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Clinical Application of a Novel Dose Deformable Algorithm for the Evaluation of Critical Organ Dose Distributions in Multiple Brachytherapy Treatment Fractions
S66
Abstracts / Brachytherapy 9 (2010) S23eS102
outermost needles on the each CT slice constituted the boundary of the target. Two weekly sessions of HDR IBT of 8-10 Gy each were given after pelvic external beam radiation therapy (EBRT). Results: A total of 40 IBT procedures were performed in 25 patients. Average duration of implant procedure was 50 minutes (range 40-75 minutes). There was no uterine perforation in any of 11 patients in whom central tandem was used. CT scan did not show needle perforation of bladder/rectum in any of the patients. During perioperative period, only 1 procedure (2.5%) was associated with hematuria which stopped within 6 hours. Severe late toxicity was observed in 3 (12%) patients. One patient had vesico-vaginal fistula and required diversion colostomy. The other 2 patients, one with bowel obstruction and another with Grade 3 proctitis, were managed conservatively. Overall pelvic control rate was 64%. Conclusions: Our experience suggests that TRUS is a practical and effective imaging device for guiding the IBT procedure of cervical cancer patients. It helps in accurate placements of needles thus avoiding the injury to normal pelvic structures.
PD22 Clinical Application of a Novel Dose Deformable Algorithm for the Evaluation of Critical Organ Dose Distributions in Multiple Brachytherapy Treatment Fractions Nathan Comsia, M.D., Matthew Quinn, Ph.D., Mark A. Hoggarth, M.S., Kevin Albuquerque, M.D., John C. Roeske, Ph.D. Radiation Oncology, Loyola University Medical Center, Maywood, IL. Purpose: Prescription dosing for fractionated brachytherapy treatments arises from summing the maximum doses from previous fractions for each critical structure. This method may produce an inaccurate calculation due to inter-treatment variations (i.e., placement geometry differences secondary to tissue changes). We present here a novel dose deformation technique based on ‘‘masking’’ the bladder, rectum and applicator within the CT image set. The goal of this study was to investigate whether masked deformable registration can be used to estimate the composite dose to the bladder and rectum over the entire brachytherapy course. Materials and Methods: To perform the deformable registration, we used a research version of the ABAS software (Elekta CMS, St. Louis, MO) which produces a file with the individual deformation fields. Prior to deformation, a masked image was created in which the bladder, rectum and applicator were assigned individual uniform CT values. These images were then used to deform the individual CT scans to a common scan. Using the deformation fields, the dose matrix associated with each plan was subsequently deformed to the common scan and summed on a pointby-point basis. Dose volume histograms of the bladder, rectum, sigmoid and CTV were calculated. The Dice Similarity Coefficient (DSC) was calculated for each organ and used as a surrogate for determining the goodness of the deformation. Results: Using the masked deformation technique, the average DSC value was approximately 0.9 for each structure considered. Without the masked deformation technique, the values were typically 0.6-0.7. Here, DSC values close to 1 indicate good agreement, while those closer to 0 indicate poor agreement. The composite DVHs were subsequently calculated and evaluated. The largest dose delivered to a 2 cc volume (D2cc) was compared using the current approach vs. summation of these doses from each individual DVH. For a representative patient, the D2cc for the bladder was 28.5 Gy vs. 34.6 Gy by summing the individual values. The corresponding maximum doses to the bladder were 46.8 Gy (ABAS) vs. 68.2 Gy (summation). For the rectum, the D2cc and maximum doses were nearly the same, 18.2 Gy and 29.9 Gy, respectively. Conclusions: Our results indicate that dose deformation based on a novel masking technique can be used to estimate the composite dose delivered over an entire course of HDR brachytherapy. In certain cases, and for some organs, the summation of normal tissue doses from individual plans may be too conservative. However, a larger study is needed to further validate this study.
