Treatment planning facilitates clinical decision making for hyperthermia treatments.

Background: Treatment quality is important in clinical hyperthermia. Guideline-based treatment protocols are used to determine system settings and treatment strategies to ensure effective tumor heating and prevent unwanted treatment-limiting normal tissue hot spots. Realizing both these goals can prove challenging using generic guideline-based and operator-dependent treatment strategies. Hyperthermia treatment planning (HTP) can be very useful to support treatment strategies. Although HTP is increasingly integrated into the standard clinical workflow, active clinical application is still limited to a small number of hyperthermia centers and should be further stimulated.Purpose: This paper aims to serve as a practical guide, demonstrating how HTP can be applied in clinical decision making for both superficial and locoregional hyperthermia treatments.HTP in clinical decision making: Seven problems that occur in daily clinical practice are described and we show how HTP can enhance insight to formulate an adequate treatment strategy. Examples use representative commercially available hyperthermia devices and cover all stages during the clinical workflow. Problems include selecting adequate phase settings, heating ability analysis, hot spot suppression, applicator selection, evaluation of target coverage and heating depth, and predicting possible thermal toxicity in case of an implant. Since we aim to promote a general use of HTP in daily practice, basic simulation strategies are used in these problems, avoiding a need for the application of dedicated advanced optimization routines that are not generally available.Conclusion: Even fairly basic HTP can facilitate clinical decision making, providing a meaningful and clinically relevant contribution to maintaining and improving treatment quality.

Is it time to move from the Unidimensional RECIST 1.1 Response Assessment Criteria to a Volumetric Evaluation in the Present Era of Image-based Oncology? An Evaluation in Locally Advanced Head Neck Cancers Undergoing Treatment.

AIMS: Tumour response assessments, as per Response Evaluation Criteria in Solid Tumours (RECIST 1.1), are based on the sum of diameters (SODs) of the primary tumour (longest diameter) and/or short axis diameter of lymph nodes. This study evaluates the response categorisation as per RECIST 1.1 vs Computed tomography (CT) based volumetric assessment of RECIST (proposed as vRECIST) in locally advanced head and neck cancers (LAHNCs) undergoing treatment. MATERIAL AND METHODS: The pre-treatment SODs and CT estimated tumour volumes were recorded in 45 LAHNCs treated with radiotherapy (RT), chemoradiotherapy (CTRT) or thermochemoradiotherapy (HTCTRT). Tumour responses were assessed independently as per RECIST 1.1 and vRECIST by two radiation oncologists and grouped into complete response (CR), partial response (PR), stable disease (SD) or progressive disease (PD). These response groups were evaluated for the likely congruence of the two approaches, as categorised independently by these two observers. RESULTS: All patients in stages III (n = 7), IVA (n = 16) and IVB (n = 22) were inoperable and had received either RT alone (n = 1), CTRT (n = 12) or HTCTRT (n = 32). Based on SODs criteria of RECIST 1.1, of the 45 patients, 5 and 40 were grouped as PR and SD by the first observer, while this changed to 34 and 10, respectively and 1 PD, with vRECIST (p < 0.001). Similarly, for the second observer, the 4 PR and 41 SD grouped using RECIST 1.1 were recategorised to 34 PR, 10 SD, and 1 PD by vRECIST (p < 0.001). Thus, a mismatch of 66.6% and 68.8%, respectively, was evident by observers first and second in categorising SD based on SODs of RECIST 1.1 vs PR on vRECIST. CONCLUSIONS: Treatment responses in LAHNCs assessed using SODs resulted in significant uncertainties and failed to reflect actual volumetric changes in tumours during treatment. It is perhaps time to consider replacing the SODs of RECIST 1.1 with vRECIST for unequivocal tumour response categorisation in the present era of image-based oncology practice.

The addition of deep hyperthermia to gemcitabine-based chemoradiation may achieve enhanced survival in unresectable locally advanced adenocarcinoma of the pancreas.

