- Email: [email protected]
The Use of DMBT-Concept T&O Applicator in Cervical Cancer: A Case Study
S64
Abstracts / Brachytherapy 14 (2015) S11eS106
3D-CT plan optimization at every vaginal cuff HDR BT fraction is not necessary when using constant applicator size with reproducible immobilization and leg positioning.
developed during commissioning were shown to be in good agreement with vendor specifications.
PHYSICS SNAP ORAL Saturday, April 11, 2015 10:45 AM - 12:15 PM PHSOR14 Presentation Time: 10:45 AM Commissioning and Acceptance Testing of a High Dose-Rate 32P Plaque for Intraoperative Brachytherapy of the Spinal Dura Brian A. Hrycushko, PhD, Strahinja Stojadinovic, PhD, Arnold Pompos, PhD, Paul Medin, PhD, Xun Jia, PhD, Ming Yang, PhD, Lucien Nedzi, MD, David Schwartz, MD, Michael R. Folkert, MD, PhD. Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA. Purpose: There is an inherent risk for local seeding or residual microscopic epidural disease during surgery of primary or metastatic lesions of the spine. Post-operative conventional or stereotactic body radiotherapy may reduce the risk of local recurrence, but the close proximity of the dura to the spinal cord limits the radiation dose that can be safely delivered. To mitigate this risk, a flexible, beta-emitting 32P plaque can be used to deliver an ablative radiation dose when placed intraoperatively on the dura. The steep dose gradient of this applicator, while sparing the underlying spinal cord, also makes dose characterization of the source a challenge for many detectors common to radiation oncology departments. This work discusses a simple commissioning and acceptance testing approach for 32P plaques using Monte Carlo-based (MC) dose calculations and radiochromic film measurements Materials and Methods: Commissioning of a 2.2 2.6 cm2 and 0.39 mm thick, 743.7 MBq (20.1 mCi) 32P source was performed by modeling the plaque material and Gafchromic EBT3 film at different distances from each other within a certified Solid Water HE medium using the EGSnrc-based MC code, DOSXYZnrc. The MC dose output was verified by comparison with film measurements within the physical phantom setup using a batchspecific film calibration curve. Source-specific treatment dimensions and uniformity were characterized at a 1 mm prescription depth by analyzing flatness, symmetry, and FWHM on film for both sides of the plaque (Figure 1A). MC simulations were performed for different plaque dimensions to evaluate changes in output and percent depth dose (PDD) curves when normalized to a 1 mm prescription depth on the central axis. Following good agreement between MC calculated dose and measured dose within the phantom medium, MC simulations were performed for a planar geometry within a water medium for patient dose calculations. A conversion factor was determined for the Solid Water HE and water mediums to be used for all future 32P plaque acceptance and treatment planning purposes. Results: For the commissioning plaque, output at 1 mm depth was in good agreement with that predicted by MC (2.4%). The FWHM distances in the long and short axes were within 1 mm of the stated plaque dimensions. MC generated PDD curves were shown to be independent of the plaque dimensions (Figure 1B) and the plaque thickness (Figure 1C) within the treatment range. The plaque thickness correction factor relative to a nominal 0.5 mm plaque thickness ranged from 1.11 - 0.93 for the 0.3 mm - 0.7 mm thick plaques, respectively. Following verification of the vendor specifications, MC-simulated output and PDD curves were generated in a water medium for a planar source to be used for treatment planning in all future patient cases. The dose rate in water at 1 mm depth from the source surface was calculated depending on accepted plaque activity, the source size dimensions, and the thickness correction factor allowing for the calculation of total treatment time to deliver a desired dose (Figure 1D). Conclusions: The 32P plaque dose characteristics were determined based on MC calculations and verified with radiochromic film measurements. MCgenerated conversion factors at 1 mm depth in Solid Water HE and water mediums allow for simple verification of the vendor specifications for source acceptance as well as patient specific treatment planning. At the time of abstract submission, we have treated our first patient with the 32 P plaque. Plaque acceptance test results following the protocol
Figure 1.
