Patterns of quality assurance and treatment planning for stereotactic body radiation therapy in India - A survey.

AIM: The use of stereotactic body radiation therapy (SBRT) is an increasing trend in the country. The aim of this study is to gain knowledge on patterns of quality assurance (QA) and treatment planning (TP) aspects with respect to SBRT. MATERIALS AND METHODS: A questionnaire with multiple choice was designed to determine practices of SBRT covering areas such as years of experience, type of linear accelerator, tumor-motion strategies, calculation algorithm used in the TP system (TPS), the protocol used for small field dosimetry, the detector used for small field dosimetry and QA, respiratory management during delivery. The survey was sent to all radiotherapy institutes in the country having a minimum of one linear accelerator, and responses were analyzed. RESULTS: From June 2022 to December 2022, 265 responses to the SBRT survey were received with response rate as 60.4%. The most common reason for not adopting SBRT was reported as a lack of capability of treatment machines to deliver SBRT (61.6%). Lung (81.1%) was the most practiced site. The most common delivery unit was a conventional linear accelerator (83%); 6 MV FFF (85.7%) was mostly used energy; volumetric-modulated arc radiotherapy (VMAT) (91.5%) was mostly used delivery technique; most of the equipment (more than 91.5%) used multileaf collimator (MLC) leaf width ≤5 mm. The most popular methods used for motion strategies during computed tomography (CT) were motion-encompassing and breath-hold techniques used by 65 (62.5%) and 62 (59.6%) respondents, respectively. The most popular method used for respiratory management during delivery was breath-hold by 55 (52.4%) respondents. Most TPS are equipped with either Type-C or Type-B algorithms. Heterogeneity was observed in the QA protocol and acceptance criteria for analysis of patient-specific QA. CONCLUSION: The survey resulted in heterogeneity in QA and TP aspects among users of SBRT and demands for harmonizing the dosimetric aspects of SBRT in the country.

Volumetric and geometric changes in the parotid glands and target volume during image-guided radiotherapy for locally advanced oropharyngeal cancers.

PURPOSE: This study aimed to evaluate the volumetric and geometric changes in the parotid glands and target volume during image-guided radiotherapy (IGRT) for locally advanced oropharyngeal cancers. MATERIALS AND METHODS: Twenty patients receiving radiotherapy using IGRT at a dose of 70 Gy/35 fractions/7 weeks for locally advanced oropharyngeal cancers were accrued. Radiotherapy planning computed tomography (CT) scans were performed at pre-radiotherapy (RT), 20, 40, and 60 Gy for each patient. Volume changes in target and parotids along with shifts of parotids were assessed with respect to pre-RT scan after co-registration. In study scans, GTVp and GTVn were recontoured as per particular CT. CTV and PTV were copied from planning CT to study CT. CTV was edited from anatomical barriers, and PTV was edited only from the skin in the study CT. The parotids were recontoured on each study scan. The center of mass (COM) of C2 vertebral body was considered as the reference to evaluate its shifts. RESULTS: There was a statistically significant percentage regression of ipsilateral and contralateral parotid mean volumes at the rate of 0.85%/0.207 cc and 0.98%/0.26 cc per day, respectively. We observed the mean medial shift of center of mass of ipsilateral parotid of 2.23 mm (p = 0.011) and contralateral parotid of 2.67 mm (p = 0.069) at the end of 60 Gy. GTVp (mean) reduced from 41.87 cc at 0 Gy to 31.13 cc (25.65%) at 60 Gy (p = 0.003), while GTVn (mean) reduced from 19.98 cc at 0 Gy to 10.79 cc (45.99%) at 60 Gy (p = 0.003). There was a statistically significant reduction in CTV and PTV volumes at 60 Gy. CONCLUSION: Statistically significant volumetric and geometric changes occurred during intensity-modulated radiation (IMRT), which were most prominent after 40 Gy and were maximum at 60 Gy. There was a medial shift of parotid glands toward the high-dose region. This study can be useful to devise an adaptive radiotherapy strategy.

A Simplified Approach for Determination of Inflection Points of Flattening Filter-Free Photon Beam Using In-House Developed Software and Derivation of Reference Levels.

