D. Nori

Intraoperative placement of MammoSite for breast brachytherapy treatment and seroma incidence

PURPOSEnTo identify possible risk factors for development of clinically significant seroma (CSS) (seroma requiring intervention) and to report on incidence of infection after intraoperative placement of MammoSite for breast brachytherapy.nnnMETHODS AND MATERIALSnFifty-eight postmenopausal patients with early stage breast cancer and no nodal metastases, treated with partial breast irradiation using the MammoSite catheter from June 2003 to November 2007 were analyzed retrospectively for CSS predictive factors and incidence of infection. After a lumpectomy, a MammoSite catheter was placed by intraoperative open-cavity technique (OCT). All the patients received wound care and prophylactic antibiotics. A dose of 3400 cGy was prescribed at 1cm from the surface of the balloon and was delivered at 340 cGy twice daily 6h apart for 5 days. The patients with seroma who underwent intervention were considered to have CSS. On the basis of the characteristics and symptoms associated with seroma, interventions, such as aspiration, core biopsy, or re-excision of the lumpectomy cavity were performed either to relieve symptoms or to rule out a local recurrence.nnnRESULTSnFifty-seven of the 58 patients were eligible for analysis. One patient, who died 4 weeks after treatment from unrelated causes, was excluded from final analysis. All the patients were postmenopausal, with a median age of 71 years (range, 53-88 years). Eighteen of the 57 patients (31.5%) had CSS; 9 of them had re-excision of the lumpectomy cavity. Pathology in all revealed evidence of fat necrosis, chronic inflammatory cells, and fibrosis. There was no evidence of tumor recurrence in any of these patients. Technical and nontechnical parameters were analyzed to determine possible risk factors for CSS, and none were found to be statistically significant. No patient developed acute postprocedural infection.nnnCONCLUSIONSnMeticulous wound care and postoperative antibiotics prevented acute infection. Infection was not a contributing factor for seroma formation in these patients. Placement of the MammoSite catheter by OCT did not increase the risk of CSS development, in postmenopausal breast cancer patients.

Prostate and seminal vesicle volume based consideration of prostate cancer patients for treatment with 3D‐conformal or intensity‐modulated radiation therapya)

PURPOSEnThe purpose of this article was to determine the suitability of the prostate and seminal vesicle volumes as factors to consider patients for treatment with image-guided 3D-conformal radiation therapy (3D-CRT) or intensity-modulated radiation therapy (IMRT), using common dosimetry parameters as comparison tools.nnnMETHODSnDosimetry of 3D and IMRT plans for 48 patients was compared. Volumes of prostate, SV, rectum, and bladder, and prescriptions were the same for both plans. For both 3D and IMRT plans, expansion margins to prostate+SV (CTV) and prostate were 0.5 cm posterior and superior and 1 cm in other dimensions to create PTV and CDPTV, respectively. Six-field 3D plans were prepared retrospectively. For 3D plans, an additional 0.5 cm margin was added to PTV and CDPTV. Prescription for both 3D and IMRT plans was the same: 45 Gy to CTV followed by a 36 Gy boost to prostate. Dosimetry parameters common to 3D and IMRT plans were used for comparison: Mean doses to prostate, CDPTV, SV, rectum, bladder, and femurs; percent volume of rectum and bladder receiving 30 (V30), 50 (V50), and 70 Gy (V70), dose to 30% of rectum and bladder, minimum and maximum point dose to CDPTV, and prescription dose covering 95% of CDPTV (D95).nnnRESULTSnWhen the data for all patients were combined, mean dose to prostate and CDPTV was higher with 3D than IMRT plans (P < 0.01). Mean D95 to CDPTV was the same for 3D and IMRT plans (P > 0.2). On average, among all cases, the minimum point dose was less for 3D-CRT plans and the maximum point dose was greater for 3D-CRT than for IMRT (P < 0.01). Mean dose to 30%, rectum with 3D and IMRT plans was comparable (P > 0.1). V30 was less (P < 0.01), V50 was the same (P > 0.2), and V70 was more (P < 0.01) for rectum with 3D than IMRT plans. Mean dose to bladder was less with 3D than IMRT plans (P < 0.01). V30 for bladder with 3D plans was less than that of IMRT plans (P < 0.01). V50 and V70 for 3D plans were the same for 3D and IMRT plans (P > 0.2). Mean dose to femurs was more with 3D than IMRT plans (P < 0.01). For a given patient, mean dose and dose to 30% rectum and bladder were less with 3D than IMRT plans for prostate or prostate+SV volumes <65 (38/48) and 85 cm3 (39/48), respectively (P < 0.01). The larger the dose to rectum or bladder with 3D plans, the larger also was the dose to these structures with IMRT (P < 0.001). For both 3D and IMRT plans, dose to rectum and bladder increased with the increase in the volumes of prostate and seminal vesicles (P < 0.02 to 0.001).nnnCONCLUSIONSnVolumes of prostate and seminal vesicles provide a reproducible and consistent basis for considering patients for treatment with image-guided 3D or IMRT plans. Patients with prostate and prostate+SV volumes <65 and 85 cm3, respectively, would be suitable for 3D-CRT. Patients with prostate and prostate+SV volumes >65 and 85 cm3, respectively, might get benefit from IMRT.