PHSOR10 Presentation Time: 10:49 AM The Use of DMBT-Concept T&O Applicator in Cervical Cancer: A Case Study Dae Yup Han, MS1,2, Daniel J. Scanderbeg, PhD3, Catheryn Yashar, MD3, William Y. Song, PhD2. 1Dept. Electrical and Computer Engineering, University of California San Diego, La Jolla, CA, USA; 2Dept. Medical Physics, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada; 3Dept. Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, CA, USA. Purpose: To test the hypothesis that utilization of direction-modulated brachytherapy (DMBT) concept T&O applicator can give similar or better dosimetric coverage, and better overall plan quality, than a conventional tandem-and-ovoids (T&O) applicator supplemented with free-hand needles, during an image guided adaptive brachytherapy (IGABT) of cervix cancer. Materials and Methods: We retrospectively reviewed a FIGO IIIB cervical cancer patient with an initial HRCTV volume of 48.3 cc, as assessed by MRI, was treated with external beam radiation therapy to 45Gy in 25 fractions, followed by 6Gy in 5 fractions of HDR, treated in UCSD. The first two fractions of brachytherapy were treated with a conventional T&O applicator alone, but were deemed unsatisfactory in dosimetric coverage to the HRCTV, and hence were supplemented with free-hand needles at subsequent fractions where 5, 5, and 7 additional needles were used in fractions 3, 4, and 5, respectively. In this study, the intrauterine tandem was re-designed to conform to the DMBT concept [1]. The ovoids were left unchanged. The DMBT tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten alloy rod (density518.0g/cc), enclosed in polyoxymethylene sheath (density51.41g/cc), with the tungsten rod and total thickness of 5.4 and 6.0mm, respectively. The total diameter of 6.0mm was chosen to match that of standard clinical tandems so as to not require further dilation. An in-house developed HDR planning platform was used for planning of the DMBT applicator. For the proposed DMBT tandem design, the plans were optimized with the same ovoids in place, as the conventional T&O plans, but without the needles. In addition, additional DMBT plans were generated that used the needles this time. All generated plans were normalized to match the HRCTV D90 of the original/clinical ‘‘T&Oþneedles’’ plans. Results: In fractions 1 and 2, no needles were inserted; therefore, it is not surprising that the DMBT plans performed better than the T&O plans. In fraction 1, the sigmoid D2cc reduction was the greatest with 40.8% (0.84Gy), followed by the rectum with 17.7% (0.76Gy), and the bladder with 4.7% (0.27Gy). In fraction 2, the bladder D2cc reduction was the greatest with 15.7% (0.99Gy), followed by the rectum with 3.2%
Abstracts / Brachytherapy 14 (2015) S11eS106 (0.15Gy), and the sigmoid was not contoured due to being largely away from the treated area. For fractions 3-5, where free-hand needles were supplemented to the T&O applicator, mostly improvements were seen in OARs but some did get worse. However, in terms of total EQD2 doses accumulated over the treatment course, for all OARs, the DMBT plans improved over the clinical plans. That is, 89.77Gy reduced to 87.27Gy, 74.25Gy reduced to 73.47Gy, and 62.51Gy reduced to 53.53Gy, for the bladder, rectum, and sigmoid, respectively. Remember, this is achieved with the same D90 coverage to the HRCTV in each fraction. For the DMBTþneedles plans, as expected, improvements were even greater compared with the clinical plans with 89.77Gy reduced to 84.99Gy, 74.25Gy reduced to 70.92Gy, and 62.51Gy to 53.38Gy, for the bladder, rectum, and sigmoid, respectively. Conclusions: This study demonstrated that, with the DMBT-concept tandem design, with same dimensions as a typical intrauterine tandem used in clinic, can give better quality plans in a course of treatment compared with a conventional T&O applicator supplemented with needles, albeit a single isolated clinical case was studied. Nevertheless, the results indicate to a possibility of avoiding (or at least reducing) needles when the DMBT tandem is available in clinic. Due to the significance of the implications, further studies with more patients will be pursued. Financial disclosure: None [1] Han D, Webster MJ, Scanderbeg DJ, et al. Direction-Modulated Brachytherapy for High-Dose-Rate Treatment of Cervical Cancer. I: Theoretical Design. Int J Radiat Oncol Biol Phys 2014;89(3)666-673. PHSOR08