PD23 Adjuvant Vaginal Brachytherapy: Fixed vs Individualized Vaginal Treatment Length Mark A. Zahra, M.D., M.R.C.P., FRCR., Louise Bleakley, Marie McCabeOncology, Western General Hospital, Edinburgh Cancer Centre, Edinburgh, Lothian, United Kingdom. Purpose: The ABS recommendations state that 3 to 5 cm of the proximal vagina should be treated, while the PORTEC-2 study stipulated prescription to the upper half of the vagina. Using data from a cohort of patients we compared the different treatment lengths and volumes to study the differences between the 2 different recommendations. Materials and Methods: 70 consecutive patients treated with HDR vaginal vault brachytherapy at our institution had the vaginal length measured using custom made perspex sizers. The length was measured from the vault to the vaginal introitus. The appropriate diameter of the vaginal cylinder used for each patient was documented. The treatment length and the associated treatment volume as proposed by PORTEC-2, along with the volumes for fixed treatment lengths of 3, 4 and 5 cm were assessed. The treatment volume for each case was obtained by calculating the volume of a cylinder as pr2h. With r 5 the radius of the treatment cylinder used for the individual patient, and h 5 treatment length. Results: Median vaginal length 5 10cm (range: 6 e 16cm). Median vaginal cylinder diameter 5 3cm (range: 2 - 3.5cm). Treatment volumes can range from 9.4cm3 -77cm3. Prescribing to the proximal upper half of the vagina will result in larger treatment volumes in 98% compared to 3cm length, 90% compared to 4cm length and 47% compared to 5cm length. Treatment volumes
median treatment volume (cm3) minimum treatment volume (cm3) maximum treatment volume (cm3)
3cm treatment length
4cm treatment length
5 cm treatment length
upper half of the vagina
21.2
28.3
35.3
38.9
9.4
12.6
15.7
15.7
28.9
38.5
48.1
77.0
Conclusions: Prescribing to the proximal vaginal upper half is likely to result in larger treatment volume particularly if associated with larger cylinder diameters. This could result in more toxicity. Fixed treatment length reduces potential for errors and appear to provide adequate coverage of the lymphatics in the upper vagina.
PD24 CT-Guided Interstitial Brachytherapy for Locally Advanced Gynecologic Malignancies Ericka Wiebe, M.D.1,2, Kathleen Surry, Ph.D.3, David D’Souza1. 1 Radiation Oncology, London Regional Cancer Program, London, ON, Canada; 2Postgraduate Medicine, University of Western, London, ON, Canada; 3Medical Physics, London Regional Cancer Program, London, ON, Canada. Purpose: To correlate dose volume parameters and toxicity outcomes in a series of patients treated with CT-guided high-dose-rate gynecologic interstitial brachytherapy (IBT). Materials and Methods: Forty patients were treated with high-dose-rate IBT in a single institution between August 2004 and October 2008. Primary malignancy included uterine (13 patients), vaginal/vulvar (13 patients), cervical (8 patients), GI (2 patients), GU (2 patients) and SCC pelvic (2 patients) organs. Four patients received prior external beam radiation therapy (EBRT), 34 patients received concurrent EBRT, and 2 patients received no EBRT (1 patient declined; 1 patient post-cystectomy
Abstracts / Brachytherapy 9 (2010) S23eS102
outermost needles on the each CT slice constituted the boundary of the target. Two weekly sessions of HDR IBT of 8-10 Gy each were given after pelvic external beam radiation therapy (EBRT). Results: A total of 40 IBT procedures were performed in 25 patients. Average duration of implant procedure was 50 minutes (range 40-75 minutes). There was no uterine perforation in any of 11 patients in whom central tandem was used. CT scan did not show needle perforation of bladder/rectum in any of the patients. During perioperative period, only 1 procedure (2.5%) was associated with hematuria which stopped within 6 hours. Severe late toxicity was observed in 3 (12%) patients. One patient had vesico-vaginal fistula and required diversion colostomy. The other 2 patients, one with bowel obstruction and another with Grade 3 proctitis, were managed conservatively. Overall pelvic control rate was 64%. Conclusions: Our experience suggests that TRUS is a practical and effective imaging device for guiding the IBT procedure of cervical cancer patients. It helps in accurate placements of needles thus avoiding the injury to normal pelvic structures.
