| Abstract|| |
Purpose: To compare CT based three-dimensional rotational (full and skip scan) treatment planning and conventional three-dimensional fixed field (four and six fields) planning in localized carcinoma prostate. Materials and Methods: Seven patients of localized carcinoma prostate were planned by different conformal rotational and fixed fields. All the plans were normalized to deliver 100 percent to the central axis and full 3D calculations were performed. Plan evaluation tools consisted of beam's eye view, multiplanar displays, isodose distribution, cumulative and differential dose volume histograms and OSCAR (Objective Scoring by Colored Areas of Regrets) software. Results: Analysis of dose volume histograms revealed that V95, D95, D05 and D95 for planning target volume (PTV) were comparatively higher when planned by skip scan technique than when planned by fixed field technique (91 percent, 91 percent, 90 percent and 91.4 percent versus 85 percent, 87 percent, 86 percent ad 88 percent). DVH analysis for organs at risk showed that V95, V50 and DM values for rectum and bladder obtained by skip-scan technique was lower than when planning was done by 4/6-field technique (1 percent, 70 percent ad 51 percent versus 13 percent, 91 percent and 55 percent for rectum and 4 percent, 25percent and 51 percent versus 16 percent, 38 percent and 56 percent for urinary bladder respectively). Full rotational technique was the best amongst all as far as doseto B/L femoral heads was concerned (0 percent, 0 percent and 29 percent versus 0 percent, 1 percent and 28 percent respectively)
Keywords: Carcinoma prostate, treatment planning, radiotherapy, three-dimensional
|How to cite this article:|
Dhankhar R, Das B P, Chauhan A K, Hooda H S, Yadav R, Manocha K K. Rotational treatment planning versus conventional fixed field treatment planning for the treatment of carcinoma prostate : A CT based three dimensional planning. Indian J Radiol Imaging 2002;12:407-12
|How to cite this URL:|
Dhankhar R, Das B P, Chauhan A K, Hooda H S, Yadav R, Manocha K K. Rotational treatment planning versus conventional fixed field treatment planning for the treatment of carcinoma prostate : A CT based three dimensional planning. Indian J Radiol Imaging [serial online] 2002 [cited 2020 Jul 9];12:407-12. Available from: http://www.ijri.org/text.asp?2002/12/3/407/28495
| Introduction|| |
Prostatic cancer has become the first diagnosed cancer in western men and is the second leading cause of cancer death in men . The aim of any kind of treatment is "First do no harm", following this concept in radiation oncology the tumor is given the maximum possible dose of radiation and the surrounding normal tissues are given the minimum possible doses of radiation. Radiation therapy has useful application in the management of all stages of prostatic cancer. Radiotherapy offers patients with early stage, clinically localized disease a non-invasive curative option that has low toxicity . It is now possible to realize these principles with the technological advances in treatment delivery and computerized planning which have provided the backdrop for an unprecedented number of options in the treatment of prostate cancer with radiation therapy. The more common choices include classical external beam radiotherapy, external beam radiotherapy using three dimensional treatment planning and conformal radiotherapy (3DCRT), ultrasound guided transperineal implant monotherapy alone or in combination with external beam radiotherapy and intensity modulated radiotherapy (IMRT) techniques . For three-dimensional conformal radiation treatment planning, patient immobilization, computed tomography (CT) scan identification of the target in three dimensions and beam's eye-view conformal treatment portals are critical.
Radiation therapy was introduced as a curative modality for localized prostate cancer in the 1950's, largely because of the work of Malcolm Bagshaw of Stanford University . In prostatic carcinoma, optimal dose distribution may be achieved by multiple stationary beams or by a combination of fixed fields and moving beam therapy such as are or full rotational techniques. Most popular field arrangement is the four-field technique commonly known as 'box' technique consisting of parallel opposed anterior and posterior fields and right and left lateral fields. Treatment involving more than four fields, historically required with orthovoltage units to treat deep, midline lesions have rarely been used with modern mega voltage therapy units until recently. However, the advent of three-dimensional conformal radiotherapy has seen an increase in use of multiple field techniques such as six-field technique used for treatment of localized prostatic carcinoma [6,7]. Moving beam therapy/arc therapy can be thought of as an extension of multiple field arrangements. The beam is always directed at the target but the direction changes continuously. It can be a full rotation through 360° or a skip-scan technique in which several small sectors are treated around the patient with intervening untreated sectors . The prostate and urinary bladders, cervix and pituitary are the sites frequently treated either initially or for boost doses with rotation or arc therapy ,.