Presentation Time: 10:53 AM
Dosimetric Evaluation of the 103Pd Civastring for Permanent Breast Brachytherapy Mark J. Rivard, PhD. Radiation Oncology, Tufts University School of Medicine, Boston, MA, USA. Purpose: Use of 103Pd for permanent breast seed implantation (PBSI) was originated by Pignol and colleagues in 2006 for the treatment of early-stage breast cancer. Since then, additional centers have adopted this conformal brachytherapy modality. Given the recent availability of elongated 103 Pd brachytherapy sources in the form of the polymer-encapsulated CivaString (CivaTech Oncology, Inc., Research Triangle Park, NC), a dosimetric evaluation was performed to consider possibilities for this new source. Materials and Methods: Implant geometries were simulated using the VariSeed (version 8.0.2, Varian Medical Systems, Palo Alto,
S65
CA) treatment planning system (TPS). A grid resolution of 0.1 cm was used throughout all plan variations. Spheres with diameters of 1.0 cm to 5.5 cm (0.5 cm increments) were manually contoured into the TPS using 24 nodes per 0.1 cm slice. Spatial accuracy of the circular cross sections was estimated to be within 0.03 cm. Using the median and range of PTV from Pignol et al (2009), spherical diameters of 3.0 to 5.0 cm (0.5 cm increments) were chosen for the PTV. Using a 1.5 cm CTV margin expansion, the corresponding CTV diameters would be 0.0 to 2.0 cm, respectively. With a prescription of 90 Gy, a planning goal of PTV100590% was chosen to match the experience of Pignol et al (2009). Multiple variations of each plan (having differing source positions, quantities, and air-kerma strengths) were performed to glean the sensitivity of the results to planning technique. The dose homogeneity index (DHI) was calculated, and dose-volume histograms (DVHs) were produced for the CTVs, PTVs, and planar ROIs for direct comparisons within a plan and across variations for plans having similar PTV dimensions. Given knowledge gained from planning spherical volumes, the geometry of a clinical case was approximated within the TPS for a representative anatomy given the observations of Pignol et al (2009). This case had a CTV that was 1.0 cm in the cranial-caudal direction, 1.0 cm in the anterior-posterior direction, and 2.0 cm laterally. The skin bridge was 1.0 cm anterior to the CTV and the chestwall was 1.5 cm posterior to the CTV. Given the treatment planning constraint of 0.5 cm from the skin surface or chestwall as recommended in the NSABP-B39/RTOG 0413 trail for partial breast irradiation of the breast, the PTV_EVAL dimensions were 4.0 cm, 2.5 cm, and 5.0 cm, respectively. The subsequent volumes for the CTV and PTV were 1.83 cm3 and 46.29 cm3, respectively. DVHs of the CTV, PTV, skin, and chestwall were produced, along with screenshots of resultant dose distributions. Results: The average DHI values for the 3.0, 3.5, 4.0, 4.5, and 5.0 cm PTVs were 0.78, 0.66, 0.63, 0.71, and 0.74, respectively, with an average of 0.72 across the 16 plans. There was good dose conformity to the CTV and PTV while providing low dose outside of the PTV. For 3.0, 3.5, 4.0, 4.5, and 5.0 cm diameter PTVs, maximum dose values to planes 0.5 cm from the PTVs were about 80%, 45%, 64%, 43%, and 47% of the prescribed dose. For planes located 1.0 cm from the PTVs, these maximum dose values diminished to 32%, 23%, 26%, 20%, and 28% of the prescribed dose. These dose values were all lower than what HDR 192Ir brachytherapy can deliver with either interstitial or balloon breast brachytherapy, and were due to the lower effective photon energy of 103Pd compared to 192Ir.
Treatment planning results for various spherical PTV with a limited number of implanted needles and CivaStrings.
