[en] Conformal radiation therapy shapes the high-dose volume so as to conform to the target volume while minimizing the dose to surrounding normal tissues. The advances that have been achieved in conformal therapy are in part due to the development of 3-dimensional treatment planning, which in turn has capitalized on 3-D imaging for tumor and normal tissue localization, as well as on available computational power for the calculation of 3-D dose distributions, visualization of anatomical and dose volumes, and numerical evaluation of treatment plans. The objective of this course is to give an overview of how 3-D conformal treatments are designed and transferred to the patient. Topics will include: 1) description of the major components of a 3-D treatment planning system, 2) techniques for designing treatments, 3) evaluation of treatment plans using dose distribution displays, dose-volume histograms and normal tissue complication probabilities, 4) implementation of treatments using shaped blocks and multileaf collimators, 5) verification of treatment delivery using portal films and electronic portal imaging devices. We will also discuss some future trends in 3D treatment planning, such as computerized treatment plan optimization, including the use of nonuniform beam profiles (intensity modulation), and incorporating treatment uncertainties due to patient positioning errors and organ motion into the treatment planning process

[en] Objective: In this presentation we will look into the basic components of 3-dimensional conformal treatment planning, and will discuss planning for some selected sites. We will also review some current and future trends in 3-D treatment planning. External beam radiation therapy is one of the arms of cancer treatment. In the recent years 3-D conformal therapy had significant impact on the practice of external beam radiation therapy. Conformal radiation therapy shapes the high-dose volume so as to conform to the target volume while minimizing the dose to the surrounding normal tissues. The advances that have been achieved in conformal therapy are in part due to the development of 3-D treatment planning, which in turn has capitalized on 3-D imaging for tumor and normal tissue localization, as well as on available computational power for the calculation of 3-D dose distributions, visualization of anatomical and dose volumes, and numerical evaluation of treatment plans. In this course we will give an overview of how 3-D conformal treatments are designed and transferred to the patient. Topics will include: 1) description of the major components of a 3-D treatment planning system, 2) techniques for designing treatments, 3) evaluation of treatment plans using dose distribution displays, dose-volume histograms and normal tissue complication probabilities, 4) implementation of treatments using shaped blocks and multileaf collimators, 5) verification of treatment delivery using portal films and electronic portal imaging devices. We will also discuss some current and future trends in 3-D treatment planning, such as field shaping with multileaf collimation, computerized treatment plan optimization, including the use of nonuniform beam profiles (intensity modulation), and incorporating treatment uncertainties due to patient positioning errors and organ motion into treatment planning process

[en] Purpose: The development of automated 'inverse planning', utilizing intensity-modulated radiation therapy (IMRT) raises the question of whether this new technique can provide a practical and efficient means of dose escalation in conformal treatment of cancer of the prostate. The purpose of this feasibility study was to determine a single set of inverse-planning parameters that can be used for a variety of different prostate patient geometries to automatically generate escalated dose (≥81 Gy) IMRT plans that satisfy normal tissue constraints for rectal and bladder walls. Methods: We studied a subset of the 46 patients who were previously treated at Memorial Sloan Kettering Cancer Center (MSKCC) to a total dose of 81 Gy using a 3D conformal approach. Six patients were selected for our study and replanned using an analytical inverse-planning algorithm (referred to as OPT3D) applied to 8 intensity modulated, co-axial radiation beams. A set of more than a dozen inverse planning parameters were adjusted by trial and error until the resulting dose distributions satisfied the critical organ dose-volume constraints imposed by our study rules (D30 ≤ 75.6 Gy and D10 ≤ 80 Gy for the rectal wall; D15 ≤ 80 Gy for the bladder wall) for the sample of patients selected. The OPT3D-generated plans were compared to hand-generated BEV plans using cumulative DVH analysis. Results: A single set of inverse-planning parameters was found that was able to automatically generate IMRT plans meeting all critical organ dose-volume constraints for all but one of the patients in our study. [The exception failed to meet bladder dose constraints for both IMRT and BEV methods, due to extensive overlap between the planning target volume (PTV) and bladder contours]. Based upon analysis of the cumulative dose-volume histogram (DVH) for the prostate PTV, the D95 (DX is defined such that x% of the volume receives a dose ≥ DX), averaged over all patients, was approximately 81 Gy. The average D90 and mean dose values were 85 Gy and 93 Gy, respectively. Although a similar D95 was achieved using the BEV-generated plans, the D90 and mean dose values were substantially higher for the inverse planning (OPT3D) method. Conclusion: This limited 'paper study' shows IMRT with inverse planning to be a promising technique for the treatment of prostate cancer to high doses. We determined a small set of inverse-planning parameter values that was able to automatically design intensity-modulated radiotherapy (IMRT) plans for a subset of 6 patients previously treated at MSKCC to 81 Gy using BEV planning techniques. With one minor exception, the resulting plans succeeded in meeting predetermined dose-volume constraints while at the same time allowing an increase in the mean dose and D90 to the prostate PTV. These 8 field plans also resulted in reduced dosage to the femoral heads. This automated technique is efficient in terms of planning effort and, with proper software for computer-controlled MLC, may be appropriate for clinical use. The clinical feasibility of this approach for a larger group of patients is currently under study