According to Perez, rotational technique is most useful when small symmetrically shaped, deep-seated tumors are treated and is usually limited to field less than about 10 cm in width . The problems of computing the dose at a large number of points in moving field therapy is simple in principal but difficult in practice. Manned dose calculations are tedious, cumbersome and time consuming, therefore rotational therapy went out of practice. But now all computer based treatment planning systems have softwares for producing dose distributions for rotation therapy, so it has generated renewed interest. The following study was carried out in localized prostate carcinoma patients to evaluate the feasibility and accuracy of CT based three dimensional rotation (full or skip-scan) treatment planning on the basis of tumor volume coverage, target volume coverage, sparing of normal surrounding tissues / organs at risk (OAR) and to find out the superiority if any of the three dimensional rotational planning over conventional three dimensional fixed field planning by comparing the isodose distribution, cumulative as well as differential dose volume histograms of tumor volumes, target volumes and appropriate organs at risk for both the methods.
| Material and Methods|| |
This prospective study was carried out in 7 previously untreated histopathologically proven patients of localized carcinoma prostate. Patients were staged according to AJC staging system, 1992 . All the patients were subjected to detailed physical examination, various investigations like hematological, biochemical and radiological investigations including CT scan abdomen and pelvis. CT scan slice thickness ranged from 0.5 cm to 1 cm. CT scan of abdomen and pelvis were performed on Schimadzu SCT-3000 TF scanner. The CT data of all these patients was transferred through eight-inch floppy disks interfacing systems from CT scanner computer to Theraplan 500-3D computer planning system. Delineation of different target volumes was done on CT scan slices according to standard target volumes as defined by ICRU report number 50, 1992 .
1. Gross tumor volume (GTV): It is the gross extent of the malignant growth as determined by palpation or imaging study.
2. Clinical Target Volume (CTV): It is the tissue volume that contains GTV and/sub clinical microscopic malignant disease.
3. Planning Target Volume (PTV): It is defined by specifying the margins that must be added around the CTV to compensate for effects of organ, tumor and patient movement and inaccuracies in beam and patient setup. The critical normal tissues/organs at risk were also outlined on each CT slice as appropriate for each patient. They included urinary bladder, rectum and bilateral femoral heads.
For all these patients 3D planning was done using rotational (full and skip-scan) techniques and conventional fixed field techniques by using 4 and 6 fields techniques.
(i) Rotational (full and skip-scan) three-dimensional treatment planning:
The treatment plans were based on whole geometric information contained in all the CT slices. Proper conformal field arrangements for full rotational techniques (360°) and appropriate skip-arc isocentric technique for each patient were made using beam's eyes view (BEV), multiplanar reconstructions and display software to achieve adequate coverage of different target volumes (GTV, CTV and PTV) and normal tissues and organs at risk [Figure - 1]. Both cumulative as well as differential dose volume histograms were obtained for target volumes and normal tissues / organs at risk [Figure - 2]. OSCAR software was also used for plan evaluations
(ii) Conventional fixed field three-dimensional planning:
Each patient was also planned by four field and six coplanar field techniques. Based on the whole geometric information in all the CT slices, conformal field placements were made. Plans evaluation was done using earlier mentioned software tools. Both cumulative as well as differential dose volume histograms were also obtained for GTV, CTV and PTV and normal tissues / organs at risk, OSCAR software was also used for plan evaluation.
For all these patients, treatment plans were designed for 6600 cGy as per standard time dose fractionation schedule. All plans were normalized to grid maximum value.
| Results|| |
All except one patient were above 65 years of age. Majority of patients (57%) were having T2 tumor followed by T1 and T3 respectively (28% and 15%) Adenocarcinoma was the histopathology in all these patients. The isodose distributions for each type of planning technique for each patient were compared by plotting the isodose distribution on each CT slice. The average values for minimum, maximum and mean dose coverage of PTV was tabulated and given in [Table - 1].