#
CTV diam. (cm)
PTV diam. (cm)
U/cm
needles
CS10
Total U
U/cm3
needles/cm2
CS10/cm3
CTV100
CTV150
CTV200
PTV100
PTV150
PTV200
L1 L2 S1 S2 S1 S2 S1 L1 S1 S2 S3 S4 L1 L2 S1 S2
0.0 0.0 0.0 0.0 0.5 0.5 1.0 1.0 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.0
3.0 3.0 3.0 3.0 3.5 3.5 4.0 4.0 4.5 4.5 4.5 4.5 5.0 5.0 5.0 5.0
2.241 1.878 2.546 2.148 1.528 1.310 1.417 1.344 0.958 1.145 1.074 1.329 0.906 0.829 0.955 1.074
9 9 9 9 12 12 17 17 24 20 21 21 32 37 32 33
36 36 28 28 40 48 61 69 112 104 110 102 160 170 144 134
81 68 71 60 61 63 86 93 107 119 118 136 145 141 138 144
5.8 4.9 5.1 4.3 4.4 4.5 2.6 2.8 2.3 2.5 2.5 2.9 2.2 2.2 2.1 2.2
0.32 0.32 0.32 0.32 0.31 0.31 0.34 0.34 0.38 0.31 0.33 0.33 0.41 0.47 0.41 0.42
2.6 2.6 2.0 2.0 1.8 2.2 1.8 2.1 2.4 2.2 2.4 2.2 2.5 2.6 2.2 2.1
NA NA NA NA 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%
NA NA NA NA 1.3% 100.0% 87.3% 79.6% 86.2% 22.6% 17.5% 25.7% 55.0% 11.3% 60.5% 17.8%
NA NA NA NA 0.0% 3.9% 27.2% 25.1% 21.8% 8.0% 6.4% 8.4% 14.6% 1.9% 17.0% 7.4%
90.0% 89.9% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.1% 89.9% 90.0% 90.0%
17.2% 18.2% 22.9% 22.0% 27.4% 34.3% 35.1% 31.5% 23.5% 22.7% 24.2% 32.9% 21.9% 21.0% 24.9% 24.8%
6.9% 8.3% 9.4% 9.5% 11.8% 14.4% 12.6% 11.7% 9.0% 9.7% 9.7% 12.4% 6.1% 5.3% 7.3% 8.7%
n.b. NA represents CTVs having zero volume. The optimal plan for a given PTV diameter is highlighted with boldface in the 1st column.
Abstracts / Brachytherapy 14 (2015) S11eS106
3D-CT plan optimization at every vaginal cuff HDR BT fraction is not necessary when using constant applicator size with reproducible immobilization and leg positioning.
developed during commissioning were shown to be in good agreement with vendor specifications.
PHYSICS SNAP ORAL Saturday, April 11, 2015 10:45 AM - 12:15 PM PHSOR14 Presentation Time: 10:45 AM Commissioning and Acceptance Testing of a High Dose-Rate 32P Plaque for Intraoperative Brachytherapy of the Spinal Dura Brian A. Hrycushko, PhD, Strahinja Stojadinovic, PhD, Arnold Pompos, PhD, Paul Medin, PhD, Xun Jia, PhD, Ming Yang, PhD, Lucien Nedzi, MD, David Schwartz, MD, Michael R. Folkert, MD, PhD. Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX, USA. Purpose: There is an inherent risk for local seeding or residual microscopic epidural disease during surgery of primary or metastatic lesions of the spine. Post-operative conventional or stereotactic body radiotherapy may reduce the risk of local recurrence, but the close proximity of the dura to the spinal cord limits the radiation dose that can be safely delivered. To mitigate this risk, a flexible, beta-emitting 32P plaque can be used to deliver an ablative radiation dose when placed intraoperatively on the dura. The steep dose gradient of this applicator, while sparing the underlying spinal cord, also makes dose characterization of the source a challenge for many detectors common to radiation oncology departments. This work discusses a simple commissioning and acceptance testing approach for 32P plaques using Monte Carlo-based (MC) dose calculations and radiochromic film measurements Materials and Methods: Commissioning of a 2.2 2.6 cm2 and 0.39 mm thick, 743.7 MBq (20.1 mCi) 32P source was performed by modeling the plaque material and Gafchromic EBT3 film at different distances from each other within a certified Solid Water HE medium using the EGSnrc-based MC code, DOSXYZnrc. The MC dose output was verified by comparison with film measurements within the physical phantom setup using a batchspecific film calibration curve. Source-specific treatment dimensions and uniformity were characterized at a 1 mm prescription depth by analyzing flatness, symmetry, and FWHM on film for both sides of the plaque (Figure 1A). MC simulations were performed for different plaque dimensions to evaluate changes in output and percent depth dose (PDD) curves