The Potential for Dose Dumping in Normal Tissues with IMRT for Pelvic and H&N Cancers

The purpose of this study is to understand the potential for dose dumping in normal tissues (>85% of prescription dose) and to analyze effectiveness of techniques used in reducing dose dumping during IMRT. Two hundred sixty-five intensity modulated radiation therapy (IMRT) plans for 55 patients with prostate, head-and-neck (H&N), and cervix cancers with 6-MV photon beams and >5 fields were reviewed to analyze why dose dumping occurred, and the techniques used to reduce dose dumping. Various factors including gantry angles, depth of beams (100-SSD), duration of optimization, severity of dose-volume constraints (DVC) on normal structures, and spatial location of planning treatment volumes (PTV) were reviewed in relation to dose dumping. In addition, the effect of partial contouring of rectum in beams path on dose dumping in rectum was studied. Dose dumping occurred at d(max) in 17 pelvic cases (85% to 129%). This was related to (1) depth of beams (100 SSD [source-to-skin distance]), (2) PTV located between normal structures with DVC, and (3) relative lack of rectum and bladder in beams path. Dose dumping could be reduced to 85% by changing beam angles and/or DVC for normal structures in 5 cases and by creating phantom structures in 12 cases. Decreasing the iterations (duration of optimization) also reduced dose dumping and monitor units (MUs). Part of uncontoured rectum, if present in the field, received a higher dose than the contoured rectum with DVC, indicating that complete delineation of normal structures and DVC is necessary to prevent dose dumping. In H&N, when PTV extends inadvertently into air beyond the body even by a few millimeters, dose dumping occurred in beams path (220% for 5-field and 170%, 7-field plans). Keeping PTV margins within body contour reduced this type of dose dumping. Beamlet optimization, duration of optimization, spatial location of PTV, and DVC on PTV and normal structures has the potential to cause dose dumping. However, these factors are an integral part of IMRT inverse planning. Therefore, understanding these aspects and use of appropriate technique/s would reduce or eliminate the dose dumping and minimize time to obtain optimum plan.

SU-FF-J-34: Influence of Volumes of Prostate, Rectum and Bladder On Treatment Planning CT-Day On Inter-Fraction Motion of Prostate During BAT Image-Guided IMRT