[en] Purpose: To prospectively assess the effect of supine vs. prone treatment position on the dose to normal tissues in prostate cancer patients with the three-dimensional conformal technique. Methods and Materials: Twenty-six patients underwent three-dimensional treatment planning in both the supine and prone treatment positions. The planning target volume and normal tissue structures were outlined on each CAT scan slice, and treatment plans were compared to assess the effect of treatment position on the volume of rectum, bladder, and bowel exposed to the high doses of irradiation. Results: The average dose to the rectal wall and the V95 (volume of rectal wall receiving at least 95% of the prescription dose) for the prone position were 64 and 24% of the prescription dose, respectively, compared to 72 and 29%, respectively, for the supine position (p < 0.05). When the average rectal wall dose was used as an endpoint, 14 of the 26 patients (54%) had an advantage for the prone position compared to 1 (4%) who demonstrated an advantage for the supine position (p < 0.0002). Similarly, when V95 of the rectal wall was used as a measure of comparison, 15 patients (58%) had an advantage for the prone position compared to 1 (4%) who demonstrated an advantage for the supine position (p < 0.0002). In 13 patients (50%), a change from supine to the prone position was associated with reduction of the V95 to levels < 30% of the prescription dose compared to 3 patients (11%) in whom such an advantage resulted from change of the prone to the supine position (p < 0.005). The effect of treatment position on the rectal wall dose was most pronounced in the region of the seminal vesicles. An increased volume of bowel was also noted in the supine position. The treatment position, however, had no significant impact on the dose to the bladder wall. Conclusions: Three-dimensional conformal radiotherapy for prostate cancer in the prone position is associated with significant reduction of the dose to the rectum and bowel resulting in an improvement in the therapeutic ratio

[en] Background and purpose: To assess the effect of internal organ motion on the dose distributions and biological indices for the target and non-target organs for three different conformal prostate treatment techniques. Materials and methods: We examined three types of treatment plans in 20 patients: (1) a six field plan, with a prescribed dose of 75.6 Gy; (2) the same six field plan to 72 Gy followed by a boost to 81 Gy; and (3) a five field plan with intensity modulated beams delivering 81 Gy. Treatment plans were designed using an initial CT data set (planning) and applied to three subsequent CT scans (treatment). The treatment CT contours were used to represent patient specific organ displacement; in addition, the dose distribution was convolved with a Gaussian distribution to model random setup error. Dose-volume histograms were calculated using an organ deformation model in which the movement between scans of individual points interior to the organs was tracked and the dose accumulated. The tumor control probability (TCP) for the prostate and proximal half of seminal vesicles (clinical target volume, CTV), normal tissue complication probability (NTCP) for the rectum and the percent volume of bladder wall receiving at least 75 Gy were calculated. Results: The patient averaged increase in the planned TCP between plan types 2 and 1 and types 3 and 1 was 9.8% (range 4.9-12.5%) for both, whereas the corresponding increases in treatment TCP were 9.0% (1.3-16%) and 8.1% (-1.3-13.8%). In all patients, plans 2 and 3 (81 Gy) exhibited equal or higher treatment TCP than plan 1 (75.6 Gy). The maximum treatment NTCP for rectum never exceeded the planning constraint and percent volume of bladder wall receiving at least 75 Gy was similar in the planning and treatment scans for all three plans. Conclusion: For plans that deliver a uniform prescribed dose to the planning target volume (PTV) (plan 1), current margins are adequate. In plans that further escalate the dose to part of the PTV (plans 2 and 3), in a fraction of the cases the CTV dose increase is less than planned, yet in all cases the TCP values are higher relative to the uniform dose PTV (plan 1). Doses to critical organs remain within the planning criteria

[en] Purpose: To analyze acute lung toxicity data of non-small-cell lung cancer patients treated with three-dimensional conformal radiation therapy in terms of dosimetric variables, location of dose within subvolumes of the lungs, and models of normal-tissue complication probability (NTCP). Methods and Materials: Dose distributions of 49 non-small-cell lung cancer patients treated in a dose escalation protocol between 1992 and 1999 were analyzed (dose range: 57.6-81 Gy). Nine patients had RTOG Grade 3 or higher acute lung toxicity. Correlation with dosimetric and physical variables, as well as Lyman and parallel NTCP models, was assessed. Lungs were evaluated as a single structure, as superior and inferior halves (to assess significance of dose to upper and lower lungs), and as ipsilateral and contralateral lungs. Results: For the whole lung, Grade 3 or higher pneumonitis was significantly correlated (p≤0.05) with mean dose and Lyman and parallel model indices (d_eff and f_dam). It was significantly correlated with these indices and with V20 for the ipsilateral lung and with mean dose and d_eff for the inferior half of the lungs. Dosimetric and NTCP model quantities for the superior half of the lungs and contralateral lung were not significantly correlated (p>0.5 for superior lung indices, and >0.1 for contralateral lung indices studied). Conclusions: For these patients, commonly used dosimetric and NTCP models are significantly correlated with ≥ Grade 3 pneumonitis. Equivalently strong correlations are found in the lower portion of the lungs and the ipsilateral lung, but not in the upper portion or contralateral lung