when normalized to a 1 mm prescription depth on the central axis. Following good agreement between MC calculated dose and measured dose within the phantom medium, MC simulations were performed for a planar geometry within a water medium for patient dose calculations. A conversion factor was determined for the Solid Water HE and water mediums to be used for all future 32P plaque acceptance and treatment planning purposes. Results: For the commissioning plaque, output at 1 mm depth was in good agreement with that predicted by MC (2.4%). The FWHM distances in the long and short axes were within 1 mm of the stated plaque dimensions. MC generated PDD curves were shown to be independent of the plaque dimensions (Figure 1B) and the plaque thickness (Figure 1C) within the treatment range. The plaque thickness correction factor relative to a nominal 0.5 mm plaque thickness ranged from 1.11 - 0.93 for the 0.3 mm - 0.7 mm thick plaques, respectively. Following verification of the vendor specifications, MC-simulated output and PDD curves were generated in a water medium for a planar source to be used for treatment planning in all future patient cases. The dose rate in water at 1 mm depth from the source surface was calculated depending on accepted plaque activity, the source size dimensions, and the thickness correction factor allowing for the calculation of total treatment time to deliver a desired dose (Figure 1D). Conclusions: The 32P plaque dose characteristics were determined based on MC calculations and verified with radiochromic film measurements. MCgenerated conversion factors at 1 mm depth in Solid Water HE and water mediums allow for simple verification of the vendor specifications for source acceptance as well as patient specific treatment planning. At the time of abstract submission, we have treated our first patient with the 32 P plaque. Plaque acceptance test results following the protocol
Figure 1.
PHSOR10 Presentation Time: 10:49 AM The Use of DMBT-Concept T&O Applicator in Cervical Cancer: A Case Study Dae Yup Han, MS1,2, Daniel J. Scanderbeg, PhD3, Catheryn Yashar, MD3, William Y. Song, PhD2. 1Dept. Electrical and Computer Engineering, University of California San Diego, La Jolla, CA, USA; 2Dept. Medical Physics, Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada; 3Dept. Radiation Medicine and Applied Sciences, University of California San Diego, La Jolla, CA, USA. Purpose: To test the hypothesis that utilization of direction-modulated brachytherapy (DMBT) concept T&O applicator can give similar or better dosimetric coverage, and better overall plan quality, than a conventional tandem-and-ovoids (T&O) applicator supplemented with free-hand needles, during an image guided adaptive brachytherapy (IGABT) of cervix cancer. Materials and Methods: We retrospectively reviewed a FIGO IIIB cervical cancer patient with an initial HRCTV volume of 48.3 cc, as assessed by MRI, was treated with external beam radiation therapy to 45Gy in 25 fractions, followed by 6Gy in 5 fractions of HDR, treated in UCSD. The first two fractions of brachytherapy were treated with a conventional T&O applicator alone, but were deemed unsatisfactory in dosimetric coverage to the HRCTV, and hence were supplemented with free-hand needles at subsequent fractions where 5, 5, and 7 additional needles were used in fractions 3, 4, and 5, respectively. In this study, the intrauterine tandem was re-designed to conform to the DMBT concept [1]. The ovoids were left unchanged. The DMBT tandem design has 6 peripheral holes of 1.3-mm diameter, grooved along a nonmagnetic tungsten alloy rod (density518.0g/cc), enclosed in polyoxymethylene sheath (density51.41g/cc), with the tungsten rod and total thickness of 5.4 and 6.0mm, respectively. The total diameter of 6.0mm was chosen to match that of standard clinical tandems so