Aim: This article aimed to present the salient features of the in-house developed Java program for the determination of inflection point and dosimetric parameters of flattening filter-free (FFF) photon beam. Reference levels for the dosimetric parameters of the FFF photon beams were also presented. Materials and Methods: Beam profiles of 6 MV FFF and 10 MV FFF photon beams for a collimator setting of 20 cm × 20 cm measured at 10 cm depth in an isocentric setup acquired from various institutions were analyzed using an in-house developed Java program and manual method. The values of reference dose value (RDV), field size, penumbra, and degree of un-flatness (defined as the lateral separation between 90% [X90%], 75% [X75%], and 60% [X60%] dose points on the profile) were calculated and compared. The reference values of field size, penumbra, and degree of un-flatness were also determined for Varian and Elekta medical electron linear accelerators (LINACs). Results: The maximum differences for RDV determined using the Java method and manual method are 2.4% and 2.7% for 6 and 10 MV FFF photon beams, respectively. The maximum difference between the values of field size, penumbra, and degree of un-flatness determined using Java and manual methods is within 1.3 mm. The reference values of field size and penumbra for Varian LINACs are 19.94 ± 0.10 cm and 0.83 ± 0.08 cm (6 MV FFF) and 19.95 ± 0.10 cm and 0.83 ± 0.08 cm (10 MV FFF). Similarly, the reference values of field size and penumbra for Elekta LINACs are 20.02 ± 0.09 cm and 0.94 ± 0.12 cm (6 MV FFF) and 20.03 ± 0.11 cm and 0.97 ± 0.16 cm (10 MV FFF). Conclusions: A software program was developed in Java for analyzing the beam profiles of FFF photon beams. The results of Java-derived values of dosimetric parameters of FFF photon beams were found in good agreement with the values determined using the manual method. The reference values of these parameters were also derived and quoted using a large cohort of the data.

Quality Improvement Process with Incident Learning Program Helped Reducing Transcriptional Errors on Telecobalt Due to Mismatched Parameters in Different Generations.

Purpose: Higher frequency of transcriptional errors in the radiotherapy electronic charts for patients on telecobalt was noted. We describe the impact of the quality improvement (QI) initiative under the department's incident learning program (ILP). Materials and Methods: The multidisciplinary quality team under ILP was formed to identify the root cause and introduce methods to reduce (smart goal) the current transcription error rate of 40% to <5% over 12 months. A root cause analysis including a fishbone diagram, Pareto chart, and action prioritization matrix was done to identify key drivers and interventions. Plan-Do-Study-Act (PDSA) Cycle strategy was undertaken. The primary outcome was percentage charts with transcriptional errors per month. The balancing measure was "new errors" due to interventions. All errors were identified and corrected before patient treatment. Results: The average baseline error rate was 44.14%. The two key drivers identified were education of the workforce involved and mechanical synchronization of various machine parameters. PDSA cycle 1 consisted of an education program and sensitization of the staff, post which the error rates dropped to 5.4% (t-test P = 0.03). Post-PDSA cycle 2 (synchronization of machine parameters), 1, 3, and 6 months and 1 year, the error rates were sustained to 5%, 4%, 3%, and 4% (t-test P > 0.05) with no new additional errors. Conclusions: With various generations of machines and technologies that are not synchronized, the proneness of transcription errors can be very high which can be identified and corrected with a typical QI process under ILP.

What is the dosimetric impact of isotropic vs anisotropic safety margins for delineation of the clinical target volume in breast brachytherapy?