PD22 Clinical Application of a Novel Dose Deformable Algorithm for the Evaluation of Critical Organ Dose Distributions in Multiple Brachytherapy Treatment Fractions Nathan Comsia, M.D., Matthew Quinn, Ph.D., Mark A. Hoggarth, M.S., Kevin Albuquerque, M.D., John C. Roeske, Ph.D. Radiation Oncology, Loyola University Medical Center, Maywood, IL. Purpose: Prescription dosing for fractionated brachytherapy treatments arises from summing the maximum doses from previous fractions for each critical structure. This method may produce an inaccurate calculation due to inter-treatment variations (i.e., placement geometry differences secondary to tissue changes). We present here a novel dose deformation technique based on ‘‘masking’’ the bladder, rectum and applicator within the CT image set. The goal of this study was to investigate whether masked deformable registration can be used to estimate the composite dose to the bladder and rectum over the entire brachytherapy course. Materials and Methods: To perform the deformable registration, we used a research version of the ABAS software (Elekta CMS, St. Louis, MO) which produces a file with the individual deformation fields. Prior to deformation, a masked image was created in which the bladder, rectum and applicator were assigned individual uniform CT values. These images were then used to deform the individual CT scans to a common scan. Using the deformation fields, the dose matrix associated with each plan was subsequently deformed to the common scan and summed on a pointby-point basis. Dose volume histograms of the bladder, rectum, sigmoid and CTV were calculated. The Dice Similarity Coefficient (DSC) was calculated for each organ and used as a surrogate for determining the goodness of the deformation. Results: Using the masked deformation technique, the average DSC value was approximately 0.9 for each structure considered. Without the masked deformation technique, the values were typically 0.6-0.7. Here, DSC values close to 1 indicate good agreement, while those closer to 0 indicate poor agreement. The composite DVHs were subsequently calculated and evaluated. The largest dose delivered to a 2 cc volume (D2cc) was compared using the current approach vs. summation of these doses from each individual DVH. For a representative patient, the D2cc for the bladder was 28.5 Gy vs. 34.6 Gy by summing the individual values. The corresponding maximum doses to the bladder were 46.8 Gy (ABAS) vs. 68.2 Gy (summation). For the rectum, the D2cc and maximum doses were nearly the same, 18.2 Gy and 29.9 Gy, respectively. Conclusions: Our results indicate that dose deformation based on a novel masking technique can be used to estimate the composite dose delivered over an entire course of HDR brachytherapy. In certain cases, and for some organs, the summation of normal tissue doses from individual plans may be too conservative. However, a larger study is needed to further validate this study.
PD23 Adjuvant Vaginal Brachytherapy: Fixed vs Individualized Vaginal Treatment Length Mark A. Zahra, M.D., M.R.C.P., FRCR., Louise Bleakley, Marie McCabeOncology, Western General Hospital, Edinburgh Cancer Centre, Edinburgh, Lothian, United Kingdom. Purpose: The ABS recommendations state that 3 to 5 cm of the proximal vagina should be treated, while the PORTEC-2 study stipulated prescription to the upper half of the vagina. Using data from a cohort of patients we compared the different treatment lengths and volumes to study the differences between the 2 different recommendations. Materials and Methods: 70 consecutive patients treated with HDR vaginal vault brachytherapy at our institution had the vaginal length measured using custom made perspex sizers. The length was measured from the vault to the vaginal introitus. The appropriate diameter of the vaginal cylinder used for each patient was documented. The treatment length and the associated treatment volume as proposed by PORTEC-2, along with the volumes for fixed treatment lengths of 3, 4 and 5 cm were assessed. The treatment volume for each case was obtained by calculating the volume of a cylinder as pr2h. With r 5 the radius of the treatment cylinder used for the individual patient, and h 5 treatment length. Results: Median vaginal length 5 10cm (range: 6 e 16cm). Median vaginal cylinder diameter 5 3cm (range: 2 - 3.5cm). Treatment volumes can range from 9.4cm3 -77cm3. Prescribing to the proximal upper half of the vagina will result in larger treatment volumes in 98% compared to 3cm length, 90% compared to 4cm length and 47% compared to 5cm length. Treatment volumes
median treatment volume (cm3) minimum treatment volume (cm3) maximum treatment volume (cm3)
3cm treatment length
4cm treatment length
5 cm treatment length
upper half of the vagina
21.2
28.3
35.3
38.9
9.4
12.6
15.7
15.7
28.9
38.5
48.1
77.0
Conclusions: Prescribing to the proximal vaginal upper half is likely to result in larger treatment volume particularly if associated with larger cylinder diameters. This could result in more toxicity. Fixed treatment length reduces potential for errors and appear to provide adequate coverage of the lymphatics in the upper vagina.
PD24 CT-Guided Interstitial Brachytherapy for Locally Advanced Gynecologic Malignancies Ericka Wiebe, M.D.1,2, Kathleen Surry, Ph.D.3, David D’Souza1. 1 Radiation Oncology, London Regional Cancer Program, London, ON, Canada; 2Postgraduate Medicine, University of Western, London, ON, Canada; 3Medical Physics, London Regional Cancer Program, London, ON, Canada. Purpose: To correlate dose volume parameters and toxicity outcomes in a series of patients treated with CT-guided high-dose-rate gynecologic interstitial brachytherapy (IBT). Materials and Methods: Forty patients were treated with high-dose-rate IBT in a single institution between August 2004 and October 2008. Primary malignancy included uterine (13 patients), vaginal/vulvar (13 patients), cervical (8 patients), GI (2 patients), GU (2 patients) and SCC pelvic (2 patients) organs. Four patients received prior external beam radiation therapy (EBRT), 34 patients received concurrent EBRT, and 2 patients received no EBRT (1 patient declined; 1 patient post-cystectomy