as to not require further dilation. An in-house developed HDR planning platform was used for planning of the DMBT applicator. For the proposed DMBT tandem design, the plans were optimized with the same ovoids in place, as the conventional T&O plans, but without the needles. In addition, additional DMBT plans were generated that used the needles this time. All generated plans were normalized to match the HRCTV D90 of the original/clinical ‘‘T&Oþneedles’’ plans. Results: In fractions 1 and 2, no needles were inserted; therefore, it is not surprising that the DMBT plans performed better than the T&O plans. In fraction 1, the sigmoid D2cc reduction was the greatest with 40.8% (0.84Gy), followed by the rectum with 17.7% (0.76Gy), and the bladder with 4.7% (0.27Gy). In fraction 2, the bladder D2cc reduction was the greatest with 15.7% (0.99Gy), followed by the rectum with 3.2%
Abstracts / Brachytherapy 14 (2015) S11eS106 (0.15Gy), and the sigmoid was not contoured due to being largely away from the treated area. For fractions 3-5, where free-hand needles were supplemented to the T&O applicator, mostly improvements were seen in OARs but some did get worse. However, in terms of total EQD2 doses accumulated over the treatment course, for all OARs, the DMBT plans improved over the clinical plans. That is, 89.77Gy reduced to 87.27Gy, 74.25Gy reduced to 73.47Gy, and 62.51Gy reduced to 53.53Gy, for the bladder, rectum, and sigmoid, respectively. Remember, this is achieved with the same D90 coverage to the HRCTV in each fraction. For the DMBTþneedles plans, as expected, improvements were even greater compared with the clinical plans with 89.77Gy reduced to 84.99Gy, 74.25Gy reduced to 70.92Gy, and 62.51Gy to 53.38Gy, for the bladder, rectum, and sigmoid, respectively. Conclusions: This study demonstrated that, with the DMBT-concept tandem design, with same dimensions as a typical intrauterine tandem used in clinic, can give better quality plans in a course of treatment compared with a conventional T&O applicator supplemented with needles, albeit a single isolated clinical case was studied. Nevertheless, the results indicate to a possibility of avoiding (or at least reducing) needles when the DMBT tandem is available in clinic. Due to the significance of the implications, further studies with more patients will be pursued. Financial disclosure: None [1] Han D, Webster MJ, Scanderbeg DJ, et al. Direction-Modulated Brachytherapy for High-Dose-Rate Treatment of Cervical Cancer. I: Theoretical Design. Int J Radiat Oncol Biol Phys 2014;89(3)666-673. PHSOR08
Presentation Time: 10:53 AM
Dosimetric Evaluation of the 103Pd Civastring for Permanent Breast Brachytherapy Mark J. Rivard, PhD. Radiation Oncology, Tufts University School of Medicine, Boston, MA, USA. Purpose: Use of 103Pd for permanent breast seed implantation (PBSI) was originated by Pignol and colleagues in 2006 for the treatment of early-stage breast cancer. Since then, additional centers have adopted this conformal brachytherapy modality. Given the recent availability of elongated 103 Pd brachytherapy sources in the form of the polymer-encapsulated CivaString (CivaTech Oncology, Inc., Research Triangle Park, NC), a dosimetric evaluation was performed to consider possibilities for this new source. Materials and Methods: Implant geometries were simulated using the VariSeed (version 8.0.2, Varian Medical Systems, Palo Alto,
S65