All values expressed as percentage of grid maximum
Various parameters used for evaluation of different target volumes i.e. GTV, CTV and PTV from dose volume histogram were: V95 (percentage of volume receiving >95% of the dose); D95 (the dose to 95% of the volume);
V95 (percentage of volume receiving >95% of the dose), D95 (the dose to 95% of the volume), D05(minimum dose to 5% of the target volume), D5 (maximum dose to a volume of no less than 5%)
- All values expressed as percentage of grid maximum
- Statistically no significant difference between any two techniques.
D05 (minimum dose to 5% of the target volume); D5 (maximum dose to a volume of no less than 5%) ,. Their mean values and range is given in [Table - 2],[Table - 3] and [Table - 4] respectively.
[Table - 2] shows the DVH analysis data for GTV. It was observed that the volume of GTV receiving 95% of the dose (V95) was 94% when planned by skip-scan was 94% when planned by skip-scan technique in comparison to 89 and 90% when planned by six field and four field techniques respectively. Similarly the dose (D95) received by 95% of volume (GTV) when planned by skip scan method and fixed field method was 95% against 92% respectively. The minimum dose to 5% of volume (D05) and maximum dose to not less than 5% of volume (D05) was found to be 93% and 95% respectively when planned by skip-scan technique against 91% and 93% when planned by fixed-field technique.
[Table - 3] shows the DVH analysis data for CTV, V95, D95, D05 and D5 values for CTV planned by skip-scan technique were 91%, 93%, 92% and 94% respectively, when the patients were planned by fixed field these above mentioned values for CTV were found to be 85%, 91%, 90% and 92% respectively.
[Table - 4] shows the DVH analysis data for planning target volume. It was observed that V95, D95, D05 and D5 value for PTV were comparatively higher when planned by skip-scan technique than when planned by fixed field technique (91%, 91%, 90% and 91.4% for skip-scan technique versus 85%, 87%, 86% and 88% by fixed field)
In three-dimensional treatment planning normal tissues/organs at risk (OAR) doses were recorded as V95 (Volume receiving >95% of dose); V50 (volume receiving >50% of dose) and Dm (mean dose to the whole volume) . [Table - 5] shows DVH analysis for organs at risk viz. urinary bladder, rectum and distant normal tissues like B/L femoral heads.
[Table - 5] shows DVH analysis for organs at risk/normal tissues, from the table it is clearly observed that organs like rectum and urinary bladder get much higher dose when treated by fixed field techniques than rotation or skip scan technique. When comparison was made for V95, V50 and DM values for rectum and urinary bladder obtained by skip-scan technique planning and 4/6 field planning the value for skip-scan/rotation technique was found to be lower than 4/6 field technique (1%, 70% and 51% versus 13%, 91% and 55% for rectum and 4%, 25% and 51% versus 16%. 38% and 56% for urinary bladder respectively). Similarly for femoral heads, planning by full rotational technique had been observed to be beneficial as compared to when planning was done by fixed field technique (0%, 0% and 29% versus 0%, 1% and 28%)
Radiotherapy with radical intention is commonly used to treat localized prostate cancer. Late chronic effects limit the dose that can be given and may be limited to the volume of normal tissues irradiated. Conformal radiotherapy allows a smaller amount of rectum and bladder to be treated, by shaping the high dose volume to the prostate. Presently the application of conformal radiotherapy techniques in localized carcinoma prostate is one of the most exciting areas of clinical research in radiation oncology for safe dose escalation studies as the dose response curve is extremely steep .
The aim of this prospective study was to evaluate the feasibility and accuracy or CT based three dimensional rotational (full or skip scan) treatment planning on the basis of tumor volume coverage, target volume coverage, sparing of normal surrounding tissues / organs and to find out the superiority if any, of the three dimensional rotational planning over conventional three dimensional fixed field planning by comparing the isodose distribution, cumulative as well as differential dose volume histograms of tumor volumes, target volumes and appropriate normal tissues for both these methods.