Purpose: To study the relationship between prostate volume/location, bladder and rectum volumes on treatment‐planning CT‐day and prostate shift in XYZ directions on treatment‐days. Method and Materials: Prostate, SV, bladder and rectum (rectosigmoid‐flexure to anorectal‐verge), were contoured on CT‐images. Isocenter was 6 cm posterior to the tip of pubic‐arch and 1 cm inferior to the pubic‐brim. IMRT plans were prepared. Contours were exported to BAT‐system. Patients were positioned on couch using skin marks. US‐probe was used to obtain US‐images of prostate, bladder and rectum and aligned with CT‐images. Shifts in XYZ directions as recommended by BAT‐system were made and recorded. 4698 couch‐shifts for 42 patients were analyzed to study a correlation between prostate shifts vs. bladder and rectum volumes and prostate volume/location on CT‐day. Spatial location of prostate was defined as distance of prostate base to isocenter. Dose to 50% of bladder vs. volume was also studied. Pearsons correlation coefficient r, and P values were used for statistical analysis.Results: Mean and range of volumes (cc): bladder: 179, 42–582, rectum: 108, 28–223 and prostate: 55, 21–154. Mean prostate shifts (cm, ±SD): R/L (X): −0.047±0.16, AP/PA (Y): 0.14±0.3 and S/I (Z): 0.19±0.26. Lateral, AP/PA and S/I shifts were not correlated with volumes of bladder, rectum and prostate; bladder and prostate; and bladder and rectum, (P>0.2), respectively. Smaller the rectal volume (P<0.001) or diameter (P<0.05) of rectum, larger was the anterior shift and vice‐versa. Smaller the prostate base distance to isocenter or volume, larger was superior shift and vice‐versa (P<0.05). Dose to bladder decreased with increase in volume up to 300cc, reaching a plateau with further increase in volume (P<0.001). Conclusions: Prostate location/volume and rectal‐volume, but not bladder‐volume on CT‐day influence prostate position. Bladder with 200–300cc volume, but not full bladder, would be optimum for patient comfort, minimizing bladder dose and US‐image quality.

Analysis of interfraction prostate motion using megavoltage cone beam computed tomography by Bylund et al. (Int J Radiat Oncol Biol Phys 2008;72:949-956).

ANALYSIS OF INTERFRACTION PROSTATE MOTION USING MEGAVOLTAGE CONE BEAM COMPUTED TOMOGRAPHY BY BYLUND ET AL. (INT J RADIAT ONCOL BIOL PHYS 2008;72:949–956) 6. Heemsbergen WD, Hoogeman MS, Witte MG, et al. Increased risk of biochemical and clinical failure for prostate patients with a large rectum at radiotherapy planning: Results from the Dutch trial of 68 Gy vs. 78 Gy. Int J Radiat Oncol Biol Phys 2007;67:1418–1424.

Single course IMRT plan to deliver 45 Gy to seminal vesicles and 81 Gy to prostate in 45 fractions

We treat prostate and seminal vesicles (SV) to 45 Gy in 25 fractions (course 1) and boost prostate to 81 Gy in 20 more fractions (course 2) with Intensity Modulated Radiation Therapy (IMRT). This two-course IMRT with 45 fractions delivered a non-uniform dose to SV and required two plans and two QA procedures. We used Linear Quadratic (LQ) model to develop a single course IMRT plan to treat SV to a uniform dose, which has the same biological effective dose (BED) as that of 45 Gy in 25 fractions and prostate to 81 Gy, in 45 fractions. Single course IMRT plans were compared with two-course IMRT plans, retrospectively for 14 patients. With two-course IMRT, prescription to prostate and SV was 45 Gy in 25 fractions and to prostate only was 36 Gy in 20 fractions, at 1.8 Gy/fraction. With 45-fraction single course IMRT plan, prescription to prostate was 81 Gy and to SV was 52 or 56 Gy for a α/β of 1 and 3, respectively. 52 Gy delivered in 45 fractions has the same BED of 72 Gy3 as that of delivering 45 Gy in 25 fractions, and is called Matched Effective Dose (MED). LQ model was used to calculate the BED and MED to SV for α/β values of 1–10. Comparison between two-course and single course IMRT plans was in terms of MUs, dose-max, and dose volume constraints (DVC). DVC were: 95% PTV to be covered by at least 95% of prescription dose; and 70, 50, and 30% of bladder and rectum should not receive more than 40, 60, and 70% of 81 Gy. SV Volumes ranged from 2.9–30 cc. With two-course IMRT plans, mean dose to SV was non-uniform and varied between patients by 48% (54 to 80 Gy). With single-course IMRT plan, mean dose to SV was more uniform and varied between patients by only 9.6% (58.2 to 63.8 Gy), to deliver MED of 56 Gy for α/β − 1. Single course IMRT plan MUs were slightly larger than those for two-course IMRT plans, but within the range seen for two-course plans (549–959 MUs, n=51). Dose max for single-course plans were similar to two-course plans. Doses to PTV, rectum and bladder with single course plans were as per DVC and comparable to two-course plans. Single course IMRT plan reduces IMRT planning and QA time to half.

