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KMID : 1164220150270010045
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Journal of Korean Society for Radiotherapeutic Technology
2015 Volume.27 No. 1 p.45 ~ p.52
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Comparison and evaluation of volumetric modulated arc therapy and intensity modulated radiation therapy plans for postoperative radiation therapy of prostate cancer patient using a rectal balloon
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Jung Hae-Yoon
Seok Jin-Yong
Hong Joo-Wan
Chang Nam-Joon
Choi Byeong-Don
Park Jin-Hong
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Abstract
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Purpose : The dose distribution of organ at risk (OAR) and normal tissue is affected by treatment technique in postoperative radiation therapy for prostate cancer. The aim of this study was to compare dose distribution characteristic and to evaluate treatment efficiency by devising VMAT plans according to applying differed number of arc and IMRT plan for postoperative patient of prostate cancer radiation therapy using a rectal balloon.
Materials and Methods : Ten patients who received postoperative prostate radiation therapy in our hospital were compared. CT images of patients who inserted rectal balloon were acquired with 3 mm thickness and 10 MV energy of HD120MLC equipped Truebeam STx (Varian, Palo Alto, USA) was applied by using Eclipse (Version 11.0, Varian, Palo Alto, USA). 1 Arc, 2 Arc VMAT plans and 7-field IMRT plan were devised for each patient and same values were applied for dose volume constraint and plan normalization. To evaluate these plans, PTV coverage, conformity index (CI) and homogeneity index (HI) were compared and R50% was calculated to assess low dose spillage as per treatment plan. D25% of rectum and bladder Dmean were compared on OAR. And to evaluate the treatment efficiency, total monitor units(MU) and delivery time were considered. Each assessed result was analyzed by average value of 10 patients. Additionally, portal dosimetry was carried out for accuracy verification of beam delivery.
Results : There was no significant difference on PTV coverage and HI among 3 plans. Especially CI and R50% on 7F-IMRT were the highest as 1.230, 3.991 respectively(p=0.00). Rectum D25% was similar between 1A-VMAT and 2A-VMAT. But
approximately 7% higher value was observed on 7F-IMRT compare to the others(p=0.02) and bladder Dmean were similar
among the all plan(P>0.05). Total MU were 494.7, 479.7, 757.9 respectively(P=0.00) for 1A-VMAT, 2A-VMAT, 7F-IMRT and at the most on 7F-IMRT. The delivery time were 65.2sec, 133.1sec, 145.5sec respectively(p=0.00). The obvious shortest time was observed on 1A-VMAT. All plans indicated over 99.5%(p=0.00) of gamma pass rate (2 mm, 2%) in portal dosimetry quality assurance.
Conclusion : As a result of study, postoperative prostate cancer radiation therapy for patient using a rectal balloon, there was no significant difference of PTV coverage but 1A-VMAT and 2A-VMAT were more efficient for dose reduction of normal tissue and OARs. Between VMAT plans. R50% and MU were little lower in 2A-VMAT but 1A-VMAT has the shortest delivery time. So it is regarded to be an effective plan and it can reduce intra-fractional motion of patient also.
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KEYWORD
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Prostate cancer, Postoperative radiation therapy, Rectal balloon, VMAT, IMRT
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