I found the manual plan to be fairly easy to construct once you had taken the time to practice the steps. It is a salient reminder of the steps needed to produce a plan which STILL holds today. The process gave me the confidence to think that I can understand the planning process (I still think I understand the planning process, and non one has yet been able to show me I don't!). The process of defining angles and wedge angles and directions is still relevant today although IMRT has made this knowledge more irrelevant.
In this re-run of the lung plan I will explain the steps as best I can remember. This was first drawn in 1996 when I was preparing for my own examinations. I actually explained the whole thing to my sister-in-law as I wrote and drew. And as it took about 50 minutes all up, I can to realize that I was ready. I believe that I was given a 4 field prostate in the exam, …. or was it a breast? Can't remember!
It is not fair when undertaking a manual plan to criticize the shape or volume of the PTV. Firstly PTVs need a CT for adequate definition, and secondly the very logical methods for construction were very poorly developed inthe days of manual plans. Often the manual plan was just prepared on a single mid plane manual outline - yep, manual outline and manual plan!
So let us start with the example of a lung cancer. The clinical history gives the idea of a localized lung cancer that would be amenable to a small field to a high dose. The PET scan would be very interesting, and for the sake of making you treat a small field, I would say that it would most definitely be negative!
| Clinical History | A 65 year old man presents with SOB, and haemoptysis. Investigation shows a 3-4 cm L hilar SCC of the lung without mediastinal adenopathy or metastases. His CT outline at the level of the hilum is provided. The mediastinal tumour is marked in red. |  |
| Step 1 | Question 1. Complete Question 1 now. There are a number of ways to treat such a case radically, decide on your approach now. Note that this question is entirely written AND reflects your normal prescription sheet. Reproduce it! At this point you must choose how to treat your patient. After this point you do not change your decision - you don't have time. The BIG mistake is to answer something like : a. 60 Gy b. 30 fractions over 6 weeks, 1 Fx per day c. spinal cord, lung. Patently this is NOT a prescription as it does not include data on position, port films, reviews, immobilisation, field number and arrangement, etc., etc. Doses to critical organs MUST be specified (eg. spinal cord <45Gy). | |
| Step 2 | Question 2. Complete Question 2 now. Use a unique colour (I used my son's sharpened wind-out crayons). Don't use the same colour elsewhere on the diagram. Don't use more than one line. Either hatch or shade - what you see here is NOT adequate (mea culpa, mea maxima culpa!) [2007! this is not adequate for an image constructed PTV either, remember this was done pre-3DCRT on CT images] |  |
| Step 3 | Question 3 Complete Q3 now. Draw what you described in your prescription. Remember to include any shielding that might be reasonable and predicted. Note that field sizes are to be recorded in MILLIMETRES. Stop using centimetres! [I have chosen to treat with ANTERIOR and LEFT POSTERIOR OBLIQUE fields. Since the skin surfaces are essentially perpendicular to the incident beam, the 60 degree angle between the beams will require the use of either one 30 degree wedge (half the angle because of the half shift - think about it!) or two 15 degree wedges (my choice). Remember to keep the thick ends together!] | [[image flickr:2137308443] |
| Step 4 | Before touching the isodose curves, I draw up a table fashioned after Question 5. The question of "applied dose" can be interpreted as the dose applied on central axis AT D max OF THAT BEAM, or the dose applied on central axis AT ISOCENTRE OF THAT BEAM. Most advise the former, I suggest doing both to prevent confusion. |  |
| Step 5 | Question 6. Do this on the isodose plot BEFORE you draw any isodoses. You can now reach for the isodose plots. Choose the field size and wedging that you require, then complete Q6 for each beam. When the isodose plot is complete, I check each individual component and complete any missing. This question should defeat no RO registrar but 90% of candidates seemed unable to comply! The common mistakes are : a. "6 MV" (no beam type) b. "FSD technique" (since you only get FSD charts this is not real hard! The correct answer is not FSD technique, but "FSD 100 cm". c. obvious! d. rarely missed, although you will see that my example has omitted this! |  |
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| Step 5 | Question 4. | To successfully complete the isodose plot, you must now choose FIELD SIZE, ENERGY, WEDGING, GANTRY ANGLE, and use of BOLUS. All of these choices were made in your prescription in Q1. Note in Q7 the ways in which your choices are unsuitable for a treatment plan. |
| Step 5 | Draw one field's isodoses - I have started with the anterior field. Remember to "half-shift" to compensate for the contour irregularity of the skin surface (ask your planners how!). [You may wish to replicate the outline so that you can keep your pictures uncluttered.] |  |
| Step 6 | Draw the other field's isodoses. I have used a separate sheet. |  |
| Step 7 | Combine the two isodose plots (either draw on the same sheet - you end up with lots of lines but my personal choice - or overlay two sheets of paper). The black dots signify where the two isodoses cross. Their respective values are added (e.g., 50% + 70% = 120%). |  |
| Step 8 | All similar values are then joined by lines to form a new composite isodose line. This represents the third set of lines on the sheet. Separate sheets are much neater at this point. |  |
| Step 9 | Question 5. Retrieve the table drawn up in Step 4. a. Decide on the isodose that covers the PTV (in this case 130%) and assign this to the PTV dose (60Gy). b. Read the necessary percent for each category. c. Apply the conversion factor (60/130 Gy per %). | [[f> image flickr:2137312635]] |
| Step 10 | Question 7. This question is your chance to redeem your plan! I keep this as a loose sheet on my right hand side so the I can fill it in as I realise my "imperfections". Some things are standard - such as CT plan, multiple levels, lung correction, isocentric technique with TAR/TMR correction. |
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| Step 11 | When you finished collect all your diagrams, calculations and pieces of paper (let me repeat that ….collect all your diagrams, calculations and pieces of paper) staple them together and hand them in for marking. |