SU-FF-T-65: Comparison of Dose to Rectum and Bladder with 3DCRT and IMRT Plans for the Treatment of Prostate

Purpose: Major goal of IMRT is to escalate dose to prostate while keeping doses to bladder and rectum equal to or less than that with 3DCRT. This study is to compare 3DCRT and IMRT to evaluate how far this goal has been achieved. Method and Materials: Dosimetry of 6-field 3DCRT and 5-field IMRT plans, generated for the same 32 patients, has been compared. With 3DCRT, prescription to SV and prostate was 45 and 75.6 Gy, respectively. With IMRT, prescription to SV and prostate was 45 and 81 Gy, respectively. IMRT required to keep doses to 30%, 50% and 70% of bladder and rectum less than 70%, 60% and 40% of 81 Gy and to cover 95% PTV with 95% isodose. Dose to rectum and bladder were estimated from DVH. Less than 5% difference in rectal and bladder doses between 3DCRT and IMRT was considered insignificant. Results: Higher the dose to rectum and bladder with 3DCRT, higher also was the dose with IMRT (P<0.001). Dose to 50% rectum with IMRT was equal to that with 3DCRT in 15 cases (47%) and more in 17 cases (53%). Dose to 10% of rectum with IMRT was equal to that with 3DCRT in 9 cases (28%) and more in 23 cases (72%). Dose to 50% and 10% bladder with IMRT were equal to that with 3DCRT in 7 cases (22%) and more in 25 cases (78%). Conclusion: Preliminary analysis suggested that the space between rectum and prostate+SV, and the volume of rectum and bladder in beams path are related to doses to these structures. Higher doses to rectum and bladder with IMRT are a result of trade-off between doses to PTV, rectum and bladder. This may be acceptable because percent dose coverage to 95% PTV is better with IMRT (93–98%) than with 3DCRT (86–93%).

The Impact of Technological Advances on the Evolution of 3D Conformal Brachytherapy for Early Prostate Cancer

Permanent implantation of I-125 and Pd-103 seeds is one of the widely used treatment options for the early stage prostate cancer with minimum normal tissue complications and long-term local control of the tumor. This is possible because of several technological advances made in the past decade to better understand the procedural aspects of implantations with the desired clinical outcome and with acceptable morbidities. In addition, with the widespread use of PSA testing, more widely disseminated information about prostate cancer and increased patient awareness, over 70% of patients are diagnosed early with localized disease and therefore are candidates for definitive local therapy. Delineation of soft tissue structures including the prostate, rectum, urethra and bladder has become more accurate with the use of imaging modalities including Ultrasound and MRI, with or without the CT. A re-evaluation of the dosimetric parameters of the radioactive sources has lead to a more precise estimate of the dose delivered to the prostate and the associated critical normal structures. Technological improvements in the post implant dosimetry have helped to understand the factors, which makes an implant a “good implant” or a “poor implant”. Intraoperative treatment planning with on line dosimetry is emerging as one of the best approaches for prostate brachytherapy. In addition, better software is now available producing dose-volume histograms with 3D target and normal tissue reconstruction. The combination of seed implant followed by IMRT would provide scope for differentially boosting the regions under-dosed because of uncontrollable and unexpected reasons during the implant and unsuspected micro extensions of the tumor.