[en] Purpose: The purpose of this paper is to use the outcome of a dose escalation protocol for three-dimensional conformal radiation therapy (3D-CRT) of prostate cancer to study the dose-response for late rectal toxicity and to identify anatomic, dosimetric, and clinical factors that correlate with late rectal bleeding in multivariate analysis. Methods and Materials: Seven hundred forty-three patients with T1c-T3 prostate cancer were treated with 3D-CRT with prescribed doses of 64.8 to 81.0 Gy. The 5-year actuarial rate of late rectal toxicity was assessed using Kaplan-Meier statistics. A retrospective dosimetric analysis was performed for patients treated to 70.2 Gy (52 patients) or 75.6 Gy (119 patients) who either exhibited late rectal bleeding (RTOG Grade 2/3) within 30 months after treatment (i.e., 70.2 Gy--13 patients, 75.6 Gy--36 patients) or were nonbleeding for at least 30 months (i.e., 70.2 Gy--39 patients, 75.6 Gy--83 patients). Univariate and multivariate logistic regression was performed to correlate late rectal bleeding with several anatomic, dosimetric, and clinical variables. Results: A dose response for ≥ Grade 2 late rectal toxicity was observed. By multivariate analysis, the following factors were significantly correlated with ≥ Grade 2 late rectal bleeding for patients prescribed 70.2 Gy: 1) enclosure of the outer rectal contour by the 50% isodose on the isocenter slice (i.e., Iso50) (p < 0.02), and 2) smaller anatomically defined rectal wall volume (p < 0.05). After 75.6 Gy, the following factors were significant: 1) smaller anatomically defined rectal wall volume (p < 0.01), 2) higher rectal D_max (p < 0.01), 3) enclosure of rectal contour by Iso50 (p < 0.01), 4) patient age (p = 0.02), and 5) history of diabetes mellitus (p = 0.04). In addition to these five factors, acute rectal toxicity was also significantly correlated (p = 0.05) with late rectal bleeding when patients from both dose groups were combined in multivariate analysis. Conclusion: A multivariate logistic regression model is presented which describes the probability of developing late rectal bleeding after conformal irradiation of prostate cancer. Late rectal bleeding correlated with factors which may indicate that a greater fractional volume of rectal wall was exposed to high dose, such as smaller rectal wall volume, inclusion of the rectum within the 50% isodose on the isocenter slice, and higher rectal D_max

[en] Purpose: Intensity-modulated radiotherapy may be improved by incorporating limited-range electrons into photon beam therapy. We examined the feasibility of inverse treatment planning with intensity-modulated photon fields, either alone or combined with uniform high-energy electron fields, for intracranial tumors. Our goal was to generate dose distributions superior to those generated with conventional three-dimensional conformal techniques. Materials and Methods: Optimized three-dimensional treatment plans were compared to intensity-modulated photon plans with and without unmodulated high-energy electron fields for a cohort of previously treated brain tumors. Our in-house optimization system employed an iterative conjugate gradient search algorithm for cost function minimizing. Each set of plans was constrained to identical dose volume limits for critical non-target structures and dose prescription specifications for the planning target volume. In addition, each set used almost identical photon beam orientations to facilitate comparisons (for intensity-modulated plans, parallel opposed fields were slightly off-set to more effectively utilize the dosimetric advantages of inverse planning). Dosimetric comparisons were performed by examining planar and volumetric isodose distributions as well as dose-volume histograms. In particular, differences in integral dose to non-target brain tissue were evaluated. All plans were designed for implementation on a standard Varian 2100C with dynamic multileaf capability. Results: Peripheral targets demonstrated the greatest benefit from mixed modality intensity-modulated treatment planning. The principle dosimetric advantage was a decreased integral dose to the normal brain when calculated by taking a first moment integral of a differential dose volume histogram of normal brain tissue. The majority of this benefit was typically achieved through at least a 50% reduction in the volume of normal tissue receiving more than 80% of the prescription dose. For centrally located tumors, intensity-modulated photon planning was superior to three-dimensional planning, but incorporation of electron fields was detrimental to normal brain sparing. Conclusion: For peripheral brain tumors, inverse planning with intensity-modulated photon fields combined with uniform electron fields permits further reductions in integral non-target brain dose when compared to conventional three-dimensional and intensity-modulated planning. This dosimetric improvement is accomplished by exploiting the rapid dose fall-off of electrons and the capacity of intensity-modulated photons plans to the conform to target regions underdosed by electrons. Since a lower dose of photons is required for mixed modality therapy, the integral dose to non-target brain is decreased compared to single modality plans