PURPOSE: The purpose of the study was to report dosimetric differences for breast brachytherapy plans optimized for clinical target volume (CTV) generated using conventional isotropic expansion of tumor bed volume (TBV) and Groupe Européen de Curiethérapie-European Society for Radiotherapy and Oncology (GEC-ESTRO) recommendations to expand the TBV anisotropically to achieve a total safety margin of 2 cm (resection margin size + added safety margin). METHODS: Institutional records of 100 patients who underwent accelerated partial breast irradiation using multicatheter interstitial brachytherapy from May 2015 to March 2020 were reviewed retrospectively. Two sets of CT-based plans were made, one with 1-cm isotropic margins around the tumor bed (CTV_ISO) and the other with anisotropic margins (CTV_GEC). Plans were evaluated and compared using the American Brachytherapy Society and GEC-ESTRO guidelines. RESULTS: The median TBV was 36.97 cc. The median margin widths were as follows: anterior 1.2, posterior 1.0, superior 1.0, inferior 0.9, medial 1.2, and lateral 1.2 cm. The mean tumor bed coverage index was 0.94; 0.93 [p.066], the CTV coverage index 0.86; 0.84 [p 0.001], the dose homogeneity index (DHI) 0.77; 0.75 [p < 0.001] and the conformity index 0.66; 0.64 [p < 0.001] in CTV_ISO and CTV_GEC plans, respectively. In smaller volume implants (TBV< 35 cc), the DHI was 0.76; 0.75 [p 0.008] and the conformity index was 0.66; 0.62 [p < 0.001], whereas in larger volumes >35 cc, the CTV coverage index was 0.86; 0.84 [p 0.003] and the DHI 0.78; 0.76 [p 0.001] in CTV_ISO and CTV_GEC plans, respectively. CONCLUSIONS: In this cohort of patients who underwent accelerated partial breast irradiation, plans with anisotropic margins had lower conformity, the impact of which was predominantly seen in smaller implants. Rest of the dosimetric constraints were achieved in both the plans as per the American Brachytherapy Society and GEC-ESTRO guidelines.

A comparison of long-term clinical outcomes of accelerated partial breast irradiation using interstitial brachytherapy as per GEC-ESTRO, ASTRO, updated ASTRO, and ABS guidelines.

PURPOSE: The purpose of this study is to evaluate long-term clinical outcomes of women treated with accelerated partial breast irradiation (APBI) using multicatheter interstitial brachytherapy (MIB-APBI) with risk groups defined by Groupe Européen de Curie-thérapie and the European Society for Radiotherapy & Oncology (GEC-ESTRO), American Society for Radiation Oncology (ASTRO), updated ASTRO, and American Brachytherapy Society (ABS) guidelines and to elucidate the most appropriate guideline that could differentiate outcomes among its risk groups. METHODS AND MATERIALS: Two hundred forty women underwent MIB-APBI during July 2000 to March 2013. Comparisons of long-term clinical outcomes (local control [LC], disease-free survival [DFS], cause-specific survival [CSS], and overall survival [OAS]) stratified by the risk groups proposed by the aforementioned patient selection guidelines were carried out on a prospectively maintained database. RESULTS: At a median follow-up of 114 months, 10-year LC, DFS, and OAS were 90%, 81%, and 83.5%, respectively, for the entire group. There was no statistically significant difference in the LC rates for risk groups by ESTRO, ASTRO, updated ASTRO and ABS guidelines. The 10-year DFS and OAS for GEC-ESTRO low-, intermediate-, and high-risk group was 75%, 88%, and 60% (p = 0.02) and 86%, 93%, and 62% (p = 0.001), respectively. Ten-year DFS and OAS in the ABS 2018-acceptable and ABS 2018-unacceptable group were 78% and 67% (p = 0.01) and 88% and 69% (p = 0.001), respectively. No significant difference in any of the outcomes was observed with risk groups suggested by ASTRO or updated ASTRO consensus guidelines. CONCLUSIONS: None of the current patient selection guidelines for APBI could differentiate LC (main APBI endpoint) among its risk groups, whereas GEC-ESTRO and ABS guideline could differentiate DFS and OAS.

Coverage with dosimetric concordance index (CDCI): a tool for evaluating dosimetric impact of inter-observer target variability in brachytherapy.