INTRODUCTION: Driven by the current unsatisfactory outcomes for patients with locally advanced pancreatic cancer (LAPC), a biologically intensified clinical protocol was developed to explore the feasibility and efficacy of FOLFORINOX chemotherapy followed by deep hyperthermia concomitant with chemoradiation and subsequent FOLFORINOX chemotherapy in patients with LAPC. METHODS: Nine patients with LAPC were treated according to the HEATPAC Phase II trial protocol which consists of 4 cycles of FOLFORINOX chemotherapy followed by gemcitabine-based chemoradiation to 56 Gy combined with weekly deep hyperthermia and then a further 8 cycles of FOLFORINOX chemotherapy. RESULTS: One grade three related toxicity was reported and two tumours became resectable. The median overall survival was 24 months and 1 year overall survival was 100%. CONCLUSIONS: Intensification of chemoradiation with deep hyperthermia was feasible in nine consecutive patients with LAPC.

Does the evidence support the use of concurrent chemoradiotherapy as a standard in the management of locally advanced cancer of the cervix, especially in developing countries?

Locally advanced cancer of the cervix (FIGO stages III and IVA) is one of the most common malignancies in developing countries. Conventional treatment has been a judicious combination of external radiotherapy and intracavitary brachytherapy. However, prompted by the results of five randomised-controlled trials (RCTs) published in close succession, The National Cancer Institute (NCI) alert in 1999, and two meta-analyses, the management of cancer of the cervix has gradually changed. Concurrent chemoradiotherapy with cisplatin alone, or in combination, is gradually being favoured for the treatment of cancer of the cervix. This overview examines whether the published evidence is sufficiently adequate to justify the use of chemoradiotherapy using cisplatin as standard care in the management of cancer of the cervix, especially in developing countries, where most women present with locally advanced cancer of the cervix. A critical review of the various phase III randomised trials and meta-analyses indicates that, although chemoradiotherapy could be a standard form of treatment for early cancer of the cervix, its role in advanced stages needs further exploration before this could be incorporated into routine clinical care.

Magnetic nanoparticle-induced hyperthermia with appropriate payloads: Paul Ehrlich's "magic (nano)bullet" for cancer theranostics?

Effective multimodal cancer management requires the optimal integration of diagnostic and therapeutic modalities. Radiation therapy, chemotherapy and immunotherapy, alone or in combination, are integral parts of various cancer treatment protocols. Hyperthermia at 39-45°C is a potent radiosensitiser and has been shown to improve therapeutic outcomes in various tumours through its synergy with chemotherapy. Gene silencing approaches, using small interfering RNAs and microRNAs, are also being explored in clinical trials in oncology. The rapid developments in multifunctional nanoparticles provide ample opportunities to integrate both diagnostic and therapeutic modalities into a single effective cancer "theranostic" vector. Nanoparticles could extravasate passively into the tumour tissues in preference to the adjacent normal tissues by capitalizing on the enhanced permeability and retention effect. Tumour targeting might be further augmented by conjugating tumour-specific peptides and antibodies onto the surface of these nanoparticles or by activation through electromagnetic radiations, laser or ultrasound. Magnetic nanoparticles can induce hyperthermia in the presence of an alternating magnetic field, thereby multifunctionally with tumour-specific payloads empowering tumour specific radiotheranostics (for both imaging and radiotherapy), chemotherapy drug delivery, immunotherapy and gene silencing therapy. Such a (nano)bullet could realise the "magic bullet" conceived by Paul Ehrlich more than a century ago. This article discusses the various aspects of this "magic (nano)bullet" and the challenges that need to be addressed to usher in this new paradigm in modern cancer diagnostics and therapeutics.

An audit of postoperative radiotherapy after non-curative resection for cancer of the oesophagus.

AIMS: The role of postoperative radiotherapy (PORT) after non-curative resections for cancer oesophagus is not well defined. A policy of offering PORT after non-curative resections for cancer oesophagus has been followed at our institution, and we report an audit of our experience. MATERIAL AND METHODS: Between March 1990 and September 2002, 139 patients underwent resections for cancer oesophagus. Of these, 86 patients received PORT to a dose of 45-50.4 Gy/25-28 fractions. Eleven of these patients also received concurrent and adjuvant 5-fluorouracil (5-FU). Disease-free survival and overall survival were computed from the day of surgery using the Kaplan-Meier method. RESULTS: Seventy-six per cent (65/86) of patients had squamous cell carcinoma and 69% (59/86) of patients had tumours in the lower-third of the oesophagus. The median interval between surgery and PORT was 41 days, and 93% of patients received doses as planned. Strictures at the anastomotic site and ulcerations in the stomach mucosa were seen in 17% and 5% of patients, respectively. The median and 5-year disease-free survival was 12 months (95% CI 9.9-14.1) and 14%; whereas the median and 5-year overall survival was 17 months (95% CI 12.4-21.6) and 17%, respectively. Local and distant failures were seen in 29% and 45% of patients, respectively. CONCLUSIONS: PORT, after a non-curative resection of cancer oesophagus, is well tolerated with acceptable morbidity and survival.

