Biomedical subjects

K J Das

Publications and source records attributed to K J Das.

6 recordsLinked to original sources

PubMed2001

Variations of intracavitary applicator geometry during multiple HDR brachytherapy insertions in carcinoma cervix and its influence on reporting as per ICRU report 38.

PURPOSE: This paper examines the extent of variation in the applicator geometry during multiple high dose rate (HDR) intracavitary brachytherapy (ICBT) applications and its impact on reporting as per ICRU report 38. MATERIALS AND METHODS: Eighty orthogonal radiographs from 20 consecutive patients of carcinoma cervix (FIGO stages, IIA-IIIB) having four HDR ICBT applications of 6 Gy each at weekly intervals following teletherapy were evaluated. The applicator consisted of a flexible intrauterine tandem (IUT) independent of the ovoid assembly. The applicator geometry was evaluated in terms of: alpha angle, beta angle, intrauterine length (IUTL), interovoid (IOV), os to right ovoid (ORT) and os to left ovoid (OLT) distances along with vertical (VDL) and anteroposterior displacements (ADL) of the os with respect to the ovoids. The Cartesian co-ordinates (X, Y, and Z) of the IUT tip, centre of both ovoids and os were also measured. Doses to right point A (ARD), left point A (ALD), along with a reference volume of 6 Gy for ICRU height (IRH), width (IRW), thickness (IRT) and volume (IRV) were estimated for each application. RESULTS: Highly significant differences (P<0.001) between four insertions in any given patient across 20 patients for alpha angle, beta angle, IUTL, IOV, ORT, VDL, co-ordinates of the IUT, ovoids and os were observed, except for ADL (P=0.041) and OLT (P=0.247). As a consequence, variations were observed in ARD (P=0.027), ALD (P=0.017); IRH, IRW, IRT and IRV (all P<0.001). Applicator factors which influenced the various dose specification parameters were: beta angle and ORT for both ARD and ALD; UTLN, VDL and ORT for IRH; UTLN and IOV for IRW; UTLN for IRT and VDL for the 6 Gy IRV. CONCLUSIONS: A significant variation of the applicator geometry and its movement was observed in patients undergoing multiple HDR ICBT. This could have implications for reporting dose and volume specifications as required by ICRU report 38.

Brachytherapy↗

PubMed2000

Biological integral dose: an alternate method for numerical scoring of rival plans.

Numerical scoring of rival plans (NSRP) are usually based either on basis of dose-volume histograms (DVH) or the relative values of corresponding normal tissue complication probabilities (NTCP) and tumor control probabilities (TCP). An alternative method for NSRP based on biological integral dose (BID) is being proposed, which is illustrated using a case of pituitary tumor planned to receive a dose of 50 Gy in 25 fractions over 5 weeks. BID for the various alternate plans -2-field (2F), 3-field (3F), 220 degrees arc (ARC) and 3-field static multileaf collimator (MLC) were calculated using the integration of the product of extrapolated response dose and the corresponding mass of the tissue enclosed separately for tumor and the normal brain in the entire planned target volume or a selected range of dose (approximately 90% and above of the normalized dose). Ratios of the BID for the brain versus the tumor were obtained and the plans were ranked on the basis of the least value of this ratio. In all of these plans, although the DVHs for normal brain were different, the DVHs for tumor were almost identical. However, the BID values for brain for 2F, 3F, ARC, and MLC were 22.53 Joules (J), 21.176 J, 21.991 J, and 10.608 J, respectively, and for tumor 0.561 J, 0.552 J, 0.555 J, and 0.556 J, respectively. The corresponding brain/tumor values were 40.16 (2F), 38.36 (3F), 39.62 (ARC), and 19.08 (MLC), thus ranking the plans in order of merit as MLC, 3F, ARC, and 2F. The BID for volumes encompassed by 90% and more of the normalized dose magnified the differences between the plans, with 2F being 29.99, compared to 3.82 for MLC. Rankings of rival plans could be based on the concept of BID. It requires a lesser number of uncertain variables and therefore could be used as an alternative technique in evaluation of the different plans in routine clinical practice.

Humans↗

PubMed1998

Partial transmission block for optimization of anterior supraclavicular-posterior axillary boost in the radiation therapy of carcinoma breast.

Radiation therapy of breast often involves an anterior supraclavicular-axillary (SC-AX) portal to irradiate the supraclavicular and axillary contents. However, the fall-off of the dose in this region leads to an inhomogeneity that could result either during the use of a single anterior SC-AX field or even with the concomitant use of a posterior axillary boost. An attempt has been made to circumvent this inhomogeneity by the use of a partial transmission block that could be placed in the anterior SC-AX portal corresponding to the posterior axillary boost field. The details of the quantum of partial transmission block to be used for different axillary separations and the reference depths of the dose prescription has been evaluated and presented.

Axilla↗

PubMed1997

Midline shield for radiation therapy of carcinoma of the uterine cervix: should it be "midline" or "individualized".

This study attempts to evaluate the advantage of individualized midline shield (IMLS) constructed on the basis of uterine geometry and applicator position in terms of the dosimetric consequences to points A-right (AR) and left (AL) as compared to standard midline shield (SMLS) in radiation therapy of carcinoma cervix. Twenty consecutive patients of carcinoma cervix (Stage I, II and III) were treated by external beam radiotherapy (EBRT) (50 Gy/5 weeks/25 fractions) and high-dose rate intracavitary brachytherapy (24 Gy/4 weeks/4 fractions) prescribed at point A. At the completion of 40 Gy by EBRT (phase I), IMLS (5 cm wide) at isocenter was fabricated on the basis of uterine geometry as ascertained by a dummy intracavitary application. The remaining 10 Gy of EBRT was delivered using IMLS (phase II) to effectively minimize and optimize the dose to point A. The dose profiles of IMLS were compared against the corresponding dose profile of a 5 cm SMLS and were found to be dependent on the positional variation of AR and AL with respect to the midline. With IMLS, the dose to AR and AL for the 10 Gy of phase II varied between 21.7-38.87% (30.01 +/- 4.87) and 22.42-35.72% (28.12 +/- 3.79) respectively. However with SMLS, the AR and AL doses would have ranged from 22.03% to 77.26% (34.55 +/- 15.94) for AR and from 20.59% to 96.2% (46.93 +/- 28.15) for AL leading to considerable inhomogeneity. Thus, in protocols incorporating midline shield for radiotherapy of carcinoma cervix, IMLS in place of SMLS could be preferred for achieving a definitive and homogeneous dose to the points AR and AL.

Brachytherapy↗

PubMed1996

Spatial information on dose distribution using multisectional dose-volume histograms.

Dose-volume histograms are useful tools to summarize the information on the dose profiles resulting within a target volume. However, the spatial relationships of the hot and the cold spots are blunted in the dose-volume histograms. This study tries to circumvent this problem using multisectional dose-volume histograms and highlight the utility of these in the optimization of a radiation therapy plan.

Brachytherapy↗

PubMed1995

Multisectional planning for external beam radiotherapy: a "poor person's" alternative to three-dimensional treatment planning.

Recent technical advances in the field of computers have led to the use of three-dimensional dose computation for optimizing a radiation therapy plan. However, in centers which lack such a state-of-the-art technology, one could explore the use of multisectional planning to obtain information about the dose profiles all along the target volume. This article highlights the utility of multisectional planning as an alternative to three-dimensional treatment planning systems for external beam radiation therapy.

Esophageal Neoplasms↗