PURPOSE: The aim of this study was to propose an index for evaluating dosimetric impact of inter-observer target delineation variability in brachytherapy. MATERIAL AND METHODS: The coverage with dosimetric concordance index (CDCI) is expressed as CDCIcommon and CDCIpair. The CDCIcommon is the mean coverage of target volume with common volume irradiated by prescription dose among all observers and represents the condition of worst target coverage. CDCIpair is the generalized form of CDCI, which is mean target coverage with common prescription volume obtained between all possible pairs of observers and represents more realistic coverage of target with dosimetric concordance. The index was used to evaluate the dosimetric impact of target delineation variability in optimized conformal plans on target volumes of five radiation oncologists for twenty patients of multi-catheter interstitial partial breast brachytherapy. RESULTS: The mean decline of 5.6 ±3.2% and 11.3 ±5.7% in CDCIpair and CDCIcommon, respectively, was observed comparing to coverage index (CI) of target volume in all patients due to inter-observer target variability. CDCIcommon and CDCIpair were found to have significant linear correlation (r = 0.964, p < 0.000). The difference between CDC and CI increased with the mean relative target volume among observers. Significant correlation (r = 0.962, p < 0.000) was also noted for the difference (Δ) in CDCIcommon and CDCIpair with CI of target volume. CONCLUSIONS: The recommended indices and difference between the dosimetric coverage of target volume (CI) with CDCI (ΔCDCI) can be used for evaluating dosimetric impact of the inter-observer target delineation variability.

Measurement of the small field output factors for 10 MV photon beam using IAEA TRS-483 dosimetry protocol and implementation in Eclipse TPS commissioning.

Dosimetry of small fields (SF) is vital for the success of highly conformal techniques. IAEA along with AAPM recently published a code of practice TRS-483 for SF dosimetry. The scope of this paper is to investigate the performance of three different detectors with 10 MV with-flatting-filter (WFF) beam using TRS-483 for SF dosimetry and subsequent commissioning of the Eclipse treatment planning system (TPS version-13.6) for SF data. SF dosimetry data (beam-quality TPR20,10(10), cross-calibration, beam-profile, and field-output-factor(F.O.F)) measurements were performed for PTW31006-pinpoint, IBA-CC01 and IBA-EFD-3G diode detectors in nominal field size (F.S) range 0.5 × 0.5cm2to 10 × 10 cm2with water and solid water medium using Varian Truebeam linac. However, Eclipse-TPS commissioning data was acquired using IBA-EFD-3G diode, and absolute dose calibration was performed with FC-65G detector. The dosimetric performance of the Eclipse-TPS was validated using TLD-LiF chips, IBA-PFD, and IBA-EFD-3G diodes. Dosimetric performance of the PTW31006-pinpoint, IBA-CC01, and IBA-EFD-3G detectors was successfully tested for SF dosimetry. The F.O.Fs were generated and found in close agreement for all F.S except 0.5 × 0.5cm2. It is also found that TPR20,10(10) value can be derived within 0.5% accuracy from a non-reference field using Palmans equation. Cross-calibration can be performed in F.S 6 × 6 cm2with a maximum variation of 0.5% with respect to 10 × 10cm2. During profile measurement, the full-width half-maxima (FWHM) of F.S 0.5 × 0.5cm2was found maximum deviated from the geometric F.S. In addition, Eclipse-TPS was commissioned along with some limitations: F.O.F below F.S 1 × 1cm2was ignored by TPS, PDD and profiles were dropped from configuration below F.S 2 × 2 cm2, and F.O.F which does not satisfy the condition 0.7 < A/B < 1.4 (A and B are FWHM in cross-line and in-line direction) have higher uncertainty than specified in TRS-483. Validation tests for Eclipse-TPS generated plans were also performed. The measured dose was in close agreement (3%) with TPS calculated dose up to F.S 1.5 × 1.5cm2.

Impact of inter-observer variations in target volume delineation on dose volume indices for accelerated partial breast irradiation with multi-catheter interstitial brachytherapy.

PURPOSE: To investigate dosimetric impact of inter-observer variation in clinical target volume(CTV) delineation for patients undergoing interstitial partial breast brachytherapy. METHODS: Five radiation oncologists delineated CTV in twenty patients who underwent multi-catheter partial breast brachytherapy. Five treatment plans for each patient were graphically optimized for CTV of all observers and evaluated using coverage index(CI), external volume index(EI), overdose volume index(OI) and conformal index(COIN). In addition, volume enclosed by prescription isodose(V100), its spatial concordance(CIcommon), mean coverage of all CTVs with common volume of prescription dose(V100_common) and mean CTV coverage for all pairs of observer with common prescription volume of respective pairs(V100_pair) were also computed. RESULTS: The mean ±â€¯standard deviation(SD) of CI and COIN ranged from 0.756 ±â€¯0.076 to 0.840 ±â€¯0.070 and 0.591 ±â€¯0.090 to 0.673 ±â€¯0.06 respectively. When a plan made for CTV of individual observer was evaluated on CTV of all observers, the maximum variations(ρ < 0.05) in the mean CI,COIN,OI and EI were 10.6%,11.4%,10.6% and 72.7% respectively. The observed mean ±â€¯SD of V100, CIcommon of V100, CTV coverage with V100_common and V100_pair was 160.7 ±â€¯52.1, 0.70 ±â€¯0.09, 73.1 ±â€¯8.1% and 77.9 ±â€¯7.3% respectively. CONCLUSION: Inter-observer variation in delineation of CTV showed significant dosimetric impact with mean CTV coverage of 73.1% and 77.9% by common and paired prescription dose volume respectively among all observers.