Variations in clinical estimates of tumor volume regression parameters and time factor during external radiotherapy in cancer cervix: does it mimic the linear-quadratic model of cell survival?

BACKGROUND: Tumor regression parameters and time factor during external radiotherapy (EXTRT) are of paramount importance. AIMS: To quantify the parameters of tumor regression and time factor during EXTRT in cancer cervix. SETTINGS AND DESIGN: Patients, treated solely with radiotherapy and enrolled for other prospective studies having weekly tumor regressions recorded were considered. MATERIALS AND METHODS: Seventy-seven patients received 50 Gy of EXTRT followed by intracavitary brachytherapy. Loco-regional regressions were assessed clinically and regression fraction (RF) was represented as RF=c + a 1D + a 2 D2 sub - a 3T, with c, D and T as constant, cumulative EXTRT dose and treatment time respectively. STATISTICAL ANALYSIS USED: Step wise linear regression was performed for RF. Scatter plots were fitted using linear-quadratic fit. RESULTS: Coefficients of parameters D, D2 sub and T were computed for various dose intervals, namely 0--20 Gy, 0--30 Gy, 0--40 Gy and 0--50 Gy. At 0--20 Gy and 0--30 Gy, only the coefficient of D2 was significant (P 2 sub and T turned significant (P 2 sub and T showed significance, leading to an estimate of 26 Gy for a1/a2 and 0.96 Gy/day for a3/a1. CONCLUSIONS: As with alpha/beta and gamma/alpha of post-irradiation cell survival curves, a1/a2 and a3/a1 represents the cumulative effect of various radiobiological factors influencing clinical regression of tumor during the course of EXTRT. The dynamic changes in the coefficients of D, D2 sub and T, indicate their relative importance during various phases of EXTRT.

Local hyperthermia combined with radiotherapy and-/or chemotherapy: recent advances and promises for the future.

Hyperthermia, one of the oldest forms of cancer treatment involves selective heating of tumor tissues to temperatures ranging between 39 and 45°C. Recent developments based on the thermoradiobiological rationale of hyperthermia indicate it to be a potent radio- and chemosensitizer. This has been further corroborated through positive clinical outcomes in various tumor sites using thermoradiotherapy or thermoradiochemotherapy approaches. Moreover, being devoid of any additional significant toxicity, hyperthermia has been safely used with low or moderate doses of reirradiation for retreatment of previously treated and recurrent tumors, resulting in significant tumor regression. Recent in vitro and in vivo studies also indicate a unique immunomodulating prospect of hyperthermia, especially when combined with radiotherapy. In addition, the technological advances over the last decade both in hardware and software have led to potent and even safer loco-regional hyperthermia treatment delivery, thermal treatment planning, thermal dose monitoring through noninvasive thermometry and online adaptive temperature modulation. The review summarizes the outcomes from various clinical studies (both randomized and nonrandomized) where hyperthermia is used as a thermal sensitizer of radiotherapy and-/or chemotherapy in various solid tumors and presents an overview of the progresses in loco-regional hyperthermia. These recent developments, supported by positive clinical outcomes should merit hyperthermia to be incorporated in the therapeutic armamentarium as a safe and an effective addendum to the existing oncological treatment modalities.

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.

Electron beam therapy at extended SSDs: an analysis of output correction factors for a Mitsubishi linear accelerator.