The isodose distribution for different fixed fields/rotational, skip-scan technique was meticulously compared on each CT slice of each patient. It was found that in all cases tumor volumes could be covered by 100% isodose lines when planned by any type of 3D planning technique. However, the sparing pattern obtained by skip-scan technique was far better than isodose pattern obtained by other technique.
All the treatment plans were also evaluated using dose volume histograms (DVHs), which are a plot of cumulative dose volume distribution and graphically summarize the simulated radiation distribution within a volume of interest of patient, which would result from a proposed radiation treatment plan. DVHs show promise as tools for comparing rival treatment plans for a specific patient by clearly presenting the uniformity of dose in the target volume and any hot spots in adjacent normal organs and tissues. However they fail to identify the location of the volume receiving the doses and thus complement spatial dose distribution. OSCAR (objective scoring by colored areas of regrets) software program was also used to evaluate dose volume histograms in a consistent way so that rapid, reliable and reproducible choices could be made between alternative treatment plans .
Volume distribution analysis parameters used were V95 (Volume receiving > 95% of dose): the greater the value, fewer geometric misses, D95 (dose to 95% of the volume) representing dose homogeneity, D05 (minimum dose to 5% of volume): relating to risk of recurrences, D5 (maximum dose to not less than 5% of volume) indicative of hot spots in the treatment volume. The data obtained indicate that on an average 94% of GTV was receiving 95% of the dose (normalized to grid maximum) when planned by skip-scan technique, whereas when planned by fixed fields the GTV receiving 95% of the dose was 85% to 90%. Similarly 95% of the CTV was receiving 93% of the dose when planned by skip-scan technique as compared to 91% when planned by fixed field technique.
It was observed in the study that skip-scan technique gave a far better target coverage than any other technique however statistically no significant difference was noted for GTC and CTV coverage by the two techniques but statistically significant difference was noted for PTV coverage.
During radiation treatment planning, doses to surrounding normal tissues / organs at risk i.e. V95, D50 and Dm should be kept to minimum. From this point of view the four techniques of four-fields, six-fields, full rotational and skip scan were analyzed and compared statistically. There was a significant difference between skip-scan technique and any other technique as far as dose delivery to OAR like rectum and urinary bladder was concerned. In the case of femoral heads, representing the normal tissues at a distance from target volume, received less dose by full rotation (360°) skip-scan technique as compared to fixed field techniques. Particularly radiation exposure sparing by rotation/skip scan technique to the distant normal tissues was found to be statistically significant (P<0.05).
Dobelbower and colleagues analyzed 3D treatment techniques for prostatic cancer using a traditional four field "box" plan, four oblique fields, two different skip scan rotations (30°-90° and 50°-60°) using a keystone type field, eight coplanar fields and an eight non coplanar beam arrangement. By analyzing DVH and NTCP they concluded that 30°-90° skip are rotation technique was superior, but also found that four-field 'box' technique provided nearly comparable clinical dose distribution .
Akazawa et al compared five different three-dimensional techniques for treatment of prostate without seminal vesicles using four and six field conformal fields, open and blocked 120° bilateral arcs. They analyzed dose volume histograms and revealed that use of blocked arcs significantly improved the dose distribution compared to using standard arcs and 4 field conformal techniques .
Cattaneo and colleagues used various fixed fields techniques (three fields, four fields with wedges and without wedges, six fields with wedges and without wedges) for plan evaluation. They concluded that there is no fixed field technique absolutely better than other technique because if one technique gives the best sparing of rectum the other gives best sparing of urinary bladder, similarly the femoral head sparing was found to be the best in another technique. It was also found that rectum is the dose limiting organ at risk (OAR) for almost all techniques .
The present study concludes that conformal skip-arc rotational technique gives the optimal dose distribution with appropriate sparing of normal tissues in selected localized carcinoma prostate patients.
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Source of Support: None, Conflict of Interest: None
[Figure - 1], [Figure - 2]
[Table - 1], [Table - 2], [Table - 3], [Table - 4], [Table - 5]