CA) treatment planning system (TPS). A grid resolution of 0.1 cm was used throughout all plan variations. Spheres with diameters of 1.0 cm to 5.5 cm (0.5 cm increments) were manually contoured into the TPS using 24 nodes per 0.1 cm slice. Spatial accuracy of the circular cross sections was estimated to be within 0.03 cm. Using the median and range of PTV from Pignol et al (2009), spherical diameters of 3.0 to 5.0 cm (0.5 cm increments) were chosen for the PTV. Using a 1.5 cm CTV margin expansion, the corresponding CTV diameters would be 0.0 to 2.0 cm, respectively. With a prescription of 90 Gy, a planning goal of PTV100590% was chosen to match the experience of Pignol et al (2009). Multiple variations of each plan (having differing source positions, quantities, and air-kerma strengths) were performed to glean the sensitivity of the results to planning technique. The dose homogeneity index (DHI) was calculated, and dose-volume histograms (DVHs) were produced for the CTVs, PTVs, and planar ROIs for direct comparisons within a plan and across variations for plans having similar PTV dimensions. Given knowledge gained from planning spherical volumes, the geometry of a clinical case was approximated within the TPS for a representative anatomy given the observations of Pignol et al (2009). This case had a CTV that was 1.0 cm in the cranial-caudal direction, 1.0 cm in the anterior-posterior direction, and 2.0 cm laterally. The skin bridge was 1.0 cm anterior to the CTV and the chestwall was 1.5 cm posterior to the CTV. Given the treatment planning constraint of 0.5 cm from the skin surface or chestwall as recommended in the NSABP-B39/RTOG 0413 trail for partial breast irradiation of the breast, the PTV_EVAL dimensions were 4.0 cm, 2.5 cm, and 5.0 cm, respectively. The subsequent volumes for the CTV and PTV were 1.83 cm3 and 46.29 cm3, respectively. DVHs of the CTV, PTV, skin, and chestwall were produced, along with screenshots of resultant dose distributions. Results: The average DHI values for the 3.0, 3.5, 4.0, 4.5, and 5.0 cm PTVs were 0.78, 0.66, 0.63, 0.71, and 0.74, respectively, with an average of 0.72 across the 16 plans. There was good dose conformity to the CTV and PTV while providing low dose outside of the PTV. For 3.0, 3.5, 4.0, 4.5, and 5.0 cm diameter PTVs, maximum dose values to planes 0.5 cm from the PTVs were about 80%, 45%, 64%, 43%, and 47% of the prescribed dose. For planes located 1.0 cm from the PTVs, these maximum dose values diminished to 32%, 23%, 26%, 20%, and 28% of the prescribed dose. These dose values were all lower than what HDR 192Ir brachytherapy can deliver with either interstitial or balloon breast brachytherapy, and were due to the lower effective photon energy of 103Pd compared to 192Ir.
Treatment planning results for various spherical PTV with a limited number of implanted needles and CivaStrings.
#
CTV diam. (cm)
PTV diam. (cm)
U/cm
needles
CS10
Total U
U/cm3
needles/cm2
CS10/cm3
CTV100
CTV150
CTV200
PTV100
PTV150
PTV200
L1 L2 S1 S2 S1 S2 S1 L1 S1 S2 S3 S4 L1 L2 S1 S2
0.0 0.0 0.0 0.0 0.5 0.5 1.0 1.0 1.5 1.5 1.5 1.5 2.0 2.0 2.0 2.0
3.0 3.0 3.0 3.0 3.5 3.5 4.0 4.0 4.5 4.5 4.5 4.5 5.0 5.0 5.0 5.0
2.241 1.878 2.546 2.148 1.528 1.310 1.417 1.344 0.958 1.145 1.074 1.329 0.906 0.829 0.955 1.074
9 9 9 9 12 12 17 17 24 20 21 21 32 37 32 33
36 36 28 28 40 48 61 69 112 104 110 102 160 170 144 134
81 68 71 60 61 63 86 93 107 119 118 136 145 141 138 144
5.8 4.9 5.1 4.3 4.4 4.5 2.6 2.8 2.3 2.5 2.5 2.9 2.2 2.2 2.1 2.2
0.32 0.32 0.32 0.32 0.31 0.31 0.34 0.34 0.38 0.31 0.33 0.33 0.41 0.47 0.41 0.42
2.6 2.6 2.0 2.0 1.8 2.2 1.8 2.1 2.4 2.2 2.4 2.2 2.5 2.6 2.2 2.1
NA NA NA NA 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0% 100.0%
NA NA NA NA 1.3% 100.0% 87.3% 79.6% 86.2% 22.6% 17.5% 25.7% 55.0% 11.3% 60.5% 17.8%
NA NA NA NA 0.0% 3.9% 27.2% 25.1% 21.8% 8.0% 6.4% 8.4% 14.6% 1.9% 17.0% 7.4%
90.0% 89.9% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.0% 90.1% 89.9% 90.0% 90.0%
17.2% 18.2% 22.9% 22.0% 27.4% 34.3% 35.1% 31.5% 23.5% 22.7% 24.2% 32.9% 21.9% 21.0% 24.9% 24.8%
6.9% 8.3% 9.4% 9.5% 11.8% 14.4% 12.6% 11.7% 9.0% 9.7% 9.7% 12.4% 6.1% 5.3% 7.3% 8.7%
n.b. NA represents CTVs having zero volume. The optimal plan for a given PTV diameter is highlighted with boldface in the 1st column.