in healthy tissues.

PurposeDifferent PDR treatment schemas are used in clinical practice, however optimal length of interval between pulses still remains unclear. The aim of this work was to compare value of BED doses measured in surrounded healthy tissues according to different intervals between pulses in PDRBT. Influence of doses optimization on BED values was analyzed.Material and methodsFifty-one patients treated in Greater Poland Cancer Centre were qualified for calculations. Calculations of doses were made in 51 patients with head and neck cancer, brain tumor, breast cancer, sarcoma, penis cancer and rectal cancer. Doses were calculated with the use of PLATO planning system in chosen critical points in surrounded healthy tissues. For all treatment plans the doses were compared using Biologically Equivalent Dose formula. Three interval lengths (1, 2 and 4 hours) between pulses were chosen for calculations. For statistical analysis Friedman ANOVA test and Kendall ratio were used.ResultsThe median value of BED in chosen critical points in healthy tissues was statistically related to the length of interval between PDR pulses and decreased exponentially with 1 hour interval to 4 hours (Kendall = from 0.48 to 1.0; p = from 0.002 to 0.00001).ConclusionsProlongation of intervals between pulses in PDR brachytherapy was connected with lower values of BED doses in healthy tissues. It seems that longer intervals between pulses reduced the risk of late complications, but also decreased the tumour control. Furthermore, optimization influenced the increase of doses in healthy tissues.

Values of biologically equivalent doses in healthy tissues: Comparison of PDR and HDR brachytherapy techniques

Purpose The aim of this work was to compare the values of doses measured in healthy tissues in chosen pulsed-dose-rate (PDR) brachytherapy (PDRBT) and high-dose-rate (HDR) brachytherapy (HDRBT) fractionation schemas. Methods and Materials Fifty-one patients treated with PDRBT were qualified for calculations. This group included patients with head and neck cancer, brain tumor, breast cancer, sarcoma, penile cancer, and rectal cancer. The doses were calculated in chosen points in surrounded organs at risk (OaR). The biologically equivalent dose (BED) formula was used to compare doses in PDRBT and HDRBT. Results One ascertained that in biologically equivalent (to PDR) HDRBT, the increase of fractional dose from 4 to 10 Gy caused the necessity to decrease the total dose in treatment target ( p < 0.001). The use of HDR instead of PDR essentially caused lower physical and biologic doses in examined OaR. In many examined critical points in OaR where BED in the treatment area was the same, one ascertained the decrease of total physical HDR dose according to the growth of the fractional dose. Similar dependences were observed for BED. Conclusions The use of biologically equivalent HDRBT instead of PDRBT caused the decrease of physical doses in the treatment target and the decrease of physical doses and BEDs in OaR. Prolongation of intervals between pulses in PDRBT was connected with lower values of BED doses in healthy tissues.

Time‐resolved in vivo luminescence dosimetry for online error detection in pulsed dose‐rate brachytherapy

The purpose of this study is to present and evaluate a dose-verification protocol for pulsed dose-rate (PDR) brachytherapy based on in vivo time-resolved (1 s time resolution) fiber-coupled luminescence dosimetry. Five cervix cancer patients undergoing PDR brachytherapy (Varian GammaMed Plus with 192Ir) were monitored. The treatments comprised from 10 to 50 pulses (1 pulse/h) delivered by intracavitary/interstitial applicators (tandem-ring systems and/or needles). For each patient, one or two dosimetry probes were placed directly in or close to the tumor region using stainless steel or titanium needles. Each dosimeter probe consisted of a small aluminum oxide crystal attached to an optical fiber cable (1 mm outer diameter) that could guide radioluminescence (RL) and optically stimulated luminescence (OSL) from the crystal to special readout instrumentation. Positioning uncertainty and hypothetical dose-delivery errors (interchanged guide tubes or applicator movements from +/-5 to +/-15 mm) were simulated in software in order to assess the ability of the system to detect errors. For three of the patients, the authors found no significant differences (P>0.01) for comparisons between in vivo measurements and calculated reference values at the level of dose per dwell position, dose per applicator, or total dose per pulse. The standard deviations of the dose per pulse were less than 3%, indicating a stable dose delivery and a highly stable geometry of applicators and dosimeter probes during the treatments. For the two other patients, the authors noted significant deviations for three individual pulses and for one dosimeter probe. These deviations could have been due to applicator movement during the treatment and one incorrectly positioned dosimeter probe, respectively. Computer simulations showed that the likelihood of detecting a pair of interchanged guide tubes increased by a factor of 10 or more for the considered patients when going from integrating to time-resolved dose verification. The likelihood of detecting a +/-15 mm displacement error increased by a factor of 1.5 or more. In vivo fiber-coupled RL/OSL dosimetry based on detectors placed in standard brachytherapy needles was demonstrated. The time-resolved dose-rate measurements were found to provide a good way to visualize the progression and stability of PDR brachytherapy dose delivery, and time-resolved dose-rate measurements provided an increased sensitivity for detection of dose-delivery errors compared with time-integrated dosimetry.

MRI-guided treatment-planning optimisation in intracavitary or combined intracavitary/interstitial PDR brachytherapy using tandem ovoid applicators in locally advanced cervical cancer

Purpose To study the impact of MRI-guided treatment planning on dose/volume parameters in pulsed dose rate (PDR) brachytherapy (BT) for cervical cancer. Additionally, we investigated the potential benefit of an intracavitary/interstitial (IC/IS) modification of the classical tandem ovoid applicator. Material and methods For 24 patients we compared Standard PDR BT plans, Scaled Standard plans and MRI-guided Optimised plans. The total EBRT/BT prescribed dose to Manchester point A or to 90% of the HR-CTV (D90 HR-CTV) [1] expressed in EQD 2 was 80 Gy αβ10 in 17 patients (Period I) and 84 Gy αβ10 in 7 patients (Period II). The constraints to 2 cm 3 of the OAR were 90 Gy αβ3 for bladder and 75 Gy αβ3 for rectum, sigmoid and bowel. Most cases were treated with a traditional intracavitary tandem ovoid applicator. In 6 patients we used a newly designed combined IC/IS modification for the second PDR fraction and investigated the benefit of the interstitial part. Results The average gain of MRI-guided optimisation expressed in D90 HR-CTV was 4 ± 9 Gy αβ10 ( p < 0.001) and 10 ± 7 Gy αβ10 ( p = 0.003) in the two periods. The dose to 2 cm 3 of the OAR met the constraints. In the group that was treated with the combined IC/IS approach, we could increase the D90 HR-CTV for the second PDR fraction with 5.4 ± 4.2 Gy αβ10 ( p = 0.005) and the D100 with 4.8 ± 3.1 Gy αβ10 ( p = 0.07). Conclusions Three-dimensional MRI-guided treatment planning and optimisation improves the DVH parameters compared to conventional planning strategies. Additional improvement can be achieved by using a combined IC/IS approach.