Impact of adjuvant systemic chemotherapy on wound healing and cosmetic outcome in 224 women treated with accelerated partial breast irradiation using interstitial brachytherapy.

PURPOSE: To evaluate the impact of timing of adjuvant chemotherapy on wound healing and cosmetic outcome in women treated with accelerated partial breast irradiation (APBI). METHODS AND MATERIALS: Between August 2000 to December 2011, 224 women were treated with APBI using multicatheter interstitial high-dose-rate brachytherapy. Patients were treated to a dose of 34 Gy/10#/5-7 days with bid regimen. Systemic chemotherapy was administered as per the standard guidelines. RESULTS: Multicatheter interstitial brachytherapy technique was open cavity in 136 (60%) and closed cavity in 88 (40%). Adjuvant chemotherapy was given in 117 (52%). Wound complications (WCs) were observed in 24 patients (11%), which included wound infections (WIs) in 20 and wound dehiscence in 14. The median gap between chemotherapy and APBI was 13 days in women who developed WCs, 20 days for prechemo, and 32 days for postchemo APBI in its absence. On multivariate analysis, gap between APBI and chemotherapy of ≤3 weeks was the only significant factor (p = 0.03) affecting WCs. Acute WI (p = 0.01) and two-dimensional planning (p = 0.04) had significant impact on cosmesis resulting in fair to poor cosmetic outcome. CONCLUSIONS: Gap of ≤3 weeks between APBI and chemotherapy resulted in increased WCs. WI and two-dimensional planning resulted in poorer cosmetic outcome. We recommend gap of at least 3 weeks for optimal outcome.

Clinical outcomes with high-dose-rate surface mould brachytherapy for intra-oral and skin malignancies involving head and neck region.

PURPOSE: The literature and experience of high-dose-rate (HDR) surface mould brachytherapy (SMB) in head and neck cancer is sparse. We report our institutional experience of SMB for such tumours. MATERIAL AND METHODS: Thirty-five patients with malignant localized early T1/T2, N0 (21 intra-oral and 14 skin) tumours treated with SMB during 2008-2014 were analyzed. Treatment was delivered using HDR 192Ir source to a median dose of 49 Gy (range, 38.5-52.5 Gy) as radical brachytherapy and 18 Gy (range, 15.5-30 Gy) as boost with 3-4 Gy/fraction twice daily using customized surface mould. RESULTS: Median follow-up was 52 months (range, 6 to 98 months). Local control (LC) for skin tumours and intra-oral malignancies at 5 years were 92% and 76%, respectively. Five-year cause specific survival was 92%. For T1 and T2 tumours, 5 year LC was 94.2% and 68.2%, respectively. T stage (p < 0.04) and dose/fractions (p < 0.003) were the only significant prognostic factors for LC on univariate analysis. CONCLUSIONS: Surface mould brachytherapy results in excellent LC rates for skin tumours and T1 intraoral tumours when considered as radical treatment, and preferable to consider it as a boost for T2 intraoral tumours. Surface mould brachytherapy results in excellent organ and function preservation.

Change of target volume and its dosimetric impact during the course of accelerated partial breast irradiation using intraoperative multicatheter interstitial brachytherapy after open cavity surgery.