The effects of extended source-to-surface distance (SSD) on the electron beam dose profiles were evaluated for various electron beam energies--6, 9, 12, 15 and 20 MeV-and the accuracy of various output correction methods was analysed on a Mitsubishi linear accelerator using a radiation field analyser (RFA). The dose fall-off region of the central axis depth-dose curves was nearly independent for SSDs up to 120 cm where as in the build-up region, a marginal reduction of surface dose was observed, particularly for lower energies and for smaller field sizes. Effective SSDs and virtual source distances were evaluated for field sizes ranging from 5 x 5 to 15 x 15 cm2 for various energies. Curve fitting was done with the measured outputs with various equations and coefficients were evaluated. The accuracy of the derived output correction factors by effective SSD, virtual source distance and curve-fit methods was assessed by evaluating correlation coefficients between the calculated and the measured values. The correlation coefficient was best with the linear-quadratic equation followed by the effective SSD method and the virtual source method. The output correction based on the linear-quadratic equation showed the best estimate of electron beam output at extended SSDs with an accuracy well within +/- 1%. The rapid reduction of dose due to the applicator-scattered component at d(max) point with an extended SSD was significant for the 5 x 5 cm2 applicator and lower energies.

A non-randomized comparison of two radiotherapy protocols in inoperable squamous cell carcinoma of the oesophagus.

We report an audit of two different telebrachytherapy schedules in inoperable carcinoma of the oesophagus. Between October 1990 and December 1996, 108 patients with a Karnofsky performance status > or = 50 were selected from our database on the basis of intention to treat by telebrachytherapy. Teletherapy in the low dose group L (55 patients) consisted of 35 Gy in 15 fractions over 3 weeks, while that in the high dose group H (53 patients) consisted of 50 Gy in 25 fractions over 5 weeks. The choice of teletherapy dose was based on physician preference. The high dose rate intraluminal radiotherapy that followed 2 weeks later was identical in both groups and consisted of two applications of 6 Gy, a week apart. The pretreatment disease characteristics of the patients in both arms were similar. Relief of dysphagia was obtained in 49% of the patients in group L and in 75% of those in group H (chi2: P = 0.004). The median dysphagia-free interval was 0 and 7 months in groups L and H respectively (log-rank: P = 0.06), while the median overall survival was identical at 8 months (log-rank: P = 0.21) for both groups. The probability of survival at 1, 2 and 5 years was 34.8% versus 35.8%, 14.5% versus 13.9% and 0% versus 10% for groups L and H respectively. Morbidity in the form of ulcers, strictures and fistulae were observed in 9%, 7% and 5% of patients in group L compared with 8%, 8% and 13% in groups H respectively. This audit suggests that the protocol used in group H, when compared with group L, results in a greater proportion of patients being rendered dysphagia free, with a statistical trend towards a greater sustainment of dysphagia relief on follow-up.

Predictors of survival end points in patients with cancer of the cervix on long-term follow-up: inferences and implications from an audit of patients treated with a specific radiotherapy protocol.

AIMS: An audit of patients with cancer of the cervix treated with a specified protocol of external beam radiotherapy (EXRT) followed by intracavitary brachytherapy (ICBT) was carried out to determine the prognosticators for major survival end points. MATERIALS AND METHODS: Patients treated between 1991 and 2003 with a uniform protocol of EXRT (50 Gy/25 fractions/5 weeks) followed by high-dose-rate ICBT (18 Gy/3 fractions/3 weeks) were selected from the database. Various clinical and treatment parameters were evaluated for extent of locoregional response at completion of EXRT, namely absence or presence of gross residual tumour (AGRT and PGRT, respectively) and survival end points. These included locoregional disease-free survival (LDFS), disease-free survival (DFS) and overall survival (OS). RESULTS: Of the 157 evaluable patients, 145 (92%) belonged to FIGO stages II and III. Eighty-three (53%) at completion of EXRT had AGRT, which was influenced by age and gross tumour features. The estimated 10-year LDFS, DFS and OS were 38.6%, 33.1% and 38.5%, respectively. Factors significant on univariate analysis for these survival end points were EXRT duration, ICBT time, overall treatment time (OTT) and EXRT response. On multivariate analysis, AGRT to EXRT, an OTT of < or = 67 days, and patients older than 50 years were the significant favourable determinants for all the above survival end points. CONCLUSION: The audit highlights that younger people, especially those with bulky tumours that determine response to EXRT, are poor prognosticators for survival end points. They could perhaps benefit from treatment intensification regimens using chemoradiotherapy, provided that OTT is not unduly prolonged.

Postoperative residual tumour imaged by contrast-enhanced computed tomography and 201Tl single photon emission tomography: can they predict progression-free survival in high-grade gliomas?