SU-GG-T-174: Comparison of Structure Contouring Efficiency and Dose-Volume Histograms (DVH) of Pinnacle3 and Eclipse Treatment Planning Systems for Prostate IMRT

Purpose: To test the hypothesis that structure contouring precision and DVH for Prostate‐PTV, rectum and bladder would be the same for Pinnacle and Eclipse treatment planning systems (TPS). Materials and Methods: DVH for 51 patients each planned with Pinnacle3 and Eclipse TPS and treated with Elekta‐Synergy and Varian Linacs, respectively, was compared. Patients and treatment planners were different for Pinnacle and Eclipse. Beams numbers, angles, energy (6X) and Radiation Oncologists were the same. Prostate, SV, rectum and bladder were contoured from CT‐images with 0.5 mm separation. Prescription was 45‐Gy to prostate+SV (CTV) and 36‐Gy boost to prostate. Margins for CTV and prostate were 0.5‐cm superiorly and posteriorly, and 1‐cm in other dimensions to create PTV and Prostate‐PTV, respectively. Dose‐volume constraints (DVC) were to cover 95% PTVs with 95% prescription dose and keep respective doses to 70%, 50% and 30% rectum and bladder to less than 30%, 50% and 70% of 81‐Gy. Pearsons correlation coefficient ‘r’ and two‐sample ‘t’ test were used for statistical analysis.Results: Structure‐contouring efficiency was the same between TPS. Mean‐volumes (±SD, cm3) of prostate (53.9±20.4 vs. 52.8±23.8), SV (13.3±6.6 vs. 11.5±6.6), prostate‐PTV (159.7±42.4 vs. 144.9±46.6), rectum (106.6±34.8 vs. 120.5±47.7) and bladder (191.8±103.9 vs. 177.2±81.3) were the same for Pinnacle and Eclipse patients, respectively, (P >0.1). Percent of 81‐Gy delivered to 95% prostate‐PTV was higher with Pinnacle (97.63±0.71) than Eclipse (96.12±0.997) TPS (P<0.001). Consequently, mean‐dose (Gy) delivered to rectum (36.1±2.7 vs. 31.5±4.8, P<0.001) and bladder (32.9±7.5 vs. 29.7±7.5, P<0.05) was higher with Pinnacle than Eclipse TPS, respectively. Conclusions: Structure‐contouring efficiency, prescriptions and DVC‐guidelines being the same, there is great potential for delivering significantly different doses to targets and normal tissues. Although these doses are within the DVC‐guidelines, clinical outcomes and normal tissue toxicities could be different. This may also be true for RTOG trials where DVC‐guidelines are general.

SU‐FF‐T‐211: Influence of Anatomical and Physical Aspects of Treatment Planning On Prostate and H&N IMRT Plan QA Results

Purpose: To study the influence of combinations of Linear Accelerators and treatment planning‐systems, anatomical site and PTV volumes on MUs, and the magnitude and direction of deviation of prostate and H&N IMRT plan QA dose from plan‐dose. Method and Materials:IMRT plans were generated using Pinnacle3 or Eclipse treatment planning‐systems for treatment with Elekta or Varian Linacs, respectively. There were 29 H&N plans for Varian, and 59 and 33 prostate plans for Varian and Elekta, respectively. Dose at a point in the MED‐TEC phantom was measured with MT‐ERI‐A12 ion chamber. QA results were calculated as percentage deviation between measured and calculated doses in the phantom. A deviation of ±5% was acceptable. The magnitude and direction of deviation of QA results vs. PTV volumes, treatment site, Linac and planning system combinations were studied. PTV volumes vs. MUs was also analyzed. Linear regression analysis was used to study the relationship between paired variables. Results: The direction and magnitude of QA result deviation was Linac dependent. For Elekta prostate cases, QA measured dose deviated to negative direction (−2.49±0.93, −0.5 to −5%). For Varian cases, QA measured dose for prostate (1.67±0.91, −0.1 to 4.9%) and H&N cases (3.58±1.80, 0.2–6.4%) deviated to positive side. These results suggest that the delivered dose could vary between Linacs and might result in under‐ or over‐dosing. Prostate QA result deviation was independent of PTV volumes (P>0.1), but MUs increased with increase in PTV volumes (P<0.001). For H&N cases, MUs and the deviation between measured and planed‐dose increased with increase in PTV volumes (84–691 cm3, P<0.001). Conclusions: This type of analysis would help to evaluate the influence of Linac and/or planning systems, anatomical site and PTV volumes on the magnitude and direction of deviation between planned and delivered dose and to develop correction strategies to minimize radiation delivery variations.