PURPOSE: To investigate the change of clinical target volume (CTV) and its dosimetric impact during the course of accelerated partial breast irradiation (APBI) using intraoperative multicatheter interstitial brachytherapy after open cavity surgery. METHODS AND MATERIALS: Twenty-two patients of APBI with intraoperative placement of catheters underwent computed tomography scans for the treatment planning before the first (CT1) and the last (CT2) treatment fraction. Delineation of lumpectomy cavity and CTV was done consistently on both CT data sets by one of the coauthors. Optimum plan (PCT1) was made on CT1. PCT1 was manually reproduced in CT2 which yielded plan PCT2. Plans were compared using coverage index (CI), dose homogeneity index (DHI), external volume index (EI), overdose volume index (OI) and conformal index (COIN). RESULTS: The mean ± SD volume of lumpectomy cavity and CTV was 78.5 ± 40.7 cm3, 156.4 ± 69.0 cm3 for PCT1, and 84.7 ± 50.1 cm3 (p = 0.11), 165.7 ± 82.8 cm3 (p = 0.15) for PCT2, respectively. CTV volume increase by ≥ 10% was observed in 9 cases however decrease of ≥10% was observed in 5 cases. Mean (SD) of absolute pairwise difference in CTV volume was found to be 13.2 (6.7) %. For cases with increase in CTV volume, significant (p < 0.05) decrease of 8.4%, 12.2%, and 5.5% was observed in CI, EI, and COIN of CTV respectively. However for cases with shrinkage of CTV, significant (p = 0.004) increase of 45% in EI was observed, whereas COIN reduced significantly (p = 0.001) by 13.5%. Overall 22 cases showed significant decrease of 5.8% and 8.1% in mean CI and COIN, respectively. CONCLUSIONS: The change of CTV during the course of APBI using intraoperative multicatheter interstitial brachytherapy after open cavity surgery was found patient specific and showed a significant impact on coverage and conformity.

Interobserver variations of target volume delineation and its impact on irradiated volume in accelerated partial breast irradiation with intraoperative interstitial breast implant.

PURPOSE: To investigate the interobserver variations in delineation of lumpectomy cavity (LC) and clinical target volume (CTV), and its impact on irradiated volume in accelerated partial breast irradiation using intraoperative multicatheter brachytherapy. MATERIAL AND METHODS: Delineation of LC and CTV was done by five radiation oncologists on planning computed tomography (CT) scans of 20 patients with intraoperative interstitial breast implant. Cavity visualization index (CVI), four-point index ranging from (0 = poor) to (3 = excellent) was created and assigned by observers for each patient. In total, 200 contours for all observers and 100 treatment plans were evaluated. Spatial concordance (conformity index, CIcommon, and CIgen), average shift in the center of mass (COM), and ratio of maximum and minimum volumes (Vmax/Vmin) of LC and CTV were quantified among all observers and statistically analyzed. Variation in active dwell positions (0.5 cm step) for each catheter, total reference air kerma (TRAK), volume enclosed by prescription isodose (V100%) among observers and its spatial concordance were analyzed. RESULTS: The mean ± SD CIcommon of LC and CTV was 0.54 ± 0.09, and 0.58 ± 0.08, respectively. Conformity index tends to increase, shift in COM and Vmax/Vmin decrease significantly (p < 0.05), as CVI increased. Out of total 309 catheters, 29.8% catheters had no change, 29.8% and 17.5% catheters had variations of 1 and 2 dwell positions (0.5 cm and 1 cm), respectively. 9.3% catheters shown variations ≥ 10 dwell positions (5 cm). The mean ± SD CIcommon of V100% was 0.75 ± 0.11. The mean observed Vmax/Vmin of prescription isodose and TRAK was 1.18 (range, 1.03 to 1.56) and 1.11 (range, 1.03 to 1.35), respectively. CONCLUSIONS: Interobserver variability in delineation of target volume was found to be significantly related to CVI. Smaller variability was observed with excellent visualization of LC. Interobserver variations showed dosimetric impact on irradiation of breast tissue volume with prescription dose.

Clinical outcomes of prospectively treated 140 women with early stage breast cancer using accelerated partial breast irradiation with 3 dimensional computerized tomography based brachytherapy.