AIMS: To evaluate if postoperative residual tumour imaged by either computed tomography or 201Tl single photon emission tomography (SPECT) carried out postoperatively could predict progression-free survival (PFS) in high-grade malignant gliomas. MATERIALS AND METHODS: Thirty-three patients with high-grade malignant gliomas underwent both contrast-enhanced CT scan and 201Tl-SPECT postoperatively before receiving radiotherapy. The PFS was evaluated against the individual reports of the above two imaging studies by univariate analysis. RESULTS: CT and 201Tl-SPECT were carried out within a median interval of 17 days after surgery. Of the 33 patients, CT and 201Tl-SPECT were reported as positive for residual tumours in 23 (69.7%) and 30 (91%) patients, respectively. Sensitivity, specificity and overall accuracy were 71.4%, 40% and 66.6% for CT, and 96.4%, 40% and 87.8% for 201Tl-SPECT, respectively, and were based on their last follow-up status (P = 0.627 for CT; P = 0.053 for 201Tl-SPECT). The median PFS for patients reported to be positive or negative on CT scan was 4 and 5 months, respectively (P = 0.202). With 201Tl-SPECT, although the median PFS for patients with a positive 201Tl uptake was also 4 months, it had not even reached for those reported having a negative 201Tl uptake (cumulative survival 66.7% at last follow-up) (P = 0.198). However, Karnofsky performance status (KPS) was the only significant predictor on univariate analysis (KPS: < 80 vs. > or = 80; P < 0.001) for PFS. CONCLUSIONS: Although both the imaging modalities have a poor specificity, postoperative 201Tl-SPECT had a significantly better accuracy to predict the status at last follow-up than contrast-enhanced CT. Nevertheless, KPS remained the most significant outcome predictor for PFS in high-grade malignant gliomas.

Problems and uncertainties with multiple point A's during multiple high-dose-rate intracavitary brachytherapy in carcinoma of the cervix.

AIMS: This study evaluates the consequences of point A as a dose prescription point during multiple high-dose-rate (HDR) intracavitary brachytherapy (ICBT) in cancer cervix. MATERIALS AND METHODS: Fifty patients who had received teletherapy were randomised into two groups of 25 to receive three HDR ICBT fractions of 6 Gy each at point A with either a flexible Ralstron (Shimadzu Corporation, Japan) or rigid Rotterdam (Nucletron, Netherlands) applicator. The orthogonal radiographs of the 150 applications were evaluated for applicator geometry and point A co-ordinates. RESULTS: Irrespective of the nature and rigidity of the applicators, its various components exhibited a highly significant variation during multiple fractionated HDR ICBT. The Cartesian co-ordinates of point A (left and right) for the applicator geometry also showed significant variation during multiple HDR ICBT procedures. This resulted in an average shift of 9.5 mm (SD= +/-4.4) and 11.1 mm (SD= +/-6.4) in right point A, 10.2 mm (SD= +/-4.5) and 10.8 mm (SD= +/-6.6) in left point A for Ralstron and Rotterdam applicator, respectively, during the three HDR ICBT. Consequently, doses to both right and left point A's showed significant variation during multiple ICBT application and were independent of the applicator type. CONCLUSION: Applicator variation in the components and spatial position in the pelvis during multiple HDR ICBT results in multiple point A's irrespective of the nature of applicator, leading to uncertainty in the dose prescription. These uncertainties, which have a bearing on clinical end points, could be minimised by shifting from point-based dose prescription to image-based target localisation and treatment planning in ICBT.

Multimodality image fusion in dose escalation studies of brain tumors.

This article examines the utility of integrating images from computed tomography (CT), magnetic resonance imaging (MRI), and single photon emission computed tomography (SPECT) for radiation treatment planning of brain tumors for dose escalation studies. The information obtained from these imaging modalities is complementary to each other and could provide anatomic (through CT and MRI) and metabolic (through SPECT) information of the target. This anato-metabolic target localization could be expected to facilitate precise radiation therapy planning for brain tumors by delineating the boundary between the tumor, edema, and the normal brain parenchyma and identify the viable tumor nidus with greater degree of certainty. This could in turn lead to minimize dose to the normal tissue and permit dose escalation to the region of interest. The utility of these anato-metabolic imaging modalities for defining the clinical target volumes along with planning target volumes for different phases of the radiation therapy is illustrated.

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.

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.

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.

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.

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.