title: Rectum dose analysis employing a multi-purpose brachytherapy phantom.
abstract: OBJECTIVE
  It is difficult to reproduce a brachytherapy measurement because of changes in the rectal shape during inter-fraction. We constructed a multi-purpose brachytherapy phantom (MPBP) and reproduced the same conditions found in actual therapy. We further attempted to apply the measured optimal dose to reduce rectal complications.
  
  
  METHODS
  A measured dose was administered at rectal reference point R1 using a diode detector in four patients who used a tandem and ovoid in brachytherapy for carcinoma of the cervix. A total number of 20 rectal dose measurements were performed five times per patient. In addition, discrepancies in the set-up of the diode detector were analyzed with each repetitive measurement. After reproducing the same conditions as found in actual therapy using a multi-function applicator (MFA) in the multi-purpose brachytherapy phantom constructed for this study, the dose was measured at reference points in the rectum using a thermoluminescence dosimeter (TLD).
  
  
  RESULTS
  According to the discrepancies measured in the set-up using a diode detector, Patient 1 showed a maximum value of 11.25 +/- 0.95 mm in the Y direction, Patients 2 and 3 exhibited 9.90 +/- 2.40 mm and 20.85 +/- 4.50 mm in the Z direction, respectively. Patient 4 showed 19.15 +/- 3.33 mm in the Z direction. In addition, values of the mean dose according to the position of the diode detector were recorded as 122.82 +/- 7.96-323.78 +/- 11.16 cGy. In the measured results for TLD in an MPBP, relative error for Patients 1 and 4 at the rectal reference point R2 were a maximum of 8.6 and 7.7%, respectively. For Patients 2 and 3 they were 1.7 and 1.2%, respectively. Furthermore, the dose measured at point R1 and R2 exhibited values approximately 1.7-8.6% higher than the dose calculated in advance, excluding point R1 in Patient 2. The discrepancies in the set-up owing to repetitive measurements and alterations in dosage according to these changes were not analyzed. It was evident that the relative error between the calculated and measured value was within 15%, which was allowable according to the recommendations by the American Association of Physicists in Medicine (AAPM).
  
  
  CONCLUSIONS
  The multi-purpose brachytherapy phantom constructed for this study successfully reproduced an optimal dose measured under the same conditions found in actual therapy in which the dose was precisely analyzed at a rectal reference point. In addition, these results were considered reliable and applicable for dose optimization before applying therapy using the measured data from the phantom in order to reduce rectal complications.
authors.affiliation: Department of Radiation Oncology, College of Medicine, Inha University, Seoul, Korea.
authors.forename: HyunDo
authors.initials: H
authors.lastname: Huh
authors.forename: WooChul
authors.initials: W
authors.lastname: Kim
authors.forename: John J K
authors.initials: JJ
authors.lastname: Loh
authors.forename: Suk
authors.initials: S
authors.lastname: Lee
authors.forename: Chul Yong
authors.initials: CY
authors.lastname: Kim
authors.forename: SangHoon
authors.initials: S
authors.lastname: Lee
authors.forename: DongOh
authors.initials: D
authors.lastname: Shin
authors.forename: Dongho
authors.initials: D
authors.lastname: Shin
authors.forename: SamJu
authors.initials: S
authors.lastname: Cho
authors.forename: Jisun
authors.initials: J
authors.lastname: Jang
authors.forename: Sangwook
authors.initials: S
authors.lastname: Lim
authors.forename: Kwang Hwan
authors.initials: KH
authors.lastname: Cho
authors.forename: Sooil
authors.initials: S
authors.lastname: Kwon
authors.forename: SeongHoon
authors.initials: S
authors.lastname: Kim
mesh_terms: D001918:Brachytherapy / Q000295:instrumentation* / Q000379:methods; D005260:Female; D006801:Humans; D019047:Phantoms, Imaging; D011879:Radiotherapy Dosage; D012007:Rectum; D013819:Thermoluminescent Dosimetry; D002583:Uterine Cervical Neoplasms / Q000532:radiotherapy