PURPOSE: To study the clinical outcomes of women with early breast cancer (EBC) treated with accelerated partial breast irradiation (APBI) with multicatheter interstitial brachytherapy (MIB) using 3 dimensional computerized tomography (3DCT) based planning. MATERIALS AND METHODS: During August 2005 to January 2013, 140 women with EBC were treated prospectively with APBI using high dose rate (HDR) MIB. After 3DCT based planning patients were treated to a dose of 34 Gy/10 #/1 week with bid regimen. RESULTS: Median age was 57 years and tumor size 2 cm (range: 0.6-3.2 cm). Infiltrating duct carcinoma (IDC) was the most common histology; grade III tumors were seen in 82%. Median dose homogeneity index (DHI) was 0.76 (range: 0.49-0.85). The median coverage index (CI) of the cavity was 90% (61.4-100) and 80.5% (53.6-97.4) for planning target volume (PTV). Median follow up was 60 months (1-102 months). The 5 and 7 year local control rates (LC) were 97% and 92% respectively. Her2 positivity was the only prognostic factor which had an adverse impact on LC (p=0.01). Five and 7 year disease free survival (DFS) and overall survival (OAS) were 93%, 84%, 97.5% and 89% respectively. Good to excellent cosmetic outcomes at last follow up were seen in 87 (77%) women. CONCLUSIONS: 3DCT based MIB results in excellent long term outcomes and good to excellent cosmesis. Her2 positivity has an adverse impact on LC rates.

Fat necrosis in women with early-stage breast cancer treated with accelerated partial breast irradiation (APBI) using interstitial brachytherapy.

PURPOSE: To report the incidence of clinical, pathological and radiological fat necrosis (FN) in women treated with accelerated partial breast irradiation (APBI) using interstitial brachytherapy (BRT) for early-stage breast cancer and to study certain variables associated with it. METHODS AND MATERIALS: Between May 2000 and August 2008, 171 women were treated with APBI using high dose rate (HDR) BRT. Patients were treated to a dose of 34 Gy/10 fractions/1 week with two fractions/day after intraoperative/postoperative placement of catheters. RESULTS: At a median follow up of 48 months (SD: 28) 20 women developed FN with median time to detection being 24 months (range: 4-62 months, SD: 20). Actuarial 5 and 7 year FN rate was 18% and 23%, respectively. Grade 1 FN was seen in 4, grade 2 in 8 and grade 4 in 8 women. Additional investigations such as aspiration/biopsy were done in 9 patients. Volume of excision was the only significant factor affecting FN (p=0.04). CONCLUSIONS: Actuarial FN rate of 18% at 5 years in our study was comparable to other reported series of FN. Median time of detection of FN was 24 months. Higher volume of excision resulted in an increased incidence of fat necrosis.

Volumetric modulated arc radiotherapy for carcinomas of the oro-pharynx, hypo-pharynx and larynx: a treatment planning comparison with fixed field IMRT.

PURPOSE: A planning study was performed to evaluate the performance of volumetric modulated arc radiotherapy on head and neck cancer patients. Conventional fixed field IMRT was used as a benchmark. METHODS AND MATERIALS: CT datasets of 29 patients with squamous cell carcinoma of the oro-pharynx, hypo-pharynx and larynx were included. Plans for fixed beam IMRT, single (RA1) and double (RA2) modulated arcs with the RapidArc technique were optimised. Dose prescription was set to 66 Gy to the primary tumour (at 2.2 Gy/fraction), 60 Gy to intermediate-risk nodes and 54 Gy to low-risk nodal levels. The planning objectives for PTV were minimum dose >95%, and maximum dose <107%. Maximum dose to spinal cord was limited to 46 Gy, maximum to brain stem to 50 Gy. For parotids, mean dose <26 Gy (or median <30 Gy) was assumed as the objective. The MU and delivery time were scored to measure expected treatment efficiency. RESULTS: Target coverage and homogeneity results improved with RA2 plans compared to both RA1 and IMRT. All the techniques fulfilled the objectives on maximum dose, while small deviations were observed on minimum dose for PTV. The conformity index (CI(95%)) was 1.7+/-0.2 for all the three techniques. RA2 allowed a reduction of D(2%) to spinal cord of approximately 3 Gy compared to IMRT (RA1 D(2%) increased it of approximately 1 Gy). On brain stem, D(2%) was reduced from 12 Gy (RA1 vs. IMRT) to 13.5 Gy (RA2 vs. IMRT). The mean dose to ipsi-lateral parotids was reduced from 40 Gy (IMRT) to 36.2 Gy (RA1) and 34.4 Gy (RA2). The mean dose to the contra-lateral gland ranged from 32.6 Gy (IMRT) to 30.9 Gy (RA1) and 28.2 Gy (RA2). CONCLUSION: RapidArc was investigated for head and neck cancer. RA1 and RA2 showed some improvements in organs at risk and healthy tissue sparing, while only RA2 offered improved target coverage with respect to conventional IMRT.

