Adrian Osian

Influence of volumes of prostate, rectum, and bladder on treatment planning CT on interfraction prostate shifts during ultrasound image-guided IMRT

PURPOSE The purpose of this study was to analyze the relationship between prostate, bladder, and rectum volumes on treatment planning CT day and prostate shifts in theXYZ directions on treatment days. METHODS Prostate, seminal vesicles, bladder, and rectum were contoured on CT images obtained in supine position. Intensity modulated radiation therapy plans was prepared. Contours were exported to BAT-ultrasound imaging system. Patients were positioned on the couch using skin marks. An ultrasound probe was used to obtain ultrasound images of prostate, bladder, and rectum, which were aligned with CT images. Couch shifts in theXYZ directions as recommended by BAT system were made and recorded. 4698 couch shifts for 42 patients were analyzed to study the correlations between interfraction prostate shifts vs bladder, rectum, and prostate volumes on planning CT. RESULTS Mean and range of volumes (cc): Bladder: 179 (42-582), rectum: 108 (28-223), and prostate: 55 (21-154). Mean systematic prostate shifts were (cm, ±SD) right and left lateral:-0.047±0.16 (-0.361-0.251), anterior and posterior: 0.14±0.3 (-0.466-0.669), and superior and inferior: 0.19±0.26 (-0.342-0.633). Bladder volume was not correlated with lateral, anterior/posterior, and superior/inferior prostate shifts (P>0.2). Rectal volume was correlated with anterior/posterior (P<0.001) but not with lateral and superior/inferior prostate shifts (P>0.2). The smaller the rectal volume or cross sectional area, the larger was the prostate shift anteriorly and vice versa (P<0.001). Prostate volume was correlated with superior/inferior (P<0.05) but not with lateral and anterior/posterior prostate shifts (P>0.2). The smaller the prostate volume, the larger was prostate shift superiorly and vice versa (P<0.05). CONCLUSIONS Prostate and rectal volumes, but not bladder volumes, on treatment planning CT influenced prostate position on treatment fractions. Daily image-guided adoptive radiotherapy would be required for patients with distended or empty rectum on planning CT to reduce rectal toxicity in the case of empty rectum and to minimize geometric miss of prostate.

Intraoperative placement of MammoSite for breast brachytherapy treatment and seroma incidence

PURPOSE To 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. METHODS AND MATERIALS Fifty-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. RESULTS Fifty-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. CONCLUSIONS Meticulous 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.

MammoSite multilumen catheter: dosimetry considerations.

PURPOSE To explore the dosimetric advantages of the new MammoSite multilumen (ML) balloon for breast brachytherapy treatment compared to conventional single lumen (SL) device plan. MATERIALS AND METHODS Patients deemed appropriate for accelerated partial breast irradiation (APBI) were implanted with the MammoSite ML balloon. Two plans were generated in each patient for the same target coverage (PTV_EVAL) and dose to normal structures were plotted. The first plan used only the central single lumen with single-dwell position (SL), and the second plan (ML) was generated using the other lumens of the device. Dose distributions of the SL and ML plans were compared. RESULTS For the same PTV_EVAL, the ML balloon improved dose coverage at the tip and base of the applicator compared to SL plan. The skin and rib doses were reduced using the ML plan versus SL plan for the same PTV_EVAL in-patient 2, where the skin-balloon distance was 7 mm and the rib-balloon distance was <1 cm. For patient 1, the skin and rib distances were greater than 1 cm and the ML plan did not further minimize the dose to normal structures. CONCLUSION In our initial experience, dosimetric goals can be better achieved using the ML MammoSite balloon when normal structures (skin and ribs) are close to PTV_EVAL with a distance of <7 mm and rib distance of <1 cm. The multiple lumen of ML balloon can optimize dose and reduce excessive dose to rib and skin and therefore minimize the long-term toxicities of rib discomfort, skin fibrosis and fat necrosis.

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.

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%).

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.