Estimation of risk of radiation-induced carcinogenesis in adolescents with nasopharyngeal cancer treated using sliding window IMRT.

PURPOSE: To estimate the risk of radiation-induced carcinogenesis based on whole-body dose measurement on adolescent patients undergoing intensity-modulated radiotherapy (IMRT). METHODS AND MATERIALS: Ten adolescent patients with nasopharyngeal cancer were planed and treated to a dose of 70.2 Gy using sliding window IMRT. Peripheral dose (PD) was measured using thermoluminescent dosimeters kept at anterior, lateral and posterior positions of each axial plane at the level of xiphoid process, umbilicus and gonads of every patient. The associated risk of radiation-induced carcinogenesis was estimated based on the measured whole-body dose and using age- and sex-specific ICRP-60 nominal probability coefficient of 7.5% (boys) and 9.5% (girls) per Sv. RESULTS: In all patients, measured PD per monitor unit (MU) decreases almost exponentially with out-of-field distance and varies with gantry angle. Highest whole-body dose equivalent ranged from 0.5318 to 0.9867 Sv (mean=0.8141 Sv, SD=0.138) which was measured posteriorly at the level of xiphoid process. Whole-body dose was represented by the average dose at xiphoid process and all measurement positions ranged from 0.3661 to 0.8766 Sv (mean=0.658 Sv, SD=0.16) and 0.2267 to 0.5277 Sv (mean=0.3859 Sv, SD=0.09), respectively. The associated mean risk of radiation-induced carcinogenesis estimated based on different representation of mean whole-body dose was 6.57%, 5.3% and 3.11%, respectively. Higher mean risk of 7.32% was estimated among girls as compared to 6.25% for boys. CONCLUSIONS: Knowledge of risk of secondary malignancy is particularly important in adolescents and should be considered when choosing the optimal treatment technique and delivery system.

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.

Use of peripheral dose data from uniform dynamic multileaf collimation fields to estimate out-of-field organ dose in patients treated employing sliding window intensity-modulated radiotherapy.

Peripheral doses (PD) from uniform dynamic multileaf collimation (DMLC) fields were measured for 6 MV x-rays on a Varian linear accelerator using a 0.6 cc ionization chamber inserted at 5 cm depth into a 35 x 35 x 105 cm3 plastic water phantom. PD measurements were also carried out under identical conditions for seven patients treated for head and neck and cervical cancer employing sliding window intensity-modulated radiotherapy (IMRT). The measured PD from these patient-specific intensity-modulated beams (IMBs) were compared with the corresponding data from uniform DMLC fields having similar jaws setting. The measured PD per monitor unit (PD/MU) decreases almost exponentially with out-of-field distance for all uniform DMLC and static fields. For the same strip field width of 1.2 cm, uniform DMLC fields with a larger size of 14 x 22 cm2 deliver an average of 3.51 (SD = 0.51) times higher PD/MU at all out-of-field distances compared to 6 x 6 cm2. Similar to uniform DMLC fields, PD/MU measured from different patient-specific IMBs was found to decrease almost exponentially with out-of-field distance and increase with increase in field dimension. PD per MU from uniform DMLC fields and patient-specific IMBs having similar jaws setting shows good agreement (+/-7%) except at the most proximal distance, where a variation of more than 10% (maximum 15%) was observed. Our study shows that PD data generated from uniform DMLC fields can be used as baseline data to estimate out-of-field critical organ or whole-body dose in patients treated employing sliding window IMRT if an appropriate correction factor for field dimension is applied. The whole-body dose information can be used to estimate the possible increase in risk of fatal secondary malignancy in patients treated employing sliding window IMRT.